Exogenous glucose oxidation during exercise is positively related to body size

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Collins, Alfonso Moreno-Cabañas, Louise Bradshaw, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4530175/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Current guidelines do not consider body size for carbohydrate intake during exercise. This study assessed whether larger people can oxidise more exogenous glucose during exercise than smaller people. Fifteen cyclists were allocated into two groups based on body mass (SMALL, 70 kg body mass, n = 6) matched for lactate threshold (SMALL: 2.3 ± 0.4 W⋅kg − 1 , LARGE: 2.3 ± 0.3 W⋅kg − 1 ). SMALL completed 120 min of cycling at 95% of lactate threshold 1 . LARGE completed two trials in a random order, one at 95% of lactate threshold 1 [thereby exercising at the same relative intensity (RELATIVE)], and one at an absolute intensity matched to SMALL (ABSOLUTE). In all trials, cyclists ingested 90 g⋅h − 1 of 13 C-enriched glucose. Total exogenous glucose oxidation was (mean ± SD) 33 ± 8 g⋅h − 1 in SMALL versus 45 ± 13 g⋅h − 1 in LARGE-RELATIVE (mean difference: 13 g⋅h − 1 , 95%CI 2 to 24 g⋅h − 1 , p = 0.03]. Large positive correlations were observed for measures of exogenous carbohydrate oxidation versus body size (body mass, height and body surface area; e.g. , body surface area versus peak exogenous glucose oxidation, r = 0.85,95%CI: 0.51 to 0.95, p < 0.01). When larger athletes reduced the intensity from RELATIVE to ABSOLUTE, total exogenous glucose oxidation was 39 ± 7 g⋅h − 1 ( p = 0.43 versus LARGE-RELATIVE). In conclusion, the capacity for exogenous glucose oxidation is, on average, higher in larger athletes than smaller athletes during exercise. Body size may therefore be a consideration in tailoring sports nutrition guidelines for carbohydrate intake during exercise. Physiology Nutrition & Dietetics Sports Medicine and Kinesiology Carbohydrate Cycling Metabolism Sports Nutrition Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 INTRODUCTION Carbohydrate ingestion during exercise is a well-established method of improving prolonged, endurance exercise performance [ 1 – 3 ]. The mechanisms by which carbohydrate ingestion can improve performance are hypothesised to include sparing of endogenous glycogen stores, preventing hypoglycaemia and/or maintaining high rates of carbohydrate oxidation [ 2 , 4 ]. Whilst some early sports nutrition guidelines made some consideration of body size [ 5 ], contemporary guidelines ignore body mass and express recommendations as a rate of carbohydrate per unit time. For example, current sports nutrition guidelines recommend athletes should ingest 30–60 grams of carbohydrate per hour ( i.e. , 0.5 to 1.0 g⋅min -1 ), for exercise lasting 1-2.5 hours, and to ingest up to 90 grams per hour ( i.e. , 1.5 g⋅min -1 ), for exercise lasting > 2.5-3 hours [ 6 , 7 ]. The rationale for these guidelines is based on a combination of outcomes including performance data, field-based observations, and metabolic data. A key outcome of interest with metabolic data, is the maximal capacity for exogenous carbohydrate oxidation (oxidation rate of ingested carbohydrate), which on average, is ~ 60 grams per hour when glucose-based carbohydrates are ingested alone, and can reach > 90 grams per hour when fructose-glucose mixtures are ingested [ 3 , 8 , 9 ]. Prior guidelines for carbohydrate intake during exercise had included some notion that body size may be relevant, with reference that 0.7 grams of carbohydrate per kilogram body mass per hour had been “shown unequivocally to extend endurance performance” [ 5 ]. More recently it has been suggested that there is no clear positive correlation between body mass and exogenous carbohydrate oxidation rates [ 3 ]. That conclusion, however, was based on secondary analyses of data from studies where the role of body size was not an aim, and therefore the range of body size was somewhat limited. This may limit the covariate space to detect a signal for body size. Therefore, it currently remains unclear whether body size is a key determinant of exogenous carbohydrate oxidation rates during exercise. It has been proposed that the primary limitation to exogenous glucose oxidation during exercise is intestinal carbohydrate absorption [ 3 , 9 ]. It is therefore appealing to speculate that exogenous carbohydrate oxidation should scale with body size, since larger people should, on average, have a larger intestinal surface area [ 10 ], and larger liver and muscle mass to metabolise exogenous carbohydrates. Indirect support from resting studies is provided by observations that people who are taller and/or have greater fat-free mass can absorb glucose from the gut into the circulation at faster rates than people who are smaller and/or have less fat-free mass [ 11 , 12 ]. However, to date, no study has directly assessed the relationship between body size and exogenous carbohydrate oxidation rates during exercise. Accordingly, the aims of this study were to: 1) establish whether larger athletes display higher rates of exogenous glucose oxidation than smaller athletes; and 2) establish whether the higher absolute exercise intensity contributes to any potential increases in exogenous glucose oxidation with larger athletes. We hypothesised that larger athletes would demonstrate higher exogenous glucose oxidation rates than smaller athletes, and that this difference would be partly (but not completely) diminished when the absolute intensity of exercise is matched. METHODS Study design This study was a cross-sectional study comparing smaller (body mass 70 kg; LARGE) athletes. This cutoff was chosen on the basis of exploratory analysis from one of our prior studies on exogenous glucose oxidation [ 13 ]. The smaller athletes completed preliminary testing followed by one experimental trial comprising of cycling at 95% of their lactate threshold 1 (LT 1 ). The larger athletes completed preliminary testing followed by two experimental trials in random order, one trial cycling at 95% of their LT 1 (RELATIVE), and another trial to match the absolute intensity (W) to the smaller athletes (ABSOLUTE). The study was conducted in accordance with the latest version of the Declaration of Helsinki. Study protocols were provided with favourable opinion by the NHS Research Ethics Committee, London – Chelsea (REF: 22/LO/0022) and pre-registered at clinicaltrials.gov (NCT05330481). Informed, written consent was provided by all participants prior to participation. Participants Twenty recreational cyclists/runners/triathletes were recruited from the local area around Bath, UK with either a smaller ( 70 kg). Inclusion criteria i) aged 18–60 years, ii) able to cycle continuously for 2 hours at a moderate intensity, iii) \(\dot{\text{V}}\) O 2 peak of between 40–75 mL/kg/min, and iv) Fat-mass index (determined by dual energy x-ray absorptiometry) < 5.5 kg·m − 2 . Whereas participants were excluded if: i) diagnosed disorders of the gastrointestinal tract (e.g., Crohn’s, colitis etc.), ii) consuming a low-carbohydrate, high-fat diet, iii) pregnant or lactating, or iv) diagnosis of any metabolic disorders (e.g., type 1 or type 2 diabetes). Finally, following group allocation, fifteen participants completed the study (SMALL, n = 7 males and n = 2 females; LARGE, n = 6 males). Preliminary tests Participants arrived at the laboratory in an overnight-fasted state and having voided. Body mass and height were determined using balance scales (BC543 Monitor, Tanita, Tokyo, Japan) and a stadiometer (Seca Ltd., Birmingham, UK), respectively. Body surface area (m 2 ) was estimated using the equation of Du Bois and Du Bois [ 14 ]. Body composition was assessed using a dual-energy X-ray absorptiometry (DXA) scan (Discovery, Hologic, Beford, UK). Following the DXA scan, participants completed three exercise tests on a cycle ergometer (Excalibur Sport, Lode Lode Groningen, Netherlands): 1) a submaximal test to determine lactate threshold; 2) a maximal test to determine \(\dot{\text{V}}\) O 2 peak and Wpeak; and 3) a familiarisation to the trial protocol. Submaximal exercise test The incremental exercise test comprised of 4-minute stages with the intensity of each stage individualised according to the method reported by Jamnick et al. [ 15 ]. Capillary blood was sampled from a fingertip in the final minute of each stage to determine blood lactate concentrations (Lactate Plus Meter, Nova Biomedical, Waltham, USA). LT 1 was determined as the point where blood lactate concentration rose by 0.5 mmol/L above baseline concentrations [ 15 ]. Participants then rested for 10 minutes before commencing the maximal exercise test. Maximal exercise test For the maximal exercise test, participants began cycling at the intensity equivalent to stage 6 of the submaximal test. The intensity increased by the increment in the submaximal test (individualised as per the method reported by Jamnick et al.[ 15 ]), but instead of every 4 minutes, the intensity increased every minute until cadence was not able to be sustained above 60 RPM. Expired breath was sampled for the final minute to determine \(\dot{\text{V}}\) O 2 peak. Following this, participants were provided with a 10-min break before completing a 1-hour familiarisation test at the exercise intensity and the carbohydrate ingestion rate that was prescribed during the main trials. Main trials Participants arrived at the laboratory in the morning in an overnight fasted state and having voided. Participants were also asked to record food intake and physical activity for 72 hours prior to their first main trial and the larger athletes were asked to replicate this ahead of their second main trial (which was performed in a random order). Upon arrival at the laboratory, participants were fitted with an intravenous cannula placed in an antecubital vein. A 5-mL blood sample was obtained and centrifuged to obtain plasma. The plasma was stored at -70ºC for later analysis of relevant metabolite [glucose, lactate, non-esterified fatty acid (NEFA)] and hormone (insulin) concentrations. Participants then began a 5-minute warm-up at 50 W before beginning a 2-hour bout of cycling at 95% of LT 1 (or the intensity matched to their counterpart in the SMALLER group). Cadence was self-selected on the cycle ergometer, but participants were asked to maintain this cadence ± 5 RPM throughout. Immediately prior to exercise, participants ingested the first bolus of a glucose solution (14% w/v solution; 300 mL, 42 g glucose). Thereafter, participants were provided with an additional 140 mL of the solutions (20 g glucose) every 15 minutes providing glucose at a mean rate of 1.5 g·min − 1 (180 g over the two hours). The drinks also contained 20 mmol·L − 1 sodium chloride to assist with replenishment of electrolytes lost through sweat. All drinks were enriched with 300 mg [U- 13 C]-glucose (99%; Cambridge Isotope Laboratories, MA) to increase the 13 C enrichment for determination of exogenous glucose oxidation rates. Expired breath was sampled every 30 minutes during exercise for the assessment of \(\dot{\text{V}}\) O 2 , \(\dot{\text{V}}\) CO 2 and the 13 C enrichment of \(\dot{\text{V}}\) CO 2 . Five-mL of blood was also sampled every 30 minutes during exercise to determine relevant metabolite and hormone concentrations in plasma. Ratings of perceived exertion and gut discomfort were also determined every 30 min using a 6–20 point and a 1–5 point scale, respectively. Blood analysis Blood samples were centrifuged (10 min at 4,000 x g and 4ºC) and the plasma obtained, frozen at − 70ºC until analysis. Plasma glucose (intra-assay coefficient of variation (CV) 3.2%; interassay CV 3.8%), lactate (intra-assay CV 1.0%; interassay CV 4.8%), and NEFA (intra-assay CV 4.7%; inter-assay CV 4.5%) concentrations were measured using an automated analyser (Daytona, Randox Laboratory, Crumlin, UK) as per the manufacturer’s instructions. Plasma insulin concentrations were measured using a commercially available enzyme-linked immunosorbent assay (ELISA; Mercodia AB, Uppsala, Sweden; intraassay CV 5.7%; interassay CV 9.9%). Breath analysis Breath samples were collected using the Douglas bag method to establish rates of oxygen consumption and carbon dioxide production. During exercise, 1-min samples were taken after 1-min equilibration periods. Concurrently, ambient O 2 and CO 2 concentrations were measured to account for changes in inspired gas concentrations [ 16 ]. Concentrations of O 2 and CO 2 were measured in a known volume of sample (Mini MP 5200, Servomex Ltd., Crowborough, UK), and the total volume of expired gas determined by evacuation using a dry gas meter (Harvard Apparatus, Holliston, USA). To determine 13 C enrichment of expired CO 2 , breath samples were collected in 12-mL exetainers (Labco Ltd, Lampeter, UK), filled in duplicate by 10 s exhalation. Whole-body substrate oxidation was calculated from \(\dot{\text{V}}\) O 2 and \(\dot{\text{V}}\) CO 2 according to stochiometric equations [ 17 , 18 ]. The 13 C/ 12 C ratio of expired CO 2 was determined by continuous flow isotope ratio mass spectrometry (Iso-Analytical, Crewe, UK) and the enrichment expressed as δ per mil difference between the 13 C/ 12 C ratio of the sample and a known standard. Exogenous glucose oxidation rates and endogenous carbohydrate oxidation rates where then calculated according to published equations [ 19 ]. Sample size justification The sample size was based on preliminary data from a study where participants ingested glucose at an mean rate of 1.2 g·min − 1 during moderate-intensity (50% Wpeak) cycling [ 13 ]. Individuals with a body mass 75 kg displayed peak exogenous carbohydrate oxidation rates of 0.97 ± 0.22 g·min − 1 . Using this effect size ( d = 1.55), 8 participants in each group should provide greater than 80% power to detect a difference in peak exogenous carbohydrate oxidation rates between groups using an independent, two-tailed t -test with an alpha level of 0.05. To account for dropouts and aim for sufficient power, it was intended to recruit 20 participants in total ( n = 10 per group). However, due to difficulties in recruiting sufficient people with the necessary characteristics to match between groups, the final sample size was n = 15. To improve statistical power for correlational analyses, we included an additional 12 participants from the placebo condition of a separate study currently in progress, where participants also met the inclusion criteria for the current study and were exercising under identical conditions (NCT05742516, ethics ref: 23/SW/0030). Statistical analysis The primary outcome variable was exogenous glucose oxidation rates expressed as the peak oxidation rate (g⋅h − 1 ) and the total exogenous glucose oxidation (g⋅h − 1 or kcal⋅h − 1 ). Data were checked for normal distribution by visual inspection (residuals for paired data). Comparisons between SMALL vs. LARGE (RELATIVE), and between the SMALL vs. LARGE (ABSOLUTE) were assessed using independent, two-tailed t -tests. Comparisons between LARGE (RELATIVE) vs. LARGE (ABSOLUTE) were assessed using paired, two-tailed t -tests. The associations between exogenous carbohydrate oxidation and participant characteristics (body mass, height, estimated body surface area, dietary intake) were quantified using Pearson’s product-moment correlation coefficients. Thresholds of 0.1, 0.3 and 0.5 were used to infer correlations as small, moderate, and large, respectively [ 20 ]. Time-series data (e.g., substrate oxidation, plasma metabolite and insulin concentrations over time) were assessed by: 1) a two-way, mixed-model (time x group) ANOVA comparing SMALL vs LARGE (RELATIVE) and 2) a two-way, repeated-measures (time x intensity) ANOVA comparing LARGE (RELATIVE) vs LARGE (ABSOLUTE). Sensitivity analyses were performed by removal of the two female participants, and the single largest athlete. Due to technical issues with blood sampling (blocked cannulae) data for blood-based variables are n = 7 for SMALL and n = 5 for LARGE). Data are presented as means ± SD, or mean differences (95%CI). Statistical significance was accepted when p ≤ 0.05. RESULTS Recruitment and retention Twenty participants (18 males and 2 females) were recruited. Following dropouts, a total of 15 participants completed the tests and all data from these participants were analysed (Fig. 1 ). Nine participants were in the SMALL group and six participants were in the LARGE group. Of the six participants in LARGE, one dropped out from the study after completing the RELATIVE trial and was retained for between-group analyses but not for repeated-measures analyses. Participant characteristics By design, the LARGE group had a greater body mass than SMALL (Table 1 ), in addition to being taller, having more fat-free mass, and a higher absolute lactate threshold (Table 1 ). However, the LARGE and SMALL groups were matched for age, percentage body fat, and relative lactate threshold (Table 1 ). Table 1 Participant characteristics. SMALL ( n = 9) LARGE ( n = 6) Mean diff (95%CI) Age (y) 31 ± 10 34 ± 10 3 (-8 to 14) Male sex ( n ) 7 6 - Height (cm) 178 ± 9 190 ± 10* 12 (1 to 23) Body mass (kg) 66.7 ± 2.5 87.3 ± 11.8* 20.6 (12.0 to 29.3) Body fat (%) 13.1 ± 6.4 15.0 ± 5.3 1.9 (-4.9 to 8.7) Fat-free mass (kg) 58.0 ± 5.3 74.4 ± 12.7* 16.4 (6.2 to 26.5) Fat mass (kg) 8.7 ± 4.2 12.9 ± 4.3 4.2 (-0.6 to 9.1) Lactate threshold 1 (W) 156 ± 29 198 ± 22* 41 (11 to 72) Lactate threshold 1 (W·kg − 1 ) 2.3 ± 0.4 2.3 ± 0.3 -0.05 (-0.5 to 0.4) Lactate threshold 1 (W·kgFFM − 1 ) 2.7 ± 0.4 2.7 ± 0.3 0.002 (-0.4 to 0.5) \(\dot{\text{V}}\) O 2 peak (L·min − 1 ) 3.85 ± 0.63 5.07 ± 0.58* 1.22 (0.52 to 1.92) \(\dot{\text{V}}\) O 2 peak (mL·kg − 1 ·min − 1 ) 58 ± 9 58 ± 5 0.6 (-8 to 9) \(\dot{\text{V}}\) O 2 peak (mL·kgFFM − 1 ·min − 1 ) 66 ± 10 69 ± 6 3 (-7 to 12) Data expressed as means ± SD and mean difference (95%CI). *, p < 0.05 vs SMALL. Dietary intake Self-reported, weighed food intake for the 3 days prior to trials is reported in Table 2 . No substantial differences in dietary intake were evident, especially relative to body size, other than a lower relative fibre intake prior to LARGE ABSOLUTE versus SMALL (Table 2 ). Table 2 Dietary intake from 3-day food diaries prior to each trial. SMALL ( n = 9) LARGE RELATIVE ( n = 6) LARGE ABSOLUTE ( n = 5) Energy (kcal·day − 1 ) 2395 + 472 2946 + 1166 2947 + 798 Carbohydrate (g·day − 1 ) 301 + 82 349 + 158 386 + 169 Fat (g·day − 1 ) 88 + 20 108 + 42 97 + 22 Protein (g·day − 1 ) 91 + 23 128 + 42 118 + 16* Ethanol (g·day − 1 ) 5 + 9 10 + 13 8 + 13 Sugar (g·day − 1 ) 103 + 45 114 + 52 133 + 45 Fibre (g·day − 1 ) 30 + 5 31 + 10 29 + 8 Energy (kcal·kg − 1 ·day − 1 ) 36.1 + 7.4 33.1 + 8.4 33.2 + 5.9 Carbohydrate (g·kg − 1 ·day − 1 ) 4.5 + 1.3 4.0 + 1.3 4.3 + 1.3 Fat (g·kg − 1 ·day − 1 ) 1.3 + 0.3 1.3 + 0.4 1.1 + 0.3 Protein (g·kg − 1 ·day − 1 ) 1.4 + 0.3 1.5 + 0.3 1.3 + 0.2 Sugar (g·kg − 1 ·day − 1 ) 1.6 + 0.7 1.5 + 0.3 1.5 + 0.4 Fibre (g·kg − 1 ·day − 1 ) 0.5 + 0.1 0.4 + 0.1 0.3 + 0.1* Carbohydrate (% energy intake) 50 + 6 46 + 3 51 + 9 Fat (% energy intake) 17 + 5 17 + 3 18 + 4 Protein (% energy intake) 16 + 4 18 + 4 17 + 4 Data expressed as means ± SD. * p ≤ 0.05 vs SMALL. Exercise intensity Absolute exercise intensity was higher during LARGE RELATIVE versus SMALL (Table 3 ), as was absolute VO 2 and VCO 2 . Also by design, absolute exercise intensity was well matched between LARGE ABSOLUTE versus SMALL (Table 3 ). Table 3 Exercise responses in smaller (SMALL) and larger (LARGE) athletes cycling at the same relative intensity (95% lactate threshold1) or the similar absolute intensity (W). SMALL ( n = 7) LARGE RELATIVE ( n = 5) LARGE ABSOLUTE ( n = 5) Mean ± SD Mean diff vs SMALL (95%CI) Mean ± SD Mean diff vs SMALL (95%CI) Exercise intensity (W) 149 + 28 180 + 23* 31 (1 to 61) 143 + 19 -7 (-38 to 24) Exercise intensity (W⋅kg − 1 ) 2.2 + 0.4 2.1 + 0.3 -0.2 (-0.6 to 0.2) 1.7 + 0.4* -0.6 (-1.0 to -0.1) Exercise intensity (%VO 2 peak) 59 + 4 57 + 7 -1 (-7 to 3) 46 + 6* -12 (-18 to -7) Cadence (rev·min − 1 ) 84 ± 5 85 ± 12 0.3 (-8 to 9) 82 ± 10 --5 (-12 to 3) VO 2 (L·min − 1 ) 2.2 + 0.3 3.0 + 0.5* 0.71 (0.26 to 1.16) 2.3 + 0.2 0.09 (-0.28 to 0.46) VO 2 (mL·kg − 1 ·min − 1 ) 34 + 5 34 + 6 -2 (-8 to 5) 27 + 4* -7 (-13 to -1) VCO 2 (L·min − 1 ) 2.0 + 0.4 2.7 + 0.4* 0.63 (0.21 to 1.05) 2.1 + 0.2 0.07 (-0.31 to 0.45) VCO 2 (mL·kg − 1 ·min − 1 ) 31 + 5 31 + 5 0.3 (-5 to 6) 24 + 4* -6 (-12 to -1) Carbohydrate oxidation (g·h − 1 ) 118 ± 36 152 ± 20 34 (-1 to 69) 126 ± 15 8 (-29 to 44) Fat oxidation (g·h − 1 ) 19 ± 9 27 ± 13 8 (-5 to 20) 20 ± 10 0.4 (-11 to 12) Respiratory exchange ratio (VCO 2 /VO 2 ) 0.91 + 0.04 0.91 + 0.03 -0.003 (-0.05 to 0.05) 0.91 + 0.03 -0.003 (-0.05 to 0.05) Gut discomfort (scale 1–5) 2 ± 1 2 ± 1 0.06 (-0.6 to 0.7) 2 ± 1 0.16 (-0.5 to 0.8) RPE (scale 6–20) 11 ± 2 12 ± 2 0.6 (-1 to 3) 10 ± 1 -1 (-3 to 1) RPE, rating of perceived exertion. Data expressed as means ± SD and mean differences (95%CI). *, p ≤ 0.05 vs SMALL. Substrate oxidation Total exogenous glucose oxidation was 13 g⋅h − 1 (95%CI 2 to 24 g⋅h − 1 , p = 0.03) higher during LARGE RELATIVE versus SMALL (Fig. 2 A). Sensitivity analysis with removal of either the two female participants (mean difference: 15 kcal⋅h − 1 ; 95%CI: -2 to 27 kcal⋅h − 1 ; p = 0.03) or the largest male (mean difference: 12 kcal⋅h − 1 ; 95%CI: -1 to 24 kcal⋅h − 1 ; p = 0.06), did not substantially change this inference. Peak exogenous glucose oxidation rates were 48 ± 9 g⋅h − 1 during SMALL, compared with 61 ± 16 g⋅h − 1 with LARGE RELATIVE, with a mean difference of 13 g⋅h − 1 (95%CI -1 to 27 g⋅h − 1 , p = 0.07). In the within-subjects analysis, total endogenous carbohydrate oxidation was 20 g⋅h − 1 (95%CI: 2 to 38 g⋅h − 1 , p = 0.04) lower during LARGE ABSOLUTE versus LARGE RELATIVE (Fig. 2 B), and peak exogenous glucose oxidation rates were 60 ± 18 g⋅h − 1 during LARGE RELATIVE, compared with 54 ± 42 g⋅h − 1 with LARGE ABSOLUTE reflecting a mean difference of 6 g⋅h − 1 (95%CI -24 to 37 g⋅h − 1 , p = 0.60). During exercise, exogenous glucose oxidation rates rose (main effect, time, p < 0.001), and were overall higher during LARGE RELTIVE versus SMALL (main effect, group, p = 0.03; Fig. 3 A). Endogenous carbohydrate oxidation rates decreased over time (main effect, time, p < 0.001), and were overall higher during LARGE RELATIVE versus LARGE ABSOLUTE (main effect, intensity, p = 0.02; Fig. 3 B). Breath 13 C enrichment over time is displayed in Fig. 3 C. Circulating metabolite and insulin concentrations At the onset of exercise plasma glucose and insulin concentrations rose transiently (time effect, p < 0.001). At the 30-min time point, plasma glucose concentration was 0.69 mmol⋅L − 1 (95%CI: -0.19 to 1.56 mmol⋅L − 1 ) higher in SMALL versus LARGE (RELATIVE) (Fig. 4 A). Similarly, at the 30-min time point, plasma lactate concentration was 1.23 mmol⋅L − 1 (95%CI: -0.03 to 2.48 mmol⋅L − 1 ) higher in SMALL versus LARGE (RELATIVE) and plasma insulin concentration was 28 pmol⋅L − 1 (95%CI: 3 to 53 pmol⋅L − 1 ) higher in SMALL versus LARGE (RELATIVE) (Fig. 4 B and 4 C). No meaningful differences were observed between groups or exercise intensities for plasma NEFA concentrations (Fig. 4 D). Associations between body size, diet and exogenous glucose oxidation When pooling data from the current study ( n = 15) and the ongoing study ( n = 12), total and peak exogenous glucose oxidation rates displayed large positive correlations with body mass (Fig. 5 A and 5 B), height (Fig. 5 C and 5 D), and estimated body surface area (Fig. 5 E and 5 F). Furthermore, these associations were robust to the exclusion of n = 12 from the ongoing study ( r = 0.56–0.72, 95%CI: 0.06 to 0.95, all p < 0.05). All correlations of diet with exogenous glucose oxidation rates (within the current study sample), when expressed relative to body mass or relative to total energy intake were small (all r 0.05). DISCUSSION The current study demonstrates that, on average, larger athletes can oxidise exogenous glucose at faster rates than smaller athletes during moderate intensity cycling. When larger athletes then exercised at the same absolute intensity as smaller athletes, the reduction in total energy expenditure was mostly accounted for by a reduction in endogenous rather than exogenous carbohydrate oxidation, suggesting that the higher absolute exercise intensity of the larger athletes does not fully account for the increase capacity to oxidise ingested carbohydrate. During prolonged, moderate-to-high intensity exercise, the ability to digest, absorb, and oxidise ingested carbohydrates can be a limiting factor to performance. Part of the rationale that current sports nutrition guidelines for carbohydrate intake during exercise do not account for body size, is that prior evidence did not show a clear positive relationship between body mass and exogenous carbohydrate oxidation rates [ 3 , 6 ]. However, no prior study was aimed at directly testing the role of body size in exogenous carbohydrate oxidation, and the range of body mass in prior data was ~ 60 to ~ 95 kg (less than a 1.6 fold range) [ 3 ], which could limit the ability to detect the signal of body mass within the variance. Therefore, we aimed to clarify whether body size is an important determinant of exogenous glucose oxidation rates during exercise. In the current study, we studied people with a wide range of body mass (53 to 110 kg; >2-fold range) with the same relative exercise intensity, exercise modality, environmental conditions and type and amount of carbohydrate. We observed large positive correlations between measures of body size and exogenous glucose oxidation rates, suggesting body size is an important determinant of exogenous glucose oxidation during exercise. The mean difference in peak exogenous glucose oxidation that we observed between larger and smaller athletes was 13 g⋅h − 1 (95%CI -1 to 27 g⋅h − 1 ) and the mean difference in total exogenous glucose oxidation was 13 g⋅h − 1 (95%CI 2 to 24 g⋅h − 1 ). These differences are likely to be physiologically meaningful, based on representing a similar mean difference in exogenous carbohydrate oxidation when ingesting glucose-fructose mixtures versus glucose only [ 21 ]. Furthermore, this difference in exogenous carbohydrate oxidation rate is similar to that seen when decreasing the fructose-maltodextrin ratio of a drink from 1.25 to 0.8, which results in an increase in 2-hour preloaded, repeated 10 x 2-min sprint performance by ~ 3% (303 versus 296 W) [ 22 ]. This suggests that the differences in exogenous glucose oxidation between larger and smaller athletes are likely to be of practical relevance. It was previously suggested that peak exogenous glucose oxidation rates were ~ 60 g⋅h − 1 independent of body size. We therefore provided participants with 90 g⋅h − 1 glucose with the rationale of saturating intestinal absorption rates and thereby potential revealing variance dependent on body-size associated intestinal surface area. We observed large, positive correlations between measures of body size (body mass, height, and estimated body surface area) and exogenous glucose oxidation rates, with the largest individual displaying a peak exogenous glucose oxidation rate of 90 g⋅h − 1 and a total exogenous glucose oxidation rate of ~ 70 g⋅h − 1 . This was confirmed with duplicate measures of breath enrichments and this challenges the concept of a fixed upper limit to exogenous glucose oxidation of 60 g⋅h − 1 . However, due to the single participant within that range of body size, this inference should be taken with some caution until further data confirm or refute this. Nevertheless, the positive associations between body size and exogenous glucose oxidation that we report are robust to the removal of this single extreme phenotype and suggest that exploration of the role of body size and other factors that may explain between-participant variance in exogenous carbohydrate oxidation rates are warranted. These data suggests a blanket 60 ⋅h − 1 recommendation for all athletes could result in relative underfueling for a larger athlete, but potentially saturating the capacity for smaller athletes to fully absorb and metabolise the ingested glucose, compromising gut comfort, and potentially increasing sympathetic drive and muscle glycogen utilisation [ 23 , 24 ]. From a practical perspective, approximate peak exogenous glucose oxidation rates based on the correlations we report are ~ 0.7 g glucose per kg body mass per hour (95%CI: 0.64 to 0.75 g⋅kg − 1 ⋅h − 1 ). Interestingly, this maps on to classical sports nutrition guidelines [ 5 ] and could be further refined with more research. A primary determinant of whole-body carbohydrate metabolism is exercise intensity [ 25 ]. We therefore sought to determine whether any potential differences in exogenous glucose oxidation between larger and smaller athletes could be explained by differences in absolute exercise intensity. To examine this, the larger athletes completed an additional exercise test where the intensity was matched to the smaller athletes. Due to dropouts, the matching was not perfect, but was within reasonable limits [mean difference: -7 W (95%CI -38 to 24 W)]. To maximise statistical power, this analysis was performed as a within-participant analysis comparing the higher versus lower exercise intensity within the larger athletes. The reduction in exercise intensity was produced by cycling at > 20% lower W (from 180 ± 23 W to 143 ± 19) which lowered total energy expenditure by ~ 20%. This reduction in total energy expenditure was largely explained by a reduction in endogenous carbohydrate oxidations rates. It is possible that the small sample size may result in a lack of statistical power to detect a difference in exogenous glucose oxidation with differences in exercise intensity. However, the mean difference in exogenous glucose oxidation between the higher and the lower intensity was only 6 g⋅h − 1 , which has been argued as not physiologically meaningful [ 26 ]. Other research has suggested a curvilinear relationship between exercise intensity and exogenous glucose oxidation rates [ 27 ], but comparisons between studies are difficult since prior work provided carbohydrate as a single bolus [ 27 ]. Therefore, the difference in exogenous glucose oxidation between larger and smaller athletes cannot be entirely explained by the higher absolute intensity of exercise, and may be due to a variety of factors related to body size including organ sizes and surface areas for digestion, absorption and metabolism. Following ingestion and intestinal absorption, glucose will enter systemic circulation via liver, where it can be released as glucose or as lactate [ 28 , 29 ]. Increases in glucose concentration, combined with intestinal L-cell signalling result in incretin hormone secretion, can stimulate insulin secretion, which in turn, regulate whole-body carbohydrate and fat metabolism [ 30 ]. To examine this, we determined concentrations of key metabolites and insulin in plasma. The smaller athletes displayed larger insulin and lactate responses at the onset of exercise compared to larger athletes, which may be explained by the greater relative dose of glucose ingested [ 31 ]. Another putative explanation for higher lactate responses could be that identification of lactate threshold was erroneous and thus exercise intensity was higher in the smaller athletes. However, it is unlikely that errors in identification of lactate threshold would be systematically biased towards the smaller athletes, and the transient increase in lactate at the onset of carbohydrate feeding during exercise is documented[ 4 ]. Furthermore, the higher insulin concentrations support the hypothesis that relative glucose dose, rather than exercise intensity explains most of the between group variance in lactate concentrations. These responses are, however, unlikely to explain the increase in exogenous glucose oxidation in larger versus smaller athletes, since increases in circulating insulin and lactate would be expected to result in higher, not lower carbohydrate oxidation rates. Due to dropouts, there may be a lack of statistical power to detect differences between exercise intensities in the larger athletes. However, the mean difference in peak exogenous glucose oxidation with higher versus lower exercise intensity was not physiologically meaningful. Furthermore, the study is sufficiently powered for the primary aim, as evidenced by clear and meaningful increases total exogenous glucose oxidation in larger versus smaller athletes, and in large, statistically significant relationships between body size and exogenous glucose oxidation. Another potential limitation is the lack of generalisability to other types of carbohydrates. The expression of intestinal transport proteins may be regulated by dietary intake [ 32 ]. Since most carbohydrates in most people’s diets in middle-to-high income countries are hydrolysed into glucose, and fructose is practically only present sugars, it is likely that dietary exposure to glucose is more consistent between people than is dietary exposure to fructose. Increased variability in fructose exposure may introduce an additional variance component to exogenous carbohydrate oxidation rates when using glucose-fructose mixtures, and this remains to be tested. It was for this reasoning, that we selected glucose as the carbohydrate within the current study. A third limitation with the current study is a lack of data on carbohydrate intake during training to explore as a potential factor mediating exogenous glucose oxidation rates. Habitual diet dietary intakes are extremely challenging to quantify [ 33 ], and therefore the ability to detect true relationships between habitual diet (including training nutrition) and exogenous carbohydrate oxidation rates will require extremely large sample sizes combined with novel ways to accurately quantify nutritional intakes. Conclusion In conclusion, these data demonstrate that, on average, larger athletes have a greater capacity to oxidise exogenous glucose during exercise than smaller athletes. In doing so, these data justify a re-evaluation of the role of body size and other factors in dictating carbohydrate fuelling during exercise. When seeking to maximise carbohydrate availability during exercise, it may benefit athletes to tailor nutrition guidelines based on body size. Declarations Acknowledgements We thank the participants for volunteering their time and effort for this work. Author Contributions JTG, GAW, TP and JAB designed the research. JTG, AJ, AJC, AMC, LB and KH conducted the research. JTG analyzed the data and performed statistical analyses. JTG primarily wrote the paper, and all authors read and approved the final version of the manuscript. FUNDING This work was part funded by the University of Bath and Clasado Biosciences. DISCLOSURES: The current manuscript was prepared without external funding. For a full list of JTG’s disclosures see https://gonzalezjt1.wordpress.com/2024/03/ , JTG has received research funding from BBSRC, MRC, British Heart Foundation, Clasado Biosciences, Lucozade Ribena Suntory, ARLA Foods Ingredients and Cosun Nutrition Center; is a scientific advisory board member to ZOE and 6d Sports Nutrition; and has completed paid consultancy for The Dairy Council, PepsiCo, Violicom Medical, Tour Racing Ltd., the European Fruit Juice Association, and SVGC. JAB is an investigator on research grants funded by BBSRC, MRC, British Heart Foundation, Rare Disease Foundation, EU Hydration Institute, GlaxoSmithKline, Nestlé, Lucozade Ribena Suntory, ARLA foods, Cosun Nutrition Center, American Academy of Sleep Medicine Foundation and Salus Optima (L3M Technologies Ltd); has completed paid consultancy for PepsiCo, Kellogg’s, SVGC and Salus Optima (L3M Technologies Ltd); is Company Director of Metabolic Solutions Ltd; receives an annual honorarium as a member of the academic advisory board for the International Olympic Committee Diploma in Sports Nutrition; and receives an annual stipend as Editor-in Chief of International Journal of Sport Nutrition & Exercise Metabolism. References Coyle EF, Coggan AR, Hemmert M, Ivy JL (1986) Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. J Appl Physiol 61(1):165–172 Rollo I, Gonzalez JT, Fuchs CJ, van Loon LJ, Williams C (2020) Primary, secondary, and tertiary effects of carbohydrate ingestion during exercise. Sports Med 50:1863–1871 Jeukendrup AE (2010) Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Curr Opin Clin Nutr Metabolic Care 13(4):452–457 Gonzalez JT, Fuchs CJ, Smith FE, Thelwall PE, Taylor R, Stevenson EJ, Trenell MI, Cermak NM, Van Loon LJ (2015) Ingestion of glucose or sucrose prevents liver but not muscle glycogen depletion during prolonged endurance-type exercise in trained cyclists. Am J Physiology-Endocrinology Metabolism 309(12):1032–1039 Rodriguez NR, Di Marco NM, Langley S (2009) American College of Sports Medicine position stand. Nutrition and athletic performance. Med Sci Sports Exerc 41(3):709–731 Thomas DT, Erdman KA, Burke LM (2016) Nutrition and athletic performance. Med Sci Sports Exerc 48:543–568 Burke LM, Hawley JA, Wong SH, Jeukendrup AE (2013) Carbohydrates for training and competition. Food, Nutrition and Sports Performance III:17–27 Fuchs CJ, Gonzalez JT, Van Loon LJ (2019) Fructose co-ingestion to increase carbohydrate availability in athletes. J Physiol 597(14):3549–3560 Gonzalez JT, Fuchs CJ, Betts JA, Van Loon LJ (2017) Glucose plus fructose ingestion for post-exercise recovery—greater than the sum of its parts? Nutrients 9(4):344 Wilson J (1967) Surface area of the small intestine in man. Gut 8(6):618 Anderwald C, Gastaldelli A, Tura A, Krebs M, Promintzer-Schifferl M, Kautzky-Willer A, Stadler M, DeFronzo RA, Pacini G, Bischof MG (2011) Mechanism and effects of glucose absorption during an oral glucose tolerance test among females and males. J Clin Endocrinol Metabolism 96(2):515–524 Færch K, Pacini G, Nolan JJ, Hansen T, Tura A, Vistisen D (2013) Impact of glucose tolerance status, sex, and body size on glucose absorption patterns during OGTTs. Diabetes Care 36(11):3691–3697 Narang BJ, Wallis GA, Gonzalez JT (2021) The effect of calcium co-ingestion on exogenous glucose oxidation during endurance exercise in healthy men: A pilot study. Eur J Sport Sci 21(8):1156–1164 Bois D (1989) A formula to estimate the approximate surface area if height and weight be known. 1916. Nutrition 5:303 Jamnick NA, Botella J, Pyne DB, Bishop DJ (2018) Manipulating graded exercise test variables affects the validity of the lactate threshold and V˙ O 2 peak. PLoS ONE 13(7):e0199794 Betts JA, Thompson D (2012) Thinking outside the bag (not necessarily outside the lab). Medicine and science in sports and exercise 44 (10):2040; author reply 2041. 10.1249/MSS.0b013e318264526f Jeukendrup AE, Wallis GA (2005) Measurement of substrate oxidation during exercise by means of gas exchange measurements. Int J Sports Med 26(Suppl 1):S28–37. 10.1055/s-2004-830512 Frayn KN (1983) Calculation of substrate oxidation rates in vivo from gaseous exchange. J Appl physiology: respiratory Environ Exerc Physiol 55(2):628–634 Gonzalez JT, King AJ (2023) For Flux Sake: Isotopic Tracer Methods of Monitoring Human Carbohydrate Metabolism During Exercise. Int J Sport Nutriiton Exerc Metabolism 33(1):60–70. 10.1123/ijsnem.2022-0170 J. C (1988) Statistical power analysis for the behavioural sciences. 2nd edn. Lawrence Erlbaum Associates, Hillsdale (NJ) Barber JFP, Thomas J, Narang B, Hengist A, Betts JA, Wallis GA, Gonzalez JT (2020) Pectin-Alginate Does Not Further Enhance Exogenous Carbohydrate Oxidation in Running. Med Sci Sports Exerc 52(6):1376–1384. 10.1249/MSS.0000000000002262 O'Brien WJ, Stannard SR, Clarke JA, Rowlands DS (2013) Fructose-maltodextrin ratio governs exogenous and other CHO oxidation and performance. Med Sci Sports Exerc 45(9):1814–1824. 10.1249/MSS.0b013e31828e12d4 Smith KA, Pugh JN, Duca FA, Close GL, Ormsbee MJ (2021) Gastrointestinal pathophysiology during endurance exercise: endocrine, microbiome, and nutritional influences. Eur J Appl Physiol 121(10):2657–2674 Wallis GA, Yeo SE, Blannin AK, Jeukendrup AE (2007) Dose-response effects of ingested carbohydrate on exercise metabolism in women. Med Sci Sports Exerc 39(1):131–138. 10.1249/01.mss.0000241645.28467.d3 van Loon LJ, Greenhaff PL, Constantin-Teodosiu D, Saris WH, Wagenmakers AJ (2001) The effects of increasing exercise intensity on muscle fuel utilisation in humans. J Physiol 536(Pt 1):295–304. 10.1111/j.1469-7793.2001.00295.x Pfeiffer B, Stellingwerff T, Zaltas E, Jeukendrup AE (2010) Oxidation of solid versus liquid CHO sources during exercise. Med Sci Sports Exerc 42(11):2030–2037 Pimay F, Scheen A, Gautier J, Lacroix M, Mosora F, Lefebvre P (1995) Exogenous glucose oxidation during exercise in relation to the power output. Int J Sports Med 16(07):456–460 Lecoultre V, Benoit R, Carrel G, Schutz Y, Millet GP, Tappy L, Schneiter P (2010) Fructose and glucose co-ingestion during prolonged exercise increases lactate and glucose fluxes and oxidation compared with an equimolar intake of glucose. Am J Clin Nutr 92(5):1071–1079. 10.3945/ajcn.2010.29566 Davis MA, Williams PE, Cherrington AD (1984) Effect of a mixed meal on hepatic lactate and gluconeogenic precursor metabolism in dogs. Am J Physiology-Endocrinology Metabolism 247(3):E362–E369 Holst JJ (2007) The physiology of glucagon-like peptide 1. Physiol Rev 87(4):1409–1439. 10.1152/physrev.00034.2006 Gonzalez JT, Lolli L, Veasey RC, Rumbold PL, Betts JA, Stevenson EJ (2024) Are there interindividual differences in the reactive hypoglycaemia response to breakfast? A replicate crossover trial Douard V, Ferraris RP (2008) Regulation of the fructose transporter GLUT5 in health and disease. Am J Physiology-Endocrinology Metabolism 295(2):E227–E237 Stubbs RJ, O'Reilly LM, Whybrow S, Fuller Z, Johnstone AM, Livingstone MB, Ritz P, Horgan GW (2014) Measuring the difference between actual and reported food intakes in the context of energy balance under laboratory conditions. Br J Nutr 111(11):2032–2043. 10.1017/S0007114514000154 Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4530175","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":310625239,"identity":"a90be3df-0d48-48b0-9f36-5eef04d98a8b","order_by":0,"name":"Abdullah Ijaz","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Abdullah","middleName":"","lastName":"Ijaz","suffix":""},{"id":310625467,"identity":"a3f56fe0-228a-4456-aa70-c547120fa255","order_by":1,"name":"Adam J. Collins","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Adam","middleName":"J.","lastName":"Collins","suffix":""},{"id":310625468,"identity":"a51cec5e-e281-4398-8c61-425136e2f4d0","order_by":2,"name":"Alfonso Moreno-Cabañas","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Alfonso","middleName":"","lastName":"Moreno-Cabañas","suffix":""},{"id":310625469,"identity":"a0296ac0-4d06-4642-910f-042ddd043578","order_by":3,"name":"Louise Bradshaw","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Louise","middleName":"","lastName":"Bradshaw","suffix":""},{"id":310625470,"identity":"3c5e0997-f166-4e4a-a72c-34d20ca38981","order_by":4,"name":"Katie Hutchins","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Katie","middleName":"","lastName":"Hutchins","suffix":""},{"id":310625471,"identity":"4932b7db-6e56-40a6-995d-6d1575267aab","order_by":5,"name":"James A. 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Gonzalez","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+0lEQVRIiWNgGAWjYBACxgYYix2IPwJ5BhBuAh4tzFAWkGac2cAgQVALWCmMZuYlRgtzA/8Bxi8Vd+z5m5kPf7bdYVdnzsD88ANjWxpehzHLnHnGLHGYLcE490yyhGUDm7EEY1sOfi2SbYfZGA7zGCTntjFLGBxgMGNgbKsgqIVH/jD/h8OWbfVALezfCGph/Nh2WMLgMA9jMyOIcYAHZAsehzUzGxxmOHPYwPAwmzFj75njkhsO8xRLJJzD7X3D9saHD39UHLaXO978+MPPHdX8BsfbN374UJaMW0szA9DjKEKgiErAqYGBQR7kuB94FIyCUTAKRsEoYAAATJxMo9XJV44AAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-9939-0074","institution":"University of Bath","correspondingAuthor":true,"prefix":"","firstName":"Javier","middleName":"T.","lastName":"Gonzalez","suffix":""}],"badges":[],"createdAt":"2024-06-04 20:29:36","currentVersionCode":1,"declarations":{"humanSubjects":true,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":true,"humanSubjectConsent":true,"humanSubjectClinicalTrial":true,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-4530175/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4530175/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":57768694,"identity":"f9708aba-7c7d-472e-be5a-9a5ec7fc2395","added_by":"auto","created_at":"2024-06-05 11:36:48","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":89446,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eParticipant flow through the study. M, males; F, females.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4530175/v1/39623f1c237ce77a2bc5c3ea.png"},{"id":57769129,"identity":"8c78b35a-c572-4855-a9b0-da0078ace098","added_by":"auto","created_at":"2024-06-05 11:44:49","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":78832,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSubstrate metabolism during 120 min cycling performed by smaller (SMALL) and larger (LARGE) athletes at 95% of lactate threshold\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e (A, RELATIVE) or at a matched absolute intensity to the smaller athletes (B, ABSOLUTE). EXO, exogenous glucose; END, endogenous carbohydrate. Data are means ± 95%CI. Mean differences in bold indicate \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ep\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e \u0026lt; 0.05. \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003en\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e = 9 for SMALL, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003en\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e = 6 for LARGE in panel A and \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003en\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e = 5 for LARGE in panel B.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4530175/v1/9443025f51a428dfdbc567a6.png"},{"id":57769128,"identity":"af6a813f-c1e0-43f1-af77-e1affafb14da","added_by":"auto","created_at":"2024-06-05 11:44:49","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":91314,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExogenous glucose oxidation rates (A), endogenous carbohydrate oxidation rates (B) and exhaled breath \u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e13\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003eC enrichment (C) during 120 min cycling performed by smaller (SMALL) and larger (LARGE) athletes at 95% of lactate threshold\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e (RELATIVE) or at a matched absolute intensity to the smaller athletes (ABSOLUTE). PDB, Pee Dee Belemnite. Data are means ± 95%CI.\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003e n\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e = 9 for SMALL, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003en\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e = 6 for LARGE (RELATIVE) and \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003en\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e = 5 for LARGE (ABSOLUTE).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4530175/v1/a0b0565db9b78549d09dd990.png"},{"id":57769685,"identity":"6bc432e5-32f0-4a54-aa93-d1c7e17686c4","added_by":"auto","created_at":"2024-06-05 11:52:49","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":50601,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePlasma glucose (A) lactate (B), insulin (C) and NEFA (D) concentrations during 120 min cycling performed by smaller (SMALL) and larger (LARGE) athletes at 95% of lactate threshold\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e (RELATIVE) or at a matched absolute intensity to the smaller athletes (ABSOLUTE). NEFA, non-esterified fatty acids. Data are means ± 95%CI. *\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ep\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e \u0026lt; 0.05 for SMALL versus LARGE (RELATIVE). \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003en\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e = 7 for SMALL and \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003en\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e = 5 for LARGE.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4530175/v1/33c17466817520e3662b582b.png"},{"id":57768698,"identity":"bc226a52-1166-48ab-96d5-986004819316","added_by":"auto","created_at":"2024-06-05 11:36:49","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":72209,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePearson’s product-moment coefficient correlations between body mass \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eversus\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003epeak (A) or total (B) exogenous glucose oxidation rates, between height \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eversus\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003epeak (C) or total (D) exogenous glucose oxidation rates, and between estimated body surface area \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eversus\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e peak (E) or total (F) exogenous glucose oxidation rates during exercise at 95% of lactate threshold. F, females; M, males; ADD, additional data from ongoing study.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4530175/v1/a9235870063090f33cef2fd4.png"},{"id":57770087,"identity":"6f18de1c-ae4d-4a0c-ab1d-bb9ad65c292c","added_by":"auto","created_at":"2024-06-05 12:00:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1621263,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4530175/v1/7672e225-b792-4eac-8f62-9b65206806a4.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003eExogenous glucose oxidation during exercise is positively related to body size\u003c/p\u003e","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eCarbohydrate ingestion during exercise is a well-established method of improving prolonged, endurance exercise performance [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The mechanisms by which carbohydrate ingestion can improve performance are hypothesised to include sparing of endogenous glycogen stores, preventing hypoglycaemia and/or maintaining high rates of carbohydrate oxidation [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Whilst some early sports nutrition guidelines made some consideration of body size [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], contemporary guidelines ignore body mass and express recommendations as a rate of carbohydrate per unit time. For example, current sports nutrition guidelines recommend athletes should ingest 30\u0026ndash;60 grams of carbohydrate per hour (\u003cem\u003ei.e.\u003c/em\u003e, 0.5 to 1.0 g\u0026sdot;min\u003csup\u003e-1\u003c/sup\u003e), for exercise lasting 1-2.5 hours, and to ingest up to 90 grams per hour (\u003cem\u003ei.e.\u003c/em\u003e, 1.5 g\u0026sdot;min\u003csup\u003e-1\u003c/sup\u003e), for exercise lasting\u0026thinsp;\u0026gt;\u0026thinsp;2.5-3 hours [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The rationale for these guidelines is based on a combination of outcomes including performance data, field-based observations, and metabolic data. A key outcome of interest with metabolic data, is the maximal capacity for exogenous carbohydrate oxidation (oxidation rate of ingested carbohydrate), which on average, is ~\u0026thinsp;60 grams per hour when glucose-based carbohydrates are ingested alone, and can reach\u0026thinsp;\u0026gt;\u0026thinsp;90 grams per hour when fructose-glucose mixtures are ingested [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePrior guidelines for carbohydrate intake during exercise had included some notion that body size may be relevant, with reference that 0.7 grams of carbohydrate per kilogram body mass per hour had been \u0026ldquo;shown unequivocally to extend endurance performance\u0026rdquo; [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. More recently it has been suggested that there is no clear positive correlation between body mass and exogenous carbohydrate oxidation rates [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. That conclusion, however, was based on secondary analyses of data from studies where the role of body size was not an aim, and therefore the range of body size was somewhat limited. This may limit the covariate space to detect a signal for body size. Therefore, it currently remains unclear whether body size is a key determinant of exogenous carbohydrate oxidation rates during exercise.\u003c/p\u003e \u003cp\u003eIt has been proposed that the primary limitation to exogenous glucose oxidation during exercise is intestinal carbohydrate absorption [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. It is therefore appealing to speculate that exogenous carbohydrate oxidation should scale with body size, since larger people should, on average, have a larger intestinal surface area [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], and larger liver and muscle mass to metabolise exogenous carbohydrates. Indirect support from resting studies is provided by observations that people who are taller and/or have greater fat-free mass can absorb glucose from the gut into the circulation at faster rates than people who are smaller and/or have less fat-free mass [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. However, to date, no study has directly assessed the relationship between body size and exogenous carbohydrate oxidation rates during exercise. Accordingly, the aims of this study were to: 1) establish whether larger athletes display higher rates of exogenous glucose oxidation than smaller athletes; and 2) establish whether the higher absolute exercise intensity contributes to any potential increases in exogenous glucose oxidation with larger athletes. We hypothesised that larger athletes would demonstrate higher exogenous glucose oxidation rates than smaller athletes, and that this difference would be partly (but not completely) diminished when the absolute intensity of exercise is matched.\u003c/p\u003e"},{"header":"METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy design\u003c/h2\u003e \u003cp\u003eThis study was a cross-sectional study comparing smaller (body mass\u0026thinsp;\u0026lt;\u0026thinsp;70 kg; SMALL) and larger (body mass\u0026thinsp;\u0026gt;\u0026thinsp;70 kg; LARGE) athletes. This cutoff was chosen on the basis of exploratory analysis from one of our prior studies on exogenous glucose oxidation [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The smaller athletes completed preliminary testing followed by one experimental trial comprising of cycling at 95% of their lactate threshold\u003csub\u003e1\u003c/sub\u003e (LT\u003csub\u003e1\u003c/sub\u003e). The larger athletes completed preliminary testing followed by two experimental trials in random order, one trial cycling at 95% of their LT\u003csub\u003e1\u003c/sub\u003e (RELATIVE), and another trial to match the absolute intensity (W) to the smaller athletes (ABSOLUTE). The study was conducted in accordance with the latest version of the Declaration of Helsinki. Study protocols were provided with favourable opinion by the NHS Research Ethics Committee, London \u0026ndash; Chelsea (REF: 22/LO/0022) and pre-registered at clinicaltrials.gov (NCT05330481). Informed, written consent was provided by all participants prior to participation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eParticipants\u003c/h2\u003e \u003cp\u003eTwenty recreational cyclists/runners/triathletes were recruited from the local area around Bath, UK with either a smaller (\u0026lt;\u0026thinsp;70 kg) or larger body mass (\u0026gt;\u0026thinsp;70 kg). Inclusion criteria i) aged 18\u0026ndash;60 years, ii) able to cycle continuously for 2 hours at a moderate intensity, iii) \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eO\u003csub\u003e2\u003c/sub\u003epeak of between 40\u0026ndash;75 mL/kg/min, and iv) Fat-mass index (determined by dual energy x-ray absorptiometry)\u0026thinsp;\u0026lt;\u0026thinsp;5.5 kg\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Whereas participants were excluded if: i) diagnosed disorders of the gastrointestinal tract (e.g., Crohn\u0026rsquo;s, colitis etc.), ii) consuming a low-carbohydrate, high-fat diet, iii) pregnant or lactating, or iv) diagnosis of any metabolic disorders (e.g., type 1 or type 2 diabetes). Finally, following group allocation, fifteen participants completed the study (SMALL, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;7 males and n\u0026thinsp;=\u0026thinsp;2 females; LARGE, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;6 males).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003ePreliminary tests\u003c/h2\u003e \u003cp\u003eParticipants arrived at the laboratory in an overnight-fasted state and having voided. Body mass and height were determined using balance scales (BC543 Monitor, Tanita, Tokyo, Japan) and a stadiometer (Seca Ltd., Birmingham, UK), respectively. Body surface area (m\u003csup\u003e2\u003c/sup\u003e) was estimated using the equation of Du Bois and Du Bois [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Body composition was assessed using a dual-energy X-ray absorptiometry (DXA) scan (Discovery, Hologic, Beford, UK). Following the DXA scan, participants completed three exercise tests on a cycle ergometer (Excalibur Sport, Lode Lode Groningen, Netherlands): 1) a submaximal test to determine lactate threshold; 2) a maximal test to determine \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eO\u003csub\u003e2\u003c/sub\u003epeak and Wpeak; and 3) a familiarisation to the trial protocol.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eSubmaximal exercise test\u003c/h2\u003e \u003cp\u003eThe incremental exercise test comprised of 4-minute stages with the intensity of each stage individualised according to the method reported by Jamnick \u003cem\u003eet al.\u003c/em\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCapillary blood was sampled from a fingertip in the final minute of each stage to determine blood lactate concentrations (Lactate Plus Meter, Nova Biomedical, Waltham, USA). LT\u003csub\u003e1\u003c/sub\u003e was determined as the point where blood lactate concentration rose by 0.5 mmol/L above baseline concentrations [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Participants then rested for 10 minutes before commencing the maximal exercise test.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eMaximal exercise test\u003c/h2\u003e \u003cp\u003eFor the maximal exercise test, participants began cycling at the intensity equivalent to stage 6 of the submaximal test. The intensity increased by the increment in the submaximal test (individualised as per the method reported by Jamnick et al.[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]), but instead of every 4 minutes, the intensity increased every minute until cadence was not able to be sustained above 60 RPM. Expired breath was sampled for the final minute to determine \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eO\u003csub\u003e2\u003c/sub\u003epeak. Following this, participants were provided with a 10-min break before completing a 1-hour familiarisation test at the exercise intensity and the carbohydrate ingestion rate that was prescribed during the main trials.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMain trials\u003c/h2\u003e \u003cp\u003eParticipants arrived at the laboratory in the morning in an overnight fasted state and having voided. Participants were also asked to record food intake and physical activity for 72 hours prior to their first main trial and the larger athletes were asked to replicate this ahead of their second main trial (which was performed in a random order).\u003c/p\u003e \u003cp\u003eUpon arrival at the laboratory, participants were fitted with an intravenous cannula placed in an antecubital vein. A 5-mL blood sample was obtained and centrifuged to obtain plasma. The plasma was stored at -70\u0026ordm;C for later analysis of relevant metabolite [glucose, lactate, non-esterified fatty acid (NEFA)] and hormone (insulin) concentrations. Participants then began a 5-minute warm-up at 50 W before beginning a 2-hour bout of cycling at 95% of LT\u003csub\u003e1\u003c/sub\u003e (or the intensity matched to their counterpart in the SMALLER group). Cadence was self-selected on the cycle ergometer, but participants were asked to maintain this cadence\u0026thinsp;\u0026plusmn;\u0026thinsp;5 RPM throughout. Immediately prior to exercise, participants ingested the first bolus of a glucose solution (14% w/v solution; 300 mL, 42 g glucose). Thereafter, participants were provided with an additional 140 mL of the solutions (20 g glucose) every 15 minutes providing glucose at a mean rate of 1.5 g\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (180 g over the two hours). The drinks also contained 20 mmol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e sodium chloride to assist with replenishment of electrolytes lost through sweat. All drinks were enriched with 300 mg [U-\u003csup\u003e13\u003c/sup\u003eC]-glucose (99%; Cambridge Isotope Laboratories, MA) to increase the \u003csup\u003e13\u003c/sup\u003eC enrichment for determination of exogenous glucose oxidation rates.\u003c/p\u003e \u003cp\u003eExpired breath was sampled every 30 minutes during exercise for the assessment of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eO\u003csub\u003e2\u003c/sub\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eCO\u003csub\u003e2\u003c/sub\u003e and the \u003csup\u003e13\u003c/sup\u003eC enrichment of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eCO\u003csub\u003e2\u003c/sub\u003e. Five-mL of blood was also sampled every 30 minutes during exercise to determine relevant metabolite and hormone concentrations in plasma. Ratings of perceived exertion and gut discomfort were also determined every 30 min using a 6\u0026ndash;20 point and a 1\u0026ndash;5 point scale, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eBlood analysis\u003c/h2\u003e \u003cp\u003eBlood samples were centrifuged (10 min at 4,000 x g and 4\u0026ordm;C) and the plasma obtained, frozen at \u0026minus;\u0026thinsp;70\u0026ordm;C until analysis. Plasma glucose (intra-assay coefficient of variation (CV) 3.2%; interassay CV 3.8%), lactate (intra-assay CV 1.0%; interassay CV 4.8%), and NEFA (intra-assay CV 4.7%; inter-assay CV 4.5%) concentrations were measured using an automated analyser (Daytona, Randox Laboratory, Crumlin, UK) as per the manufacturer\u0026rsquo;s instructions. Plasma insulin concentrations were measured using a commercially available enzyme-linked immunosorbent assay (ELISA; Mercodia AB, Uppsala, Sweden; intraassay CV 5.7%; interassay CV 9.9%).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eBreath analysis\u003c/h2\u003e \u003cp\u003eBreath samples were collected using the Douglas bag method to establish rates of oxygen consumption and carbon dioxide production. During exercise, 1-min samples were taken after 1-min equilibration periods. Concurrently, ambient O\u003csub\u003e2\u003c/sub\u003e and CO\u003csub\u003e2\u003c/sub\u003e concentrations were measured to account for changes in inspired gas concentrations [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Concentrations of O\u003csub\u003e2\u003c/sub\u003e and CO\u003csub\u003e2\u003c/sub\u003e were measured in a known volume of sample (Mini MP 5200, Servomex Ltd., Crowborough, UK), and the total volume of expired gas determined by evacuation using a dry gas meter (Harvard Apparatus, Holliston, USA). To determine \u003csup\u003e13\u003c/sup\u003eC enrichment of expired CO\u003csub\u003e2\u003c/sub\u003e, breath samples were collected in 12-mL exetainers (Labco Ltd, Lampeter, UK), filled in duplicate by 10 s exhalation. Whole-body substrate oxidation was calculated from \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eO\u003csub\u003e2\u003c/sub\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eCO\u003csub\u003e2\u003c/sub\u003e according to stochiometric equations [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The \u003csup\u003e13\u003c/sup\u003eC/\u003csup\u003e12\u003c/sup\u003eC ratio of expired CO\u003csub\u003e2\u003c/sub\u003e was determined by continuous flow isotope ratio mass spectrometry (Iso-Analytical, Crewe, UK) and the enrichment expressed as δ per mil difference between the \u003csup\u003e13\u003c/sup\u003eC/\u003csup\u003e12\u003c/sup\u003eC ratio of the sample and a known standard. Exogenous glucose oxidation rates and endogenous carbohydrate oxidation rates where then calculated according to published equations [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eSample size justification\u003c/h2\u003e \u003cp\u003eThe sample size was based on preliminary data from a study where participants ingested glucose at an mean rate of 1.2 g\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e during moderate-intensity (50% Wpeak) cycling [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Individuals with a body mass\u0026thinsp;\u0026lt;\u0026thinsp;75 kg displayed peak exogenous carbohydrate oxidation rates of (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) 0.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13 g\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, whereas individuals with a body mass\u0026thinsp;\u0026gt;\u0026thinsp;75 kg displayed peak exogenous carbohydrate oxidation rates of 0.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22 g\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Using this effect size (\u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.55), 8 participants in each group should provide greater than 80% power to detect a difference in peak exogenous carbohydrate oxidation rates between groups using an independent, two-tailed \u003cem\u003et\u003c/em\u003e-test with an alpha level of 0.05. To account for dropouts and aim for sufficient power, it was intended to recruit 20 participants in total (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;10 per group). However, due to difficulties in recruiting sufficient people with the necessary characteristics to match between groups, the final sample size was \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;15. To improve statistical power for correlational analyses, we included an additional 12 participants from the placebo condition of a separate study currently in progress, where participants also met the inclusion criteria for the current study and were exercising under identical conditions (NCT05742516, ethics ref: 23/SW/0030).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eThe primary outcome variable was exogenous glucose oxidation rates expressed as the peak oxidation rate (g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and the total exogenous glucose oxidation (g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e or kcal\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Data were checked for normal distribution by visual inspection (residuals for paired data). Comparisons between SMALL \u003cem\u003evs.\u003c/em\u003e LARGE (RELATIVE), and between the SMALL \u003cem\u003evs.\u003c/em\u003e LARGE (ABSOLUTE) were assessed using independent, two-tailed \u003cem\u003et\u003c/em\u003e-tests. Comparisons between LARGE (RELATIVE) \u003cem\u003evs.\u003c/em\u003e LARGE (ABSOLUTE) were assessed using paired, two-tailed \u003cem\u003et\u003c/em\u003e-tests. The associations between exogenous carbohydrate oxidation and participant characteristics (body mass, height, estimated body surface area, dietary intake) were quantified using Pearson\u0026rsquo;s product-moment correlation coefficients. Thresholds of 0.1, 0.3 and 0.5 were used to infer correlations as small, moderate, and large, respectively [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Time-series data (e.g., substrate oxidation, plasma metabolite and insulin concentrations over time) were assessed by: 1) a two-way, mixed-model (time x group) ANOVA comparing SMALL vs LARGE (RELATIVE) and 2) a two-way, repeated-measures (time x intensity) ANOVA comparing LARGE (RELATIVE) vs LARGE (ABSOLUTE). Sensitivity analyses were performed by removal of the two female participants, and the single largest athlete. Due to technical issues with blood sampling (blocked cannulae) data for blood-based variables are \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;7 for SMALL and \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5 for LARGE). Data are presented as means\u0026thinsp;\u0026plusmn;\u0026thinsp;SD, or mean differences (95%CI). Statistical significance was accepted when \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026le;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eRecruitment and retention\u003c/h2\u003e \u003cp\u003eTwenty participants (18 males and 2 females) were recruited. Following dropouts, a total of 15 participants completed the tests and all data from these participants were analysed (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Nine participants were in the SMALL group and six participants were in the LARGE group. Of the six participants in LARGE, one dropped out from the study after completing the RELATIVE trial and was retained for between-group analyses but not for repeated-measures analyses.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eParticipant characteristics\u003c/h2\u003e \u003cp\u003eBy design, the LARGE group had a greater body mass than SMALL (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), in addition to being taller, having more fat-free mass, and a higher absolute lactate threshold (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). However, the LARGE and SMALL groups were matched for age, percentage body fat, and relative lactate threshold (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParticipant characteristics.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSMALL\u003c/p\u003e \u003cp\u003e(\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;9)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLARGE\u003c/p\u003e \u003cp\u003e(\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;6)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMean diff (95%CI)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge\u003c/p\u003e \u003cp\u003e(y)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3 (-8 to 14)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale sex\u003c/p\u003e \u003cp\u003e(\u003cem\u003en\u003c/em\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeight\u003c/p\u003e \u003cp\u003e(cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e178\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e190\u0026thinsp;\u0026plusmn;\u0026thinsp;10*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e12 (1 to 23)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBody mass\u003c/p\u003e \u003cp\u003e(kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e66.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e87.3\u0026thinsp;\u0026plusmn;\u0026thinsp;11.8*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e20.6 (12.0 to 29.3)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBody fat\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15.0\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.9 (-4.9 to 8.7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFat-free mass\u003c/p\u003e \u003cp\u003e(kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e58.0\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e74.4\u0026thinsp;\u0026plusmn;\u0026thinsp;12.7*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e16.4 (6.2 to 26.5)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFat mass\u003c/p\u003e \u003cp\u003e(kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.2 (-0.6 to 9.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLactate threshold\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e156\u0026thinsp;\u0026plusmn;\u0026thinsp;29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e198\u0026thinsp;\u0026plusmn;\u0026thinsp;22*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e41 (11 to 72)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLactate threshold\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(W\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.05 (-0.5 to 0.4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLactate threshold\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(W\u0026middot;kgFFM\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.002 (-0.4 to 0.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eO\u003csub\u003e2\u003c/sub\u003epeak\u003c/p\u003e \u003cp\u003e(L\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.07\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e1.22 (0.52 to 1.92)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eO\u003csub\u003e2\u003c/sub\u003epeak\u003c/p\u003e \u003cp\u003e(mL\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e58\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e58\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.6 (-8 to 9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\dot{\\text{V}}\\)\u003c/span\u003e\u003c/span\u003eO\u003csub\u003e2\u003c/sub\u003epeak\u003c/p\u003e \u003cp\u003e(mL\u0026middot;kgFFM\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e66\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e69\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3 (-7 to 12)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003eData expressed as means\u0026thinsp;\u0026plusmn;\u0026thinsp;SD and mean difference (95%CI). *,\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs SMALL.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eDietary intake\u003c/h2\u003e \u003cp\u003eSelf-reported, weighed food intake for the 3 days prior to trials is reported in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. No substantial differences in dietary intake were evident, especially relative to body size, other than a lower relative fibre intake prior to LARGE ABSOLUTE \u003cem\u003eversus\u003c/em\u003e SMALL (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDietary intake from 3-day food diaries prior to each trial.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSMALL\u003c/p\u003e \u003cp\u003e(\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;9)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLARGE RELATIVE\u003c/p\u003e \u003cp\u003e(\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;6)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLARGE\u003c/p\u003e \u003cp\u003eABSOLUTE\u003c/p\u003e \u003cp\u003e(\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEnergy\u003c/p\u003e \u003cp\u003e(kcal\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2395\u0026thinsp;+\u0026thinsp;472\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2946\u0026thinsp;+\u0026thinsp;1166\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2947\u0026thinsp;+\u0026thinsp;798\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbohydrate\u003c/p\u003e \u003cp\u003e(g\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e301\u0026thinsp;+\u0026thinsp;82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e349\u0026thinsp;+\u0026thinsp;158\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e386\u0026thinsp;+\u0026thinsp;169\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFat\u003c/p\u003e \u003cp\u003e(g\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e88\u0026thinsp;+\u0026thinsp;20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e108\u0026thinsp;+\u0026thinsp;42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e97\u0026thinsp;+\u0026thinsp;22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProtein\u003c/p\u003e \u003cp\u003e(g\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e91\u0026thinsp;+\u0026thinsp;23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e128\u0026thinsp;+\u0026thinsp;42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e118\u0026thinsp;+\u0026thinsp;16*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEthanol\u003c/p\u003e \u003cp\u003e(g\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u0026thinsp;+\u0026thinsp;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u0026thinsp;+\u0026thinsp;13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u0026thinsp;+\u0026thinsp;13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSugar\u003c/p\u003e \u003cp\u003e(g\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e103\u0026thinsp;+\u0026thinsp;45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e114\u0026thinsp;+\u0026thinsp;52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e133\u0026thinsp;+\u0026thinsp;45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFibre\u003c/p\u003e \u003cp\u003e(g\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30\u0026thinsp;+\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31\u0026thinsp;+\u0026thinsp;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e29\u0026thinsp;+\u0026thinsp;8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEnergy\u003c/p\u003e \u003cp\u003e(kcal\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36.1\u0026thinsp;+\u0026thinsp;7.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33.1\u0026thinsp;+\u0026thinsp;8.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e33.2\u0026thinsp;+\u0026thinsp;5.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbohydrate\u003c/p\u003e \u003cp\u003e(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.5\u0026thinsp;+\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.0\u0026thinsp;+\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.3\u0026thinsp;+\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFat\u003c/p\u003e \u003cp\u003e(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.3\u0026thinsp;+\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.3\u0026thinsp;+\u0026thinsp;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.1\u0026thinsp;+\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProtein\u003c/p\u003e \u003cp\u003e(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.4\u0026thinsp;+\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.5\u0026thinsp;+\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.3\u0026thinsp;+\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSugar\u003c/p\u003e \u003cp\u003e(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.6\u0026thinsp;+\u0026thinsp;0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.5\u0026thinsp;+\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.5\u0026thinsp;+\u0026thinsp;0.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFibre\u003c/p\u003e \u003cp\u003e(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;day\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5\u0026thinsp;+\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.4\u0026thinsp;+\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u0026thinsp;+\u0026thinsp;0.1*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbohydrate\u003c/p\u003e \u003cp\u003e(% energy intake)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50\u0026thinsp;+\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e46\u0026thinsp;+\u0026thinsp;3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e51\u0026thinsp;+\u0026thinsp;9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFat\u003c/p\u003e \u003cp\u003e(% energy intake)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17\u0026thinsp;+\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17\u0026thinsp;+\u0026thinsp;3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18\u0026thinsp;+\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProtein\u003c/p\u003e \u003cp\u003e(% energy intake)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16\u0026thinsp;+\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18\u0026thinsp;+\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e17\u0026thinsp;+\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003eData expressed as means\u0026thinsp;\u0026plusmn;\u0026thinsp;SD. *\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026le;\u0026thinsp;0.05 vs SMALL.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eExercise intensity\u003c/h2\u003e \u003cp\u003eAbsolute exercise intensity was higher during LARGE RELATIVE \u003cem\u003eversus\u003c/em\u003e SMALL (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), as was absolute VO\u003csub\u003e2\u003c/sub\u003e and VCO\u003csub\u003e2\u003c/sub\u003e. Also by design, absolute exercise intensity was well matched between LARGE ABSOLUTE \u003cem\u003eversus\u003c/em\u003e SMALL (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExercise responses in smaller (SMALL) and larger (LARGE) athletes cycling at the same relative intensity (95% lactate threshold1) or the similar absolute intensity (W).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSMALL\u003c/p\u003e \u003cp\u003e(\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;7)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eLARGE RELATIVE\u003c/p\u003e \u003cp\u003e(\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eLARGE ABSOLUTE\u003c/p\u003e \u003cp\u003e(\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMean diff vs SMALL\u003c/p\u003e \u003cp\u003e(95%CI)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMean diff vs SMALL (95%CI)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExercise intensity\u003c/p\u003e \u003cp\u003e(W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e149\u0026thinsp;+\u0026thinsp;28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e180\u0026thinsp;+\u0026thinsp;23*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e31 (1 to 61)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e143\u0026thinsp;+\u0026thinsp;19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-7 (-38 to 24)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExercise intensity\u003c/p\u003e \u003cp\u003e(W\u0026sdot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.2\u0026thinsp;+\u0026thinsp;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.1\u0026thinsp;+\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.2 (-0.6 to 0.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.7\u0026thinsp;+\u0026thinsp;0.4*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e-0.6 (-1.0 to -0.1)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExercise intensity\u003c/p\u003e \u003cp\u003e(%VO\u003csub\u003e2\u003c/sub\u003epeak)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e59\u0026thinsp;+\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e57\u0026thinsp;+\u0026thinsp;7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1 (-7 to 3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e46\u0026thinsp;+\u0026thinsp;6*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e-12 (-18 to -7)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCadence\u003c/p\u003e \u003cp\u003e(rev\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e84\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e85\u0026thinsp;\u0026plusmn;\u0026thinsp;12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3 (-8 to 9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e82\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e--5 (-12 to 3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(L\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.2\u0026thinsp;+\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.0\u0026thinsp;+\u0026thinsp;0.5*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.71 (0.26 to 1.16)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.3\u0026thinsp;+\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.09 (-0.28 to 0.46)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(mL\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e34\u0026thinsp;+\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34\u0026thinsp;+\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-2 (-8 to 5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e27\u0026thinsp;+\u0026thinsp;4*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e-7 (-13 to -1)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVCO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(L\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.0\u0026thinsp;+\u0026thinsp;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.7\u0026thinsp;+\u0026thinsp;0.4*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.63 (0.21 to 1.05)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.1\u0026thinsp;+\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.07 (-0.31 to 0.45)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVCO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(mL\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31\u0026thinsp;+\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31\u0026thinsp;+\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3 (-5 to 6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e24\u0026thinsp;+\u0026thinsp;4*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e-6 (-12 to -1)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbohydrate oxidation\u003c/p\u003e \u003cp\u003e(g\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e118\u0026thinsp;\u0026plusmn;\u0026thinsp;36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e152\u0026thinsp;\u0026plusmn;\u0026thinsp;20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e34 (-1 to 69)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e126\u0026thinsp;\u0026plusmn;\u0026thinsp;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e8 (-29 to 44)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFat oxidation\u003c/p\u003e \u003cp\u003e(g\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27\u0026thinsp;\u0026plusmn;\u0026thinsp;13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8 (-5 to 20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.4 (-11 to 12)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRespiratory exchange ratio\u003c/p\u003e \u003cp\u003e(VCO\u003csub\u003e2\u003c/sub\u003e/VO\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.91\u0026thinsp;+\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.91\u0026thinsp;+\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.003 (-0.05 to 0.05)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.91\u0026thinsp;+\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-0.003 (-0.05 to 0.05)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGut discomfort\u003c/p\u003e \u003cp\u003e(scale 1\u0026ndash;5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.06 (-0.6 to 0.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.16 (-0.5 to 0.8)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRPE\u003c/p\u003e \u003cp\u003e(scale 6\u0026ndash;20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.6 (-1 to 3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-1 (-3 to 1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eRPE, rating of perceived exertion. Data expressed as means\u0026thinsp;\u0026plusmn;\u0026thinsp;SD and mean differences (95%CI). *, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026le;\u0026thinsp;0.05 vs SMALL.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eSubstrate oxidation\u003c/h2\u003e \u003cp\u003eTotal exogenous glucose oxidation was 13 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (95%CI 2 to 24 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.03) higher during LARGE RELATIVE versus SMALL (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). Sensitivity analysis with removal of either the two female participants (mean difference: 15 kcal\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; 95%CI: -2 to 27 kcal\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.03) or the largest male (mean difference: 12 kcal\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; 95%CI: -1 to 24 kcal\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.06), did not substantially change this inference. Peak exogenous glucose oxidation rates were 48\u0026thinsp;\u0026plusmn;\u0026thinsp;9 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e during SMALL, compared with 61\u0026thinsp;\u0026plusmn;\u0026thinsp;16 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with LARGE RELATIVE, with a mean difference of 13 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (95%CI -1 to 27 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.07). In the within-subjects analysis, total endogenous carbohydrate oxidation was 20 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (95%CI: 2 to 38 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.04) lower during LARGE ABSOLUTE versus LARGE RELATIVE (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB), and peak exogenous glucose oxidation rates were 60\u0026thinsp;\u0026plusmn;\u0026thinsp;18 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e during LARGE RELATIVE, compared with 54\u0026thinsp;\u0026plusmn;\u0026thinsp;42 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with LARGE ABSOLUTE reflecting a mean difference of 6 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (95%CI -24 to 37 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.60).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDuring exercise, exogenous glucose oxidation rates rose (main effect, time, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001), and were overall higher during LARGE RELTIVE \u003cem\u003eversus\u003c/em\u003e SMALL (main effect, group, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.03; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). Endogenous carbohydrate oxidation rates decreased over time (main effect, time, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001), and were overall higher during LARGE RELATIVE \u003cem\u003eversus\u003c/em\u003e LARGE ABSOLUTE (main effect, intensity, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.02; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). Breath \u003csup\u003e13\u003c/sup\u003eC enrichment over time is displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eCirculating metabolite and insulin concentrations\u003c/h2\u003e \u003cp\u003eAt the onset of exercise plasma glucose and insulin concentrations rose transiently (time effect, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001). At the 30-min time point, plasma glucose concentration was 0.69 mmol\u0026sdot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (95%CI: -0.19 to 1.56 mmol\u0026sdot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) higher in SMALL \u003cem\u003eversus\u003c/em\u003e LARGE (RELATIVE) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). Similarly, at the 30-min time point, plasma lactate concentration was 1.23 mmol\u0026sdot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (95%CI: -0.03 to 2.48 mmol\u0026sdot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) higher in SMALL \u003cem\u003eversus\u003c/em\u003e LARGE (RELATIVE) and plasma insulin concentration was 28 pmol\u0026sdot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (95%CI: 3 to 53 pmol\u0026sdot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) higher in SMALL \u003cem\u003eversus\u003c/em\u003e LARGE (RELATIVE) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). No meaningful differences were observed between groups or exercise intensities for plasma NEFA concentrations (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eAssociations between body size, diet and exogenous glucose oxidation\u003c/h2\u003e \u003cp\u003eWhen pooling data from the current study (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;15) and the ongoing study (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;12), total and peak exogenous glucose oxidation rates displayed large positive correlations with body mass (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB), height (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD), and estimated body surface area (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eE and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eF). Furthermore, these associations were robust to the exclusion of \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;12 from the ongoing study (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.56\u0026ndash;0.72, 95%CI: 0.06 to 0.95, all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). All correlations of diet with exogenous glucose oxidation rates (within the current study sample), when expressed relative to body mass or relative to total energy intake were small (all \u003cem\u003er\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.21, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThe current study demonstrates that, on average, larger athletes can oxidise exogenous glucose at faster rates than smaller athletes during moderate intensity cycling. When larger athletes then exercised at the same absolute intensity as smaller athletes, the reduction in total energy expenditure was mostly accounted for by a reduction in endogenous rather than exogenous carbohydrate oxidation, suggesting that the higher absolute exercise intensity of the larger athletes does not fully account for the increase capacity to oxidise ingested carbohydrate.\u003c/p\u003e \u003cp\u003eDuring prolonged, moderate-to-high intensity exercise, the ability to digest, absorb, and oxidise ingested carbohydrates can be a limiting factor to performance. Part of the rationale that current sports nutrition guidelines for carbohydrate intake during exercise do not account for body size, is that prior evidence did not show a clear positive relationship between body mass and exogenous carbohydrate oxidation rates [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, no prior study was aimed at directly testing the role of body size in exogenous carbohydrate oxidation, and the range of body mass in prior data was ~\u0026thinsp;60 to ~\u0026thinsp;95 kg (less than a 1.6 fold range) [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], which could limit the ability to detect the signal of body mass within the variance. Therefore, we aimed to clarify whether body size is an important determinant of exogenous glucose oxidation rates during exercise. In the current study, we studied people with a wide range of body mass (53 to 110 kg; \u0026gt;2-fold range) with the same relative exercise intensity, exercise modality, environmental conditions and type and amount of carbohydrate. We observed large positive correlations between measures of body size and exogenous glucose oxidation rates, suggesting body size is an important determinant of exogenous glucose oxidation during exercise.\u003c/p\u003e \u003cp\u003eThe mean difference in peak exogenous glucose oxidation that we observed between larger and smaller athletes was 13 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (95%CI -1 to 27 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and the mean difference in total exogenous glucose oxidation was 13 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (95%CI 2 to 24 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). These differences are likely to be physiologically meaningful, based on representing a similar mean difference in exogenous carbohydrate oxidation when ingesting glucose-fructose mixtures \u003cem\u003eversus\u003c/em\u003e glucose only [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Furthermore, this difference in exogenous carbohydrate oxidation rate is similar to that seen when decreasing the fructose-maltodextrin ratio of a drink from 1.25 to 0.8, which results in an increase in 2-hour preloaded, repeated 10 x 2-min sprint performance by ~\u0026thinsp;3% (303 \u003cem\u003eversus\u003c/em\u003e 296 W) [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. This suggests that the differences in exogenous glucose oxidation between larger and smaller athletes are likely to be of practical relevance.\u003c/p\u003e \u003cp\u003eIt was previously suggested that peak exogenous glucose oxidation rates were ~\u0026thinsp;60 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e independent of body size. We therefore provided participants with 90 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e glucose with the rationale of saturating intestinal absorption rates and thereby potential revealing variance dependent on body-size associated intestinal surface area. We observed large, positive correlations between measures of body size (body mass, height, and estimated body surface area) and exogenous glucose oxidation rates, with the largest individual displaying a peak exogenous glucose oxidation rate of 90 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and a total exogenous glucose oxidation rate of ~\u0026thinsp;70 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. This was confirmed with duplicate measures of breath enrichments and this challenges the concept of a fixed upper limit to exogenous glucose oxidation of 60 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. However, due to the single participant within that range of body size, this inference should be taken with some caution until further data confirm or refute this. Nevertheless, the positive associations between body size and exogenous glucose oxidation that we report are robust to the removal of this single extreme phenotype and suggest that exploration of the role of body size and other factors that may explain between-participant variance in exogenous carbohydrate oxidation rates are warranted. These data suggests a blanket 60 \u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e recommendation for all athletes could result in relative underfueling for a larger athlete, but potentially saturating the capacity for smaller athletes to fully absorb and metabolise the ingested glucose, compromising gut comfort, and potentially increasing sympathetic drive and muscle glycogen utilisation [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. From a practical perspective, approximate peak exogenous glucose oxidation rates based on the correlations we report are ~\u0026thinsp;0.7 g glucose per kg body mass per hour (95%CI: 0.64 to 0.75 g\u0026sdot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Interestingly, this maps on to classical sports nutrition guidelines [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] and could be further refined with more research.\u003c/p\u003e \u003cp\u003eA primary determinant of whole-body carbohydrate metabolism is exercise intensity [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. We therefore sought to determine whether any potential differences in exogenous glucose oxidation between larger and smaller athletes could be explained by differences in absolute exercise intensity. To examine this, the larger athletes completed an additional exercise test where the intensity was matched to the smaller athletes. Due to dropouts, the matching was not perfect, but was within reasonable limits [mean difference: -7 W (95%CI -38 to 24 W)]. To maximise statistical power, this analysis was performed as a within-participant analysis comparing the higher \u003cem\u003eversus\u003c/em\u003e lower exercise intensity within the larger athletes. The reduction in exercise intensity was produced by cycling at \u0026gt;\u0026thinsp;20% lower W (from 180\u0026thinsp;\u0026plusmn;\u0026thinsp;23 W to 143\u0026thinsp;\u0026plusmn;\u0026thinsp;19) which lowered total energy expenditure by ~\u0026thinsp;20%. This reduction in total energy expenditure was largely explained by a reduction in endogenous carbohydrate oxidations rates. It is possible that the small sample size may result in a lack of statistical power to detect a difference in exogenous glucose oxidation with differences in exercise intensity. However, the mean difference in exogenous glucose oxidation between the higher and the lower intensity was only 6 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which has been argued as not physiologically meaningful [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Other research has suggested a curvilinear relationship between exercise intensity and exogenous glucose oxidation rates [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], but comparisons between studies are difficult since prior work provided carbohydrate as a single bolus [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Therefore, the difference in exogenous glucose oxidation between larger and smaller athletes cannot be entirely explained by the higher absolute intensity of exercise, and may be due to a variety of factors related to body size including organ sizes and surface areas for digestion, absorption and metabolism.\u003c/p\u003e \u003cp\u003eFollowing ingestion and intestinal absorption, glucose will enter systemic circulation via liver, where it can be released as glucose or as lactate [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Increases in glucose concentration, combined with intestinal L-cell signalling result in incretin hormone secretion, can stimulate insulin secretion, which in turn, regulate whole-body carbohydrate and fat metabolism [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. To examine this, we determined concentrations of key metabolites and insulin in plasma. The smaller athletes displayed larger insulin and lactate responses at the onset of exercise compared to larger athletes, which may be explained by the greater relative dose of glucose ingested [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Another putative explanation for higher lactate responses could be that identification of lactate threshold was erroneous and thus exercise intensity was higher in the smaller athletes. However, it is unlikely that errors in identification of lactate threshold would be systematically biased towards the smaller athletes, and the transient increase in lactate at the onset of carbohydrate feeding during exercise is documented[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Furthermore, the higher insulin concentrations support the hypothesis that relative glucose dose, rather than exercise intensity explains most of the between group variance in lactate concentrations. These responses are, however, unlikely to explain the increase in exogenous glucose oxidation in larger \u003cem\u003eversus\u003c/em\u003e smaller athletes, since increases in circulating insulin and lactate would be expected to result in higher, not lower carbohydrate oxidation rates.\u003c/p\u003e \u003cp\u003eDue to dropouts, there may be a lack of statistical power to detect differences between exercise intensities in the larger athletes. However, the mean difference in peak exogenous glucose oxidation with higher \u003cem\u003eversus\u003c/em\u003e lower exercise intensity was not physiologically meaningful. Furthermore, the study is sufficiently powered for the primary aim, as evidenced by clear and meaningful increases total exogenous glucose oxidation in larger \u003cem\u003eversus\u003c/em\u003e smaller athletes, and in large, statistically significant relationships between body size and exogenous glucose oxidation. Another potential limitation is the lack of generalisability to other types of carbohydrates. The expression of intestinal transport proteins may be regulated by dietary intake [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Since most carbohydrates in most people\u0026rsquo;s diets in middle-to-high income countries are hydrolysed into glucose, and fructose is practically only present sugars, it is likely that dietary exposure to glucose is more consistent between people than is dietary exposure to fructose. Increased variability in fructose exposure may introduce an additional variance component to exogenous carbohydrate oxidation rates when using glucose-fructose mixtures, and this remains to be tested. It was for this reasoning, that we selected glucose as the carbohydrate within the current study. A third limitation with the current study is a lack of data on carbohydrate intake during training to explore as a potential factor mediating exogenous glucose oxidation rates. Habitual diet dietary intakes are extremely challenging to quantify [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], and therefore the ability to detect true relationships between habitual diet (including training nutrition) and exogenous carbohydrate oxidation rates will require extremely large sample sizes combined with novel ways to accurately quantify nutritional intakes.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn conclusion, these data demonstrate that, on average, larger athletes have a greater capacity to oxidise exogenous glucose during exercise than smaller athletes. In doing so, these data justify a re-evaluation of the role of body size and other factors in dictating carbohydrate fuelling during exercise. When seeking to maximise carbohydrate availability during exercise, it may benefit athletes to tailor nutrition guidelines based on body size.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank the participants for volunteering their time and effort for this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJTG, GAW, TP and JAB designed the research. JTG, AJ, AJC, AMC, LB and KH conducted the research. JTG analyzed the data and performed statistical analyses. JTG primarily wrote the paper, and all authors read and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFUNDING\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was part funded by the University of Bath and Clasado Biosciences.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDISCLOSURES:\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe current manuscript was prepared without external funding.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eFor a full list of JTG\u0026rsquo;s disclosures see https://gonzalezjt1.wordpress.com/2024/03/\u003cstrong\u003e,\u0026nbsp;\u003c/strong\u003eJTG has received research funding from BBSRC, MRC, British Heart Foundation, Clasado Biosciences, Lucozade Ribena Suntory, ARLA Foods Ingredients and Cosun Nutrition Center; is a scientific advisory board member to ZOE and 6d Sports Nutrition; and has completed paid consultancy for The Dairy Council, PepsiCo, Violicom Medical, Tour Racing Ltd., the European Fruit Juice Association, and SVGC. JAB is an investigator on research grants funded by BBSRC, MRC, British Heart Foundation, Rare Disease Foundation, EU Hydration Institute, GlaxoSmithKline, Nestl\u0026eacute;, Lucozade Ribena Suntory, ARLA foods, Cosun Nutrition Center, American Academy of Sleep Medicine Foundation and Salus Optima (L3M Technologies Ltd); has completed paid consultancy for PepsiCo, Kellogg\u0026rsquo;s, SVGC and Salus Optima (L3M Technologies Ltd); is Company Director of Metabolic Solutions Ltd; receives an annual honorarium as a member of the academic advisory board for the International Olympic Committee Diploma in Sports Nutrition; and receives an annual stipend as Editor-in Chief of \u003cem\u003eInternational Journal of Sport Nutrition \u0026amp; Exercise Metabolism.\u003c/em\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eCoyle EF, Coggan AR, Hemmert M, Ivy JL (1986) Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. 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Am J Physiology-Endocrinology Metabolism 295(2):E227\u0026ndash;E237\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStubbs RJ, O'Reilly LM, Whybrow S, Fuller Z, Johnstone AM, Livingstone MB, Ritz P, Horgan GW (2014) Measuring the difference between actual and reported food intakes in the context of energy balance under laboratory conditions. Br J Nutr 111(11):2032\u0026ndash;2043. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1017/S0007114514000154\u003c/span\u003e\u003cspan address=\"10.1017/S0007114514000154\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"University of Bath","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Carbohydrate, Cycling, Metabolism, Sports Nutrition","lastPublishedDoi":"10.21203/rs.3.rs-4530175/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4530175/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e Current guidelines do not consider body size for carbohydrate intake during exercise. This study assessed whether larger people can oxidise more exogenous glucose during exercise than smaller people. Fifteen cyclists were allocated into two groups based on body mass (SMALL, \u0026lt;\u0026thinsp;70 kg body mass, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;9, 2 female) or (LARGE, \u0026gt;\u0026thinsp;70 kg body mass, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;6) matched for lactate threshold (SMALL: 2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 W\u0026sdot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, LARGE: 2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 W\u0026sdot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). SMALL completed 120 min of cycling at 95% of lactate threshold\u003csub\u003e1\u003c/sub\u003e. LARGE completed two trials in a random order, one at 95% of lactate threshold\u003csub\u003e1\u003c/sub\u003e [thereby exercising at the same relative intensity (RELATIVE)], and one at an absolute intensity matched to SMALL (ABSOLUTE). In all trials, cyclists ingested 90 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of \u003csup\u003e13\u003c/sup\u003eC-enriched glucose. Total exogenous glucose oxidation was (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) 33\u0026thinsp;\u0026plusmn;\u0026thinsp;8 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in SMALL \u003cem\u003eversus\u003c/em\u003e 45\u0026thinsp;\u0026plusmn;\u0026thinsp;13 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in LARGE-RELATIVE (mean difference: 13 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 95%CI 2 to 24 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.03]. Large positive correlations were observed for measures of exogenous carbohydrate oxidation \u003cem\u003eversus\u003c/em\u003e body size (body mass, height and body surface area; \u003cem\u003ee.g.\u003c/em\u003e, body surface area \u003cem\u003eversus\u003c/em\u003e peak exogenous glucose oxidation, \u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.85,95%CI: 0.51 to 0.95, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). When larger athletes reduced the intensity from RELATIVE to ABSOLUTE, total exogenous glucose oxidation was 39\u0026thinsp;\u0026plusmn;\u0026thinsp;7 g\u0026sdot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.43 \u003cem\u003eversus\u003c/em\u003e LARGE-RELATIVE). In conclusion, the capacity for exogenous glucose oxidation is, on average, higher in larger athletes than smaller athletes during exercise. Body size may therefore be a consideration in tailoring sports nutrition guidelines for carbohydrate intake during exercise.\u003c/p\u003e","manuscriptTitle":"Exogenous glucose oxidation during exercise is positively related to body size","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-05 11:36:44","doi":"10.21203/rs.3.rs-4530175/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f0a32115-b230-4921-8412-d7605fa3d7ed","owner":[],"postedDate":"June 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":32827489,"name":"Physiology"},{"id":32827490,"name":"Nutrition \u0026 Dietetics"},{"id":32827491,"name":"Sports Medicine and Kinesiology"}],"tags":[],"updatedAt":"2024-06-05T11:36:44+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-05 11:36:44","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4530175","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4530175","identity":"rs-4530175","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}