A new incremental cycling cognitive-motor dual-task test to assess simultaneous sustained attention and neuromuscular fatigue in trained athletes.

A new incremental cycling cognitive-motor dual-task test to assess simultaneous sustained attention and neuromuscular fatigue in trained athletes. | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 2 May 2025 V1 Latest version Share on A new incremental cycling cognitive-motor dual-task test to assess simultaneous sustained attention and neuromuscular fatigue in trained athletes. Authors : Thomas Goepp 0009-0000-6166-4992 , Mark Hayes , Pascal Hot , and Thomas Rupp [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.174616416.60847490/v1 Published Scandinavian Journal of Medicine & Science in Sports Version of record Peer review timeline 306 views 114 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract INTRODUCTION . Cognitive efficiency during cognitive-motor dual-task (CMDT) varies with exercise intensity, with low-to-moderate intensities supposed to enhance performance according to an inverted-U theory. This effect remains unexplored in trained individuals, who may better preserve cognitive function at high intensities due to improved prefrontal cortex (PFC) homeostasis. Additionally, neuromuscular fatigue from high-effort exercise is influenced by sustained attention tasks, but its development during whole-body CMDT remains unclear. This study aimed to explore sustained attention and neuromuscular fatigue simultaneously during incremental cycling in trained individuals using an innovative ergometer. METHODS . Forty well-trained adults performed an incremental cycling test combined with a sustained attention Mackworth task. The test involved 3-min ramp stages starting at 1 W·kg -1 , increasing by 0.4 W·kg -1 per stage, until achieving “extremely strong” perceived effort (CR 100 Borg scale, task-failure TF). At each stage, concurrent psycho-physiological assessments included Mackworth score, quadriceps isometric maximum voluntary contraction (IMVC), neuromuscular fatigue indices (peripheral: twitch force, Pt; central: voluntary activation, VA), PFC oxygenation via near-infrared spectroscopy, and mental effort. Data were interpolated at 20, 40, 60, and 80% of TF. RESULTS . Pt decreased linearly throughout the test (Baseline-TF= –40.7±15.1%, P<0.001). VA started to decrease at 40%TF (–1.5±0.9%, P=0.003), with an exacerbated decline from 80%TF (Baseline-TF= –6.9±2.4%, P<0.001), concomitant to IMVC exacerbated declines (Baseline-TF= –20.9±8.9%, P<0.001). PFC oxygenation declined from 60%TF up to TF (–7.9±2.2%, P<0.001). The Mackworth score was not significantly affected during the test until 80%TF (–11.0±6.7% at TF, P<0.001), associated to ≥84±7% of maximal heart rate. CONCLUSION . Sustained attention did not follow the inverted-U theory during incremental cycling in trained adults. Cognitive impairments were observed at very strong intensities, in correlation with PFC deoxygenation. Central fatigue emerged early, itself correlated with increased mental effort and cerebral deoxygenation, questioning the relevance of dedicated CMDT training in sports and occupational settings. A new incremental cycling cognitive-motor dual-task test to assess simultaneous sustained attention and neuromuscular fatigue in trained athletes. Goepp, Thomas. 1 , Hayes, Mark. 2 , Hot, Pascal. 3,4 , Rupp, Thomas. 1,5 1 Inter-University Laboratory of Human Movement Sciences, LIBM University Savoie Mont-Blanc, EA 7424, Chambéry, France; 2 Environmental Extremes Laboratory, School of Education, Sport and Health Sciences, University of Brighton, Brighton, UK 3 LPNC, CNRS URM 5105, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, 38000 Grenoble, France 4 Institut universitaire de France, France 5 Center for Magnetic Resonance in Biology and Medicine, UMR CNRS 6612, Faculty of Medicine of Marseille, Marseille, France Corresponding author: Dr Thomas Rupp [email protected] Abstract count: 295 words Text-only count (introduction through conclusion): 5983 ††slugcomment: To be submitted to the Astrophysical Journal Letter words Number of tables/figures: 1/6 Short title: Incremental cognitive-motor test CONFLICT OF INTEREST The authors declare no competing interests. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Keywords: oxygenation, exercise, performance, central fatigue, mental effort ABSTRACT INTRODUCTION . Cognitive efficiency during cognitive-motor dual-task (CMDT) varies with exercise intensity, with low-to-moderate intensities supposed to enhance performance according to an inverted-U theory. This effect remains unexplored in trained individuals, who may better preserve cognitive function at high intensities due to improved prefrontal cortex (PFC) homeostasis. Additionally, neuromuscular fatigue from high-effort exercise is influenced by sustained attention tasks, but its development during whole-body CMDT remains unclear. This study aimed to explore sustained attention and neuromuscular fatigue simultaneously during incremental cycling in trained individuals using an innovative ergometer. METHODS . Forty well-trained adults performed an incremental cycling test combined with a sustained attention Mackworth task. The test involved 3-min ramp stages starting at 1 W·kg⁻¹, increasing by 0.4 W·kg⁻¹ per stage, until achieving “extremely strong” perceived effort (CR 100 Borg scale, task-failure TF). At each stage, concurrent psycho-physiological assessments included Mackworth score, quadriceps isometric maximum voluntary contraction (IMVC), neuromuscular fatigue indices (peripheral: twitch force, Pt; central: voluntary activation, VA), PFC oxygenation via near-infrared spectroscopy, and mental effort. Data were interpolated at 20, 40, 60, and 80% of TF. RESULTS . Pt decreased linearly throughout the test (Baseline-TF= –40.7±15.1%, P<0.001). VA started to decrease at 40%TF (–1.5±0.9%, P=0.003), with an exacerbated decline from 80%TF (Baseline-TF= –6.9±2.4%, P<0.001), concomitant to IMVC exacerbated declines (Baseline-TF= –20.9±8.9%, P<0.001). PFC oxygenation declined from 60%TF up to TF (–7.9±2.2%, P<0.001). The Mackworth score was not significantly affected during the test until 80%TF (–11.0±6.7% at TF, P<0.001), associated to ≥84±7% of maximal heart rate. CONCLUSION . Sustained attention did not follow the inverted-U theory during incremental cycling in trained adults. Cognitive impairments were observed at very strong intensities, in correlation with PFC deoxygenation. Central fatigue emerged early, itself correlated with increased mental effort and cerebral deoxygenation, questioning the relevance of dedicated CMDT training in sports and occupational settings. ††slugcomment: To be submitted to the Astrophysical Journal Letter INTRODUCTION Cognitive-motor dual-task (CMDT) involves the simultaneous execution of motor and cognitive tasks (Tuena et al., 2023). CMDT scenarios are commonly observed in occupations and sports where intense physical exertion combined with high cognitive demand—such as maintaining sustained attention while carrying a load in military operations or during high-intensity soccer gameplay—may reduce task effectiveness. A leading hypothesis proposes an inverted-U relationship between exercise intensity and cognitive performance (Chang et al., 2012; Lambourne & Tomporowski, 2010; Moore et al., 2012). According to this model, cognitive performance is supposed to peak at moderate exercise intensity (the highest point of the inverted-U curve), likely due to increased arousal facilitated by neurotransmitter release (McMorris et al., 2016). However, the decline in cognitive performance at higher intensities, as suggested by the inverted-U relationship, is debated across trained populations (Browne et al., 2017). It is suggested that cognitive performance may be less impaired during high-intensity exercise when individuals experience lower physiological stress at a given relative workload (Browne et al., 2017). The physiological profile associated with trained individuals may help attenuate the typical prefrontal cortex (PFC) deoxygenation observed above the respiratory compensation point during physical exercise (Oussaidene et al., 2015). Functional magnetic resonance imaging studies highlighted that PFC networks are highly implicated by physical exercise (Li et al., 2014) and cognitive tasks as executive functions (Banich et al., 2000) or attentional fields (Langner & Eickhoff, 2013). These statements suggest that sustained PFC oxygenation could help to preserve cognitive performance in a model of neural resources allocation during task execution (Dietrich & Audiffren, 2011). However, it is likely that all cognitive dimensions are not equally sensitive to PFC networks (McMorris & Hale, 2012), although other brain regions may also be modulated by exercise intensity during CMDT situations. This raises the question of how specific cognitive domains are differentially affected by exercise-induced changes in PFC activity in trained individuals. The inverted-U framework has primarily been applied to executive functions—higher-order cognitive processes such as working memory, inhibitory control, cognitive flexibility, planning, reasoning, and problem-solving (Cristofori et al., 2019)—which represent some of the most extensively studied domains in neuroscience (Miyake et al., 2000). These functions are thought to be particularly sensitive to fluctuations in PFC oxygenation, with performance modulations frequently observed during concurrent physical exercise (Leh et al., 2010). Attention, as a fundamental cognitive resource underlying executive functioning, has also received increasing interest in recent years. Among its subtypes, sustained attention (SA)—defined as the capacity to maintain focus over time—is especially relevant in many sport and occupational contexts (Hajar et al., 2019). Some authors suggest that SA may be less dependent on PFC activation than executive functions, and thus potentially less affected by simultaneous physical effort (McMorris & Hale, 2012). As a result, it remains unclear whether SA follows the same inverted-U pattern across different exercise intensities. In parallel, our recent findings indicate that physically demanding CMDT can modulate the etiology of neuromuscular fatigue, particularly during high-intensity efforts, suggesting substantial interactions between cognitive load and neuromuscular function efficiency. Neuromuscular fatigue, defined as the exercise-induced decline in isometric maximal voluntary contraction (IMVC), stems from both peripheral mechanisms (within the muscle) and central mechanisms (proximal to the neuromuscular junction, including the central nervous system) (Bigland-Ritchie et al., 1986). Recent literature highlighted that CMDTs possibly modulate neuromuscular fatigue etiology by specifically increase central fatigue compared to exercising alone but evidence are scarce and limited to two different cases: at exhaustion after isometric contractions at 15% IMVC with surimposed executive function task (Chatain et al., 2019) or after 15 min of cycling at 80% of maximal heart rate with a surimposed SA task (Goepp et al., 2024). It remains unknown how neuromuscular function is progressively impacted by exercise intensity across a CMDT that would involve large muscle mass (cycling) and a SA task. Neuromuscular fatigue and particularly central alterations are known to recover very quickly (Gruet et al., 2014). Most of the studies involving neuromuscular function assessment after global exercise ( e.g ., cycling, running) suffer from possibly biased interpretations due to the time needed to move the participants to the isometric knee-extensor ergometer after completion of exercising (30-180s) (Collins et al., 2018). This time-delay issue weakens the ability to put in correspondence a given level of cognitive efficiency and a given amount and aetiology of fatigue but can be addressed using an innovative cycle ergometer (Di Domenico et al., 2022; Doyle-Baker et al., 2018). For that purpose, a new incremental cycling test involving a surimposed cognitive task with regular neuromuscular fatigue assessments at the end of each cycling stage may be relevant to better understand the interaction between cognitive performance and neuromuscular fatigue development. The present study aimed to simultaneous explore SA efficiency, PFC oxygenation and neuromuscular fatigue etiology during an incremental cycling exercise in trained participants. We hypothesised that SA performance would be enhanced for low-to-moderate exercise intensities and slightly impaired close to task-failure, alongside significant PFC deoxygenation and exacerbated central fatigue. MATERIALS AND METHODS Based on resource constraint (Lakens, 2022), we recruited 40 participants to answer to the main aims of this study (COG EX group; 10 women and 30 men; age: 28.5 ± 7.4 yrs, mass: 72.2 ± 9.5 kg, body mass index: 22.9 ± 2.2 kg.m -2 , training per week: 8.0 ± 3.1 hours). Our reached sample size, according to GPower 3.1 software calculation, allows detecting a small effect size of f = 0.19 ( i.e. η p 2 ~ 0.035), with a power of 0.95, for the within interaction of a repeated-measures ANOVA and with correlations among measures being equal to 0.5. All the participants were considered as trained (Tier 2) in the Participant Classification Framework (McKay et al., 2022) and the main sports identified were cycling, running and CrossFit. The participants refrained from intense or unhabitual physical exercise for 24 hours before the experimental sessions. We decided to recruit a posteriori 40 additional participants, matched on the sex, age and the training status of the COG EX group (COG MATCHED group; 10 women and 30 men; age: 26.4 ± 6.7 yrs, mass: 70.3 ± 8.7 kg, body mass index: 22.3 ± 2.0 kg.m -2 , training per week: 8.4 ± 3.2 hours). These participants were engaged in a single session of repetitive cognitive tasks without exercise, to check for confounding effects ( e.g ., learning effect, mental fatigue) in the interpretation of cognitive efficiency across the experimental session in the COG EX group. The study followed the principles of the Declaration of Helsinki (2008 edition) and was approved by the local ethics committee (CER-USMB, 2024-03-BFRDT). All participants provided written consent prior to the study and were naive to the study aims and hypotheses. Experimental design Participants performed 2 sessions (familiarization followed by experimental session), interspaced by at least 24 hours, on an innovative cycle ergometer (Di Domenico et al., 2022), allowing neuromuscular fatigue assessments with a short delay ( i.e. 1 st visit: familiarization The first visit was conducted to familiarize the participants with cycling at various levels of perceived effort, using the 100-points Borg scale (CR 100 , Borg et al., 2020) in a semi-supine position on the ergometer, as well as with the procedures for neuromuscular function assessment. The participant’s position on the innovative cycle ergometer was set to allow pedaling as well as isometric contractions of the right leg extensors to allow maximum force production in the horizontal axis ( i.e., knees and hips flexed at 90°, as recommended by Doyle-Baker et al., 2018. This position was maintained during the experimental visit. The participants were also used to complete the Mackworth task ( cf . cognitive task section) at rest (2×30 trials) and while cycling (1×60 trials). 2 nd visit: experimental session After positioning on the ergometer, the participants performed a short practice of the Mackworth task (1×30 trials) followed by a 2 min 30 s-block of trials, at rest. After a baseline evaluation of the knee-extensor neuromuscular function (see dedicated section below), participants were involved in a new incremental cycling cognitive test (ICCT) on the innovative cycle ergometer. Stages of the ICCT were 3-min, at a free cadence ranging between 70 and 90 RPM and the participants started cycling at 1 watt.kg -1 with 0.4 watt.kg -1 increments up to a cycling effort of ≥90/100 (extremely strong) on the CR 100 . Each cycling stage was combined with the Mackworth task for the first 2 min 30 s and perceptual responses were assessed during the last 30s of the stage. PFC oxygenation and heart rate (HR) were continuously recorded while neuromuscular fatigue was evaluated immediately at the end of each stage. Individual data were extrapolated at 20, 40, 60, and 80% of task failure (TF) to analyse progressive changes across ICCT. This method allowed a relative comparison of participants who completed different numbers of stages before reaching maximality criteria. The experimental session is presented in Fig. 1 . Measurements Cognitive task . The Mackworth task was employed to evaluate sustained attention (SA) at rest and divided attention during each ICCT stage, using the web-based platform PsyToolkit. The task involved visualizing a clock-like dial displaying a green arrow that moved like the second hand of a watch, randomly performing a larger temporal jump (15% of the trials). Participants were instructed to respond to these jumps as quickly as possible by clicking, while ignoring the normal movements of the second hand during the remaining 900 ms intervals when no response was required. Participants were instructed to prioritize both speed and accuracy to mitigate potential trade-offs between these variables. Reaction time, accuracy, and a composite score that equally weighed these two factors were systematically evaluated. Each block of the task lasted 2min 30s, and the three performance indicators were averaged across blocks. Prior to data collection, participants were provided with a comprehensive description of the task and its instructions. At the beginning of the experimental session, participants completed a brief practice block of 30 trials (~30 s) to remind with the task mechanics. A video of a typical Mackworth task sequence is provided in Supplementary Material n°01 . Innovative ergocycle and neuromuscular function assessments . The ICCT was performed using a cycling ergometer developed in the laboratory to allow immediate evaluation (<3-5 s) of the isometric maximal voluntary contraction (IMVC) of the knee-extensor neuromuscular function at the end of each cycling stage in the semi recumbent position, allowing regular neuromuscular function evaluations. Cycling powers were imposed during the ICCTs from a Wingate Velotron setup (Racermate Inc., Seattle, WA), connected to the ergometer. Cycling power was normalized to bodyweight and expressed in watt.kg -1 . ††slugcomment: To be submitted to the Astrophysical Journal Letter Neuromuscular function assessments. To assess peripheral and central indices of neuromuscular fatigue, electrical stimulations were administered percutaneously to the femoral nerve via a cathode electrode (10-mm diameter; Meditrace 100, Covidien) placed on the inguinal triangle. A rectangular anode electrode (50 × 90-mm, Durastick Plus, DJO Global, Vista, CA, USA) was attached to the gluteal fold. An electrically induced square wave of 1-ms duration was delivered using a constant current stimulator (DS7A, Digitimer, Welwyn Garden City, Hertfordshire, UK). At the beginning of each session, to determine the optimal intensity of stimulation, single stimuli were delivered incrementally in steps of 10 mA, every 5 s, until the twitch amplitudes plateaued. The optimal intensity was then increased by 20% for subsequent evaluations, to ensure supramaximality. The evaluation started with a 3-s IMVC with one high-frequency doublet (Db 100, HF) evoked during the force plateau. Three electrical stimuli were then delivered to the relaxed muscle interspersed with 3 s between each stimulus: one Db 100 , one low-frequency doublet (Db 10, LF), and one singlet (pic twitch, Pt). The ratio of Db 10 to Db 100 (LF/HF) was calculated as an index of low-frequency fatigue (Verges et al., 2009). Voluntary activation (VA) corresponding to a central fatigue indicator was calculated using the formula below (Strojnik & Komi, 1998) : \begin{equation} \text{VA}\left(\%\right)=\left(\ 1-\frac{SIT*\frac{F_{\text{init}}}{\text{MVC}}}{\text{Db}_{100}}\ \right)*100\nonumber \\ \end{equation} where SIT is the amplitude evoked when stimulation was delivered on MVC, F init is the initial force during the stimulation, Db 100 is the amplitude evoked by Db 100 on relaxed muscle. Neuromuscular evaluation was performed in a non-fatigated state, before the ICCT (Baseline), immediately at the end of each 3-min stage and at the end of the ICCT. The duration of the neuromuscular function assessment (inter-stage delay) was approximately 15 s. Prefrontal cortex oxygenation. PFC oxygenation was continuously monitored during the ICCT using NIRS (Portalite, Artinis Medical Systems, Elst, The Netherlands). The source generated two wavelengths of continuous near-infrared light (780 and 850 nm), allowing monitoring of changes in oxy-, deoxy- and total haemoglobin concentrations (O 2 Hb, HHb and tHb respectively). The theoretical and performance details of NIRS have been previously described (Perrey, 2008). The PFC tissue saturation index (TSI, expressed in %) was calculated by the device based on spatially resolved spectroscopy and was used to assume changes in intracortical oxygen status. The detection probe was positioned over the left PFC area between Fp1 and F3, according to the modified international EEG 10-20 system and firmly secured to the skin with double-sided tape. A black sweatband was placed over the probe to shield the optodes from the ambient light. NIRS data were collected at 50 Hz, filtered with a 2-sec moving Gaussian smoothing algorithm, and averaged over the first 2 min 30 s of each stage. A standardized baseline sited position on the cycle ergometer, without moving the legs, was maintained during 2min just before starting the ICCT. NIRS-derived haemoglobin concentrations were expressed as relative changes from this baseline. Heart rate . HR was monitored throughout the entire experimental session, using a cardiothoracic girdle sensor (Polar E10, Polar Electro 2024, France). HR data were averaged over each 3-min stage and presented as percentage of maximal HR (%HR max ) achieved during a field intermittent maximal test (IFT30/15, (Buchheit, 2010)) performed in the 2 weeks before experiment by each participant (mean HR max of 191.6 ± 8.8 bpm). Perceived cycling effort and mental effort. Cycling effort, defined as “the conscious sensation of how hard, heavy, and strenuous exercise is” (Marcora, 2010) and mental effort asked as “what is the mental effort associated with the situation?” were assessed during the last 20-sec of each stage across ICCT, using the CR 100 Borg scale. Once a perceived cycling effort rating of ≥90/100 (“extremely strong”) was reported by the participant, the ICCT was stopped, and a last neuromuscular function assessment was performed. ††slugcomment: To be submitted to the Astrophysical Journal Letter Complementary experimentation conducted on a COG MATCHED group to get deeper insights on cognitive function responses observed in the COG EX group. The participants recruited a posteriori (COG MATCHED ), performed a single experimental session consisting of a repetition of 3-min blocks of SA task with the exact same parameters and timings as was performed during the ICCT for the COG EX group. These participants were familiarized to the task exactly in the same manner as the COG EX participants. The number of blocks realized was matched on the number of blocks performed by the participants of the COG EX group. This was done to identify possible task-learning effect (potentiation) or task efficiency deterioration that would be due to mental fatigue or demotivation with the repetitions of the tasks. As for the COG EX group, reaction time, accuracy, and a composite score were evaluated on the Mackworth tasks (see cognitive task section) and mental effort was assessed during the last 30 s of each 3-min block. The inter-block delay was 15 s to mimic ICCT design. The participants were asked to be as efficient as possible on each block and were not informed about the number of SA blocks to be performed to prevent motivational interference and to be placed in the same situation as the COG EX participants. The Mackworth task and mental effort values were analyzed as deltas from resting values to better comprehend the effects of exercise intensity. For ethical issues related to the main objective of this complementary experimentation, other variables than cognitive responses ( e.g ., prefrontal oxygenation, neuromuscular responses) were not assessed in the COG MATCHED participants. Statistical analysis All statistical analyses were performed using JASP software (version 16, Amsterdam, The Netherlands) and statistical significance was set at P<0.05. Data are presented as mean ± SD in the text and in the figures. Shapiro Wilk tests were conducted to assess the normal distribution of the data. In cases where sphericity was violated (Mauchly test), Greenhouse-Geisser corrections were applied. To examine the effects of the ICCT on SA (Mackworth task) and mental effort, two-way analysis of variance for repeated measures (ANOVAs RM) were performed on 6 time points (main effect of time at baseline, 20%, 40%, 60%, 80% and TF) between COG EX and COG MATCHED (main effect of group ). Secondly, one-way ANOVAs RM were conducted on NIRS-derived and neuromuscular function indices on these same 6 time points only for the COG EX group. Power output, %HR max and cycling effort were examined with one-way ANOVAs RM at 20%, 40%, 60%, 80% and TF. Pairwise Bonferroni procedures were applied for post-hoc analyses when ANOVA revealed significant results. The partial eta squared (η p 2 ) for ANOVA analysis was calculated, where η p 2 <0.01 indicates a very small effect, 0.01≤η p 2 <0.06 a small effect, 0.06≤η p 2 <0.14 a moderate effect, and η p 2 ≥0.14 a large effect (Cohen, 2013). For COG EX group, within-participant repeated measures correlations were used to assess the relationships between SA, mental effort, VA and TSI responses (deltas from baseline across ICCT) using the rmcorr package in R (version 0.3, Nick Golding, CRAN, The Netherlands) (Bakdash & Marusich, 2017). This was performed to assess possible interdependences between variables considering the 5 time points per participants (∆20%, ∆40%, ∆60%, ∆80%, ∆TF from baseline). The coefficient provided by the correlations (r rm ) was interpreted according to conventional effect size guidelines, where r rm <0.1 indicates a very small effect, 0.1≤r rm <0.2 a small effect, 0.2≤r rm <0.3 a moderate effect, and r rm ≥0.3 a large effect (Gignac & Szodorai, 2016). RESULTS ICCT cycling performance and HR responses . The COG EX group performed 7.0 ± 1.4 stages before reaching TF as defined as a cycling effort ≥90/100. As shown in Table 1 , the maximal cycling power at TF was 3.29 ± 0.51 watt.kg -1 with a HR max of 175 ± 12 bpm (91.3 ± 6.4% HR max ). Sustained attention performance. As a reminder, cognitive assessments have been performed in a matched way in both COG EX and COG MATCHED group. For Mackworth score, main effect of time (F (5, 390) =3.6, P=0.005, η p 2 =0.044), group (F (1, 78) =17.1, P<0.001, η p 2 =0.18) and time × group interaction (F (5, 390) =6.1, P<0.001, η p 2 =0.072) were reported ( Fig. 2A ). Mackworth score was lowered at 80%TF (–8.3 ± 5.7, P=0.026) and TF (–11.0 ± 6.7, P<0.001) in COG EX compared to COG MATCHED . For Mackworth accuracy, main effect of time (F (5, 390) =5.6, P<0.001, η p 2 =0.067), group (F (1, 78) =5.6, P=0.020, η p 2 =0.068) and time × group interaction (F (5, 390) =5.9, P<0.001, η p 2 =0.071) were reported ( Fig. 2B ). Mackworth accuracy was lowered at TF (–17.1 ± 6.8, P<0.001) in COG EX compared to COG MATCHED . For Mackworth reaction time, main effect of time (F (5, 390) =2.4, P=0.045, η p 2 =0.030), group (F (1, 78) =9.4, P=0.003, η p 2 =0.11) and time × group interaction (F (5, 390) =6.2, P<0.001, η p 2 =0.074) were reported ( Fig. 2C ). Mackworth reaction time was increased at 80%TF (+58.2. ± 29.4ms, P=0.007) and TF (+68.1 ± 38.6ms, P<0.001) in COG EX compared to COG MATCHED . Neuromuscular function responses. Regarding IMVC assessed during the ICCT on the COG EX group exclusively, a main time effect was reported (F (4, 133) =64.7, P<0.001, η p 2 =0.63; Fig. 3A ). IMVC was reduced from 20%TF (P0.05), and IMVC was further decreased between 80%TF and TF (–6.7 ± 4.5%, P<0.001). For peripheral indices of fatigue, a main effect of time was reported for LF/HF (F (4, 123) =88.6, P<0.001, η p 2 =0.71; Fig. 3B ) and Pt changes (F (4, 123) =87.7, P<0.001, η p 2 =0.71; Fig. 3C ). LF/HF and Pt changes were lowered at 20%TF compared to baseline (P=0.003 and P<0.001, respectively) and were further decreased at 80%TF and TF (–7.4 ± 7.6%, P<0.001 and –11.4 ± 9.8%, P<0.001, respectively). For VA as a central index of fatigue, a main effect of time was reported (F (4, 125) =50.9, P<0.001, η p 2 =0.59; Fig 3D ). VA was lowered at 40%TF compared to baseline (P=0.003) and was further decreased between 60 to 80%TF (–1.2 ± 0.8%, P=0.03) and between 80%TF and TF (–3.5 ± 1.3%, P<0.001). PFC oxygenation responses. For prefrontal TSI during ICCT, a main effect of time was observed (F (2, 53) =48.4, P<0.001, η p 2 =0.57; Fig. 4A ). TSI was decreased at 60%TF compared to baseline (P<0.001) and was further decreased at 80%TF (–2.4 ± 1.2%, P<0.001) and between 80%TF and TF (–2.1 ± 1.4%, P=0.002). A main effect of time was observed for prefrontal O 2 Hb (F (2, 53) =88.3, P<0.001, η p 2 =0.75), HHb (F (2, 53) =94.8, P<0.001, η p 2 =0.76) and tHb (F (2, 53) =118, P<0.001, η p 2 =0.80). O 2 Hb and tHb ( Fig. 4B/D ) were increased at 40%TF compared to baseline (P=0.032 and P=0.013, respectively) and were further increased at 60%TF (+6.8 ± 2.3 µmol, P<0.001, +8.8 ± 3.2 µmol, P<0.001, respectively), and at 80%TF (+3.7 ± 1.8 µmol, P=0.005, +5.1 ± 2.6 µmol, P<0.001, respectively) before plateauing between 80%TF and TF (both P=1.0). HHb ( Fig. 4C ) was increased at 60%TF compared to baseline (P<0.001) and was further increased at 80%TF (+1.4 ± 0.7 µmol, P<0.001) and between 80%TF and TF (+1.7 ± 0.8 µmol, P<0.001). Perceived cycling effort and mental effort responses . For the COG EX group, the cycling effort increased linearly across the ICCT (F (4, 156) =818, P<0.001, η p 2 =0.96) up to TF criteria (92 ± 2.3 on the CR 100 scale; Table 1 ). For mental effort, main effects of time (F (5, 390) =133, P<0.001, η p 2 =0.63), group (F (1, 78) =109, P<0.001, η p 2 =0.58) and time × group interaction (F (5, 390) =106, P<0.001, η p 2 =0.057) were reported ( Fig. 5 ). Mental effort was higher from 40%TF (+11.4 ± 6.2, P=0.001) to TF (+48.9 ± 10.3, P<0.001) in COG EX compared to COG MATCHED . Repeated measures correlations between SA, mental effort, VA and TSI . Six analyses were performed to explore the interplay between ∆SA, ∆mental effort, ∆VA and ∆TSI from baseline across the ICCT. The Mackworth score displayed positive correlations with TSI and VA (r rm =0.30 [95% CI: 0.15, 0.43], p<0.001 and r rm =0.18 [95% CI: 0.03, 0.33], p=0.02, respectively) and negative correlations with mental effort (r rm = –0.32 [95% CI: –0.45, –0.17], p<0.001) ( Fig. 6A/B/C ). The TSI displayed negatives correlation with mental effort (r rm = –0.75 [95% CI: –0.81, –0.68], p<0.001) and positive correlations with VA (r rm =0.58 [95% CI: 0.47, 0.68], p<0.001) ( Fig. 6D/E ). The VA displayed negative correlations with mental effort (r rm = –0.60 [95% CI: –0.69, –0.49], p<0.001) ( Fig. 6F ). DISCUSSION The aim of this investigation was to explore simultaneous SA efficiency, PFC oxygenation and neuromuscular fatigue etiology during a new incremental cognitivo-motor exercise in trained participants. The main findings are that: (i) SA performance was not enhanced for low-to-moderate cycling intensities but was impaired for strong to extremely strong cycling efforts (≥80%TF, ≥84%HR max ); (ii) significant PFC deoxygenation appeared for strong cycling effort (≥60%TF, ≥77%HR max ) and was correlated with SA performance; (iii) central fatigue appeared early for moderate cycling effort (≥40%TF, ≥64%HR max ) and was mainly correlated with PFC deoxygenation and mental effort. SA performance did not follow an inverted-U curve across incremental cycling. To our knowledge, this is one of the first studies to examine SA across exercise intensities throughout an incremental cycling and cognitive test ( cf . CMDT). Mackworth score was preserved until COG EX participants reached a very strong (score –8.3 ± 5.7%) to extremely strong (score –11.0 ± 6.7%) cycling thresholds (≥80%TF, ≥84%HR max ). Our results are reinforced by the observations in the COG MATCHED group for whom the performance along the Mackworth task was maintained from baseline (score of 63.6 ± 10.9%) to TF (score of 67.4 ± 10.4%), dismissing any learning effect, or any mental fatigue effect with such a succession of Mackworth sequences. The unimproved SA performance during low-to-moderate exercise intensities contradicts our initial hypothesis, while its impairment near TF aligns with our expectations. We challenged two main principles of the inverted U-shaped theory (Lambourne & Tomporowski, 2010; Moore et al., 2012). Firstly, for efforts rated as “low” (20%TF, 13.6 ± 8.4 /CR 100 ) to “moderate” (40%TF, 25.3 ± 11.4 /CR 100 ), SA performance was not statistically different to baseline values, suggesting that cycling at these intensities did not improve SA. While it has been suggested that physical activity increases arousal ( e.g. noradrenaline secretion), improving cognition facilitated by neurotransmitter release, it is possible that SA performance remained unchanged in the present study for these cycling intensities owing to the timing of consideration of the so-called dual-task ( i.e . during vs . post-moderate cycling). Indeed, lower effect sizes related to the cognition modifications have been reported during CMDT compared to when the studied cognitive task was performed a few minutes post-exercise (Lambourne & Tomporowski, 2010). Also, despite Stone et al., (2020) examining executive function tasks, they found no improvement of cognition during an incremental running test performed by trained soldiers, aligning with our results using a SA task. Secondly, contrary to what could have been expected, SA efficiency with cycling efforts rated as strong (60%TF, 44.2 ± 12.7 /CR 100 ) was not impaired in trained adults. We suggest that the fitness level is an important factor that likely explains this result, as less trained participants were shown to decrease their SA performance during “strong” cycling efforts (Goepp et al., 2024). A direct comparison between these two types of population would therefore be of interest to assess the impact of training level on our measurements. We observed correlations between Mackworth score and TSI (r rm = 0.30) suggesting that the PFC oxygenation is a possible mechanism engaged in cognitive performance during CMDT, supporting the model of neural resources allocation during task execution (Dietrich & Audiffren, 2011). We may speculate that the increase in oxy- and total haemoglobin observed with NIRS up to 80%TF is a proxy of the likely efficient neurovascular coupling in the PFC, at least efficient enough to cope with the progressive task-induced metabolic activity so that the SA performance can still be maintained for submaximal intensities. The observation of a decreased TSI associated with a plateau in oxy- and total hemoglobin under the prefrontal probe are signs that the neurovascular coupling is challenged in its ability to fully cope with the metabolic activity of the local cerebral networks above 80%TF. These findings underscore the importance of investigating the interactions between oxygenation profiles and SA performance during CMDT in populations that are more susceptible to cerebral deoxygenation during submaximal exercise or due to challenging environmental conditions ( e.g ., heat, hypoxia), where oxygen delivery to the prefrontal cortex may be suboptimal. When participants rated cycling effort as very strong or higher (≥80%TF, 68.4 ± 11.0 on the CR 100 scale; 83.9 ± 6.9%HR max ), we observed a noticeable decrease in SA performance. These results are consistent with those obtained in a previous study assessing executive functions abilities in soldiers during incremental running (Stone et al., 2020). In the latter, they reported cognition to be impaired for intensities ≥80%HR reserve . This suggests that high-intensity physical exertion, which also demands significant cognitive resources, can reduce performance on concurrent cognitive tasks. Accepting we are unable to attribute their larger effect size (η p 2 = 0.59 compared to η p 2 = 0.067 in the present study) to either the cognitive domain considered (executive function vs . sustained attention) (Leh et al., 2010), or the type of whole-body exercise performed (running vs . cycling CMDT in the present study) (Lambourne & Tomporowski, 2010), our study is the first to confirm in a larger sample size (N=40 in the present study) that these observations are also consistent during cycling and that these results can be put in perspective of the kinetics of PFC oxygenation, but also in correlation with mental effort and neuromuscular fatigue development. Our findings provide clear evidence of the deleterious impact of very intense exercise (≥87%HR max ) on SA performance in trained adults, addressing the uncertainty noted by Browne et al. (2017) in their review. CMDT situation: a catalyst of central fatigue. One of our hypotheses was the development of neuromuscular fatigue across ICCT explaining in part a decrease in SA performance. Fatiguability appeared progressively from the beginning of the ICCT, as indicated by a linear decrease in IMVC (Baseline-TF = –21 ± 9.2%). Comparable amounts of global fatigue were observed at the end of an incremental cycling test without a surimposed cognitive task, conducted up to volitional exhaustion (TF, ~187 bpm) using a very similar ergometer capable of rapidly assessing neuromuscular fatigue (Mira et al., 2018). These findings suggest that the decrease in IMVC between CMDT and exercising alone was not different, but the aetiology of fatigue remained scarcely reported (Chatain et al., 2019; Goepp et al., 2024). With the aim of clarifying the origin of the neuromuscular impairments during the ICCT, we investigated the kinetics of peripheral and central mechanisms of fatigue. Peripheral fatigue, as measured by Pt and LF/HF ratio, developed linearly along ICCT (–40.7 ± 15.1% and –25.2 ± 9.5%, respectively), what is consistent with the decline in IMVC. These decreases in Pt and LF/HF ratio are consistent with findings by Mira et al. (2018), who reported similar values under iso-HR conditions near the end of a comparable incremental cycling protocol [at 92% HR max (comparable to the TF condition in the present study): –44.5 ± 13.4% and –32.4 ± 14.6%, respectively]. These similarities suggest that the surimposed cognitive task does not exacerbate the development of peripheral fatigue. Indeed, previous studies using repeated measures randomized designs with exercise protocols involving isolated leg exercises or cycling have found similar levels of peripheral fatigue between CMDT and physical exercise alone conditions and further supports the notion that CMDT situations exert a more direct influence on motor command. Voluntary activation tracked to estimate the central fatigue started to be significantly decreased at 40%TF (–1.5 ± 0.6%) and was further depressed at TF (–7.0 ± 1.4%). The companion studies by Aboodarda et al. (2018) and Mira et al. (2018) reported only modest impairments in VA under iso-HR conditions “at 64% HR max , corresponding to the 40%TF condition in the present study: +0.9 ± 0.8%; and at 92% HR max corresponding to the TF condition in the present study: –1.3 ± 0.6%, respectively”. Notably, these reductions were statistically significant only at the very end of the incremental cycling test without any superimposed cognitive task (≥96.2% HR max ) (Aboodarda et al., 2018). The reported VA impairments with high intensities of cycling are traditionally explained by the increased release of metabolites (Allen et al., 2008), stimulating III/IV afference fibers known to project centrally and inhibit central command (Gandevia, 2001). We suggest that in our case, the earlier onset and greater extent of central fatigue may be attributed to the concurrent cognitive task, which likely recruited additional brain resources. Recent studies suggested that central fatigue is increased at the end of challenging physical exercises performed with superimposed cognitive tasks ( i.e . intermittent knee-extensor contractions up to TF or 15-min strong cycling exercise) (Chatain et al., 2019; Goepp et al., 2024). Thanks to a unique assessment design and setup, the present study is the first to reliably provide evidence on the relevant VA perturbation on whole-body CMDT where exercise intensity is incrementally manipulated. Although it remains complex to draw causal effects, repeated measure correlations underline the interdependence between VA decrement and cognitive efficiency (small correlation between Mackworth score and VA; r rm = –0.18), likely mediated by the concurrent interdependence of those variables to cerebral oxygenation alterations and mental effort. The ICCT increased progressively the mental effort (Baseline-TF= +52.2 ± 22.1 /CR 100 ) compared to the COG MATCHED group who performed the SA tasks alone (+3.5 ± 4.2 /CR 100 ), suggesting that CMDT elicits significant mental fatigue compared to a cognitive task alone. It has been proposed that an increased mental effort originating through a complex non-automated dual-task paradigm can be associated with mental fatigue (Behrens et al., 2023), and this may be detrimental for cognitive performance. Indeed, similar results were obtained by Chatain et al., (2019) who reported mental effort to be increased only in CMDT situations. It is unlikely that mental fatigue directly inhibits the neural drive to muscles (Alix-Fages et al., 2022; Pageaux et al., 2015) but recent theorical frameworks propose that it may be associated with increased brain metabolites as glutamate or adenosine, possibly indirectly modulating the motor command (Pageaux et al., 2014; Wiehler et al., 2022). Other studies should explore the neuro-metabolic substrates associated with mental fatigue in CMDT contexts to better understand its origin, as well as its direct and indirect effects on cognitive performance and neuromuscular control. Limitations and perspectives CMDT efficiency across motor, perceptual, and cognitive domains is likely influenced by the duration and difficulty of the cognitive task itself, independently of the associated physical constrain. In this study, we designed 3-min CMDT stages to reflect ecologically valid, real-world scenarios. However, further research is warranted to investigate how the duration of physical exercise, even at intensities that are not necessarily high, interacts with fatigue development and subsequently impacts SA performance. Additionally, the characteristics of the Mackworth task used here—notably its repetitive structure and relatively automatized nature—may have contributed to the limited performance variation observed across moderate intensities. Although sustained attention (SA) shares certain operational characteristics with selective and focused attention, it is generally regarded as a distinct cognitive process. The Mackworth clock task is hence commonly used as a proxy for SA efficiency. However, in the context of the present study, the broader nature of the task likely engages multiple attentional components, including the abilities to select, shift, and distribute attention. This broader attentional involvement should be acknowledged as a potential limitation when interpreting results solely in terms of SA. One limitation of this study is that VA assessed from peripheral nerve stimulation technique does not allow differentiating spinal from supraspinal mechanisms implicated in central fatigue. Future studies using for instance transcranial and cervicomedullar magnetic stimulation should be conducted to further explore supraspinal alteration in the cortico-motor pathways as changes in cortical excitability and inhibition of the motor cortex during fatiguing whole-body CMDT (Gruet et al., 2013). Some inherent limitations of NIRS must also be acknowledged. Due to its limited penetration depth - approximately half the interoptode distance - NIRS is primarily sensitive to cortical regions within the upper capture deeper or more distributed changes in cerebral microcirculation, which can vary heterogeneously during exercise and cognitive tasks. The regional nature of the measurements restricts generalizability to the whole brain, or to other areas that may also be critical for complex motor and dual-task performance. Future studies employing functional NIRS in whole-body CMDT paradigms are warranted to further advance our understanding of cerebrovascular responses and to help address these limitations. Finally, we decided not to include a control group performing the incremental cycling test without the superimposed cognitive task. Although several methodological parameters align with those employed by companion papers from Mira and Aboodarda et al. (2018) ( e.g ., supine position, increment duration, and proximity to task failure), allowing for meaningful contextualization of our findings, we acknowledge that a direct comparison —ideally using a paired or crossover design— would have provided clearer insights into the kinetics of neuromuscular fatigue induced specifically by the CMDT configuration. Due to ethical constraints, participants did not complete an additional experimental session; however, we remain confident that this limitation does not compromise the study’s main conclusions. Taken together, these findings offer valuable guidance for designing CMDT interventions in both athletic, professional or clinical settings aiming to enhance the brain’s capacity to manage competing demands (Fortenbaugh et al., 2017; Vestberg et al., 2012). The extent to which sustained cognitive performance and resilience to central fatigue are trainable, particularly under high-pressure CMDT conditions involving intense exercise or environmental stressors—remain an open question and a promising avenue for future research. CONCLUSION This study investigated the interplay between sustained attention (SA), prefrontal cortex (PFC) oxygenation, neuromuscular fatigue and mental effort during a novel incremental cognitively demanding motor task (CMDT) in trained individuals. The findings challenge traditional interpretations of the inverted-U hypothesis by showing no SA enhancement at low to moderate cycling intensities while SA was significantly deteriorated during very strong to maximal perceived efforts (≥80%TF; ≥84%HR max ), coinciding with PFC deoxygenation and increased mental and physical fatigue. Crucially, central fatigue emerged early—at moderate intensities—and was closely associated with reductions in PFC oxygenation and heightened mental effort, suggesting a direct link between neural resource allocation, cerebral oxygenation, and motor output regulation. ††slugcomment: To be submitted to the Astrophysical Journal Letter ACKNOWLEDGEMENTS We thank the participants who dedicated their time and commitment to this study. ††slugcomment: To be submitted to the Astrophysical Journal Letter CONFLICT OF INTEREST The authors declare that they have no conflicts of interest. The results of this study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. AUTHOR CONTRIBUTIONS TG, MH, PH and TR were involved in the design of the study. TG performed the data collection. TG drafted the first version of the manuscript, with all authors involved in subsequent revisions and approval of the final document. REFERENCES Aboodarda, S. 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Fig. 1 Overview of the experimental session including the incremental cycling cognitive test (ICCT). HF: high-frequency doublet. HR: heart rate. IMVC: isometric maximal voluntary contraction. LF: low-frequency doublet. PFC: prefrontal cortex. Fig. 2 Global score (A), accuracy (B) and reaction time (C) from the Mackworth task performed either without exercise (COG MATCHED ) or during ICCT (COG EX ). Data are presented at baseline, 20%, 40%, 60%, 80% and task failure (TF) of the total ICCT duration, or at matched time-points in the COG MATCHED group. Data are presented as mean ± standard deviation (colored areas) for N = 40 in each group. P-values for main effects of Time (T), Group (G) and Time \(\ \times\) Group (T\(\times\)G) are indicated on the panels. Post-hoc significant differences for Group effect are shown in boxes above each graph. Post-hoc significant differences for Time \(\times\) Group interaction are marked with the following symbols: # (##, ###): P-value <0.05 (<0.01, <0.001) vs . respective COG MATCHED time-point. Fig. 3 Changes in isometric maximal voluntary contraction (IMVC, A), pic twitch (Pt, B), low to high frequency ratio (LF/HF, C) and voluntary activation (VA, D), throughout ICCT. Data are presented at baseline, 20%, 40%, 60%, 80% and task failure (TF) of total ICCT duration. Data are presented as mean ± standard deviation (grey area) for N = 40. P-values for main effects of Time (T) are indicated on the panels. Post-hoc significant differences for Time effect are marked with the following symbols: ** (***): P-value <0.01 (<0.001) vs . Baseline. $ ($$, $$$): P-value time-point. Fig. 4 PFC oxygen tissue saturation index (TSI, 4A) and changes in NIRS-derived indices (O 2 Hb, HHb, tHb, 4B/C/D) throughout ICCT. Data are presented at baseline, 20%, 40%, 60%, 80% and task failure (TF) of the total ICCT duration. Data are presented as mean ± standard deviation (grey areas) for N = 40. P-values for main effects of Time (T) are indicated on the panels. Post-hoc significant differences for Time effect are marked with the following symbols: * (***): P-value <0.05 (<0.001) vs . Baseline. $$ ($$$): P-value <0.01 (<0.001) vs . previous time-point. Fig. 5 Mental effort associated with performing the Mackworth task, repeated without exercise (COG MATCHED ) and during the ICCT (COG EX ). Data are presented at baseline, 20%, 40%, 60%, 80% and task failure (TF) of the total ICCT duration, or at matched time-points in the COG MATCHED group. Data are presented as mean ± standard deviation (colored areas) for N = 40 in each group. P-values for main effects of Time (T), Group (G) and Time \(\ \times\) Group (T\(\times\)G) are indicated on the panels. Post-hoc significant differences for Group effect are shown in boxes above each graph. Post-hoc significant differences for Time \(\ \times\) Group interaction are marked with the following symbols: ###: P-value time-point. Fig. 6 Repeated measures correlations at 20%, 40%, 60%, 80% and task-failure (TF) of the total ICCT duration for variables expressed as delta from baseline. The correlated variables are sustained attention (ΔMackworth score) with mental effort (ΔMental effort, 6A), PFC oxygenation (ΔTSI, 6B), and voluntary activation (ΔVA, 6C), as well as ΔTSI with ΔMental effort (6D), ΔVA (6E), and finally ΔVA with ΔMental effort (6F). Data points represent individual trials, with points of the same color corresponding to the same participant. Dashed lines indicate individual regression lines, while the solid red line shows the overall repeated measures correlation for N = 40 (COG EX group). The shaded red area represents the 95% confidence interval. Each subfigure includes the repeated measures correlation coefficient (r rm ), and the associated P-value, calculated using the rmcorr package. Information & Authors Information Version history V1 Version 1 02 May 2025 Peer review timeline Published Scandinavian Journal of Medicine & Science in Sports Version of Record 1 Sep 2025 Published Copyright This work is licensed under a Non Exclusive No Reuse License. Authors Affiliations Thomas Goepp 0009-0000-6166-4992 Universite Savoie Mont Blanc - Campus du Bourget-du-Lac View all articles by this author Mark Hayes University of Brighton School of Sport and Health Sciences View all articles by this author Pascal Hot CNRS Delegation Alpes View all articles by this author Thomas Rupp [email protected] Universite Savoie Mont Blanc - Campus du Bourget-du-Lac View all articles by this author Metrics & Citations Metrics Article Usage 306 views 114 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Thomas Goepp, Mark Hayes, Pascal Hot, et al. A new incremental cycling cognitive-motor dual-task test to assess simultaneous sustained attention and neuromuscular fatigue in trained athletes.. Authorea . 02 May 2025. DOI: https://doi.org/10.22541/au.174616416.60847490/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. 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