Impact of Body Composition on Peak Oxygen Uptake After Cardiac Rehabilitation

Impact of Body Composition on Peak Oxygen Uptake After Cardiac Rehabilitation | medRxiv /* */ /* */ <!-- <!-- /*! * yepnope1.5.4 * (c) WTFPL, GPLv2 */ (function(a,b,c){function d(a){return"[object Function]"==o.call(a)}function e(a){return"string"==typeof a}function f(){}function g(a){return!a||"loaded"==a||"complete"==a||"uninitialized"==a}function h(){var a=p.shift();q=1,a?a.t?m(function(){("c"==a.t?B.injectCss:B.injectJs)(a.s,0,a.a,a.x,a.e,1)},0):(a(),h()):q=0}function i(a,c,d,e,f,i,j){function k(b){if(!o&&g(l.readyState)&&(u.r=o=1,!q&&h(),l.onload=l.onreadystatechange=null,b)){"img"!=a&&m(function(){t.removeChild(l)},50);for(var d in y[c])y[c].hasOwnProperty(d)&&y[c][d].onload()}}var j=j||B.errorTimeout,l=b.createElement(a),o=0,r=0,u={t:d,s:c,e:f,a:i,x:j};1===y[c]&&(r=1,y[c]=[]),"object"==a?l.data=c:(l.src=c,l.type=a),l.width=l.height="0",l.onerror=l.onload=l.onreadystatechange=function(){k.call(this,r)},p.splice(e,0,u),"img"!=a&&(r||2===y[c]?(t.insertBefore(l,s?null:n),m(k,j)):y[c].push(l))}function j(a,b,c,d,f){return q=0,b=b||"j",e(a)?i("c"==b?v:u,a,b,this.i++,c,d,f):(p.splice(this.i++,0,a),1==p.length&&h()),this}function k(){var a=B;return a.loader={load:j,i:0},a}var l=b.documentElement,m=a.setTimeout,n=b.getElementsByTagName("script")[0],o={}.toString,p=[],q=0,r="MozAppearance"in l.style,s=r&&!!b.createRange().compareNode,t=s?l:n.parentNode,l=a.opera&&"[object Opera]"==o.call(a.opera),l=!!b.attachEvent&&!l,u=r?"object":l?"script":"img",v=l?"script":u,w=Array.isArray||function(a){return"[object Array]"==o.call(a)},x=[],y={},z={timeout:function(a,b){return b.length&&(a.timeout=b[0]),a}},A,B;B=function(a){function b(a){var a=a.split("!"),b=x.length,c=a.pop(),d=a.length,c={url:c,origUrl:c,prefixes:a},e,f,g;for(f=0;f<d;f++)g=a[f].split("="),(e=z[g.shift()])&&(c=e(c,g));for(f=0;f<b;f++)c=x[f](c);return c}function g(a,e,f,g,h){var i=b(a),j=i.autoCallback;i.url.split(".").pop().split("?").shift(),i.bypass||(e&&(e=d(e)?e:e[a]||e[g]||e[a.split("/").pop().split("?")[0]]),i.instead?i.instead(a,e,f,g,h):(y[i.url]?i.noexec=!0:y[i.url]=1,f.load(i.url,i.forceCSS||!i.forceJS&&"css"==i.url.split(".").pop().split("?").shift()?"c":c,i.noexec,i.attrs,i.timeout),(d(e)||d(j))&&f.load(function(){k(),e&&e(i.origUrl,h,g),j&&j(i.origUrl,h,g),y[i.url]=2})))}function h(a,b){function c(a,c){if(a){if(e(a))c||(j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}),g(a,j,b,0,h);else if(Object(a)===a)for(n in m=function(){var b=0,c;for(c in a)a.hasOwnProperty(c)&&b++;return b}(),a)a.hasOwnProperty(n)&&(!c&&!--m&&(d(j)?j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}:j[n]=function(a){return function(){var b=[].slice.call(arguments);a&&a.apply(this,b),l()}}(k[n])),g(a[n],j,b,n,h))}else!c&&l()}var h=!!a.test,i=a.load||a.both,j=a.callback||f,k=j,l=a.complete||f,m,n;c(h?a.yep:a.nope,!!i),i&&c(i)}var i,j,l=this.yepnope.loader;if(e(a))g(a,0,l,0);else if(w(a))for(i=0;i (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0];var j=d.createElement(s);var dl=l!='dataLayer'?'&l='+l:'';j.src='//www.googletagmanager.com/gtm.js?id='+i+dl;j.type='text/javascript';j.async=true;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-P4HH5NV'); Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search Impact of Body Composition on Peak Oxygen Uptake After Cardiac Rehabilitation View ORCID Profile Wiaam Elkhatib , View ORCID Profile Thomas Olson doi: https://doi.org/10.1101/2025.08.22.25334270 Wiaam Elkhatib 1 Mayo Clinic Department of Cardiovascular Disease MD, MPH Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Wiaam Elkhatib For correspondence: Elkhatib.Wiaam{at}mayo.edu Thomas Olson 1 Mayo Clinic Department of Cardiovascular Disease PhD, MS Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Thomas Olson Abstract Full Text Info/History Metrics Data/Code Preview PDF ABSTRACT Background Peak oxygen uptake (VO 2 peak), standardized to total body mass (ml/kg/min) is a predictor of morbidity and mortality in cardiovascular disease patients. However, subsets of individuals undergoing exercise based cardiac rehabilitation (CR) show no improvement or reduction in VO 2 peak despite improvement in other functional measures. Our aim is to assess the influence of CR on lean mass, and the effect of body composition compared to total body mass changes on peak VO 2 following CR. Methods This pre-post intervention study included adults >18 years old who completed CR between 2015-2022 at Mayo Clinic, Rochester. All patients completed both dual energy X-ray absorptiometry (DXA) and cardiopulmonary exercise testing (CPET) for measurement of body composition (total mass and lean mass) and VO 2 peak pre-post CR. Improvement in VO 2 peak was defined as positive percent change. Descriptive statistics, paired t-tests, univariable and multivariable linear regression modeling were performed. Results Of 140 subjects, 19.3% were female and 96.4% White with a mean (SD) age of 63 (12.5) years, BMI of 30.2 (5.82), and a mean of 27.1 (11.7) completed number CR sessions. Pre-post CR total body mass loss was −1.28 (3.18) kg and lean mass gain was 0.84 (2.86) kg. All changes were statistically significant (p<0.05). Pre-post CR VO 2 peak in absolute units had a percent change increase of 6.52 (13.1) mL/min, relative (corrected for total body mass) increase of 8.24 (13.6) mL/kg/min, and relative to lean mass increase of 5.73 (13.4) mL/lean-kg/min. Pre-post percentage of subjects with a positive change in peak VO 2 in absolute units was 70%, relative was 75%, and relative to lean mass was 67.9%. Multivariable regression showed statistical significance in peak VO 2 percent change for all units when adjusted for pre-CR peak VO 2 . Conclusions Our findings demonstrate significant increases in lean mass and VO 2 peak following CR, with larger improvements reflected in units adjusted for total mass compared to other methods. These data suggest the reporting methodology for change in VO 2 peak following CR impact overall results. CLINICAL PERSPECTIVE Published studies have reported that subsets of patients undergoing exercise-based cardiac rehabilitation (CR) may show no improvement or even reduction in peak oxygen uptake (VO 2 peak), a predictor of mortality in individuals with cardiovascular disease, which may be partly influenced by body composition. This pre-post intervention study of 140 adult patients who completed CR demonstrated significant increases in lean mass and VO 2 peak following CR across the cohort while suggesting the reporting methodology for change in VO 2 peak impacts overall results. Our findings could imply that a proportion of patients continue to demonstrate additional abnormalities that inhibit improvement in VO 2 peak independent of body composition alterations, partially explaining why a subset of patients have a lack of positive change in VO 2 peak. Significant predictors for reduced VO 2 peak improvement following CR may include female sex and pre-CR VO 2 peak. Despite CR significantly improving lean body mass, the ability to utilize that mass to generate useful oxidative metabolism could be limited and may require a longer duration of CR to maximize oxidative metabolic efficiency and improve patient outcomes following acute cardiac events. INTRODUCTION Measurement of peak oxygen uptake (VO 2 peak) is considered the gold standard metric of cardiopulmonary fitness and is inversely related to hospitalization and mortality, independent of age, sex, race, and comorbid conditions [ 1 ]. This metric is most used clinically, via cardiopulmonary exercise testing (CPET), to determine cardiorespiratory fitness, examine origin of exertional symptoms, as a surveillance tool for prognosis and timing of interventions, and determine efficacy of interventions. Importantly, as VO 2 peak is inversely related to hospitalizations and mortality, clinical interventions designed to improve VO 2 peak are imperative. Exercise based cardiac rehabilitation (CR) is a Class 1 therapy for the secondary prevention of cardiovascular disease [ 2 ]. Exercise training, as prescribed during CR, is known to have a positive impact on modifiable cardiovascular disease risk factors (e.g. obesity, diabetes, hypertension, etc.) including improving VO 2 peak. Interestingly, a proportion of CR patients are known to have no improvement, or even a reduction, in VO 2 peak after CR [ 3 ]. The absolute volume of oxygen an individual can consume is related to the size/mass of the individual. Therefore, larger individuals will, by definition, consume larger amounts of oxygen to maintain vital organ function. As such, the units to describe VO 2 peak are often standardized to total body mass to make comparisons across populations in which body mass differs, allowing for more accurate comparisons across different patient groups [ 4 ]. However, bias using these units may arise towards obese patients (with larger, less metabolically active adipose stores) relative to other subsets of patients (with larger amounts of highly metabolically active lean muscle mass) since the composition of the total body mass is not accounted for [ 5 ]. With this, overweight persons with high body fat demonstrate a lower VO 2 peak relative to their body mass, though difficult to differentiate from persons with high lean body mass [ 6 ]. This may directly influence the results of interventions specifically designed to improve VO 2 peak, body composition, or both, as may be the case with CR. Therefore, the change in VO 2 peak based on total mass may not reflect true change in fitness for patients who differentially alter body composition (e.g., increase lean mass vs. decrease fat mass) following CR. Studies examining the influence of body composition on aerobic performance in cardiac rehabilitation are limited despite VO 2 peak normalization serving as a determining factor in results interpretation [ 7 ]. Assessment of change in VO 2 peak based on total body mass alone may not be optimal. Therefore, the objective of this study was to assess the influence of CR on lean mass and the effect of body composition compared to total body mass changes on VO 2 peak following CR. We hypothesized that the change in VO 2 peak post-CR, adjusted for lean mass rather than total mass, will better reflect improvements in VO 2 peak. METHODS Study Design Reporting of data adheres to STROBE guidelines [ 8 ]. This retrospective pre-post intervention cohort study at a large tertiary-care center which included consecutive clinically stable adult patients over the age of 18 years referred to and enrolled in an early outpatient (phase II) comprehensive exercise-based CR program between January 2015 to October 2022. The CR occurred at the Mayo Clinic Cardiovascular Health Center in Rochester, Minnesota within 2-to-4 weeks following referral after major cardiac event fulfilling approved clinical indication for CR. All included patients approved to have their medical records used for research purposes. The Mayo Clinic Institutional Review Board approved this study. Involved patients had provided medical record use authorization. Patient Identification Clinical and demographic characteristics were electronically obtained using resources of the Rochester Epidemiology Project (REP), a records linkage system that captures data on health conditions (diagnosis, procedures, and other vital information) of all Olmsted County residents who receive medical care at Olmsted Medical Center or the Mayo Clinic and its allied health care centers. Cardiac Rehabilitation The Mayo Clinic comprehensive outpatient CR program adheres to the American Association of Cardiovascular and Pulmonary Rehabilitation established guidelines [ 9 ]. A total of 36 supervised CR sessions were prescribed over a 3 days per week regimen completed over 12 weeks. Sessions involved supervised aerobic activity for 20-45 minutes followed by resistance training for 10-15 minutes. Equivalent home-based aerobic exercise was recommended on days outside of supervised CR sessions. Individualized exercise prescriptions utilizing the Borg rating of perceived exertion scale were updated as patients advanced through their program, with all patients having attended a minimum of 1 documented session [ 10 ]. Ancillary lifestyle education was provided and centered around sleep hygiene, nutrition, medication adherence, smoking cessation (as necessary), and cardiovascular risk factors modification. Data Collection Patients had multiple indications recorded for CR program referral obtained via documental medical record review. Sex and birth date were logged. Height and weight measures were documented for computation of body mass index (BMI, kg/m2). Symptom-limited maximal cardiopulmonary exercise testing (CPET) via motor-driven treadmill pre-post CR was obtained electronically from an institutional registry and used to ascertain VO 2 peak. Medications were not withheld prior. When multiple tests were identified, the test performed closest to CR enrollment and graduation were used for analysis. The CPETs incorporated an institutionally designed incremental exercise protocol increasing 2 metabolic equivalents every 2 minutes under cardiologist oversight by a specially trained nurse or exercise physiologist [ 11 ]. At each stage, the rating of perceived exertion and manual sphygmomanometry were completed alongside a continuous 12-lead electrocardiogram for safety monitoring. Indirect calorimetry was used to measure gas exchange variables (MGC Diagnostics). Peak values were recorded for oxygen consumption, carbon dioxide production, O 2 pulse (oxygen consumption divided by heart rate) and respiratory exchange ratio averaging over 10 seconds during the test. All patients included in this analysis achieved a peak respiratory exchange ratio of equal to or greater than 1.0 during both pre-post CR CPETs completed within 12 months of program graduation [ 12 ]. All pre-CR dual energy X-ray absorptiometry (DXA) was completed after their CR qualifying event and prior to enrollment in CR whereas the post-CR DXA was completed within 4 weeks of graduation (GE Lunar iDXA whole body scanner). Standard institutional procedure was followed. Relevant body composition measurements included total body mass (kg) and lean mass (kg). VO 2 peak units were reported using CPET and DXA results in three different units. Absolute units (mL/min) constituted the first method of reporting. Units relative to total body mass were reported as absolute units divided by total body mass (mL/kg/min). Units relative to lean mass were reported as absolute units divided by lean body mass (ml/lean-kg/min). Statistical Analysis Categorical variables were descriptively reported as number (percentage) and continuous variables were reported as mean values with standard deviation (SD). Improvement in VO 2 peak for each of the three reported unit groups before and after CR was defined as a positive ( >0) percent change and/or positive mean difference. Paired student t-tests were completed for pre-post CR measures of VO 2 peak per unit, total body mass and lean body mass. For the primary outcome, linear regression models for the percent change in VO 2 peak per reported unit group were constructed to compare the VO 2 peak percent change of the cohort to the population at large after controlling for age, sex, pre-CR BMI, number of CR sessions, and pre-CR VO 2 peak per unit. Beta coefficients were provided with standard errors (SE), 95% confidence intervals (CI), and p-values. Statistical significance for all methods was defined as a p-value <0.05. Variable selection was determined by clinical expertise, univariable analysis, and previous literature. All statistical analyses were conducted via RStudio Version 4.4.2 (RStudio, PBC). RESULTS Of 140 patients, 19.3% were female. Caucasian patients constituted 96.4% of the cohort. The mean age was 63.0±12.5 years. Mean pre-CR BMI was 30.2±5.8. On average, patients completed 27.1±11.7 supervised CR sessions. The most common CR indications were percutaneous coronary intervention [81 (58.7)] and acute coronary syndrome [66 (47.8)]. Demographics and CR indication are provided in Table 1 . View this table: View inline View popup Download powerpoint Table 1: Patient demographics are outlined by frequency [n (%)] or mean (SD) as appropriate. CR = cardiac rehabilitation; BMI = body mass index; ACS = acute coronary syndrome; CABG = coronary artery bypass graft; PCI = percutaneous coronary intervention. Pre-post CR VO 2 peak in absolute units (mL/min) had a percent change increase of 6.5±13.1%, relative to total body mass units (mL/kg/min) increase of 8.2±13.6, and relative to lean mass units (mL/lean-kg/min) increase of 5.7±13.4. Pre-post CR delta for VO 2 peak in absolute units (mL/min) was 109, relative to lean mass units (mL/lean-kg/min) was 1.7 and relative to total body mass units (mL/kg/min) was 1.7. Pre-post CR total body mass reduction was −1.3 (3.2) kg and lean body mass gain was 0.8±2.9 kg. BMI similarly had a delta of −0.4 (kg/m 2 ). All changes were statistically significant (p<0.05). Results are shown in Table 2 . View this table: View inline View popup Download powerpoint Table 2: Pre-Post cardiac rehabilitation (CR) metrics are shown for cardiopulmonary exercise stress tests (CPET) and dual energy X-ray absorptiometry (DXA) as means (SD) of percent (%) change and absolute delta. *p-values <0.05 represent statistical significance. VO 2 peak = peak oxygen uptake; BMI = body mass index. Most patients achieved improvements in VO 2 peak following CR with a fraction of non-responders. Waterfall and bar plots of data are shown in Figure 1 . The post-CR percent of patients with a positive change in VO 2 peak was 70.0%, 75.0%, and 67.9% in the grouped units of ml/min, ml/kg/min, ml/lean-kg/min, respectively. These are shown in Figure 2 . Download figure Open in new tab Figure 1: Percent changes of peak oxygen uptake (VO 2 peak) are plotted by respective units. (A) Absolute VO 2 peak in ml/min (B) Relative to total body mass VO 2 peak in ml/kg/min (C) Relative to lean body mass VO 2 peak in ml/lean-mass/min (D) Proportion of patients by percentage having a positive percent change of VO 2 peak by grouped units. Download figure Open in new tab Figure 2: Proportion of patients by percentage having a positive percent change of peak oxygen uptake (VO 2 peak) by grouped units. Univariate and multivariate linear regression analyses were completed for VO 2 peak percent change using several predictors and stratified by unit group. Models were explored for all listed predictors shown in Table 3 . These included age, female sex, number of CR sessions, pre-CR BMI, and pre-CR VO 2 . Assuming all else fixed, patients with higher pre-CR VO 2 peak across all unit groups experienced lower post-CR VO 2 peak mean percent change per unit increase of pre-CR VO 2 peak [−0.01 (−0.08, −0.01) ml/min, −0.45 (−0.81, −0.10) ml/kg/min, −0.48 (−0.74, −0.23) ml/lean-kg/min]. Of the tested univariate predictors, only pre-CR VO 2 for all unit groups showed statistical significance (p <0.05). After adjusting for these predictors in the multivariate model, there was found to be statistical significance only for female sex for absolute VO 2 units [−7.12 (−13.5, −0.74) ml/min] and pre-CR VO 2 [−0.01 (−0.02, −0.01) ml/min, −0.73 (−1.17, −0.28) ml/kg/min, −0.59 (−0.89, −0.30) ml/lean-kg/min] for all VO 2 unit groups. The remaining predictors revealed varying directions and magnitude of change without statistical significance. View this table: View inline View popup Table 3: Univariable and multivariable linear regression model outputs for cardiac rehab (CR) patients stratified by peak oxygen uptake (VO 2 peak) per unit group are shown, including beta coefficients with standard errors (SE), 95% confidence intervals (CI), and p-values. *p-values <0.05 represent statistical significance. Interaction terms were not considered with the limited number of significant predictors in our multivariable model. DISCUSSION The purpose of this study was to assess the influence of body composition on change in VO 2 following CR. The primary findings of this study are: 1) Regardless of units used for describing change in cardiorespiratory fitness, approximately 30% of patients continue to demonstrate no improvement in VO 2 peak, 2) The magnitude of change in VO 2 peak is partly dependent on units used to describe the metric, resulting in an approximate 7% swing in the number of patients who demonstrate improvement in VO 2 based only on the united used to report VO 2 , 3) Regardless of units used to describe the outcome, similar predictors surface for predicting improvement in VO 2 . The gold standard metric for assessment of cardiorespiratory fitness remains the measurement of VO 2 peak during a cardiopulmonary exercise test (CPET) [ 1 ]. The units used to describe VO 2 peak are often made relative to an individual’s body mass to provide comparable units across the spectrum of different sized individuals. For most baseline or static measurements, this works well; however, when individuals are engaged in an intervention that could impact both VO 2 and body mass, the ability to determine improvement in cardiorespiratory fitness relative to the change in body mass is complex. Further complicating this relationship is the change in body composition for which the total body mass is made up. Reductions in fat mass with increases in metabolically dominant lean mass may result in no change to total body mass while having a significantly positive impact on body composition and overall metabolic health [ 13 ]. Concomitant lifestyle changes also play a role. These intricate relationships have not been fully elucidated in patients enrolled in CR, in which both cardiorespiratory fitness and body composition are meaningful outcomes. Our data confirms that such changes in body mass composition impact reporting of oxygen consumption. Pre-post CR VO 2 peak relative to total body mass units (mL/kg/min) had the largest statistically significant percent change increase followed by absolute units (mL/min), and relative to lean mass units (mL/lean-kg/min). However, the pre-post CR delta was significantly highest for VO 2 peak in absolute units (mL/min), followed by units relative to lean mass units (mL/lean-kg/min) and lastly relative to total body mass units (mL/kg/min). The larger reduction in total body mass relative to improvement in lean mass may partly explain why reporting VO 2 peak in units relative to lean body mass demonstrated a smaller percent improvement relative to other reporting units. It is also worthwhile to consider that since fat mass consumes an exceptionally small amount of oxygen, greater non-lean mass reductions relative to lean mass increases may lend an observed rise in the traditional VO 2 peak relative to total mass (ml/kg/min) in the absence of an actual rise in peak aerobic capacity. After normalizing by body mass composition and adjusting for predictors of age, number of CR sessions, pre-CR BMI, and pre-CR VO 2 in the multivariable regression models, pre-CR VO 2 for all VO 2 unit groups was found statistically significant. Patients with higher pre-CR VO 2 peak experienced lower mean percent change post-CR VO 2 peak. Lower pre-CR VO 2 being a significant predictor for greater improvements in post-CR VO 2 , regardless of reported units, is consistent with some recent studies the literature [ 3 , 14 ]. Our data highlights that the units used to report VO 2 peak influences the magnitude of change seen following CR. Total body mass compared to lean body mass standardization reflected the greatest percent change improvement, but lean mass standardization reflected the greatest mean delta. Measuring VO 2 peak using units traditionally relative to total body mass may not necessarily be better than units relative to lean body mass knowing the variable changes in fat mass and lean mass with CR. The beneficial effects of CR on VO 2 peak, independent of other predictors and despite the modest increases, support this metric remaining a primary goal for CR enrollment given its established relationship to improved mortality [ 1 , 15 ]. Additionally, between 25% to 32.1% of our patient cohort across all VO 2 peak unit groups had a seemingly poor response to CR. It has been previously described that approximately 20-30% of patients completing CR could be termed “non-responders” who may reflect neutral or decreased change in VO 2 peak [ 3 ]. VO 2 peak changes post-CR can also vary widely in the literature [ 3 , 16 ]. The exact mechanisms remain unclear, though the ability to increase oxygen uptake following CR may potentially outpace the increase in lean body mass to subsequently impart an overall improvement in VO 2 peak relative to lean body mass. Evidence in young athletes suggests that the initial phase of a new exercise training program results primarily in neuromuscular facilitation changes with minimal change in lean body mass or mitochondrial function [ 17 , 18 ]. Afterwards, lean mass and mitochondrial changes become exercise intensity, volume, and dose dependent. Our findings could imply that a proportion of patients continue to demonstrate additional abnormalities (e.g., comorbidities) that inhibit improvement in VO 2 peak independent of change in body composition. This may partially explain why a subset of patients do not have a positive percent change in VO 2 peak. Despite CR significantly improving lean body mass, the ability to utilize that mass to generate useful oxidative metabolism could be limited and may require a longer duration of CR to maximize oxidative metabolic efficiency. The oxidative metabolic efficiency of newly acquired lean mass may therefore require a longer duration of CR to maximize expected individual fitness improvements. Given exercise intensity may play a significant role, incorporating high-intensity interval training into CR programs may prove beneficial [ 19 , 20 , 21 ]. Exercise intensity, patient adherence, CR indication, age, and several other factors also play a role. Exercise-based CR has been consistently shown to lead to meaningful improvements in VO 2 peak for certain patient subsets [ 22 , 23 ]. Interestingly, however, some recent studies including a clinical trial and systematic review have even challenged the notion that CR imparts significant improvements in measures like VO 2 peak, mortality, or fitness [ 24 , 25 ]. Potential reasons include insufficient exercise duration or intensity, patient compliance with the program, or a lack of sufficient statistical power imparted in interventional studies [ 21 ]. Improved medical management for patients suffering from cardiovascular events may overshadow benefits from CR previously described in the literature as well. Cardiac rehabilitation programs were originally designed with exercise training as the primary intervention, designed to improve functional capacity and elicit the multitude of health benefits associated with regular structured exercise. Additionally, counselling on general physical activity is included as a corollary to exercise training and plays an important part in minimization of sedentary behavior. Further, as obesity is a major risk factor for the development and progression of cardiovascular disease, education and counselling focused on nutrition and dietary change to meaningfully improve behaviors associated with poor nutritional choices are now standard of practice for CR programs. These interventions work together to improve cardiorespiratory fitness, improve body composition, and engender positive behavior change for CR patients. This study examined the impact of body composition on change in VO 2 per unit group in CR patients. However, we acknowledge potential limitations. The population included in this study arises from a single center with a fairly homogenous population. Our sample was predominately male and Caucasian potentially limiting generalizability based on demographics. Further, we only included individuals who had completed both pre- and post-CR measurements of VO 2 peak as well as body composition resulting in a limited sample size. Additionally, this is a retrospective cohort study and by design inference of causality cannot be made. CONCLUSION Significant decreases in total body mass and increases in lean body mass and VO 2 occur following CR regardless of units reported, seeming to contribute a meaningful portion of peak VO 2 improvements. Larger improvements are also reflected in units adjusted for total mass compared to other units. Lower pre-CR VO 2 is a significant predictor for greater improvements in post-CR VO 2 . These data suggest the reporting methodology for change in VO 2 following CR may impact overall findings. Data Availability Data are to be made available upon reasonable request. ACKNOWLEDMENTS The authors wish to acknowledge the dedicated nursing and cardiology rehabilitation staff who contributed to the care of our patients. SOURCES OF FUNDING This work was supported in part by the National Institutes of Nursing Research (R01NR018832). DISCLOSURES The authors have no disclosures to report. 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