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Cardiac Rehabilitation

Response to Exercise Training During Cardiac Rehabilitation Differs by Sex

Rengo, Jason L. MS; Khadanga, Sherrie MD; Savage, Patrick D. MS; Ades, Philip A. MD

Author Information
Journal of Cardiopulmonary Rehabilitation and Prevention: September 2020 - Volume 40 - Issue 5 - p 319-324
doi: 10.1097/HCR.0000000000000536
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Cardiac rehabilitation (CR) has been shown to reduce mortality and morbidity and improve quality of life, exercise capacity, and physical function.1–3 Directly measured peak aerobic capacity or oxygen uptake (V˙o2 peak ) is a powerful predictor of prognosis in individuals with cardiovascular disease.4–7 Women enter CR programs with significantly lower baseline measures, and there is evidence that they do not improve their cardiorespiratory fitness (CRF) as much as men.8,9 When estimating improvement in CRF based on treadmill time, men and women improve similarly.10 Conversely, when CRF is directly measured, a differing response is evident, with women improving to a lesser degree than men at approximately 12% and 18%, respectively.9,11

With women accounting for approximately one-third of CR participants and lower cardiovascular mortality linked with improvement in V˙o2 peak ,11,12 it is important to elucidate the training response in this population. The aim of this study was to examine training response and V˙o2 peak at entry and exit in patients participating in phase II CR. Furthermore, we analyze improvements by diagnosis and identify sex differences that may influence change in V˙o2 peak .

METHODS

SUBJECTS

We analyzed prospective data gathered from January 1996 to December 2015 on consecutive patients enrolled in CR who performed an entry and exit exercise tolerance test (ETT). At the initial visit, age, sex, body weight, height, waist circumference, comorbidities (including abdominal obesity [waist circumference >88 cm for women or >102 cm for men], orthopedic limitations, chronic obstructive pulmonary disease, peripheral arterial disease, diabetes mellitus, and cerebrovascular accident), and self-reported smoking status were recorded. In addition, patients completed the Medical Outcome Study Short Form-36 Physical Function component (MOS SF-36),13 and handgrip strength using a hydraulic dynamometer (Jamar) was obtained.

The Centers for Medicare & Medicaid Services expanded CR coverage to include heart valve surgery (HVS) in 2006 and chronic systolic heart failure (CHF) in 2014. Therefore, the diagnostic distribution of patients has altered appreciably. To assess the effect of HVS and CHF on overall training and sex differences, we analyzed results by diagnosis. Diagnosis was classified as coronary artery bypass graft (CABG), myocardial infarction (MI), percutaneous intervention (PCI), stable angina, CHF, cardiac arrhythmia (atrial fibrillation or ventricular tachycardia), HVS, or percutaneous transcatheter aortic valve replacement (TAVR). Diagnosis at CR entry was recorded in a hierarchal fashion (ie, patients with CABG for any indication were coded as CABG, those with MI without CABG were coded as MI, those without CABG/MI who received PCI were coded as PCI, followed by those who have their angina treated medically and other diagnoses, such as HVS, CHF, or TAVR). HVS predominately consisted of aortic valve surgery. Because of the small number of mitral valve surgical procedures, they were combined with patients with aortic valve surgery and reported as HVS. For patients who enrolled in CR multiple times, only data from the initial event were included. Patients were considered to have completed CR if they returned for an exit evaluation.

EXERCISE TOLERANCE TESTING

Expired gas analysis was measured during the ETT for determination of V˙o2 peak in mL·kg−1·min−1 (relative) and L·min−1 (absolute). At entry and exit from CR, patients performed a symptom-limited treadmill ETT until volitional exhaustion, progressive angina, or other medical findings that would warrant termination of the test. Protocols included the modified-Balke, modified-Naughton, or Bruce depending on an estimation of CRF. To determine V˙o2 peak and respiratory exchange ratio (RER), expired gas analysis was measured throughout the ETT with a Vmax 29C (Sensormedics) metabolic cart from January 1996 through March 2011 and with Ultima CPX (Medgraphics) from April 2011 through 2015. The highest average 30-sec value was defined as V˙o2 peak . Calibration was performed prior to each test, and quality control was performed according to guidelines.14,15 The workload performed on the last completed stage of the ETT was defined as estimated peak metabolic equivalents of task (METs).16 While estimated MET is a less precise method of assessing V˙o2 peak , we report it to compare the difference between a commonly employed clinical assessment and measures obtained with cardiopulmonary exercise testing.

EXERCISE TRAINING

The exercise training program consisted of 2–3 sessions/wk over 3-4 mo to a maximum of 36 sessions. Patients were monitored during training sessions, and exercise intensity was adjusted to maintain heart rates (HRs) in the range of 70–85% of the peak HR obtained on the entry ETT and/or a rating of perceived exertion (RPE) between fairly light and hard (11-14 on a scale of 6-20). Beginning in 2012, higher-intensity interval training was incorporated into the exercise regimen for patients who were physically able.17 Physical ability was determined through clinical judgment, with consideration of CRF levels, absence of orthopedic or musculoskeletal issues, and cognitive or other factors that would preclude interval training. In general, the interval sessions consisted of a 5-min warm-up, followed by 4 intervals of 4 min at 90–95% peak HR with 3 min of active recovery. Exercise equipment included treadmills, elliptical trainers, upright and seated steppers, and cycle, arm, and rowing ergometers. Patients were encouraged to exercise on their own for a total of 3–5 sessions/wk.

STATISTICAL ANALYSIS

Paired t tests, χ2, and analysis of variance were used for within- and between-group differences. Post hoc pairwise comparisons of V˙o2 peak and diagnosis were performed with least significant difference adjustments for multiple comparisons. Analysis of covariance (ANCOVA) was used to adjust for baseline sex differences (age, handgrip strength, abdominal obesity, and RER) that could influence V˙o2 peak . Statistical significance was set at the level of P < .05, and results are presented as mean ± SD. Analysis was performed using SPSS Statistics version 26 (IBM).

RESULTS

DEMOGRAPHICS

The cohort consisted of 3925 patients, with the majority being male (76%). Mean baseline V˙o2 peak was 19.1 ± 6.7 mL·kg−1·min−1 and mean age was 62 ± 11 yr. Cardiac surgery (CABG and HVS; 37%) was the most frequent diagnosis, followed by MI (31%), and the mean time from cardiac event to enrolling in CR was 39 ± 27 d (Table 1). Men were younger, started CR sooner, had higher V˙o2 peak and handgrip strength, as well as greater levels of self-reported physical function compared with women (all Ps < .001). Beginning in 2012, 34% of patients (20% women, 39% men) who enrolled in CR performed interval training.

Table 1 - Clinical Data and Demographics at Entry to Cardiac Rehabilitationa
Total (N = 3925) Women (n = 940) Men (n = 2985)
Age, yr 62 ± 11 64 ± 12 62 ± 11b
Weight, kg 87 ± 19 76 ± 17 90 ± 18b
Body mass index, kg·m−2 29.4 ± 5.6 29.4 ± 6.6 29.4 ± 5.2
Waist circumference, cm 102.1 ± 14.2 95.5 ± 15.1 104.1 ± 13.2b
V˙o2 peak , mL·kg−1·min−1 19.1 ± 6.7 15.2 ± 4.7 20.4 ± 6.7b
RER 1.09 ± 0.12 1.06 ± 0.12 1.12 ± 0.11b
Handgrip strength, kg 37 ± 12 23 ± 6 41 ± 10b
MOS SF-36 Physical Function 64 ± 26 56 ± 25 66 ± 25b
Days to CR entry 39 ± 27 42 ± 27 38 ± 26b
Index diagnosis
Cardiac surgery (CABG and HVS) 37 31 38b
Myocardial infarction 31 34 30c
Percutaneous intervention 23 23 23
Chronic heart failure 4 4 4
Cardiac arrhythmia 3 4 2
Stable angina 2 3 2
Transcatheter aortic valve replacement <1 <1 <1
Abbreviations: CABG, coronary artery bypass graft; CR, cardiac rehabilitation; HVS, heart valve surgery; MOS SF-36 Physical Function, Medical Outcomes Study Short Form-36 Physical Function Component; RER, respiratory exchange ratio;
V˙o2 peak
, peak oxygen uptake.
aData are presented as mean ± SD or %.
bBetween-group P < .001.
cBetween-group P < .05.

There was a significant interaction between baseline V˙o2 peak and diagnosis (P < .001). Post hoc analyses showed V˙o2 peak values for PCI and MI were significantly greater than those for CABG, HVS, stable angina, CHF, and TAVR (P < .001) but not for cardiac arrhythmia (Table 2). There was a significant difference in V˙o2 peak between cardiac arrhythmia and CABG and CHF (P < .001), HVS and TAVR (P < .01), and stable angina (P < .05).

Table 2 - Baseline Aerobic Capacity (mL·kg−1·min−1) by Index Diagnosisa
Index Diagnosis Total Women Men
PCI 20.8 ± 7.3 (898) 15.8 ± 4.6 (219) 22.4 ± 7.3b (679)
MI 20.4 ± 7.3 (1219) 15.8 ± 5.0 (320) 22.0 ± 7.3b (899)
CA 19.6 ± 7.1 (109) 16.8 ± 7.4 (35) 21.0 ± 6.5c (74)
CABG 17.4 ± 5.0 (1249) 13.9 ± 3.5 (222) 18.2 ± 5.0b (1027)
HVS 17.4 ± 5.7 (189) 15.1 ± 5.1 (67) 18.7 ± 5.6b (122)
Stable angina 17.4 ± 5.5 (78) 15.3 ± 3.7 (24) 18.4 ± 5.9d (54)
CHF 16.6 ± 5.5 (138) 13.6 ± 3.6 (37) 17.8 ± 5.7b (101)
TAVR 14.2 ± 4.3 (12) 12.7 ± 3.2 (5) 15.2 ± 4.9 (7)
Abbreviations: CA, cardiac arrhythmia; CABG, coronary artery bypass graft; CHF, chronic heart failure; HVS, heart valve surgery; MI, myocardial infarction; PCI, percutaneous intervention; TAVR, transcatheter aortic valve replacement.
aData are presented as mean ± SD (n). There was a significant interaction between baseline aerobic capacity and diagnosis (P < .001). Post hoc comparisons with LSD:
PCI vs CABG,b CHF,b stable angina,b HVS,b TAVRb; MI vs CABG,b CHF,b stable angina,b HVS,b TAVRb; CA vs CABG,b CHF,b HVS,c TAVR,c stable angina.d
bBetween-group P < .001.
cBetween-group P < .01.
dBetween-group P < .05.

There was a significant interaction between baseline V˙o2 peak , diagnosis, and sex (P = .001). Post hoc analysis of baseline V˙o2 peak by diagnosis in men showed that both PCI and MI diagnoses were significantly greater than those for CABG, HVS, stable angina, CHF (P < .001), and TAVR (P < .01) but not for cardiac arrhythmia. Cardiac arrhythmia was significantly different from CABG and CHF (P < .001), as well as from stable angina, HVS, and TAVR (P < .05). For women, baseline V˙o2 peak values for CABG (P < .001) and CHF (P < .01) diagnoses were lower than those for PCI, MI, and cardiac arrhythmia. Women had lower mean entry V˙o2 peak than men for PCI, MI, HVS, CABG, and CHF (P <.001), cardiac arrhythmia (P <.01), and stable angina (P <.05), but not TAVR (Table 2).

RESPONSE TO CR TRAINING

V˙o2 peak was obtained during an exit evaluation in 1789 patients (23% women). Reasons for not completing an exit ETT included dropout for medical, work, or insurance issues (36%), dropout with no reason given (28%), declined or unable to perform exit evaluation (30%), and completed CR elsewhere (5%). Baseline V˙o2 peak was similar between those performing exit evaluations and noncompleters (data not shown), although completers of CR were older (65 ± 11 vs 60 ± 11 yr, P < .001) with lower handgrip strength (36 ± 11 vs 37 ± 12 kg, P < .001) and entered CR sooner (38 ± 22 vs 41 ± 30 d, P = .001) despite being more likely to have a surgical diagnosis (39 vs 34%, P = .001). A higher percentage of noncompleters had a diagnosis of CHF (5 vs 2%, P < .001) and cardiac arrhythmia (4 vs 2%, P < .001). Patients performing exit evaluations completed a mean of 27 ± 10 sessions, with no differences between women and men in the number of sessions attended or the time to enter CR. Overall, V˙o2 peak increased from 19.2 ± 6.4 to 22.4 ± 7.5 mL·kg−1·min−1 (+17%; P < .001). Improvements in body composition were noted, with weight and waist circumference decreasing from 85.2 ± 17.4 to 84.2 ± 17.0 kg (−1%; P < .001) and from 39.9 ± 5.3 to 39.2 ± 5.1 cm (−2%; P < .001), respectively. Muscle strength and self-reported physical function increased, with handgrip strength rising from 36 ± 11 to 37 ± 12 kg (+3%; P < .001) and MOS SF-36 scores increasing from 64 ± 25 to 83 ± 20 (+30%; P < .001). Despite an overall mean increase in V˙o2 peak , 18% of patients failed to demonstrate any improvement with exercise training (exit V˙o2 peak ≤ entry V˙o2 peak ).

Women improved V˙o2 peak by +2.0 ± 2.7 mL·kg−1·min−1 (+13%; P < .001), while men increased by +3.5 ± 2.0 mL·kg−1·min−1 (+17%; P < .001). There was a significant interaction between improvement in V˙o2 peak and diagnosis (P < .001), with surgical diagnoses increasing more than for MI, PCI, stable angina, cardiac arrhythmia, and TAVR (Table 3). Furthermore, both MI and CHF diagnoses showed larger increases in V˙o2 peak than for patients with stable angina. There was no significant interaction between change in V˙o2 peak , diagnosis, and sex (P = NS).

Table 3 - Improvement in Aerobic Capacity (mL·kg−1·min−1) by Index Diagnosisa
Index Diagnosis Total Women Men
HVS 4.5 ± 3.4 (+26%) (110) 3.5 ± 2.2 (+23%) (38) 5.0 ± 3.8 (+27%) (72)
CABG 4.0 ± 3.8 (+23%) (597) 2.3 ± 2.5 (+16%) (99) 4.4 ± 4.0 (+25%) (498)
CHF 3.3 ± 3.4 (+20%) (34) 2.3 ± 2.4 (+16%) (11) 3.7 ± 3.8 (+22%) (23)
MI 2.8 ± 3.4 (+14%) (568) 1.8 ± 2.6 (+11%) (139) 3.2 ± 3.5 (+14%) (429)
PCI 2.4 ± 3.6 (+12%) (415) 1.3 ± 2.9 (+8%) (99) 2.7 ± 3.7 (+12%) (316)
CA 2.3 ± 3.9 (+11%) (26) 3.7 ± 3.2 (+18%) (10) 1.5 ± 4.2 (+7%) (16)
Stable angina 1.4 ± 3.1 (+7%) (29) 0.7 ± 2.5 (+5%) (7) 1.6 ± 3.3 (+8%) (22)
TAVR −1.0 ± 2.1 (−8%) (3) 0.2 ± 0.8 (+2%) (2) −3.3 (−20%) (1)
Abbreviations: CA, cardiac arrhythmia; CABG, coronary artery bypass graft; CHF, chronic heart failure; HVS, heart valve surgery; MI, myocardial infarction; PCI, percutaneous intervention; TAVR, transcatheter aortic valve replacement.
aData are presented as mean ± SD (% improvement) (n). There was a significant interaction between baseline aerobic capacity and diagnosis (P < .001). Post hoc comparisons with LSD: HVS vs MI,b PCI,b stable angina,b CA,c TAVRc; CABG vs MI,b PCI,b stable angina,b CA,d TAVRd; CHF vs stable anginad; MI vs stable angina.d
bBetween-group P < .001.
cBetween-group P < .01.
dBetween-group P < .05.

Both women and men demonstrated favorable changes in body composition, muscle strength, and self-reported physical function (Table 4). When analyzing CRF based on treadmill time (268 women, 917 men), women improved estimated peak METs from 5.1 ± 2.4 to 6.8 ± 2.9 (P < .001) while men increased from 7.0 ± 3.2 to 9.2 ± 3.4 (P < .001). To determine whether the additions of HVS (2006) and CHF (2014) as covered diagnoses and interval training (2012) altered exercise training response, change in V˙o2 peak was compared pre- and post-2006, with no differences noted between time periods (3.1 ± 3.7 vs 3.3 ± 3.6 mL·kg−1·min−1, P = .20). However, there was a greater rate of patients failing to improve pre-2006 (20 vs 16%, P = .05).

Table 4 - Cardiac Rehabilitation Training Responsea
Women (n = 407) Men (n = 1382) Delta Change, P Value
Entry Exit Entry Exit
Age, yr 66 ± 11 64 ± 10 <.001
Days to CR entry 39 ± 22 37 ± 22 .121
Weight, kg 73.9 ± 16.1 73.0 ± 15.7b 88.5 ± 16.3 88 ± 15.7b .869
Body mass index, kg·m−2 28.8 ± 6.3 28.4 ± 6.0b 29.0 ± 4.9 28.7 ± 4.7b .331
Waist circumference, cm 94.2 ± 13.8 92.7 ± 13.7b 103.5 ± 12.4 101.4 ± 11.9b .033
V˙o2 peak mL·kg−1·min−1 15.6 ± 4.6 17.6 ± 5.0b 20.3 ± 6.5 23.8 ± 7.5b <.001
RER 1.06 ± 0.11 1.07 ± 0.11c 1.12 ± 0.11 1.11 ± 0.10b <.001
Handgrip strength, kg 23 ± 6 24 ± 6b 39 ± 10 41 ± 10b <.001
MOS SF-36 Physical Function 58 ± 26 76 ± 23b 67 ± 25 85 ± 19b .662
Abbreviations: CR, cardiac rehabilitation; MOS SF-36 Physical Function, Medical Outcomes Study Short Form-36 Physical Function Component; RER, respiratory exchange ratio;
V˙o2 peak
, peak oxygen uptake.
aData are presented as mean ± SD.
bWithin-group significant difference of P < .001.
cWithin-group significant difference of P < .05.

FEMALE AND MALE COMPARISONS

When comparing those who completed CR, women demonstrated less improvement in V˙o2 peak than men (13 vs 17%, P < .001). Although women improved estimated peak METs to a lesser degree than men (+1.7 ± 1.7 vs 2.2 ± 2.0 METs, P < .01), percent improvement was similar at 33% for women and 31% for men (P = NS). Women were older with lower handgrip strength, had greater rates of abdominal obesity (63 vs 53%, P < .001), and were more likely to suffer from orthopedic limitations (21 vs 16%, P = .007). Of those who completed CR since 2012, 11% of women performed interval training while for men it was 22%. Peak RER values were lower in women, but values remained consistent across entry and exit ETT (Table 4). Differences in V˙o2 peak remained when expressed as an absolute value in L·min−1, with women improving +0.3 ± 0.4 L·min−1 and men +0.4 ± 0.5 L·min−1 (14 vs 19%, P < .001). In addition, a higher percentage of women failed to demonstrate any improvement in V˙o2 peak than did men (24 vs 16%, P = .001) (Figure). Differences in handgrip strength were noted after CR completion, with women improving +1 ± 3 kg (+4%) compared with +2 ± 5 kg (+5%) for men (P < .001). ANCOVA was performed to adjust for baseline differences (age, handgrip strength, abdominal obesity, and RER) that could influence change in V˙o2 peak , with sex differences persisting (data not shown).

Figure.
Figure.:
Percentage of patients who fail to improve aerobic capacity (women: n = 407; men: n = 1382) following cardiac rehabilitation.

DISCUSSION

Our results, utilizing directly measured gas analysis, demonstrate that women experience significantly less improvement in V˙o2 peak than men (13 vs 17%). This is despite the fact that women enter CR with significantly lower values for V˙o2 peak . When reported in estimated peak METs from treadmill time, however, women (+33%) and men (+31%) appear to improve similarly. In addition, 24% of women failed to exhibit any change in V˙o2 peak whatsoever. Increases in V˙o2 peak are an important prognostic factor.11,12 Given this, one of the major goals in CR is to increase CRF; based on our results, women may not experience the full benefits of CR following program completion.

Previous studies of both otherwise healthy individuals and participants in CR have reported that sex and age have a primary bearing on CRF.8,18 We have previously reported normative values for participants entering CR relative to individual age, sex, and diagnosis.8 Women entering CR are older, with more comorbidities than men, which could influence the ability to perform and respond to exercise training.19 In this current study, women were older, had lower grip strength, achieved lower RER values during an ETT, and had lower physical function by self-report. Differences in V˙o2 peak remained when results were expressed in absolute terms (L·min−1) and when adjusted for baseline differences in age, handgrip strength, abdominal obesity, and baseline RER. Therefore, it is unlikely that age and differences in lean muscle mass were a major determinant in the sex differences observed in this analysis.

There are potential reasons for the differing training response observed in this study. First, mean RER was 1.06 at entry for women. This potentially represents a submaximal effort and might have resulted in lower peak HRs, which, subsequently, impact calculated target HR ranges. Therefore, exercise prescriptions may have been too conservative and contributed to attenuated improvement in V˙o2 peak . Furthermore, we noted diminished improvements in handgrip strength, which may indicate women performed resistance training at lower intensities or less often during exercise sessions and potentially contributed to our findings. Improvements in physical function, submaximal endurance time, and 6-min walk performance have been noted when strength training is emphasized.20–22 A focus on resistance training in CR, therefore, may affect changes in V˙o2 peak or improve the ability to tolerate higher-intensity training.

A recent study demonstrated that high-intensity interval exercise training protocols induced positive changes in CRF in individuals after an MI.23 Our program began incorporating interval training in 2012, with 11% of women and 22% of men exercising at higher intensities. The lower rate of interval training would suggest that women may have exercised at lower relative workloads during CR, thus limiting changes in V˙o2 peak . While we noted similar sex differences in our population in a previous study,9 our current improvement of 13% in V˙o2 peak is higher than that reported in 2009 (11%). The addition of interval training could partially explain the enhanced training effect, and a further emphasis on exercise intensity could possibly reduce the gap between women and men. Conversely, the addition of HVS and CHF as covered diagnoses for CR could have influenced improvements in V˙o2 peak , as women demonstrated improvements of +23% and +16%, respectively. Finally, women in CR tend to report a higher RPE for a similar relative intensity.9 While exercise RPE and workloads were not recorded in this analysis, we hypothesize that exercise prescriptions may have been overly conservative or not advanced at the same rate as men due to bias, given that women are older and have more comorbidities, resulting in diminished training responses.

While we demonstrate progress since our previous study (21% nonimprovers),9 we continue to see a failure to improve in 18% of our population. In our previous study,9 we reported that predictors of nonimprovement included lower training intensities, greater comorbidity burden, higher baseline V˙o2 peak and handgrip strength, and the presence of diabetes mellitus. The primary factor associated with failure to improve in that study was exercise training at a lower intensity. While we lack the ability to assess exercise intensity and RPE in our current analysis, this likely remains a contributing factor, particularly for women, as demonstrated by lower RER, less improvement in handgrip strength, and low rates of interval training. Furthermore, despite the addition of diagnoses associated with large improvements in V˙o2 peak (HVS: +26%; CHF: +20%), training effects remained similar pre- and post-2006, suggesting that exercise intensity remains the most likely predictor of change. Therefore, caution should be used when reporting functional improvements as a percentage since a significant portion of the population may not demonstrate any improvement with CR training. It is important for both clinicians and researchers to address failure to improve V˙o2 peak by considering alternatives to traditional CR exercise programming and including rates in outcomes analyses.

Limitations of this study include that this was a single-center, nonrandomized controlled study. We are unable to report on physical activity performed outside of CR or compare various exercise prescriptions. Another limitation was lack of direct measure of lean muscle mass and fat mass; rather, handgrip and waist circumference were used as proxy. In addition, besides handgrip strength, resistance and aerobic training intensity was not available. Therefore, there may have been an inherent bias toward not progressing in women as much as in men due to age or perceived frailty.

Strengths of this study include a large sample of female patients, a vulnerable population often underrepresented in prior studies. Second, V˙o2 peak was measured directly to assess CRF as estimated peak METs may not be as sensitive.24 Previous studies have reported a similar improvement in CRF between men and women, but these studies have used estimated METs. The ability to directly assess V˙o2 peak removes the potential for error inherent in predictive equations based on treadmill time. Finally, we were able to analyze the effect of various diagnoses on baseline V˙o2 peak and training response to CR.

CONCLUSION

Following CR, participants improve their CRF, body composition, and muscle strength, but the extent differs between sexes. This despite correcting for variables that may influence V˙o2 peak . While there are no differences in training effect using estimated METs, directly measured V˙o2 peak showed significantly less improvement for women than for men. In addition, 18% of patients did not see any improvement in V˙o2 peak . Potential causes of lesser improvement involve lower training intensity or lack of progression of exercise prescriptions. While a surgical diagnosis is associated with lower baseline CRF, greater improvements are shown following CR. Further studies investigating optimal exercise prescriptions, specifically for women, are needed.

ACKNOWLEDGMENT

This study was funded by the National Institutes of Health Center of Biomedical Research Excellence award from the National Institute of General Medical Sciences: P20GM103644 (Dr Ades).

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Keywords:

aerobic capacity; cardiac rehabilitation; exercise

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