High-Intensity Interval Training vs Moderate-Intensity Continuous Training for Women Receiving Cardiovascular Rehabilitation—Reply

Abstract

To the Editor Women continue to be highly underrepresented in cardiovascular rehabilitation (CR) research. Randomized clinical trials (RCTs) have demonstrated the similar and superior efficacy of high-intensity interval training (HIIT) on increasing peak oxygen uptake (peak VO 2 ) compared with moderate-intensity continuous training (MCT). 1 However, these studies predominantly included men; HIIT in women with cardiovascular disease is, thus, recommended without empirical support. 2 To address this gap, Khadanga et al 3 evaluated the effect of HIIT combined with high-intensity lower extremity resistance training (RT) and MCT with moderate-intensity RT on peak VO 2 in women enrolled in CR. The key finding was that HIIT led to a significantly greater increase in peak VO 2 compared with MCT in women.While we commend the authors for completing this highly needed women-only RCT, there are several key points that merit discussion. First, the use of absolute peak VO 2 (L/min) warrants attention. While the authors indicated that peak VO 2 is a powerful predictor of mortality among patients with cardiovascular disease, it is essential to note that changes in relative (ie, peak VO 2 relative to body mass; mL/kg/min) and not absolute peak VO 2 are associated with prognosis. 4 Second, the findings did not show the superiority of HIIT on relative peak VO 2 . This is not surprising considering the intensity of their MCT (70% to 85% peak heart rate, ie, moderate to vigorous intensity) and significantly greater loss in body mass following MCT than HIIT. The authors chose absolute peak VO 2 to account for possible changes in body mass during CR; however, we argue that a reduction in body mass is an important outcome of CR that improves prognosis. 5 Third, reporting percentage changes in peak VO 2 can be misleading as these are influenced by baseline values. While +23% and +7% following HIIT and MCT, respectively, can be interpreted as a large difference, there was a small difference in posttraining mean (SD) peak VO 2 (HIIT, 1.6 [0.4] L/min; MCT, 1.5 [0.4] L/min). Lastly, the statistical analyses are unclear; paired t test and χ 2 do not test the research questions.Overall, although the authors concluded that HIIT is superior to MCT for increasing peak VO 2 in women with cardiovascular disease, this is inconsequential as it is based on absolute peak VO 2 . The implications of this study have a different meaning if relative peak VO 2 was used as the primary outcome (ie, HIIT and MCT have similar effects on peak VO 2 ). Relative peak VO 2 accounts for differences in body mass and predicts cardiovascular events and mortality. 4 Future studies should use relative peak VO 2 (mL/kg/min) for an exercise training outcome.