Mechanical efficiency of high versus moderate intensity aerobic exercise in coronary heart disease patients: A randomized clinical trial

Background: Mechanical efficiency (ME) refers to the ability of an individual to transfer energy consumed by external work. A decreased ME, could represent an increased energy cost during exercise and may, therefore, be limited in terms of physical activity. This study aimed to compare the influence of two different exercise protocols: moderate continuous training (MCT) versus high intensity interval training (HIIT), as part of a cardiac rehabilitation program on ME values among coronary patients. Methods: 110 coronary patients were assigned to either HIIT or MCT groups for 8 weeks. Incremental exercise tests in a cycle ergometer were performed to obtain VO 2 peak. Net energy expenditure (EE) and ME were obtained at intensities corresponding to the first (VT 1 ) and second (VT 2 ) ventilatory thresholds, and at VO 2 peak. Results: Both exercise programs significantly increase VO 2 peak with a higher increase in the HIIT group (2.96 ± 2.33 mL/kg/min vs. 3.88 ± 2.40 mL/kg/min, for patients of the MCT and HIIT groups respectively, p < 0.001). The ME at VO 2 peak and VT 2 only significantly increased in the HIIT group. At VT 1 , ME significantly increased in both groups, with a greater increase in the HIIT group (2.20 ± 6.25% vs. 5.52 ± 5.53%, for patients of the MCT and HIIT groups respectively, p < 0.001). Conclusions: The application of HIIT to patients with chronic ischemic heart disease of low risk resulted in a greater improvement in VO 2 peak and in ME at VT 1 , than when MCT was applied. Moreover, only the application of HIIT brought about a significant increase in ME at VT 2 and at VO 2 peak.