Effects of high‐intensity interval training on trajectories of gas‐exchange measures and blood lactate concentrations during cardiopulmonary exercise tests in cardiac rehabilitation—A randomized controlled trial

Abstract

Background: The optimal allocation of training time to different intensities in cardiac rehabilitation is still under debate. The objective of this study was to explore whether in a 12-week cardiac rehabilitation program, replacement of two of four usual continuous endurance training (CET) sessions per week with energy expenditure-matched high-intensity interval training (HIIT) affects the trajectories of cardiopulmonary exercise test (CPET) variables such as ventilatory equivalents for O 2 (EqO 2 ) and CO 2 (EqCO 2 ), and blood lactate (BLa) during CPET.Methods: Eighty-two male patients undergoing outpatient cardiac rehabilitation after an acute coronary syndrome were randomized to CET (age [mean ± SD] 61.7 ± 9.8 years, body mass index [BMI] 28.1 ± 3.4) or HIIT+CET (60.0 ± 9.4 years, BMI 28.5 ± 3.5). CPET was performed at baseline, after 6 and after 12 weeks. HIIT consisted of ten 60-s bouts of cycling at an intensity of 100% of the maximal power output (P max ) achieved in an incremental test to exhaustion, interspersed with 60 s at 20% P max . CET was performed at 60% P max with equal duration. Training intensities were adjusted after 6 weeks to account for the training-induced improvement in cardiorespiratory fitness. The entire functions defining the relationship between EqO 2 , EqCO 2 , and BLa, with power output were modeled using linear mixed models to assess how these trajectories are affected by HIIT.Results: After 6 and 12 weeks, P max increased to 112.9% and 117.5% of baseline after CET, and to 113.9% and 124.7% after HIIT+CET (means). Twelve weeks of HIIT+CET elicited greater reductions of EqO 2 and EqCO 2 than CET alone (p < 0.0001 each) in a range above 100% baseline P max . Specifically, at 100% of baseline P max , least squares arithmetic mean EqO 2 values of CET and HIIT+CET patients were 36.2 versus 33.5. At 115% and 130% of baseline P max , EqO 2 values were 41.2 versus 37.1 and 47.2 versus 41.7. Similarly, corresponding EqCO 2