Muscle Oxygenation and Aerobic Metabolism During High-Intensity Interval Training Bodyweight Squat Exercise in Comparison to Continuous Cycling




Kates, Andrew

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The purpose of this study was to evaluate muscle oxygenation, cardiorespiratory, and blood lactate responses to an acute bout of a high-intensity interval training (HIIT) bodyweight squat protocol (HIIT-squats) in comparison to (continuous) moderate intensity cycling exercise (MOD). On separate days, within a two week period, 15 recreationally active males (28 (4.6) years) performed: 1) incremental test to exhaustion on a cycle ergometer, 2) 30-minutes of moderate intensity cycling (MOD; 65% VO2max), and 3) HIIT-squats consisting of eight x 20 seconds of bodyweight squats performed at maximal cadence with 10-s rest intervals. During each exercise condition, oxygen consumption (VO2) and heart rate were monitored continuously, and muscle oxygenation (tissue saturation index, TSI) at the left vastus lateralis muscle was measured for 2 minutes pre-, throughout, and for 5 minutes post-exercise using Near-Infrared Spectroscopy (NIRS; Portalite, Artinis Medical Systems, Netherlands). Blood lactate was measured at pre- and one, three, and five minutes post-exercise. Mean and peak changes in TSI were similar in both HIIT-squats (mean = -14.6 (5.3)%, peak = -19.7 (5.2)%; p > 0.05) and MOD (mean = -13.2 (5.6)%, peak = -18.2 (7.6)%; p > 0.05), with peak changes in TSI occurring significantly faster in HIIT-squats (71.2 (95.2) seconds (s) after onset of exercise) than in MOD (1452.9 (647.8)s; p < 0.05). The half time of TSI recovery following HIIT-squats (T1/2TSI = 25 (7.9)s) was not significantly different post-MOD (25 (9.6)s). Mean VO2 during HIIT-squats (31.48 (4.58) was similar to MOD (33.76 (5.71), however minute ventilation (VE), respiratory exchange ratio (RER) and all post-exercise blood lactate concentrations were significantly higher in HIIT-squats compared to MOD (p < 0.05). Despite the different durations of HIIT-squats and MOD, mean and peak changes in aerobic metabolism during and after exercise were similar. Results provide evidence of both aerobic and anaerobic contributions to energy metabolism in response to HIIT-squats, and highlight possible mechanisms for the commonly reported improvements in aerobic power following chronic HIIT.



HIIT, Muscle Physiology, Muscle Metabolism