P. Gonzalez, T. Lizee, L. Gehring, M. Charter, K. Witzke, FACSM

Oregon State University - Cascades, Bend, OR

Whole-body high-intensity interval training (HIIT) has gained wide popularity in the fitness industry. Research suggests that HIIT benefits can be achieved in less time compared with steady state, moderate-intensity exercise. Published studies using HIIT, however, focus primarily on bicycle ergometer or treadmill-based exercises, with very limited research on the effects of functional exercise such as that used during whole-body HIIT, on heart rate and post-exercise oxygen consumption (EPOC). PURPOSE: To compare the exercise heart rate (HR), respiratory exchange ratio (RER), VO2 and EPOC following a 10-minute whole-body HIIT workout and a 20-minute steady-state, moderate-intensity workout. METHODS: Seven low-risk subjects (6 females and 1 male) aged 33.4±7.2y, who participated in whole-body HIIT a minimum of 3 d/wk for 6 months provided consent for the study. On day one, subjects performed a 20-minute rowing ergometer exercise at an intensity of +5 bpm of 70% age-predicted max HR. On a separate day, they performed a 10-minute whole-body HIIT workout consisting of as many continuous reps as possible of 10 barbell thrusters (men 75lbs/women 55 lbs) and 10 burpees over the barbell. Heart rate, VO2, RER and EPOC were measured using indirect calorimetry immediately following each exercise and throughout recovery until VO2 and RER returned to pre-workout levels. Heart rate was continuously monitored during the workouts and throughout recovery. Differences in time to recovery for VO2 and RER were determined using dependent t-tests (p<0.05). RESULTS: Subjects achieved 97.3+3.7% of their predicted max HR during the whole-body HIIT workout, classifying it as a maximal-effort exercise. A significant difference was found in the time to return to resting RER values between the two workouts (16.7+4.0 min after the row vs. 29.2+9.7 min after whole-body HIIT, p<0.01). Peak VO2 levels immediately after exercise differed between workouts (19.5+4.8 ml/kg/min after rowing vs. 32.9+6.0 ml/kg/min after whole-body HIIT, p<0.001), as did the time for VO2 recovery (13.25+8.5 min after rowing vs. 25.5+14.75 min after whole-body HIIT, p<0.05). CONCLUSION: There was a significant 12.5 and 12.25 min longer recovery time for RER and VO2, respectively, following whole-body HIIT. This was likely due to a longer time to restore ATP-PC and O2 stores, remove lactate, and restore cardiovascular and respiratory function following whole-body HIIT. Heart rate never returned to baseline during recovery following whole-body HIIT. Longer recovery times suggest a higher caloric expenditure following whole-body HIIT compared to moderate-intensity exercise, despite half the workout time.

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