VO2, RER, And Heart Rate During Recovery Following A Whole-body High-Intensity And Moderate-Intensity Workout

Abstract

Whole-body high-intensity interval training (WB HIIT), including CrossFit®, has gained wide popularity, partly because HIIT benefits can be achieved in less time than moderate-intensity exercise. Most HIIT research, however, has used bicycle ergometer or treadmill-based exercises that emphasize only the lower body. PURPOSE: To compare heart rate (HR), respiratory exchange ratio (RER), and VO2 following a 10-minute functional, WB HIIT CrossFit® workout and a 20-minute steady-state, moderate-intensity workout. METHODS: Fourteen CrossFit® athletes (11 F/3 M) aged 36.6±9.2y performed a 20-minute rowing ergometer exercise at 70% +5 bpm of age-predicted max and a 10-minute WB 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, on separate days. VO2 and RER 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. Differences in time to return to baseline for VO2 and RER between the two modalities were determined using dependent t-tests (p<0.05). RESULTS: Participants achieved 96.4+4.4% of age-predicted max HR during the WB HIIT workout, classifying it as a max-effort exercise. Time to return to resting RER values between the two workouts was significantly different (19.1+3.8 ml/kg/min after rowing vs. 32.5+5.4 min after WB HIIT, p<0.001). Peak VO2 levels immediately after exercise also differed (19.5+4.8 ml/kg/min after rowing vs. 32.9+6.0 ml/kg/min after WB HIIT, p<0.001), as did the time for VO2 recovery (8.2+1.6 min after rowing vs. 22.3+7.7 min after WB HIIT, p<0.001). CONCLUSION: RER and VO2 remained elevated over 11 and 14 min longer, respectively, following WB HIIT, despite half the workout time. This is likely due to a longer time to restore ATP-PC stores, recycle lactate, and reduce body temperature. Heart rate remained elevated following the observed recovery period after WB HIIT suggesting a higher EPOC and caloric expenditure compared to moderate-intensity exercise. Our equipment prevented the measurement of VO2 during the workout, so future research should use equipment that would allow for testing VO2 during WB HIIT exercise so that EPOC can be accurately calculated.