Higher Oxygen Uptake And Heart Rate Response In Recovery From Acute High Intensity Interval Exercise

Abstract

Optimizing energy expenditure is paramount to achieving negative energy balance and promoting weight loss. High intensity interval exercise (HIIE) has been popularized for its ability to reduce body fat despite its time efficiency, yet it is unknown if the majority of calories burned during acute HIIE stems from completion of each interval or subsequent recovery period. Moreover, it is thought that the adaptive response to HIIE is mediated by the acute metabolic stress, but it is unknown if this stems from the interval or recovery phase of training. PURPOSE: To compare oxygen uptake (VO2) and heart values (HR) acquired during HIIE and in subsequent recovery to various HIIE regimens. METHODS: Data from 6 previously-published studies requiring various cycling-based HIIE regimens were analyzed from 89 healthy and active men and women (age, BMI, PPO, and VO2max = 25 ± 6 yr, 24 ± 3 kg/m2, 276 ± 59 W, and 40 ± 7 mL/kg/min). HIIE protocols included six to twelve 30 s - 2.5 min efforts at intensities ranging from 70 - 85 %PPO, with recovery periods ranging from 30 - 75 s. During exercise, VO2, HR, and blood lactate concentration (BLa) were acquired. RESULTS: HIIE bouts elicited peak HR, VO2, and BLa equal to 90 ± 6 %HRmax, 76 ± 12 %VO2max, and 10 ± 4 mM, respectively, and calorie expenditure was equal to 173 ± 47 kcal. Paired t-test revealed significantly higher VO2 (1.95 ± 0.46 L/min vs. 2.02 ± 0.46 L/min, p < 0.001) and HR (158 ± 14 b/min vs. 161 ± 15 b/min, p < 0.001) during recovery from acute HIIE versus the intervals. Significant inverse associations were demonstrated between VO2max and peak VO2 (r = -0.40, p < 0.001) and peak HR (r = -0.30, p = 0.004) attained during HIIE. CONCLUSIONS: Data reveal a significantly higher VO2 during recovery from HIIE compared to each interval, which may be due to slow O2 kinetics of these average fitness adults. HR was also higher in recovery suggesting a severe stress on the cardiovascular system not only during each interval, but also in recovery despite the low power outputs completed. More fit participants showed a blunted VO2 and HR response to HIIE suggesting that they may be at lower relative intensities versus less fit individuals. The structure of recovery periods as well as the interval efforts may be modified by clinicians to optimize calorie expenditure and metabolic stress of acute HIIE.