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OXYGEN UPTAKE KINETICS DURING TEN SHORT-DURATION, HIGH-INTENSITY INTERVALS AT A CONSTANT WORK RATE

Abstract

PURPOSE: Oxygen uptake (VO2) kinetics at intensities below lactate threshold (LT) are better understood than those closer to VO2peak. Additionally, there is little information on the behavior of kinetics across repeated intervals of exercise. Thus, the purpose of this study was to analyze how VO2 kinetics change throughout a short-duration, high-intensity interval exercise (HIIE) protocol. METHODS: Subjects (n = 13) visited the laboratory on two separate occasions. The first visit included a graded exercise test to determine VO2peak and LT. The second visit included ten 2-minute intervals at a power halfway between LT and VO2peak, with 2minute resting periods between. VO2, minute ventilation (VE), and heart rate (HR) were collected during the exercise and resting portions of each interval. Previously published VO2 kinetics models were used to compare the phase II time constant (��) and amplitude (Ap) across intervals. RESULTS: �� was significantly faster during interval 2 compared to interval 1 of exercise (mean difference = 21.09 sec, CI: [9.66, 32.51], p<.001), but no different thereafter. Ap was significantly decreased during interval 2 compared to interval 1 (mean difference = 0.24, CI: [0.07, 0.41], p<.001), but no different thereafter. Significant increases were observed for peak exercise and minimum (min) resting values across the intervals for VO2 (peak: b = 0.033 L/min, CI: [0.029, 0.038], p<.001; min: b = 0.01 L/min, CI: [0.006, 0.013], p<.001), VE (peak: b = 2.79 L/min, CI: [2.47, 3.14], p<.001; min: b = 0.418 L/min, CI: [0.27, 0.67], p<.001), and HR (peak: b = 1.79 bpm, CI: [1.58, 2.01], p<.001; min: b = 1.94 bpm, CI: [1.62, 2.26], p<.001). CONCLUSION: This study indicates that the first bout of HIIE shortens �� and decreases Ap in the second bout. However, �� and Ap remain unchanged beyond the second interval, suggesting that only one bout is necessary to speed the kinetics of subsequent bouts. Linear increases in VO2, VE, and HR suggests that 2-minute rests between HIIE are likely insufficient for full recovery. Future studies should examine if kinetics change before volitional exhaustion and if there is an optimal length of recovery periods during HIIE.

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