Williams, A. M., Paterson, D. H., & Kowalchuk, J. M. (2012). High-intensity interval training speeds VO2 kinetics in moderate-intensity exercise Presentation 2212 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.transitions initiated from elevated metabolic rates.

During step-transitions in work rate within the moderate-intensity exercise domain, pulmonary oxygen uptake kinetics are slowed and pulmonary oxygen uptake gain is greater when exercise is initiated from an elevated metabolic rate. High-intensity interval-training has been shown to speed pulmonary oxygen uptake kinetics, without affecting kinetics of local muscle deoxygenation, when step-transitions to moderate-intensity exercise are initiated from lower, light-intensity baseline metabolic rates. The effects of high-intensity interval-training on step-transitions initiated from elevated metabolic rates have not been established.

This study investigated the effects high-intensity interval-training on pulmonary oxygen uptake and muscle deoxygenation kinetics during transitions from low and elevated metabolic rates, within the moderate-intensity exercise domain. Ss (males; N = 8) completed 12 sessions of high-intensity interval-training over four weeks. High-intensity interval-training consisted of 8-12 1-minute intervals on a cycle ergometer, at a work rate corresponding to 110% of pre-training maximum work rate. Pre-, mid-, and post-training, Ss completed another incremental ramp test to determine VO2max, maximum work rate, and estimated lactate threshold. Ss additionally completed double-step constant-load tests, consisting of step transitions from 20W to approximately 45% of lactate threshold and the approximate 45% value to 90 % of lactate threshold. Pulmonary oxygen uptake was measured breath-by-breath using mass spectrometry and volume turbine, and the local muscle deoxygenation profile was monitored using near-infrared spectroscopy. The ensemble averaged pulmonary oxygen uptake and local muscle deoxygenation profiles for each transition were modeled as mono-exponential responses using non-linear regression techniques. The time constant and amplitude of the fundamental, phase II pulmonary oxygen uptake response were estimated for each S and transition.

High-intensity interval-training led to a greater VO2max and lower oxygen-uptake time-constant for both the lower and upper steps. However, mean response time of local muscle deoxygenation was unchanged in the lower and upper steps within the moderate work range.

Implication. Following 12 sessions of high-intensity interval-training, the speeding of pulmonary oxygen uptake kinetics in both the lower and upper work levels of moderate intensity exercise may be due, in part, to better matching of the muscle oxygen utilization to microvascular oxygen delivery relationship within the working muscle.

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