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Effect of short-term high-intensity interval training vs. continuous training on O₂ uptake kinetics, muscle deoxygenation, and exercise performance

¹Canadian Centre for Activity and Aging, ²School of Kinesiology, Faculty of Health Sciences, and ³Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada

Submitted 27 June 2008 ; accepted in final form 8 May 2009

The early time course of adaptation of pulmonary O₂ uptake (O_2p) (reflecting muscle O₂ consumption) and muscle deoxygenation kinetics (reflecting the rate of O₂ extraction) were examined during high-intensity interval (HIT) and lower-intensity continuous endurance (END) training. Twelve male volunteers underwent eight sessions of either HIT (8–12 x 1-min intervals at 120% maximal O₂ uptake separated by 1 min of rest) or END (90–120 min at 65% maximal O₂ uptake). Subjects completed step transitions to a moderate-intensity work rate (90% estimated lactate threshold) on five occasions throughout training, and ramp incremental and constant-load performance tests were conducted at pre-, mid-, and posttraining periods. O_2p was measured breath-by-breath by mass spectrometry and volume turbine. Deoxygenation (change in deoxygenated hemoglobin concentration; [HHb]) of the vastus lateralis muscle was monitored by near-infrared spectroscopy. The fundamental phase II time constants for O_2p (O₂) and deoxygenation kinetics {effective time constant, ' = (time delay + ), [HHb]} during moderate-intensity exercise were estimated using nonlinear least-squares regression techniques. The O₂ was reduced by 20% (P < 0.05) after only two training sessions and by 40% (P < 0.05) after eight training sessions (i.e., posttraining), with no differences between HIT and END. The '[HHb] (20 s) did not change over the course of eight training sessions. These data suggest that faster activation of muscle O₂ utilization is an early adaptive response to both HIT and lower-intensity END training. That [HHb] kinetics (a measure of fractional O₂ extraction) did not change despite faster O_2p kinetics suggests that faster kinetics of muscle O₂ utilization were accompanied by adaptations in local muscle (microvascular) blood flow and O₂ delivery, resulting in a similar "matching" of blood flow to O₂ utilization. Thus faster kinetics of O_2p during the transition to moderate-intensity exercise occurs after only 2 days HIT and END training and without changes to muscle deoxygenation kinetics, suggesting concurrent adaptations to microvascular perfusion.

near-infrared spectroscopy; aerobic power; lactate threshold

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				H. J. Green, E. Bombardier, M. E. Burnett, I. C. Smith, S. M. Tupling, and D. A. Ranney Time-dependent effects of short-term training on muscle metabolism during the early phase of exercise Am J Physiol Regulatory Integrative Comp Physiol, November 1, 2009; 297(5): R1383 - R1391. [Abstract] [Full Text] [PDF]