Effect of short-term high-intensity interval training vs. continuous training on O 2 uptake kinetics, muscle deoxygenation, and exercise performance

• Published in: Journal of applied physiology (1985) Vol. 107; no. 1; pp. 128 - 138
• Main Authors: McKay, Bryon R., Paterson, Donald H., Kowalchuk, John M.
• Format: Journal Article
• Language: English
• Published: 01.07.2009
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.90828.2008

The early time course of adaptation of pulmonary O 2 uptake (V̇o 2 p ) (reflecting muscle O 2 consumption) and muscle deoxygenation kinetics (reflecting the rate of O 2 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 × 1-min intervals at 120% maximal O 2 uptake separated by 1 min of rest) or END (90–120 min at 65% maximal O 2 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. V̇o 2 p was measured breath-by-breath by mass spectrometry and volume turbine. Deoxygenation (change in deoxygenated hemoglobin concentration; Δ[HHb]) of the vastus lateralis muscle was monitored by near-infrared spectroscopy. The fundamental phase II time constants for V̇o 2 p (τV̇o 2 ) and deoxygenation kinetics {effective time constant, τ′ = (time delay + τ), Δ[HHb]} during moderate-intensity exercise were estimated using nonlinear least-squares regression techniques. The τV̇o 2 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 τ′Δ[HHb] (∼20 s) did not change over the course of eight training sessions. These data suggest that faster activation of muscle O 2 utilization is an early adaptive response to both HIT and lower-intensity END training. That Δ[HHb] kinetics (a measure of fractional O 2 extraction) did not change despite faster V̇o 2 p kinetics suggests that faster kinetics of muscle O 2 utilization were accompanied by adaptations in local muscle (microvascular) blood flow and O 2 delivery, resulting in a similar “matching” of blood flow to O 2 utilization. Thus faster kinetics of V̇o 2 p 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.