A prior bout of contractions speeds oxygen uptake and blood flow on‐kinetics and reduces the slow component of oxygen uptake in highly‐oxidative skeletal muscle

Abstract

It was the purpose of this study to examine the prior contractions effect in highly‐oxidative skeletal muscle. With arterial [O2] maintained constant, a step change in metabolic rate was elicited by stimulating canine gastrocnemii (n=12) via their sciatic nerves (6–8 V, 0.2 ms duration, 50 Hz, 200 ms train) at a rate of 2 contractions · 3 s−1 for two, 2‐min bouts separated by 2 min of recovery. Blood flow was recorded with an ultrasonic flowmeter and muscle oxygenation was monitored via near infrared spectroscopy. In comparison to the first bout, the VO2 primary τ (9.4±2.3 vs. 12.0±3.9 s), TD (1.9±1.3 vs. 4.9±1.4 s), and slow component amplitude (5.9±6.3 vs. 12.1±9.0 mlO2·kg−1ww·min−1) were significantly reduced (p<0.05) during the second bout. Blood flow on‐kinetics were significantly speeded during the second bout (7.7±2.6 vs. 14.8±5.8 s). Kinetics of muscle deoxygenation were significantly slower at the onset of the second bout (7.2±2.2 vs. 4.4±1.2 s) while relative [O2Hb] was elevated throughout the second bout. These results argue in favor of enhanced O2 delivery and/or microvascular O2 availability as underlying mechanisms for the prior contractions effect in highly‐oxidative skeletal muscle at a high contraction intensity. Additionally, altered motor unit recruitment at the onset of a second bout is not a prerequisite for reductions in the VO2 slow component amplitude after a priming contractile bout.