Muscle Reoxygenation Rate after Isometric Exercise at Various Intensities in Relation to Muscle Oxidative Capacity

Abstract

The purpose of this study was to determine whether the reoxygenation rate (Reoxy-rate) immediately after static exercise at various submaximal intensities would be related to muscle oxidative capacity. Seven healthy male subjects performed isometric handgrip exercise for 10 sec at 30%, 60% and 90% of maximal voluntary contraction (MVC). The Reoxy-rate and muscle oxygen consumption during exercise (muscleVO_2EX) were monitored by near infrared continuous wave spectroscopy (NIRcws). The muscle oxidative capacity was evaluated by the time constant for phosphocreatine resynthesis (PCrTc) using ³¹-phosphorus magnetic resonance spectroscopy (³¹P-MRS). The Peak blood flow of brachial artery after exercise (BABFpeak) was measured using Doppler ultrasound. There was no correlation between PCrTc and Reoxy-rate at 30% and 60% MVC. In contrast, Reoxy-rate at 90% MVC was positively correlated to PCrTc (r=0.825, p<0.05). The muscle VO_2EX increased 5.9, 8.8 and 12.6-fold of the resting on average at 30%, 60% and 90% MVC, respectively, and the muscle VO_2EX at 90% MVC was significantly higher than that at 30% and 60% MVC. On the other hand, BABFpeak increased only just 1.9, 2.4 and 2.7-fold of the resting on average at 30%, 60% and 90% MVC, respectively (Fig. 4). These results suggest that the higher oxidative capacity muscle shows slower muscle reoxygenation after 10 sec isometric exercise at 90% MVC because the Reoxy-rate after this type of exercise may be influenced more by muscle VO₂ than by O₂ supply. In contrast, 60%MVC and lower exercise intensities may not be severe enough to influence the muscle VO₂ dependent Reoxy-rate.

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