Delayed reoxygenation after maximal isometric handgrip exercise in high oxidative capacity muscle

We hypothesized that after maximal short-term isometric exercise, when O-2 demand is still high and O-2 supply is not fully activated, higher oxidative capacity muscle may exhibit slower muscle reoxygenation after the exercise than low oxidative capacity muscle. Seven healthy male subjects performed a maximal voluntary isometric handgrip exercise for 10 s. The reoxygenation rate after the exercise (Reoxy-rate) in the finger flexor muscle was determined by near infrared continuous wave spectroscopy (NIRcws) while phosphocreatine (PCr) was measured simultaneously by P-31 magnetic resonance spectroscopy. Muscle oxygen consumption (muscle (V) over dot O-2) and muscle oxidative capacity were evaluated using the rate of PCr resynthesis post-exercise. The forearm blood flow (FBF) index at the end of exercise was measured using NIRcws. There was a significant positive correlation between the Reoxy-rate, which ranged between 0.53% s(-1) and 12.47% s(-1) and the time constant for PCr resynthesis, which ranged between 17.8 s and 38.3 s (r(2) = 0.939, P < 0.001). At the end of the exercise, muscle (V) over dot O-2 exceeded the resting level by approximately 25-fold, while the FBF index exceeded the resting level by only 3-fold on average. The Reoxyrate closely correlated with muscle (V) over dot O-2 (r(2) = 0.727, P < 0.05), but not with the FBF index. Also, the estimated O-2 balance (muscle (V) over dot O-2 index/FBF index) was negatively correlated with the Reoxy-rate (r(2) = 0.820, P < 0.001). These results support our hypothesis that higher oxidative capacity muscle shows slower muscle reoxygenation after maximal short-term isometric exercise because the Reoxy-rate after this type of exercise may be influenced more by muscle (V) over dot O-2 than by O-2 supply.