Changes in oxygenation and phosphocreatine during exercise and recovery in relation to fiber types and capillary supply in human skeletal muscle
The purpose of this study was to examine the relationship between histochemical characteristics obtained from the gastrocnemius and changes in muscle energetics. Muscle oxygenation was determined by near infrared spectroscopy (NIRS), and phosphocreatine (PCr) by 31-phosphorus magnetic resonance spectroscopy (31P-MRS) during a submaximal plantar flexion exercise and recovery. The relative occurrence (%) of slow-twitch fibers (ST), fast-twitch oxidative fibers (FTa), fast-twitch glycolytic fibers (FTb), and the number of capillaries per fiber (Cap/Fiber) were also determined. The sum of %ST and %FTa (%ST+%FTa) was 85.8±8.74% (mean±SD), while the number of Cap/Fiber was 2.52±0.63. The initial rate of deoxygenation (Ratedeoxy) at the beginning of the exercise was 2.43±0.95 %·sec-1. The time constants (Tc) for the recovery of PCr and muscle oxygenation after exercise were 22.1±6.3 sec. and 20.3±13.6 sec., respectively. The %ST+%FTa, and the number of Cap/Fiber were each positively correlated to the Ratedeoxy (<0.05). The %ST+%FTa, and the number of Cap/Fiber were negatively correlated to the Tc for PCr recovery (P<0.05), but not correlated to that for muscle oxygenation recovery. In conclusion, the Ratedeoxy during localized submaximal exercise, and the Tc for PCr recovery are indicators of the muscle's oxidative capacity.
