Effects of bicycle exercise duration (i. e., 20, 40 and 60 min) on post-exercise glucose metabolism was studied in four healthy untrained men (19.8±0.4 yr), who were previously considered normal on a resting oral glucose tolerance test (OGTT) . These three exercises were performed on different days. The intensity of exercise corresponded to approximately 60% of VO₂max. A glucose sample of 100-g/300 ml was orally administered on 20 min after the completion of each exercise. Blood samples were obtained from a forearm vein before exercise, immediately after and on 20 min after the cessation of exercise, and on 30, 60, 90, 120 and 180 min after glucose ingestion. The following results were obtained. 1) Blood glucose concentrations observed on 60, 90, 120 and 180 min after glucose ingestion following 60 min exercise appeared to be higher than OGTT levels, indicating the time delay to return to the resting level. 2) Serum insulin concentrations after glucose ingestion following 20 and 40 min exercise were lower than OGTT levels. Changes in serum insulin concentrations following 60 min exercise were similar to those on OGTT levels with the exception of the level on 30 min after glucose ingestion. Serum C-peptide response curves were similar to serum insulin response curves after each exercise. 3) Serum free fatty acids (FFA) increased during each exercise as compared to a resting level and increased further after each exercise. The degree of changes in FFA was most significant during a recovery period following 60 min exercise, however, it decreased abruptly after glucose ingestion as a case after 20 and 40 min exercise. 4) Plasma cyclic-AMP concentrations increased most profoundly during 60 min exercise. Plasma cyclic-AMP level before glucose ingestion was also higher following 60 min exercise. These results suggested that postexercise glucose metabolism after glucose ingestion tended to be decreased with elevated rates of serum FFA during a recovery period following 60 min exercise.

This study investigated the relationship between the intensity of muscle contraction and muscle oxygenation during dynamic knee extension. Six healthy male subjects (age 24.6±1.2 years) performed knee extension (concentric : 1 s/eccentric : 1 s) to exhaustion at 3 different intensities, 30%, 20% and 10% of maximum voluntary contractile strength (MVC) . A near-infrared spectroscopy (NIRS) probe and surface electrodes of the electromyogram were fixed on the m. rectus femoris. The muscle oxygenation and integral electromyogram (IEMG) were recorded both during and after dynamic knee extension.
The summary of the results was as follows.
1) Continuous time of knee extension decreased with increasing intensity of muscle contraction. There were significant differences between 10%MVC and 20%MVC (p<0.001), and 10%MVC and 30%MVC (p<0.001) .
2) The oxy-hemoglobin level during knee extension decreased with increasing intensity of muscle contraction. There were significant differences between 10%MVC and 30%MVC (p<0.001), 20%MVC and 30%MVC (p<0.001), and 10%MVC and 20%MVC (p<0.05) .
3) Recovery time after knee extension increased with increasing intensity of muscle contraction. There were significant differences between 10%MVC and 30%MVC (p<0.01), and 20%MVC and 30%MVC (p<0.01) .
4) The IEMG increased with increasing time of knee extension. The maximum value was observed just before completing the knee extension on the IEMG. The rate of increase in the IEMG increased with decreasing intensity of muscle contraction.
These results suggest that muscle oxygenation during dynamic knee extension decreases with increasing intensity of muscle contraction, and influences continuous time of muscle contraction.