The present studies were performed to investigate changes of reaction time and increase of muscle strength by isometric training of biceps brachii muscle. The intensity of its training was the three types of maximal voluntary contraction (MVC), 70%MVC and 50%MVC. EMG reaction time (EMG-RT) as a function of motor control in center nervous system was measured by isometric contraction on fixed elbow.
After training for 8 weeks period, integrated EMG (IEMG) and power spectorum (mean power frequency, MPF) were increased as a component of muscle strength. IEMG and MPF were increased 83.6% and 16.6% in MVC training group, and were increased 86.2% and 20.8% in 70%MVC training group, and were increased 69.2% and 13.2% in 50%MVC training group. Increase of muscle strength in MVC, 70%MVC and 50%MVC training group increased 36.8%, 42, 3% and 30.6%, respectively. Consequently, decrease of EMG-RT was markdly associated with increase of muscle strength. The heavy intensity of isometric training, MVC and 70%MVC groups, decreased the EMG-RT greater than 50%MVC training group. Therefore, the decrease of training-induced EMG-RT correlated to development of muscle strength due to stimulation by training intensity. These results suggest that the decreased EMG-RT might be due to stimulation on motor central system by muscle training of heavy intensity.

The present studies were performed to investigate changes of reaction time and increase of muscle strength by isometric training of biceps brachii muscle. The intensity of its training was the three types of maximal voluntary contraction (MVC), 70%MVC and 50%MVC. EMG reaction time (EMG-RT) as a function of motor control in center nervous system was measured by isometric contraction on fixed elbow.
After training for 8 weeks period, integrated EMG (IEMG) and power spectorum (mean power frequency, MPF) were increased as a component of muscle strength. IEMG and MPF were increased 83.6% and 16.6% in MVC training group, and were increased 86.2% and 20.8% in 70%MVC training group, and were increased 69.2% and 13.2% in 50%MVC training group. Increase of muscle strength in MVC, 70%MVC and 50%MVC training group increased 36.8%, 42, 3% and 30.6%, respectively. Consequently, decrease of EMG-RT was markdly associated with increase of muscle strength. The heavy intensity of isometric training, MVC and 70%MVC groups, decreased the EMG-RT greater than 50%MVC training group. Therefore, the decrease of training-induced EMG-RT correlated to development of muscle strength due to stimulation by training intensity. These results suggest that the decreased EMG-RT might be due to stimulation on motor central system by muscle training of heavy intensity.