H-13P Free Communication/Poster Skeletal Muscle Physiology
To determine the effects of 21 day forearm immobilization and muscle endurance training on the muscle strength, muscle endurance and metabolic characteristics of the forearm muscle.
Ten healthy males (age: 22.0 ± 1.2 yrs, mean ± SD) participated in this study. The non-dominant arm was immobilized for 21 days with a cast. The subjects consisted of immobilized group (I group; n=6), and immobilization with training group (IT group; n=4). Exercise training consisted of a handgrip exercise at 30% of maximum voluntary contraction (MVC), with 1Hz to exhaustion, 2 times a week during a period of immobilization. MVC, forearm muscle energetics, and grip endurance were measured. Muscle energy metabolism was measured by 31P-magnetic resonance spectroscopy. Grip endurance test was performed at 30%MVC with 1Hz until exhaustion.
After the 21 day forearm immobilization MVC was 42.0 ± 3.5 kg and 34.5 ± 3.4 kg (PRE vs POST, p < 0.01) for I-group, and 45.9±5.7 kg and 38.5±8.6 kg (PRE vs POST, p < 0.05) for IT-group. Grip endurance at 30% MVC did not change for I-group (PRE; 49.3 ± 7.1 sec and POST; 47.5 ± 11.3 sec). However, grip endurance for IT-group significantly increased (PRE; 47.7 ± 1.7 sec and POST; 56.0 ± 6.7 sec, p < 0.05). The decrease in muscle pH at exhaustion during grip endurance test was slightly attenuated for IT-group (PRE; 6.55 ± 0.30, POST; 6.77 ± 0.21, p < 0.1), but did not change for I-group (PRE; 6.58 ± 0.28, POST; 6.64 ± 0.16).
Although muscle endurance training used in this study could not prevent the decrease in MVC due to immobilization, the training improved muscle endurance and decreased the change in muscle pH during exercise. The results of this study suggest that muscle endurance training 2 times a week is effective for improving muscle H+ elimination during exercise. This study was funded as part of the Ground Research for Space Utilization program promoted by NASDA and the Japan Space Forum (T. Hamaoka).