ラット前脛骨筋筋線維構成の走行実験による変化

抄録

Myofibrous organization of the M. tibialis anterior of 9, one and a half year old rats which were subjected to running exercise on a treadmill, were examined and compared with controls.
The following results were achieved:
1) Muscle weight, cross sectional area of venter, total number of muscle fibers and thickness of muscle fibers were greater in males and the number of muscle fibers per sq. mm, was higher in females. On the other hand, the experimental males were well developed in cross sectional area of venter, total number of muscle fibers and thickness of muscle fiber, and the control females had greater thickness of muscle fibers, in general.
2) White or red muscle fibers always exceeded intermediate fibers in control females. Intermediate fibers were always least in evidence. Exercise increased the number of white fibers in both sexes, slightly decreased red fibers in females ; and decreased intermediate fibers, slightly in females, and greatly in males.
3) The thickness order for each type of muscle fiber was always : largest, white; then intermediate ; and red, smallest. All three of these types were larger in male than in female. On the other hand, white and red fibers in males were larger in the experimental group than in the control group, and those of females were larger in the control group.
4) In comparison of body weight with thickness of muscle fiber for experimental and control groups, no significant differences were observed in the red muscle fiber of both groups. For the intermediate fiber, there was no correlation with body weight of the control group, but muscle size was positively correlated with body weight in the experimental group. White fiber size was positively correlated with body weight for both control and experimental groups.
5) The thickness of muscle fiber was increased in male and decreased in female by exercise. The increase rate was greatest in white fiber, second in red fiber and least in intermediate fiber ; and the rate of decrease was largest in the intermediate fiber.
6) The relative cross sectional area occupied by the each type of muscle fiber was always largest for white fiber. Comparing the experimental with the control group, white fiber was larger in both sexes in the experimental group, red fiber was larger in females in the control group, and in males in the experimental groups. Intermediate fiber was larger in both sexes in the control group than in the experimental groups.
7) It is concluded that the following factors are important in the sex related differences of muscle fiber change: decrease in the number of intermediate fibers and increase of the red fibers in the male; and decrease in size of each type of muscle fiber, especially intermediate fiber, in the female, and which were caused by excessive exercises, especially for females.