HISTOLOGICAL STUDY ON THE EFFECT OF MUSCULAR TRAINING UPON THE MEDIUM MUSCLE FIBERS IN SKELETAL MUSCLES

Abstract

Skeletal muscle fiber of certain mammals consists of three types, namely, red muscle fiber, white muscle fiber and medium muscle fiber.
The purpose of this study is to inquire histologically the effect of training upon medium muscle fibers by comparing with red and white muscle fibers.
First, the form, size and distribution of red muscle fibers, white muscle fibers and medium muscle fibers of M. tibialis ant. of rats and mice were studied, and then the effect of training on those muscles was investigated.
Wistar-strain rats and dd-strain mice were devided into training and control groups. One training group of Wistar-strain rats was made to run a treadmill with a speed of 40 m/min., a distance of 250 m and for a period of 90 days. Another training group of dd-strain mice was compelled to run on the treadmill with a speed of 20 m/min., a distance of 250 m and for a period of 60 days.
After the training period, the anterior tibial muscle was removed and the histological method, using Sudan black B, was adopted in this experiment.
The results obtained were as follows:
1) Form and size ; Red muscle fibers are more or less roundish, and white muscle fibers are polygonal. In gereral red muscle fibers are thinner than white muscle fibers. Medium muscle fibers are intermediate between the two in all respects. Red muscle fibers, white muscle fibers and medium muscle fibers are all thick at the peripheral part of the muscle, and become thinner towards the central part.
2) Number ; The ratio of number of medium muscle fibers involved in the anterior tibial muscles is less than that of red and white muscle fibers in rats and mice.
3) Distribution ; The outer layer of the peripheral region of the muscle is composed mostly white muscle fibers, and red muscle fibers are more abundant in the central part of the muscle and near the tibia. Medium muscle fibers reveal a gradual increase in the central part.
4) In rats, increasing rate of the entire cross sectional area of medium muscle fibers was 19.1%, that of red muscle fibers was 18.0%, and that of white muscle fibers was 33.0%. In mice, each value of medium, red and white muscle fibers was 13.4%, 10.6% and 31.5%.
5) The effect of training on the average cross sectional area per fiber showed the same tendency as the effect of training on the entire area of cross section in medium, red and white muscle fibers.