The present study was carried out to examine the structural changes of the skeletal muscle fibers induced by exercise at the electron microscopic level. Twelve male albino rats were examined, of which six were used for the training group and the remainings were as controls. After training for ten weeks, the rats were sacrificed and their M. tibialis anterior was prepared for the examination with a light and electron microscope. The results obtained were summarized as follows :
1) The muscular training caused the hypertrophy of muscle fibers, the rate of which was about 20 percent in their cross section.
2) After training, the number of myofibrils per unit area of fiber cross section decreased. There were correlations between the fiber diameter and the number of myofibrils. Thus these relations can be expressed by a different regression equation for each group ; that is, Y = 50.17X -1391.47 for trained group and Y=53.89X -1182.91 for control group, respectively. (X: fiber diameter in micron, Y : number of myofibrils)
3) No significant difference existed between the trained and the control rats in the relative volumes of fiber components.
4) There were no significant differences between the trained and the control rats in respect to the myofilamental parameters, such as myosin filament concentration, distance between myosin filaments, myosin filament diameter, actin filament diameter and ratio of actin to myosin filament.
From the present study, it may be concluded that the hypertrophy of muscle fibers induced by exercise is attributed not to the increase in the number of myofibrils, but to the relative increase of both the size of each myofibril and the sarcoplasmic volume.

Specifically designed programs of sprint and endurance running were used to comparison of each training effect on muscle fibers and those of capillary supply.
Wistar strain male rats (42 days after birth) were trained by treadmill for 10 weeks.
The gastrocnemius muscle were histochemically studied.
The results obtained were summarized as follows:
1) The body and muscle weight of the rats in both training groups were significantly smaller than those of the control group.
2) The sprint training caused hypertrophy of muscle fiber, but the endurance training did not.
3) The endurance training group showed the higher value in the number of capillaries per fiber (CF ratio), per mm² (CD), around each fiber type (CC) than control group. And the endurance training group showed the lower value in the distance of diffusion than sprint training group and control group.
4) The sprint training group showed the higher value in CF ratio and CC than control group, but not so high as endurance training group.
These results suggest that training effects are specific to the type of training program used.

Relationship between muscle fiber conduction velocity and muscle fiber composition was studied in vastus lateralis of well-trained athlete students, who differed considerably regarding their fiber type distribution with averaged 69.2% fast twitch (FT) muscle fibers for sprinters (12 male subjects) and 39.7% FT muscle fibers for distance runners (7 male subjects) . Measurement of muscle fiber conduction velocity during brief and maintained isometric contraction was made directly, using the zero-crossing time delay method between two surface myoelectric signals. Muscle fiber conduction velocities increased 4.40 to 4.84 m/sec for sprinters and 3.91 to 4.31 m/sec for distance runners as developing force increased from 25 to 100% maximum voluntary contraction (MVC) . The correlation coefficients between conduction velocity and % FT fibers were 0.59, 0.63, 0.64 and 0.84 for 25, 50, 75 and 100% MVC, respectively. During maintained at 50% of MVC conduction velocities in sprinters decreased linealy from 4.77 to 4.38 m/sec and in distance runners decreased from 4.11 to 3.96 m/sec at only last stage. It was suggested that the individual difference in conduction velocity was caused by different muscle fiber composition and that the changes of conduction velocity depended on the recruitment of muscle fibers.

The purpose of this study was to investigate effects of intermittent running trainings with trot and gallop on glycogen consumption patterns of antagonistics (m. gastrocnemius and m. tibialis anterior) in male Wistar strain rats (4 weeks after birth, n=46) . The animals were devided into three groups, control (n=18), trot training (n=14), and gallop training (n=14) . In order to evaluate glycogen consumption patterns, serial sections of the muscles were stained for Myosin ATPase, DPNH-diaphorase, and Periodic acid-Schiff (PAS) reaction.
The results were summarized as follows ;
1) Significant change in fiber distribution occurred on both training groups, where the percentage of FOG fiber increased and there was a concomitant decrease in the FG fiber percentage. On the gallop tiaining group this effect was shown in the deep and peripheral regions of both muscles, but on the trot training group that wasn't shown in the peripheral region of m. tibialis anterior.
2) According to glycogen depletion patterns after transient running exercises, during gallop the participation of m. tibialis anterior was shown a tendency to increase.
3) With the trainings, decrease of glycogen consumption in muscle fiber occurred in deep and peripheral regions of the both muscles on gallop training group and in the m. gastrocnemius on trot training group.
These results suggest that the trainings with different running forms have different effects on the antagonistics.

Changes in myoproteins during development of rat skeletal muscle were investigated using two-dimensional gel electrophoresis. In M, soleus (SOL) which in adult, is composed predominantly of slow twitch fibers, fast type myosin light chains (fLC) were the major species and slow type light chains (sLC) were the minor species at birth. During development, the replacement rate of fLC to sLC sequentially occured so that LC patterns at 21 days postpartum were similar to adult where fLC were difficult to visualize. In contrast, M. extensor digitorum longus (EDL) always contained dominant fLC although sLC were found only for 5-9 days. LC 3 f became detectable at 5 days and gradually increased. In α-tropomyosin there were isozymes of fast and slow type based on difference in molecular weight, but not in β-tropo-myosin. Changes in isozymes of α-tropomyosin approximately corresponded with that in isozymes (fast and slow type) of LC in both EDL and SOL. During adult stage following birth, in EDL creatine kinase underwent a three-fold increase in molecular ratio to actin, whereas in SOL there was little change though increase took place transiently. These results suggest that with develoment many myoproteins change more dramatically in slow muscle than in fast muscle, and that transitions in LC isozymes and changes in distribution of histochemically typed muscle fibers may follow different time courses.

To investigate whether or not retardation of body weight increase by reduced food intake could change enzyme activities in the soleus and extensor digitorum longus (EDL) muscles during growth, rats were divided into three groups. Group 1 included rats aged 5, 7, 9, 11 weeks fed ad libitum. Group 2 included rats aged 5, 7, 9, 11 weeks fed a restricted diet. These animals weighed as much as the 5-week-old rats in group 1. Group 3 included four subgroups of 11-week-old rats. Their body weights were adjusted to the weights of rats 5, 7, 9 and 11 weeks old in group 1 by restriction of food intake. Succinate dehydrogenase (SDH) activity in the soleus muscle increased significantly with growth. Though a similar change was not observed with age in group 2, SDH activity in the soleus muscle in group 3 was enhanced with increasing body weight. Phosphofructokinase (PFK) activity in the soleus muscle decreased with growth in groups 1 and 2, but this change was not statistically significant. In group 3, PFK activity in the soleus muscle did not fluctuate with increasing body weight. In groups 1 and 2 there was a significant correlation between PFK activity and percentage area of type I fibers in the soleus muscle (r=-0.63, p<0.01, r=-0.55, p<0.01, respectively), but no significant relationship between them was evident in group 3. PFK activity in the EDL muscle increased significantly with growth in groups 1 and 2, but did not change with increasing body weight in group 3. It is suggested that the increase of SDH activity in the soleus muscle between the ages of 5 and 11 weeks is influenced primarily by changes in body weight, but that the changes of PFK in the soleus and EDL muscles are not modified by this factor.

In the present study, we examined whether GLUT4 concentration in rat skeletal muscle is dependent on local muscle activity level or not. In ten male Sprague-Dawley rats, one side of gastrocnemius muscle was tenotomized, and the other side contralateral muscle was treated sham operation as a control. Gastrocnemius and plantaris muscles were excised from both legs at the five weeks after surgery. After the muscles were weighed, GLUT 4 concentration and citrate synthase (CS) activity were measured. The results are summarized as follows:
In gastrocnemius muscle, tenotomy induced decreases of 25% in muscle weight, 16% in CS activity, and 25% in GLUT 4 concentration as compared with the control muscle. These data suggest that although extramuscular environment is similar, different GLUT 4 concen-tration in both muscles is induced by different muscle activity level. Therefore, it is con-cluded that muscle activity level regulates GLUT 4 concentration in skeletal muscle. In over-loaded synergistic plantaris muscle, muscle weight and GLUT 4 content per whole muscle were increased by 18% and 17%, respectively, but GLUT 4 concentration and CS activity were not changed as compared with the control muscle. These data could be interpreted that GLUT 4 concentration and mitochondrial oxidative enzyme activity in skeletal muscle are coregulated.

The purpose of this study was to investigate the optimal starting period of muscle power training during growth. Thirty-three Wistar strain male rats were used and classified into four groups, control group, 3T group started a training at 3 weeks after birth (weaning period), 8T group started a training at 8 weeks after birth (puberty period) and 13T group started a training at 13 weeks after birth (beginning of mature period) . Each training group was subjected to a power sprint training till 23 weeks after birth (mature period) .
The results were summarlized as follows;
1) Hypertrophy and increase of contractile properties in muscle were not seen in each training group.
2) Muscle glycogen contents increased significantly in 3T group (p<0.05) and in 8T, 13T group (p<0.01) .
3) Muscle fiber area increased significantly in 8T group only.
4) Phosphofructokinase activity in muscle increased significantly in 8T group only.
These results suggest that 8 weeks after birth, the puberty period may be the most effective starting period of power sprint training during growth in rats.

Wistar strain male albino rats were sacrificed at 1, 3, 5, 7, 9, 11, 13, 15, 17, 19 and 21 days of age, and the histochemical properties of nerve cell and muscle fibre were examined.
We obtained the following differentiation process in the muscle with postnatal growth;
phase I (newborn-7 days) undifferentiated fibre
phase II (7-15 days) FT fibre ST fibre
phase III (after 15 days) FG fibre FOG fibre SO fibre
On the other hand, histochemical differentiation of nerve cell was recognized earlier than that of muscle fibre, and there was no redistribution of soma type with growth.
Therefore, it may be said bhat histochemical differentiation process in the muscle is largely effected by the neuronal influences exerted from the lower motoneurons.