The variation of lengths, cross-sectional areas, weights, tetanic tensions, and passive tensions in extensor digitorum longus muscles in mice were investigated during postnatal growth. The increase of tetanic tension was discussed in relation to morphological changes of muscle. The muscle lengths were measured at right angle of articulatio genus and talocruralis (L₀) . Following results were obtained: 1) The length, cross-sectional area and weight of muscle increased rapidly up to 7 th weeks, and tetanic tension developed significantly in 2 nd to 5 th week. 2) The muscle length (ML), muscle cross-sectional area (MCA) and muscle weight (MW) correlated significantly with the measured tetanic tension (TT) at L₀ (the correlation coefficient r=0.852, 0.886 and 0.903 in ML, MCA and MW respectively) . 3) TT/MCA and TT/MW decreased in 7 th to 8 th week. 4) The passive tension at 130% L₀per MCA showed maximum values in 8 th and 9 th weeks. 5) Relative muscle endurance were reduced in 2 nd to 4 th week and reached to steady level after 4 th week. These observations suggest that the functional development of muscle is late for morphological one and/or rapid morphological increment affects the contractile properties of muscle.

A study was conducted to investigate the influence of a series of quick stretches during tetanic stimulation of skeletal muscle fibers in growing mice.
Mice were anesthetized with pentobarbital sodium. The distal tendon of the extensor digitorum longus muscle was attached to a servomotor. The effects on the muscles of a series of isometric contractions (ISO), a series of quick stretches during contractions (ST), and a sham operation for 1 h were assessed in terms of changes in tetanic tension, serum creatine kinase and lactate dehydrogenase activities, and the histological appearance of the muscle.
The data indicated the following ; 1) Serum enzyme activities were not altered in any of the experiments. 2) ST resulted in a decrease in tetanic tension compared with ISO values in mice of all ages. The rate of decrease in tetanic tension for 1 h ST was higher in muscles of young mice than in those of mature mice. 3) Muscle histology demonstrated numerous areas of localized sarcomere widening immediately after the series of ST.
These observations suggest that muscle stretching during contraction causes greater injury to developing skeletal muscles.

Variation of the length of skeletal muscle fibers and sarcomere lengths were investigated in extensor digitorum longus (EDL) and soleus (SOL) muscles in mice (ICR) during postnatal growth in the range from 2 to 12 weeks after the birth. EDL and SOL were fixed in 2.5% gultaraldehyde contained Lock's solution at right angle position of articulatio genus and talocruralis. Single muscle fibers were dissected and lengths of fibers were measured under the dissecting microscope. For measuring sarcomere lengthes, laser diffraction technique was used. Following results were obtained; (1) the length of muscles and muscle fibers increased rapidly up to 8 and 5 weeks in EDL and SOL respectively; (2) relative muscle and fiber lengths at 12 weeks against 2 weeks were 1.72 and 1.30 in EDL, 1.60 and 1.32 in SOL; (3) sarcomere lengths at both ends of the fiber showed no significant change during growth; (4) on the other hand, sarcomere lengths at mid point showed maximum values at 8 and 5 weeks in EDL and SOL respectively. These observations suggest that the sarcomere are stretched especially at mid point when lengths of muscle fibers increase rapidly. It would be possible to consider that this changes of the sarcomere length during postnatal growth affect the contractile properties of muscles.

The purpose of present study was to investigate the relationship between the increase of sarcomere length, sarcomere number and tetanic tension of the extensor digitorum longus muscles during postnatal growth in mice. The following results were obtained ; 1) The cross-sectional area, length of muscle and fiber length increased rapidly up to 7th week. 2) The sarcomere number increased up to 9 th week, 3) The tetanic tension per cross-sectional area decreased significantly in 7 th week, 4) The maximum value of sarcomere length which was obtained at middle region of the fiber correlated significantly with the tetanic tension per cross-sectional area (the correlation coefficient : r=-0.675) . These observations suggest that the local expansion of sarcomere length during postnatal growth affects the tension development.

The effects of testosterone on the structural and contractile properties of the denervated rat skeletal muscles that were not influenced by neurotrophic-effects were investigated. Male Wistar strain rats (3-week-old, n=28) were used in the present study. All rats were divided into four (n=7, for each) groups; control (C), testosterone control (TC), denervated (DN), and denervated with testosterone (DNT) groups. Sciatic nerves of DN and DNT groups' rats were resected at the 4-week-old after birth. Testosterone that was melted in corn-oil was administered (40 mg/kg body weight/week) for the TC and DNT groups. At the end of breeding period (15-week-old), soleus (SOL) and extensor digitorum longus (EDL) muscles were dissected from both hindlimbs and contractile profiles were analyzed in vitro. Relative weight (muscle weight/body weight) of SOL muscle in the DNT group was significantly (p<0.01) higher than that of the DN group. There is no significant difference in EDL muscle between the DN and DNT groups. Time to peak tension and half relaxation time in EDL muscle of the DNT group was significantly (p<0.05) higher than those of the DN group. Maximum twitch tension was prone to decrease following denervation, and significantly (p<0.01) difference between the DN and DNT groups in both muscles regarding the maximum twitch tension was observed. There is no significant difference of myosin and actomyosin ATPase activities comparison of each group in SOL muscle, however, the TC group were significantly higher than those of the C group in EDL muscle. These results suggested that the effects of testosterone for the hypertrophy in skeletal muscles were not synergistic effects with the neurotrophiceffects, however, for the ATPase in fast muscle act synergistically with the neurotrophic effect to change of myosin ATPase. Moreover, it was also suggested that the sensitivity to the testosterone was different in each type of fiber.

Markedly smaller myofibers including branched myofibers (SF) were contained in regenerated skeletal muscles. However, its functional properties are not yet sufficiently understood. The present study examined the metabolic, contractile properties and hypertrophy of SF included in rat skeletal plantaris muscles regenerated from eccentric contraction-induced muscle injury. Succinate dehydrogenase and alpha-glycerophosphate dehydrogenase activity of SF were respectively similar to that of other normal size myofibers (NF) within regenerated muscles. The shortening velocity of skinned fibers prepared from branched myofibers isolated from regenerated muscles was slightly slower than that of control muscles. In addition, the extent of glycogen depletion in SF was similar to that of NF after exhaustive running. Therefore, SF were innervated by motoneurons and recruited during the contractile activity of the skeletal muscle. No matter when the regenerated muscle was loaded by synergistic ablation, the continued existence of SF was observed. Therefore, the ability of hypertrophy in SF may be distinct from that in NF. The physiological properties of SF were similar to that of normal myofiber, except for the ability to regulate hypertrophy.

The variation of venous concentration of FFA as the effect of exercise under several nutritive conditions were tested on two subjects, i, e., 56 years old male and 20 years old female.
Arrhythmia were recorded when sudden increase in palmitoleic acid in venous concentration was observed, while no arrhythmia were recorded otherwise. Arrtythmia seemed to have been prevented by intaking glucose prior to exercise.
It was also observed that arrhythmia would easily be produced by sudden uprise of palmitoleic acid under hunger after low carbohydrate nutrition.

The inter of this study was to observe the effects of training on histochemical and biochemical properties in the skeletal muscle fibers.
Wistar strain albino rats were assigned to endurance (E), sprint (S) and control (C) group at 4 weeks old. Animals of trained groups were trained by treadmill for 12 weeks. After training, all animals were sacrificed and M. Soleus (SOL) and M. Extensor Digitorum Longus (EDL) were taken out.
Using histochemical staining methods for Hematoxylin and Eosin, Actomyosin ATPase and Succinate Dehydrogenase (SDH), area and composition of the three muscle fiber types were examined. Furthermore, the chemical properties of glycolytic and oxidative enzyme activities were examined.
The results obtained were as follows:
1. The E and S trained groups, respectivelly, showed lower increase of body weight than the control group.
2. Hypertrophy of all fiber types in EDL were observed in the both trained groups. Area of SO fibers in SOL were also increased in the E group as compared to the C group.
3. The differences observed for fiber composition among the three groups. The rate of FOG fiber in SOL decreased significantly in the both trained groups as compared to the C group. The rate of SO fiber in both muscles were slightly higer for the E group relative to the C Group, but these differences were no significant. However, in the E group significant increase was observed for oxidative enzyme activity. The Phosphofructo-kinase activity in EDL of the S group was significantly higher in comparison to the other groups.
These results suggested that there is the discrepancy between histochemical proper-ties and biochemical properties in the effects of training on skeletal muscle fibers and that the necessity of histochemical and biochemical analysis.

Four myosin heavy chain (MHC) isoforms were detected in rat hind-limb fast muscles. MHC isoforms are particularly good candidates for fiber type-specific markers in myofibril proteins. We studied the effect of running or jumping training on MHC isoform composition in 18, 6 month-old female rats. The animals were divided into three groups : sedentary (S; n=6), running (R; n=5) and jumping (J; n=7) at 4 months of age. Animals in group R were trained with treadmill running (30 m/min, 60 min/day and 5 days/wk) for 8 weeks. Animals in group J were trained with vertical jumping (40 cm high, 100 repetitions/day, 5 days/wk) for 8 weeks.
There was no significant difference in body weight among the groups. Muscle weight and muscle weight/body weight for the plantaris were significantly increased in both trained groups, but there was no significant difference in the protein concentration. With regard to MHC isoform composition, there was no significant difference in the compositions of the type I and type ha MHC isoforms. In the type lid MHC isoform, the values for both trained groups were significantly higher than that of group S (p<0.05) . The values for both trained groups in the type lib MHC isoform were lower than that of group S. In particular, there was a significant difference between groups S and J (p<0.05) .
These results indicate that a relative increment of the type lid MHC isoform is a typical adaptation phenomenon of the olantaris muscle in rats riven runninr and iumoinr training.

The contractile and morphological effects of chronic overload induced by synergist gastrocne mius and soleus ablation were studied in regenerating plantaris muscle of rats after injuries produced by eccentric exercise. Rats were randomly divided into control (C), eccentric exercise (E) synergistic ablation (S) and eccentric exercise+synergistic ablation (ES) groups. At 6 weeks after the experimental treatment, contractile or morphological muscle properties were measured. The maximum tetanic tension of ES group was significantly larger than that of S group (p<0.05), although there was not significant difference between C and E groups. There was not significant difference in contraction time between S group and ES group. While there was not significant difference in mean cross-sectional area of any fiber types between C group and E group, all fiber types of ES group were significantly smaller than that of S group (p<0.05) . It is concluded that the overload on injured muscle by eccentric exercise may restrain muscle hypertrophy.