It is said that number of muscle fibers does not change in the postnatal period. However, it has been reported that shortly after birth, the uni-motor neuron innervates may muscle fibers (Changeux) . Further it has been shown by Changeux that, during the growth of the immature muscle fiber, various neuromuscular junctions are developed. Also, as Rayne has pointed out, 50% of the total muscle fibers are developed within 6 weeks after birth. In addition it has been shown that during the aging process, the number of muscle fibers decreases.
This report, based on the aging phenomena of rats, discusses the change in the number of muscle fibers and the period of differentiation of muscle fiber type. Rats ware used from the one day of birth until the 540^th day. Using an optical microgram, the total number of muscle fibers of both EDL and SOL muscle was counted. At the same time using the histochemical method, the differentiation of muscle fiber type was studied. The results are as follows : (1) Differentiation of muscle fiber type in both EDL and SOL muscle occurred within 3 weeks of birth. (2) 70% of the total muscle fibers in both EDL and SQL muscle developed from the first day to the 21^st day after birth. (3) From the 21^st day to the 105^th day after birth, the number of muscle fibers decreased by 10%.
There are two possible reasons for the apparent increase in muscle fiber number. (1) Those immature muscle fibers not having sufficient sarcoplasma could not be detected and consequently couldn't be counted. (2) Satellite cells, which are thought to have a relation to myotube fusion, exist in large numbers even after birth and new muscle fibers may be frormed by myoblast fusion.
The decrease in the number of muscle fibers may occur as a function of the change from poly-innervation to uni-innervation. It is possible to think that as natural extinction takes place in the case of the former, some of the muscle fibers which were innervated in this manner also become extinct.

To clarify the relationship between cardiac myosin isozyme composition in running-trained rats and the sympathetic nervous system, we examined whether the sympathetic nervous system could contribute to the modulation of cardiac myosin isozyme in running-trained rats, using atenolol, a selective blocker of cardiac β₁ adrenegic receptor. Male Wistar strain rats (4 weeks old) were used, and divided into four groups: control sedentary (CS), control trained (CT), atenolol sedentary (AS), and atenolol trained (AT) . The AS and AT groups were treated with atenolol in drinking water (65 mg/kg/day) for 9 weeks. The CT and AT groups were trained by treadmill running (at 30 m/min for 1 h/day, 5 days/week), starting at 7 weeks old, for 6 weeks. At 13 weeks old, the hearts were excised. The left and right ventricular myosin isozymes were examined by electrophoresis on pyrophosphate gel. The results showed the followings: 1) In the CT and the AT groups, the citrate synthase activities of the plantaris muscle were increased by 26% compared with the CS group (p<0.05) . 2) In the CT group, the running training had no effect on the myosin isozyme composition, in both ventricular muscles. 3) In the AS group, the atenolol treatment resulted in a decrease in the proportion of the V1 myosin and in an increase in that of the V3 myosin. Therefore, the proportion of the β-myosin heavy chain (MHC) in both ventricles of the AS group showed a significant increase compared with the CS group (p<0.05) . 4) The AT group showed a marked increase in the proportion of the β-MHC in both ventricles, compared with that of the AS group, especially in the left ventricle (p<0.05) .
From the results presented here, we did not observe any effect of the sympathetic nervous system on cardiac myosin isozyme composition in the running-trained rats.
It is generally accepted that hemodynamic overload results in an increase in the proportion of β-MHC, and in contrast, the stimulation of the sympathetic nervous system induces an increase in α-MHC. Therefore, we speculated that the effect of running training on cardiac myosin isozyme composition was induced by the effects of both the sympathetic nervous system and hemodynamic overload. Consequently, running training had apparently no effect on myosin isozyme composition.

At early stage of rats after birth, each innervation muscle fiber is supplied by two or more motor axones which converge on to a single end-plate and become one single axon in future. And undifferentiated cells frequently observed in the interspace among muscle fibers. About 70% of number of total muscle fibers in soleus developed in 21st day after birth.
Effect of denervation on the process of muscle development is studied in this paper. Left saiatic nerve of the rats was cut at 1st, 7th, 14th, and 21st day after birth. After 2 and 4 weeks, soleus and extensor digitorum longus muscle of both legs were dissected. Right side muscles used as control. Each muscle was cut transversely at the muscle belly and quickly frozen. Frozen sections, about 10 pm thick, were stained with hematoxylin eosin and other histochemical agents. Many optical micrographs of 50 or 100 magnifications were obtained from one cross-sectioned specimen. Number of muscle fibers were calculated on combined micrographs.
The results were as follows : (1) At 2 and 4 weeks after denervation, percentage loss of muscle weight was always higher than the loss of muscle cross-sectional area. At 2 and 4 weeks after denervation, the muscle weights were reduced to 45-80% and 70-90% of the control. And denervation muscle weights highly reduced in order that of let, 7th, , 14th and 21st eray rate after birth (2) At 2 and 4 weeks after denervation, number of soleus muscle fibers were reduced to 20-50% and 50-70% of the control. (3) At 2 weeks after denervation the reduction of number of muscle fibers of 1st day old rats was smaller than that of 7 days old rats.
First and second results suggest that muscle development is certainly influenced by neurotrophic foctors. But from third result it is possible to think that muscle development at 1st day old rats is influenced by inheritfactors of the muscle.

In this study, the rats were subjected to a partial denervation of the soleus muscle at the age of three weeks. After this, histochemical investigations were carried out to establish what kind of changes had occurred in the differentiation of the muscle fiber type as a result of this partial drop in muscle activity.
The partial denervation was performed on the sinistral rat's soleus muscle, roughly 20% of the nerve bundles. After this, the dextral soleus muscle was used as the contralateral control muscle and excised after two, four and eight weeks, respectively. Frozen sections of muscle were stained with HE and myosin ATPase. The cross sectioned specimen were used for determining the muscle fiber count and type II fiber count.
The results thus obtained show that, compared with the contralateral control muscle, the partially denervated muscle have an approximately 5% reduced muscle fiber count two and four weeks after the partial denervation, and the type II fiber count, too, decreased to approximately 2/3 and 1/5, respectively. However, at eight weeks post-operatively, the muscle fiber count for the partially denervated muscle become almost the same as that for the contralateral control muscle, while the type II fiber count has, at this stage, recovered to approximately half its contralateral control muscle.
From these observations, it had been concluded that the reduction in muscle activity due to its partial denervation continues to act as a causal factor in the fiber type transformation untill four weeks after the partial denervation. The muscles evaluted eight weeks postoperatively showed an increase in type II fiber over the count determined four weeks after the partial denervation, and the muscle fiber count had also developed at eight weeks to value identical to that of the contralateral control muscles. Therefore, it has been concluded that the fiber type transformation in the muscle eight weeks after partial denervation is attributable to the reinnervation of the denervated muscle fibers due to the remaining intact motoneurons and to the resulting changes in motor unit size.

We examined the effect of running training on regional cardiac myosin isozyme composition in rats. Male Sprague-Dawley strain rats (4 weeks old) were used, and divided into two groups: sedentary control (C) and trained (T) groups. The T group was trained by treadmill running (40 m/min, 1h/day, 5 days/week, for 12 weeks) . At 16 weeks old, their hearts were excised. The left ventricle was separated into the subendocardium (Endo) and subepicardium (Epi) by dissecting the ventricle at the mid-wall. The ventricular myosin isozymes were examined by electrophoresis on pyrophosphate gel under non-dissociating conditions. The results showed the following: 1) The relative heart weight of the T group was significantly higher than the C group. 2) Left ventricular myosin isozyme composition showed a region-specific distribution in the C rats, and the proportion of V3 myosin or β-myosin heavy chain in the Endo was significantly higher than that of the Epi. However, the training had no effect on the cardiac myosin isozyme in either portion. 3) The activity of citrate synthase did not show transmural gradient in the ventricle of C animals. Training had no effect on the activities of either portion. 4) The activity of lactate dehydrogenase (LDH) showed transmural gradient in the ventricle of C rats. Training-induced changes in the activity of LDH were found in both portions, therefore, training abolished the transmural gradient in the activity of LDH, suggesting a corresponding redistribution of the myocardial work load.
These results indicate that running training might induce the redistribution of the myocardial work load, whereas the stimulation apparently has no effect on the regional distribution of cardiac myosin isozyme composition.

Five long-distance runners and five non-athletes were examined on lipoprotein metabolism at rest, during, and after pedaling exercise (60% of the maximal oxygen uptake) . At rest, the concentrations of the cholesterol (Cho.), triglyceride (TG), and phospholipid (PL) of very low density lipoprotein (VLDL) were kept at low level in the longdistance group compared with the non-athletes. The difference is significant (p<0.01) . On the other hand, the levels of the Cho, and PL of high density lipoprotein (HDL) were maintained high (p<0.05) . The concentrations of the TG of VLDL are in negative correlation with those of the Cho. (p<0.01) and PL (p<0.001) of HDL at rest. A positive correlation between Cho. and PL of HDL was also noted (p<0.001) . The TG of the VLDL decreased gradually with pedaling exercise in the long-distance group, reaching about 12 percent below the resting value just after exercise. However, no apparent change was noted in the non-athletes.
The results obtained indicate that the long-distance runners, compared with nonathletes, tends to use lipids in order to produce energy for exercise. There is little possibility of transferring from the Cho. and PL of VLDL to the lipoprotein during exercise for the results of no change in concentrations of the Cho. and PL of low density lipoprotein (LDL) and HDL. We concluded that the Cho, and PL of VLDL could gradually transfer to HDL by a heap of the endurance exercise for long period.

In this study, we investigated the effects of prolonged voluntary running training on bone mass in the tiba of growing male SD rats. At 5 weeks old, the rats were divided into 4 groups : group 15 VE (n=7) exercised voluntarily on a running wheel for 10 weeks from 5- to 15-weeks old ; group 35 VE (n=7) exercised voluntarily on a running wheel for 30 weeks from 5- to 35-weeks old ; in groups 15SC (n=6) and 35 SC (n=5), rats were housed individually in normal plastic cages for the same periods as groups 15 VE and 35 VE, respectively. At the end of each experimental period, the right tibia from each rat was used for bone- mass analysis using peripheral quantitative cumputed tomography (pQCT) . The evaluated portions were the proximal methaphysis and the diaphysis, with total, cortical, and trabecular data from these portions being obtained as volumetric bone mineral content (vBMC) and volumetric bone mineral density (vBMD) . The results indicated that 1) although voluntary running distance tended to decline during the later period (1635 wk old) in 35 VE rats, some mean values obtained for bone mass parameters using pQCT were significant greater in 35 VE than in 35SC ; 2) the mean values from those parameters in 15 VE were not significantly different from those in 15 SC. These results suggest that the continuation of voluntary exercise may be important for bone- mass enhancement in rat tibia.

The purpose of this study was to assess the status of nutrients intake in male Japanese collegiate athletes. Each 20 of baseball (B), soccer (S), volley ball (V), and long distance (L) athletes participated in this study. The B, S, and V athletes lived by themselves, whereas the L athletes lived in an athletes dormitory with provided meal. The nutritional status was assessed for 2 days. Mean energy intakes in the B, S, V, and L groups were 43.6, 53.7, 47.0, and 55.0 kcal/kg body weight, respectively. Mean protein intakes were 1.2, 1.6, 1.3 and 2.4 g/kg, respectively. In B athletes, skipping of breakfast was recognized frequently. Most of micronutrients intakes in the B, S, and V groups were less than the recommended dietary allowances for athletes. We suggest that a provided meal system is a better system for collegiate athletes and more nutritional education is necessary for Japanese male collegiate athletes, in particular, those living by themselves.

In the present studies it was examined to begin with, whether intentional fixed quantity of exercise in response to previously defined level of heart rate could be loaded by treadmill connected with“Heart Rate Controller” (Quinton Co., Ltd.) i.e. a series of patterns in running exercise of the normal adult males were analysed.
The obtained results in short are in the following ;
1) Running exercise in response to previously defined level of heart rate being carried out by use of the above“Heart Rate Controler”, speed of treadmill needed to be adjusted manually until heart rate reached the defined level and then controlled automatically.
2) The relations between treadmill speed and heart rate defined at 130 Beats/min, 150 or 170 each, are as follows.
a) Treadmill speed at heart rate, previously defined as 130 B/min was 80±5-12 meters/min, actual heart rate during above exercise was 130±3-8 B/min in record.
b) Treadmill speed at heart rate, 150 B/min was 100±9-18 m/min, actual heart rate 150±6-8 B/min in record.
c) Treadmill speed at heart rate, 170 B/min was 130±10-33 m/min, actual heart rate 170±3-9 B/min in record.
As previously defined heart rate level was indreased, actual level in record deviated from the former within some extent and treadmill speed was also raised to maintain the defined heart rate level.
Fluctuation width of treadmill speed varied remarkably by the individuals.
Adjustment of treadmill speed was considered to be well under control by feedback mechanism of“Heart Rate Controller”.