Changes in the numbers of muscle fibers and proliferating cells detected by immunohistochemistry were studied in correlation with various growth parameters including changes in body weight, lower hindlimb length, muscle length, muscle weight and age in Wistar-strain rats at various developmental stages. The total fiber number in plantaris (PLA) muscles increased gradually between 2 weeks and 10 weeks of age (about 300g body weight), and then remained constant between 10, 000 and 11, 000 these after. In contrast, proliferating cells labeled by bromodeoxyuridine decreased gradually during the same period, and were hardly evident after 10 weeks. In the growth curves for the body weight, lower hindlimb length, muscle weight, and the length of the extensor digitorum longus (EDL) muscle, turning points were observed at 10 weeks (300 g body weight), respectively, suggesting that the turning point between growth in length and growth in width occurred at this point. Furthermore, the growth curves for the body weight and PLA muscle weight were correlated between 2 and 20 weeks, including the turning point. Therefore it is suggested that the development of muscle weight from 2 to 10 weeks depends mainly on the increment of fiber number (hyperplasia), whereas development after 10 weeks depends on the increment of individual fiber diameter (hypertrophy), in relation to the tendency for an increase in fiber number and a decrease in proliferating cells. These results indicate that maturation of skeletal muscle in male Wistar rats occurs at 10 weeks of age and a body weight of 300g. Accordingly, these facts should be considered when investigating muscle hypertrophy or hyperplasia.

The effects of 6 weeks (5 days/week) of endurance training under hyperoxia (60% O₂ plus 40% N₂) on carbohydrate and fat metabolism were studied in 42 male rats. The rats were divided into four groups ; normoxia control (NC, n=8), hyperoxia control (HC, n=9), normoxia training (NT, n=12), and hyperoxia training (HT, n=13) . NT and HT groups were made to run on a treadmill in a metabolic chamber at a speed of 20 m/min for 30 min. The metabolic chamber was perfused with hyperoxic gas. VCO₂ values at rest (HC) and during exercise (HT) under hyperoxia were significantly lower (p<0.01) than VCO₂ values at rest (NC) and during exercise (NT) under normoxia, respectively. These results appear to indicate that a decreased respiratory exchange ratio was induced by hyperoxia. The results showed that at 15 min after the last training there were no differences between NT and HT in the glycogen or triglyceride content of the liver, heart, m, gastrocnemius, and m. soleus. However, blood glucose at 15 min in NT (109±13 mg/dl) was significantly lower (p<0.05) than the corresponding value at 15 min in HT (133±11 mg/dl) and at 48 h after the last training in NT (149±7 mg/dl) . The glycogen content of the liver in HC (36.4±2.6 mg/g wet wt) was significantly higher (p<0.05) than the corresponding value in NC (26.1±1.9 mg/g wet wt) . In the HT group, the triglyceride content of the liver at 48 h was lower (p<0.01) than the corresponding value at 15 min. However, the triglyceride content of the heart at 48 h in HT was significantly higher (p<0.05) than the value at 15 min. Basal lipolysis in HC was significantly higher than the corresponding values in NC, NT and HT, but there were no differences among the groups in norepinephrine-induced lipolysis. These results indicate that endurance training under hyperoxia might alter the content of tissue glycogen and triglyceride as a result of decreased carbohydrate consumption and increased fat utilization during fasting and/or exercise.

This study aimed to examine the effects of college baseball pitching on movement, performance, physical strength, and physiological and psychological functions of pitchers. The participants were 10 right-handed male pitchers from the University baseball team. The number of pitches were 15 per inning and 135 per nine innings. Ball speed and accuracy were measured for each pitching. The grip strength, back muscle strength, and standing long jump were measured before and after all pitches. Blood lactate levels were measured before pitching, at the end of the 5th and 7th innings, and at 3rd, 6th, and 9th minutes after pitching. The participant’s heart rate and subjective exercise intensity were measured at the beginning and end of each inning using the Borg scale measurement. Five high-speed cameras were used to capture the pitching motions. The displacement of the center of gravity, lower and upper limb joint angles, and the speed of each segment were calculated. The baseball speed and accuracy did not change with the increased number of pitches. However, the grip strength decreased. Although blood lactate and heart rate were not altered, subjective exercise intensity was increased. The lower limb kinematics remained unchanged; however, elbow height was reduced in the upper limb. These results suggest that highly competitive pitchers experience subjective fatigue with the increased number of pitches, however, they maintain pitch performance, speed, and accuracy without altering whole-body physiology and lower-body function and form.