Ventilation threshold (VET), threshold of decompensated metabolic acidosis (TDMA) and lactate threshold (LT₁, LT₂) were investigated during incremental bicycle exercise for 20 boys (11.7±0.1 years) and 10 girls (11.2±0.2 years) .
Maximum oxygen uptake (VO₂max) was measured by treadmill running. There was significant difference between boys and girls in VO₂max per body weight, but no signif-icant difference per LBM. Mean values of each threshold (% peak VO₂) were as follows. VET was 53.3±2.2%, TDMA was 69.0±2.2%, LT₁was 51.8±2.2% and LT₂was 72.8±2.2%. These values were not higher than those of previous adult's data. There was no significant difference in lactate and ventilatory parameters between boys and girls, except LT₂and LT₄mM.
In conclusion, it seems that no difference is seen in lactate and ventilatory responses between 9-12 year boys and girls. VET and TDMA by bicycle exercise could be estimated by ventilatory responses in prepubertal children.

In this paper, effects of physical activity in daily life on m. triceps surae were considered comparing the cadavers with decubitus with those without decubitus on muscle weight and relative muscle weight. The muscles were dissected from 18 cadavers (13 males and 5 females) aged 36 to 90 which were preserved in a 10% formalin solution for about one year. Immediately after the removal, weights of gastrocnemius and soleus were measured.
Mean values of the muscle weights of soleus, gastrocnemius and combined total were heavier in male than in female. Those of the relative weights of soleus were larger than those of gastrocnemius in both sexes. The muscle weights showed remarkable inter-individ-ual variations and sexual differences. The decubitus group (non-active group) showed lighter muscle weight than the normal group did in both sexes. However, there were no differences in the relative muscle weight between both groups in both sexes.
The rate of lack of m. plantaris was 11.1%.
From these results, it was suggested that the relative muscle weight might not be influenced by physical activity in daily life but the muscle weight might change consid-erably related to it.

Oxidation of lactate at rest (RE, n=4), or after short strenuous exercise (EX, n=6) was investigated in rats. Food and water were given ad libitum before experiment. In EX, rats ran to exhaustion at the speed of 80-100 m·min^-1. Immediately after exercise, 4 μCi of (U-¹⁴C) lactate was injected into aorta through an indwelling catheter. In RE, (U-¹⁴C) lactate was injected into the rats at rest. Expired gas was collected by a Brooks type bottomless chamber on treadmill belt for 120 min. In EX, exercise duration was 109±18 sec (mean±SE), and maximum blood lactate concentration after the exercise was 23.7±2.1 mM (mean±SE) . Cumulative percent recovery of ¹⁴C as ¹⁴CO₂ for 120 min was 48.5±2.8% for EX and 61.7±0.9% for RE (mean±SE) . Significant difference was found between these two rates (p<0.01) . After 50 min of recovery, mean volume of ¹⁴CO₂ expired per min in RE was significantly greater than that in EX (p<0.01) . Mean volume of ¹⁴CO₂ expired per min per VCO₂ in RE was always greater than that in EX, and significant difference was found at 7.5 min of recovery (p<0.01) . It is concluded that although the rate of recovery of ¹⁴C as ¹⁴CO₂ after exercise is lower than that at rest, the major pathway of lactate metabolism after short strenuous exercise is oxidation.

The influence of daily physical exercise on oxygen utilizing capacity of working muscle investigated by means of measureing lactate threshold (LT) during progressive treadmill running from the comparison between soccer group (S group: N=12, 11.9±0.1 years of age) and control group (C group ; N=14, 11.8±0.1 years of age) . LT₁ was determined as the point where blood lactate concentration (La) increased from rest level, and LT₂ was determined by the gradient, La/VO₂. body weight^-1 (2 mM/10 ml. kg^-1, min^-1) .
LT₁ and LT₂ in S group were significantly higher than those in C group expressed with absolute and relative values of VO₂ (1. min^-1, ml. kg^-1. min^-1, % VO₂max) . No significant differences in La, ventilation responses, and heart rate at the point of LT₁ and LT₂ were observed between S and C group, La showed slight decrease and was kept at lower level in S group with increase of VO₂, compared with C group. On the contrary, La in C group began to increase at lower level of VO₂. From our previous longitudinal study of LT in non-athletic children, we observed that LT shifted to lower level with growth. It was sugesed that La curve of S group, such shift had not occurred. Differences of these patterns in VO₂ and La between athletic children and non-athletic children were similar to those observed in adults athletes and non-athletes.
In conclusion it was supposed that sufficient daily physical training in 10-12 year of age might increase oxygen utilizing capacity of leg working muscle during running exercise.

In order to investigate an effect of exercise on physical growth and maturation, physical characteristics (height, weight, chest girth, bi-acromial diameter, bi-iliac diameter and span) and skeletal age were measured for 34 boys of control group and 37 boys of soccer group. Skeletal age was evaluated from hand wrist radiographs by TW II method.
Result showed that the values of physical characteristics in the control group were larger than those in the soccer group, but the differences were not statistically significant. Mean skeletal age in each age group of the soccer group closely approximated the chronological age, but that in the control group was inclined to proceed earlier than the chronological age. The correlations of all the physical characteristics with skeletal age were higher than with chronological age in both groups. Those correlations with chrono-logical age in the soccer group were lower than those in the control group.
Based on the values of the subjects in this study, this fact leads to the conclusion that skeletal age is in fact a better predictor of physical characteristics than chronological age is. Physical characteristics of the boys in the soccer group correlate higher with skeletal age than with chronological age. In relation to the skeletal maturation, each physical characteristics in the control group shows a similar growth. In the soccer group, weight and chest girth show differences of growth from other physical characteristics.

A study was undertaken to evaluate the effect of aerobic training on lactate oxidative capacity during aerobic exercise using [U-¹⁴C] lactate. Male ddY mice were trained by means of treadmill running 5 days a week for 6 weeks. [U-¹⁴C] lactate was injected after the first 5 min of running at a speed of 30m⋅min^-1. The mice then continued to run for another 25 min at the same speed. Expired gas was collected to estimate the amount of ¹⁴CO₂ expired during the exercise. The amount of [¹⁴C] lactate expired as ¹⁴CO₂ during the first 10 min after injection of [14C] lactate was significantly higher in the trained group (T) than in the control group (C) . The blood lactate concentration, and muscle lactate concentration in the soleus immediately after exercise were significantly lower in T than in C. The muscle glycogen and blood glucose concentrations were higher in T than in C. It is concluded that aerobic training in mice decreases the blood lactate concentration during exercise, and also enhances oxidative removal of lactate.

In this study the effects of endurance exercise on cardiorespiratory functions and performance in developing age were exemined in 12 year old boys. Sujects were consisted of 11 boys who had been participating in training for soccer more than 2 hours a day for 6 days per week (S) and 10 non-participating boys for control (C) . Maximal oxygen uptake (Vo₂max), maximal heart rate (HRmax) and maximal cardiac output (Qmax) by acetylnerebreathing method were measured on the exercise on a treadmill. Five minute run was also administered.
Significant differences were found in Vo₂max (p<0.05), values of which were 2.13±0.07 1⋅min^-1 for S. and 1.86±0.08 1⋅min^-1 for C., respectively, and in Qmax (p<0.001), values of which were 17.9±1.41⋅min^-1 for S. and 12.4+0.71⋅min^-1 for C. G., respectively. There were no significant differences in HRmax and V_E between both groups. Values of stroke volume and V_E/Vo₂max were significantly higher for S.. Performances on 5 minute-run were 1164 m for S. and 1083 m for C, which showed significant difference (p<0.01) . Significant correlationship (r=0.746, p<0.001) was obtained between Vo₂max and Qmax. It was also found that the higher Vo₂max was, the higher Qmax was attaind.

Little is known about the effects of aerobic exercise on cardiac structure in children. Echocardiographic study was performed at rest in 38 boys aged 11-12 (18 soccer players and 20 untrained) . Soccer players had significantly increased left ventricular end-diastolic dimension (43.6±2.8 vs 40.1±2.8 mm) and left atrial dimension (27.7±3.7 vs 23.0±2.8 mm) . There was no difference in interventricular septum and left ventricular posterior wall thickness between the two groups, these data show that intensive aerobic exercise may influence on cardiac structure in children.

The relationships between running performances (200 m running time and 5-min run) and VO₂max, Lactate Threshold (LT), or percent fat were investigated on 11-12-year old boys. Subjects were 21 control boys (group C) and 21 soccer boys (group S) . Mean 200 m running time in group S was significantly better than that in group C. Mean distance of 5-min run in group S was significantly longer than that in group C. No significant difference was found between mean running speed of 5-min run and mean speed at exhaustion in LT experiment. In group C, 200 m running time correlated significantly with VO₂max. In group S, faster runners showed higher peak post 200 m run lactate concentration. 5-min run correlated significantly with VO₂max for group C, group S and all subjects combined. LT correlated significantly with 200 m running time and 5-min run. No significant relation was found between running petformances and percent fat. It is suggested that VO₂max and LT determine, in part, boy's running performances, but percent fat do not.