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.

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.

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.

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 this study, we investigated the effect of exercise training on serum and liver chblesterol levels and on biosynthesis of liver cholesterol in rats. The training was carried out at low [Low-Ex, 60% max O₂ consumption (VO₂) ] and high (High-Ex, 75% max VO₂) intensities for 16 weeks. The energy expenditure was adjusted to be equivalent. The succinate dehydrogenase activities of gastrocnemius muscle in the Low-Ex group and High-Ex group were higher than that of control, 36% and 109% (p<0.05) respectively. The levels of total and high density lipoprotein cholesterol in serum were 14-26% lower than those of control, but no difference was detected between the trained groups. The activity of HMG-CoA reductase in liver microsome was significantly higher than that of control for both trained groups. However, the stimulation of this enzyme activity was not changed by training intensity.

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.