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 purpose of this study was to investigate the hypothesis that the reduction in walking ability is due to muscle atrophy in the lower limb muscles with aging using equational structure modeling as well as investigate the influence of muscle on walking ability. The subjects consisted of 127 persons (57 males and 70 females) aged 20-84 year, who were grouped into 6 age brackets of 20-39, 40-49, 50-59, 60-69, 70-74, and 75 or older. Using MRI, muscle cross-sectional area was measured on psoas major and thigh muscle (divided into extensor and flexor) . For walking patterns, each subject walked along a 7-m walking passage at normal speed for VTR-recording of the motion. The resulting pictures were used to analyze stride length, trunk inclination and walking speeds. Walking speeds showed a statistically significant decrease in value from the 50's age group in males and the 60's age group in females when compared with the 20-39 age bracket (p<0.05) . In males, a significant co-relationship was observed only between the muscle cross-sectional area of thigh extensor and walking speed (p<0.01) while in females, a significant co-relationship was found between the muscle cross-sectional area of psoas major (p<0.001) /thigh muscle extensor (p<0.01) and walking speed. These results indicate that the muscle atrophy with aging in psoas major and thigh muscle extensor is a factor responsible for the decrease in walking speed. Meanwhile, a difference in sex was observed between the muscle cross-sectional area of psoas major and walking speed. It was considered that the muscle atrophy rate of the female's psoas major being higher than the male's influenced this. Furthermore, it was suggested possibility that the decline of walking ability is due to decreased muscle mass of the lower limbs with aging.