Male mice of dd-strain, at 4 and 8 week-ages were used at the start of the trained. The trained continued for successive during 4 to 34 week-ages and 8 to 70 week-ages. The trained group was exercised on a treadmill, and the untrained group used as control under normal laboratry condition. The skin of the right dorsum near the tail was sampled and its collagen content was examined by means of concentration of hydroxyproline. The collagen content in the skin of the trained group is lower than in that of the untrained one at each week-age, 14-18, 27-34 and 63-70 week-ages. The trained group was depressed hydroxyproline concentration of defatted skin, compared with untrained one at each weekage. The continuous exercise reduced the accumulation of collagen in the skin of mice.

Male mice of dd-strain, at 4 weeks of age were used in the present study. The materials were divided into four groups; namely, mildly, moderately, severely trained and untrained. The treadmill exercise program for mildly, moderately and severely trained groups consisted of running at speeds of 6 m/min, 10m/min and running up a 10% grade at a speed of 12m/min for 10 min 5 times a week, respectively. The collagen content of the skin was measured by means of concentration of hydroxyproline. Moreover, the proportion of neutral salt-soluble (NSC), acetic acid-soluble (ASC) and insoluble collagen (ISC) in the skin was isolated. We attempted to study about the effects of physical activity on the metabolism of collagen by aging. Hydroxyproline concentration of the skin in untrained group increased rapidly until 6 weeks of age. Maximum hydroxyproline concentration was observed at 7 weeks of age in untrianed group. In three trained groups, maximum hydroxyproline concentration was observed at 9 weeks of age. The collagen content of the skin in the three groups was higher than that in untrained group at 9 and 11 weeks of age. The proportion of NSC, ASC and ISC of the skin varied with age in four groups. In the untrained group, the proportion of ISC increased with age and was recognized to reach 81.9% at 15 weeks of age. The proportion of NSC and ASC in both the moderately and severely trained groups indicated approximately 20% increase compared with that in the untrained group. This fact suggests that the degree of maturation of collagen is influenced by physical activity, especially, moderately and severely training. The authors conclude that continuous exercise training control the formation of intramolecular and intermolecular cross-links in skin collagen.

Male mice of dd-strain, at 3 weeks of age were used at the start of the exercise training. The exercise training continued successively throughout the 3 to 7 weeks of age. The trained group was divided groups ; namely, light-, middle- and heavy-trained groups, which were exercised on a treadmill. The treadmill exercise program for light-, middle- and heavy-trained groups consisted of running at speeds of 6 m/min, 10 m/min and running up a 10% grade at a speed of 12 m/min for 10 min 5 times a week, respectively. The untrained group was used as control under normal laboratory condition. The skin and Achilles tendon of the four groups were sampled and their collagen content were examined by means of concentration of hydroxyproline. The collagen content in the skin of growing mice did not recognize significant difference among the four groups. On the other hand, the collagen content in the Achilles tendon of growing mice clearly recognized significant difference between the middle-trained and untrained groups and/or between the middle-trained and light-trained groups. However, middle-exercise training reduced the accumulation of collagen in the Achilles tendon of grow. ing mice.