The authors have studied the effects of physical exercise on extracellular substances of several tissues in animals. Hydroxyproline (Hyp) exist in the form of peptide and the free state in blood. It is generally thought that Hyp in blood derived from the decomposition of collagen in tissue. To clarify the influence on collagen metabolism due to aging and exercise training, we attempted to see the changes of Hyp content of serum before and after exercise in human being. Subjects were 51 adult aged 20 to 74 years, and 10 nonathletes and 51 athletes, aged 18 to 22 years. The Hyp content in serum was measured by woessner's method. The Hyp content of serum decreased with age. This fact suggests that the formation of intramolecular and intermolecular cross-links in collagen of tissue is accelerated by aging. And there is a possibil-ity that the proportion of insoluble collagen increased in tissue of aged human being. Before the exercise, Hyp content of serum in athlete was lower than that in nonathletes. Hyp content of serum increased remarkably after the exercise in athlete. These results suggest that the collagen metabolism may be accelerated by continuous exercise training.
