Physical and chemical properties of skin in habitually trained and sedentary men.

A number of physical and chemical properties of skin were examined in a study of 29 habitually trained and 29 sedentary men. Compared to the control group, the trained subjects had significantly higher values in the weights of skin samples of equal surface areas as well as the contents of hydroxyproline and nitrogen per skin surface area. When measured by a diaphragm method in vivo, the 'elastic stiffness' (uncorrected for thickness) and 'elastic efficiency' (the recovery of the deformation energy) of skin were significantly higher in the trained men compared to those in the untrained men. The results suggest that skin reflects the adaptation to habitual endurance training by increasing its mass and strengthening its structure. The study did not, however, reveal any differences between physically active and sedentary men in changes due to biological ageing.