The duration of exercise as a regulator of bone turnover.

The relationship between duration of exercise and serum remodeling markers of bone turnover was evaluated by osteocalcin (OC), carboxy-terminal propeptide of type I collagen (PICP), total and bone-specific alkaline phosphatase (ALP) and carboxyterminal cross-linked telopeptide of type I collagen (ICTP) in 24 male premier league soccer players exercising 12 hours/week (range 8-18), 19 third league players exercising 8 hours/week (range 3-18) and 20 sixth league players exercising 6 hours/week (range 2-10). Twenty-seven volunteers served as controls. Forty-six former male soccer players (mean age 38 years, range 19-47), mean 15 years older than the current players, were compared with 41 matched controls. Data is presented as mean +/- SEM. Active male players had 18 +/- 4% higher OC, 37 +/- 9% higher bone ALP and 36 +/- 7% higher ICTP than controls (all P < 0.01). There were no differences in remodeling markers within the three groups of active players but each group had higher OC and ICTP than controls (both P < 0.05). Former players had no difference in bone remodeling markers compared to matched controls, but 39 +/- 4% lower OC and 69 +/- 8% lower ICTP than active players (both P < 0.001). Duration of activity was correlated with bone ALP and ICTP (both r = 0.3, P < 0.05) in individuals exercising 6 hours/week or less. No correlation was found in those exercising above this level. It seems as if the bone turnover, evaluated by serum bone remodeling markers, adapts to the current activity needed to maintain bone strength, and a duration of exercise above that level seems to confer no additional benefits.