Marathon running accompanied by transient decreases in urinary calcium and serum osteocalcin levels.

We evaluated the effects of marathon running on bone metabolism in 23 noncompetitive athletes (15 women, 8 men, age range 23-55 years). The volunteers were studied 10 days before, immediately after, and 1, 3, and 5 days after the run. Serum osteocalcin levels were decreased on average by 20% (from 4.9 to 3.9 micrograms/liter, P = 0.005) in men and by 10% (from 4.9 to 4.4 micrograms/liter, P < 0.05) in women at the end of the marathon, with lowest osteocalcin levels (67-55% of the prerun levels) encountered 1 day after the marathon. The activity of bone alkaline phosphatase was decreased in women (from 66.3 to 62.3 U/liter, P < 0.05) after the run, and this drop was detectable at each checkup after the run. Urinary excretion of calcium was lowered on average by 82% in men (from 2.8 to 0.5 mumol/minute, P < 0.05) and by 76% in women (from 2.5 to 0.6 mumol/minute, P < 0.005) after the run, but had already returned to prerun levels 1 day after the marathon. Urinary excretion of hydroxyproline tended to rise in both men and women, but the change did not reach statistical significance in either sex. These changes suggest a transient suppression in osteoblast function during the marathon.