Increase in serum parathyroid hormone levels after prolonged physical exercise.

Serum concentrations of parathyroid hormone (PTH), calcium, magnesium, phosphate and myoglobin were measured regularly during a 5-d recovery period in 17 men who had participated in a 7-d field exercise maneuver with intense physical activity. Immediately after the exercise, there was an increase in serum PTH levels of the same magnitude as the maximal rise during a hypocalcemic test. The rise in PTH was not related to changes in serum electrolytes, but was significantly correlated to an increase in serum myoglobin, indicating that those who performed the largest amount of work also experienced the greatest stimulus for secretion of PTH. There were no significant changes of the serum total calcium and only a small initial rise of the magnesium concentrations. Serum phosphate levels were greatly reduced and gradually returned during recovery. This study extends previous observations, from short-term investigations, that physical activity stimulates secretion of PTH.