Exercise-induced hypercalcemia and the calciotropic hormones.

Sixteen healthy male volunteers exercised on a bicycle ergometer starting at 40% Vo2max and progressing at 5-minute intervals up to 75% Vo2max over a 20-minute period. Blood was drawn from an indwelling venous catheter at baseline, at 5 minutes through 20 minutes, and at 10 and 20 minutes after the exercise was ended. Significant increases (which returned toward baseline in the rest period) were observed during the exercise period in total calcium and calcium ion activity, phosphate, potassium, magnesium, albumin, and lactic acid levels. Plasma volume (based on hematocrit value) decreased during the exercise period. Serum parathyroid hormone levels decreased and calcitonin levels increased at the early period of the short-term exercise. Although hemoconcentration was of sufficient magnitude to explain the change in calcium ion activity, the increase in potassium and phosphate were caused in part by additional factors.