Effects of physical exercise on serum calcium and parathyroid hormone

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Abstract
The effects of physical exercise on plasma ionized Ca, total serum Ca and parathyroid hormone (PTH) concentrations were evaluated in healthy subjects submitted to work on an ergometer bicycle. When the workload was increased stepwise, there was a significant increase (P < 0.001) in the Ca concentrations (ionized Ca from 1.13 .+-. 0.03 (SD) to 1.24 .+-. 0.03 mmol l-1 and total Ca from 2.35 .+-. 0.07 to 2.48 .+-. 0.07 mmol l-1) when the workload exceeded approximately 65% of the estimated maximum, i.e., a load that caused accumulation in blood of lactic acid. The rise in plasma ionized Ca was, therefore, presumably largely attributed to the acidosis but reduction of plasma volume and influx from extracellular sources might also have contributed. .beta.-Blockade (with oral intake of propranolol) reduced physical capacity, shortened the duration of work and caused less acidosis. These factors were probably responsible for a smaller rise in ionized Ca during .beta.-blockade (7 .+-. 4%) than in control studies (21 .+-. 5%) without medication in subjects examined during short-term maximal exercise. Long-term (1 h) steady-state work which caused fatigue without producing lactic acidosis did not affect the Ca concentrations. Despite the effects of work on Ca levels there was no discernible suppression of the PTH concentrations. This might have been due to a concomitant stimulation of PTH secretion by work.