Regional and systemic effects of short-term intense muscular work on plasma concentration and content of total and ionized calcium

Isokinetic work with one leg was carried out with maximal force for 2 min by five healthy subjects. The concentrations of plasma total calcium and of ionized calcium in the effluent from the leg increased by a mean of 13.6 +/- 1.8% (SD) and 16.2 +/- 2.0%, respectively. The corresponding rises in the resting arm were 7.7 +/- 4.3% and 8.1 +/- 3.0%. There was a close correlation (r = 0.86; P less than 0.001) between the degree of exercise-induced acidosis and the rise in plasma ionized calcium. However, the calcium values normalized both in the leg and in the arm within 5 min after the exercise and were similar at the two measuring sites despite a lower pH in the leg sample. During work there was a reduction of the plasma volume of 11.2 +/- 6.0% in the regional (femoral) and 12.4 +/- 4.2% in the systemic (antecubital) sample (P less than 0.001 compared to baseline values for both measurements). When adjustments were made for the reduction in plasma volume as well as for acidosis it was evident that, despite the apparent increases in the calcium concentrations, there was a net reduction of the plasma ionized calcium content (the total amount of plasma ionized calcium). This decrease was significantly (P less than 0.05) more pronounced in the exercising leg than in the systemic circulation but the difference could largely be explained by higher calcium-lactate complex formation in the leg.