Erythrocyte, plasma and urinary magnesium in men before and after a marathon

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Abstract
Erythrocyte, plasma and urinary magnesium (Mg2+) concentration was measured in 23 runners before and after a marathon race. Blood samples were drawn from an antecubital vein the morning before the race (baseline), at 3 p.m. (2 h before the start), upon finishing and 12 h later. Compared with the baseline values, the intra-erythrocyte and plasma Mg2+ were decreased (p−1 cells and from 0.88±0.06 to 0.81±0.07 mmol · l−1 respectively. The Mg2+ concentration returned to pre-race values 12 h after completion of the marathon. The urinary Mg2+ excretion rate decreased (p−1 during the marathon and increased (p−1. It is concluded that the reduction in plasma Mg2+ ion concentration during the marathon cannot be attributed to erythrocyte uptake, urinary excretion or loss in sweat. It is suggested that Mg2+ may be released from erythrocytes into the extracellular fluids during sustained exercise and taken up from these fluids by the adipose cells.