New experimental and clinical data on the relationship between magnesium and sport

Exercise under certain conditions appears to lead to Mg depletion and may worsen a state of deficiency when Mg intake is inadequate. Whereas hypermagnesaemia occurs following short term high intensity exercise as the consequence of a decrease in plasma volume and a shift of cellular magnesium resulting from acidosis, prolonged submaximal exercise is accompanied by hypomagnesaemia. Discordant findings on the effect of physical exercise on erythrocyte concentrations have been reported. A mechanism for the observed decrease in plasma magnesium concentration after long term physical exercise could be a shift of Mg into the erythrocyte. However, in several studies the decrease in plasma Mg was not accompanied by an increase in RBC Mg, but a decrease in cellular Mg was observed. Urinary Mg losses during an endurance event could play a role in this depletion but are often reduced, reflecting renal compensation. Loss of Mg by sweating takes place only when there is a failure in sweat homeostasis, a situation which arises when exercise is made in conditions of damp atmosphere and high temperature. Stress caused by physical exercise is capable of inducing Mg deficit by various mechanisms. A possible explanation for decreased plasma Mg concentration during long endurance events is the effect of lipolysis. Since fatty acids are mobilized for muscle energy, lipolysis would cause a decrease in plasma Mg. In developed countries Mg intake is often marginal and sport is a factor which is particularly likely to expose athletes to Mg deficit through metabolic depletion linked to exercise itself, which can only aggravate the consequences of a frequent marginal deficiency. Mg depletion and deficiency therefore play a role in the pathophysiology of physical exercise. Experiments on animals have shown that severe Mg deficiency reduces physical performance and in particular the efficiency of energy metabolism. These data, however, do not correspond to those of marginal deficiency most commonly observed in humans. Clinical symptomatology, both in athletes and in other patients, is dominated by the symptomatology of neuromuscular hyperexcitability. Medical authorities in sport have enforced obligatory tests for latent tetany in athletes, with ionic assessment. The effects of the correction of magnesium deficiency are judged from clinical signs, Chvosteck sign, electromyogram and echocardiogram findings and plasma Mg, erythrocyte and urine analysis. These may also be complemented by cardiac and respiratory investigations after exercise. The positive effects (analysis after a minimum period of one month) of a simple oral supplement administered in physiological doses (5 mg/kg body weight/day) provides evidence for the existence of a deficiency.(ABSTRACT TRUNCATED AT 400 WORDS)