Whole Blood, Serum and Erythrocyte Magnesium Concentrations after Repeated Heavy Exercise of Long Duration

Abstract

The whole blood, serum and erythrocyte Mg concentrations were determined in 16 men before and for several days after two cross-country skiing competitions, 90 and 70 km, respectively, one week apart. Both races were accompanied by a transient fall in the serum Mg concentration, from 1.78 before to 1.58 mEq/l immediately after the 90-km race (P < 0.001), and from 1.81 to 1.66 mEq/l after the 70-km (P < 0.001), and increase in the erythrocyte Mg concentration from 4.47 to 4.74 mEq/l (P < 0.01), and from 4.58 to 4.78 mEq/l (P < 0.05), respectively, whereas the whole blood concentration remained unchanged. On the days after the races and throughout the rest of the observation period the serum, erythrocyte and whole blood Mg concentrations were the same as before the first race. In one case, however, there was a slight fall in the serum Mg concentration, whereas the erythrocyte and whole blood concentrations decreased continuously throughout the observation period. The urinary Mg excretion during the races was low. It is concluded that the fall in serum Mg concentration associated with prolonged heavy exercise is due to a transient shift of Mg from the extracellular to the cellular fluid.

Key Words:

• Blood
• erythrocytes
• exercise
• magnesium
• serum
• urine