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The effect of magnesium supplementation on exercise performance remains controversial. In the present study, the effects of magnesium sulfate on exercise performance and blood glucose metabolism were examined. In order to provide a non-invasive measure of continuous exercise, we developed an auto-blood sampling system was coupled to a microdialysis analyzer to detect the dynamic changes in glucose metabolism in conscious and freely moving gerbils subjected to forced swimming. Gerbils were pretreated with saline or magnesium sulfate (90 mg kg−1, ip) 30 min before exercise. The duration times were significantly increased by 71% in the magnesium sulfate-treated groups ( p < 0.01) when compared with those in the control. Another group of gerbils were subjected to blood sampling assay. A catheter was implanted in the jugular vein of each gerbil for collecting blood samples by the computer-aided blood sampler. The basal levels of plasma glucose, lactate, and magnesium were 6,245 ± 662, 1,067 ± 309, and 590 ± 50 μM, respectively, with no significant difference between groups. Plasma glucose, lactate, and magnesium levels increased to 134 and 204%, 369 and 220%, and 155 and 422% of basal levels during swimming in both the control and magnesium sulfate-treated groups, respectively ( p < 0.05). Pretreatment with magnesium sulfate elevated glucose and magnesium levels to 175 and 302% of the basal levels ( p < 0.05), respectively, whereas pretreatment with magnesium sulfate reduced the lactate levels 150% of the basal level ( p < 0.05) during swimming. Furthermore, the magnesium levels increased to about 152–422% of basal levels during forced swimming and the recovery period ( p < 0.05). The present study demonstrates that magnesium sulfate improved the duration time of forced swimming exercise. In addition, magnesium raised glucose levels and attenuated lactate levels during forced swimming. These results indicate that positive effects of magnesium supplementation may contribute to the enhancement of exercise performance in athletes. [ABSTRACT FROM AUTHOR]

This investigation examined the acute effects of magnesium on the dynamic changes of brain glucose, lactate, pyruvate and magnesium levels in conscious gerbils during forced swimming. Gerbils were pretreated with saline (control group) and magnesium sulfate (90 mg kg−1, intraperitoneal injection) before a 15 min forced swimming period. The basal levels of glucose, pyruvate, lactate, and magnesium in brain dialysates were 338 ± 18, 21 ± 2, 450 ± 39, and 2.1 ± 0.1 μM, respectively, with no significant difference between groups. Magnesium levels were found slightly higher (but not significant) in the magnesium-treated group. However, brain glucose and pyruvate levels in the control group decreased to about 50 and 60% of the basal level ( P = 0.01) after swimming, respectively. Pretreatment with magnesium sulfate immediately increased glucose levels to about 140% of the basal level, and increased pyruvate levels to about 150% of the basal level during forced swimming ( P = 0.01). Both glucose and pyruvate levels returned to the basal level after 30 min of the recovery. The lactate levels of the control group increased to about 160% of the basal level ( P = 0.01) during swimming, whereas pretreatment with magnesium sulfate attenuated lactate levels to 130% of the basal level ( P = 0.01). Magnesium supplementation may be beneficial because it provides an additional glucose source and may also promote the recovery of energy substrates in the brain during and after forced exercise. In order to achieve optimal physical performance, further investigation as to dosage of magnesium supplementation is needed. [ABSTRACT FROM AUTHOR]