The effects of magnesium supplementation on exercise performance

Purpose: To determine the effects of magnesium (Mg2+) supplementation on pe rformance and recovery in physically active women using the sensitive and r ecently advanced measure of ionic Mg2+ (iMg). Methods: Participants (N = 12 1) were screened for [iMg] in plasma, with 44 (36.4%) exhibiting [iMg] belo w the normal range of 0.53-0.67 mmol.L-1 (4). Thirty-two subjects (21 +/- 3 yr) representing a broad range of [iMg] (0.54 +/- 0.04 mmol.L-1) completed the main 14-wk study. Ar baseline, participants submitted to a resting blo od pressure measurement, and they completed both an anaerobic treadmill tes t and an incremental (aerobic) treadmill rest. For the latter. values for w orkload, oxygen uptake, and heart rate were obtained at both anaerobic thre shold and maximal effort. Blood samples for iMg, total serum Mg2+ (TMg), er ythrocyte Mg2+ (EMg), Ca2+, K+, Na+, hemoglobin, hematocrit, lactate, and g lucose were also collected pretest, and 4, 10, 30 min, and 24 h posttest. S ubjects received 212 mg.d(-1) Mg oxide or placebo in a double-blind fashion and were retested after 4 wk. After a 6-wk washout period, the testing was repeated with a treatment crossover. Results: Ionic Mg2+ increased with Mg 2- treatment versus placebo (P < 0.05); however, performance and recovery i ndices were not significantly affected. Conclusion: Four weeks of 212 mg.d( -1) Mg oxide supplementation improves resting [iMg] levels but not performa nce or recovery in physically active women.