The effects of magnesium supplementation on exercise performance.
OBJECTIVE
To determine the effects of magnesium (Mg2+) supplementation on performance and recovery in physically active women using the sensitive and recently advanced measure of ionic Mg2+ (iMg).


METHODS
Participants (N = 121) were screened for [iMg] in plasma, with 44 (36.4%) exhibiting [iMg] below 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. At baseline, participants submitted to a resting blood pressure measurement, and they completed both an anaerobic treadmill test and an incremental (aerobic) treadmill test. For the latter, values for workload, oxygen uptake, and heart rate were obtained at both anaerobic threshold and maximal effort. Blood samples for iMg, total serum Mg2+ (TMg), erythrocyte Mg2+ (EMg), Ca2+, K+, Na+, hemoglobin, hematocrit, lactate, and glucose were also collected pretest, and 4, 10, 30 min, and 24 h posttest. Subjects 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 Mg2+ treatment versus placebo (P < 0.05); however, performance and recovery indices were not significantly affected.


CONCLUSIONS
Four weeks of 212 mg.d-1 Mg oxide supplementation improves resting [iMg] levels but not performance or recovery in physically active women.
Finstad
E W
EW
School of Kinesiology, Lakehead University, Thunder Bay, Ontario, Canada.
Newhouse
I J
IJ
Lukaski
H C
HC
Mcauliffe
J E
JE
Stewart
C R
CR
D000293:Adolescent; D000328:Adult; D000863:Antacids / Q000494:pharmacology*; D018592:Cross-Over Studies; D019587:Dietary Supplements; D004311:Double-Blind Method; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006801:Humans; D008274:Magnesium / Q000097:blood; D008277:Magnesium Oxide / Q000494:pharmacology*; D010101:Oxygen Consumption; D010807:Physical Endurance; D010919:Placebos
D000863:Antacids; D010919:Placebos; D008277:Magnesium Oxide; D008274:Magnesium