Magnesium deficiency can reduce exercise performance and contribute to muscle cramps, but sub-optimal intake does not appear to be a problem among most groups of athletes.^{1, 2} Controlled trials suggest that magnesium supplementation might improve some aspects of physiology important to sports performance in some athletes,^{3, 4} but controlled and double-blind trials focusing on performance benefits of 212 to 500 mg per day of magnesium have been inconsistent.^{5, 6, 7, 8, 9, 10} It is possible that magnesium supplementation benefits only those who are deficient or who are not highly trained athletes. ^{11, 12}