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SUMMARY
MAGNESIUM (Mg^sup 2+^) IS ONE OF THE MOST ABUNDANT POSITIVELY CHARGED IONS (CATION) WITHIN THE HUMAN BODY AND HAS BEEN LINKED WITH MUSCULAR, NEURAL, ENZYME, AND CELLULAR PROCESSES. HOWEVER, Mg^sup 2+^ HAS RECEIVED RELATIVELY LITTLE ACKNOWLEDGMENT COMPARED WITH OTHER CATION PARTICLES SUCH AS CALCIUM OR POTASSIUM. THIS REVIEW AIMS TO INCREASE THE AWARENESS OF COACHES AND ATHLETES REGARDING Mg^sup 2+^'S PHYSIOLOGICAL CHARACTERISTICS AND FUNCTIONS. THE IMPORTANCE OF THIS CATION, IN TERMS OF MUSCLE CONTRACTION AND ENERGY REGULATION, INCLUDING OTHER RELATED PROCESSES WILL BE EXPLORED. CONSEQUENCES OF Mg^sup 2+^ DEFICIENCY IN ATHLETIC AND UNTRAINED POPULATIONS WILL ALSO BE DISCUSSED, INCLUDING STRATEGIES TO OPTIMIZE Mg^sup 2+^ LEVELS.
KEYWORDS:
calcium; muscle contraction; energy; regulation
INTRODUCTION
Magnesium (Mg^sup 2+^), to human knowledge, is the ninth most abundant mineral in the universe and the second most profuse cation within the intracellular compartments oí the human body (19,29). In exercise physiology, Mg^sup 2+^ has tended to be overlooked, with a variety of textbooks (8,20,23,27,28,43) lending only a few token sentences to its function and applicability to exercise, compared with other micronutrients including phosphorus and calcium. A recent generic search of PubMed, using the key words "magnesium" and "human" yielded 512 publications; when Mg2+ was substituted for calcium (Ca2+), 4977 hits were reported. The same search was narrowed to include "Muscle", resulting in 15 and 187 publications, respectively. These numbers reflect an imbalance in Mg2 ' research that may stem from a lack of scientific interest, driven by methodological difficulties in determining Mg2 ' concentration within the human body (12,40). It is also probable that only recently because of the advances in technology, such as nuclear magnetic resonance (NMR) spectroscopy and florescent dye techniques, whole body processes and cellular interactions involving Mg2 ' in vivo could be studied (36) because the majority of research has been on animal models in vitro, which do not give an overall indication of events (25).
Despite the previous difficulties encountered in assessing an individual's Mg^sup 2+^ status, the role of Mg^sup 2+^ within the body is of fundamental importance, involved with or linked to the promotion of Ca21 transport in/out of the sarcoplasmic retículum (SR) (39), regulation of glycolytic metabolic pathways (22), oxygen delivery and uptake (26), adenosine triphosphate (ATP) production (19), an...