Supplement Reviews

Magnesium

Magnesium in the human body ranks fourth in overall abundance, but intracellularly (within cells) it is second only to potassium. Between 60-65% of magnesium in the human body is found in bone. Magnesium that does not exist as part of bone, is mainly found within muscle intracellularly. About 1% of magnesium is found in the extracellular fluid. Inside cells, magnesium may be found bound to phospholipids. In animal studies, it has been shown that bone magnesium is used to maintain levels throughout the body and muscle magnesium is maintained, when magnesium intake is restricted. Magnesium absorption when ingested is carrier-mediated and is influenced by transit time through the gut, dietary intake of magnesium, and the amounts of phosphorous and calcium in the diet. These minerals compete for absorption sites in the intestinal mucosa. Excess magnesium that is not deposited in bone or retained in tissue is excreted through the urine.

This mineral is involved in over 300 enzymatic reactions in the body including glycolysis, the krebs cycle, creatine phosphate formation, nucleic acid synthesis, amino acid activation, cardiac and smooth muscle contractability, cyclic AMP formation, and most importantly for strength athletes, protein synthesis. Some of the functions of this important macromineral are relevant to endurance and strength athletes. To fully understand the implications this mineral has on athletes, we must explore the roles of magnesium further.

ATP (adenosine triphosphate or energy) is always present as a magnesium: ATP complex. Magnesium basically provides stability to ATP. Magnesium binds to phosphate groups in ATP, thus making a complex that aids in the transfer of ATP phosphate. Since working muscles generally contain more ADP (adenosine diphosphate), allowing ATP to release a phosphate group is important to exercising individuals.

Magnesium is also a cofactor to the enzyme creatine kinase which converts creatine into creatine phosphate or phosphocreatine (which is the storage form of creatine). Since creatine monohydrate supplements are extremely popular and proven to be effective, magnesium may be an important mineral in helping to optimize creatine function. In active muscle, creatine kinase also helps phosphocreatine combine with ADP to resynthesize ATP in contractile activity. This process, which involves magnesium, basically increases anaerobic endurance. By the way, phosphocreatine possesses a higher phosphate group transfer potential than ATP so it may be able to form ATP quickly and provide energy for muscular activity.

One 1992 study published in the Journal of the American College of nutrition entitled "Effect of Magnesium Supplementation on Strength Training in Humans" (15) studied the effects of a dietary magnesium supplement (magnesium oxide given in a ratio of 8 mg/kg/day including dietary magnesium) on strength development during a double-blind, 7 week strength training program in 26 untrained subjects. There was a magnesium supplemented group and a control or placebo group. For example, a 200 lb. individual in the magnesium supplemented group would receive about 725 mg of magnesium daily. The results of the study showed that the oral magnesium supplementation group produced significantly greater results in strength than the control group. The researchers also concluded that magnesium’s role in protein synthesis may be at the ribosomal level.

Magnesium is also an important mineral for endurance athletes. Endurance athletes may become magnesium deficient because of increased magnesium losses in sweat. Increased energy expenditure may also cause an increase in magnesium requirements. Magnesium supplementation has also been shown to improve cellular metabolism in competitive athletes. Another clinical trial which studied the effects of magnesium supplementation (360 mg/day) for 4 weeks in male competitive rowers showed a decrease in serum lactate concentration and oxygen consumption when compared to rowers receiving a placebo. In other words, the results of this study suggested that magnesium supplementation may have a beneficial effect on energy metabolism and work efficiency.

Other research studies show that serum magnesium levels may be reduced in response to strength training. Also, it has also been noted in research studies that maximal contraction of the quadriceps is positively correlated to serum magnesium status.
 

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