Magnesium Supplementation Has Modest Detrimental Effects On Cycle Ergometer Exercise Performance And Skeletal Muscle Mitochondria

PURPOSE: Although the importance of magnesium for overall health and physiological function is well established, its influence on exercise performance is less clear. The primary study objective was to determine the effect of short-term magnesium supplementation on cycle ergometer exercise performance. The hypothesis was that magnesium would elicit an ergogenic effect. METHODS: A randomized, double-blind, placebo-controlled, two-period crossover design was used to study men and women who were regular exercisers. Participants ingested either placebo or magnesium chloride (MgCl2 300 mg) twice per day, for 9 days, separated by a 3-week washout. During days 8 and 9, participants completed a battery of cycle ergometer exercise tests, and whole blood and vastus lateralis were sampled. Primary outcomes were maximal oxygen uptake (VO2max), a simulated 10 km time trial, and sprint exercise performance. Additional outcomes included skeletal muscle mitochondrial respiration. RESULTS: Compared with placebo, MgCl2 supplementation increased circulating ionized Mg concentration (P < 0.03), decreased VO2max (44.4 ± 7.7 vs. 41.3 ± 8.0 ml/kg/min; P = 0.005), and decreased mean power output during a 30-second sprint (439 ± 88 vs. 415 ± 88 W; P = 0.03). The 10 km time trial was unaffected (1282 ± 126 vs. 1281 ± 97 s; P = 0.89). In skeletal muscle, MgCl2 decreased mitochondrial respiration in the presence of fatty acids at complex II (P = 0.04). CONCLUSION: In summary, magnesium supplementation had modest ergolytic effects on cycle ergometer exercise performance and mitochondrial respiration. Findings from this study do not support the use of Mg supplementation in regular exercisers without hypomagnesemia. Supported by: This research was funded by New Capstone, Inc., Mooresville, NC, USA. Interaction between the research team at Colorado State University and the sponsor, including contract negotiation, and progress and final reports, was administered by Think Healthy Group.