Journal Article

Short-Term Magnesium Supplementation Has Modest Detrimental Effects on Cycle Ergometer Exercise Performance and Skeletal Muscle Mitochondria and Negligible Effects on the Gut Microbiota: A Randomized Crossover Clinical Trial

Walsh, Maureen A., Williams, Natasha N. B., Hamilton, Karyn L., Abbotts, Kieran S. S., Bell, Christopher, Weir, Tiffany L., Ewell, Taylor R., Brown, Reagan L., Butterklee, Hannah M., Kwarteng, Beatrice S., Thomson, David P., Bomar, Matthew C., Brown, David M., Wrigley, Scott D.

2025

Overview

Background/Objectives: 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 influence 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. Fifteen participants ingested either a 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, vastus lateralis, and stools were sampled. The primary outcomes were the maximal oxygen uptake (VO2max), a simulated 10 km time trial, and the sprint exercise performance. Additional outcomes included skeletal muscle mitochondrial respiration, and, on account of the known laxative effects of magnesium, the gut microbiota diversity. Results: Compared with a placebo, MgCl2 supplementation increased the circulating ionized Mg concentration (p < 0.03), decreased the VO2max (44.4 ± 7.7 vs. 41.3 ± 8.0 mL/kg/min; p = 0.005), and decreased the mean power output during a 30 s 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). There were no significant impacts on the gut microbiota richness (CHAO1; p = 0.68), Shannon’s Diversity (p = 0.23), or the beta-diversity (Bray–Curtis distances; p = 0.74). Conclusions: In summary, magnesium supplementation had modest ergolytic effects on cycle ergometer exercise performance and mitochondrial respiration. We recommend that regular exercisers, free from hypomagnesemia, should not supplement their diet with magnesium.

• Publisher: MDPI AG,MDPI
• Subject: Adenosine triphosphatase / Adult / Athletic Performance - physiology / Bioavailability / Body composition / Cardiac stress tests / Chloride / Clinical trials / Cross-Over Studies / Data collection / Dietary supplements / Dietary Supplements - adverse effects / Double-Blind Method / Exercise / Exercise - physiology / Exercise Test / Fatty acids / Female / Gastrointestinal Microbiome - drug effects / Gut microbiota / Humans / Laboratories / Magnesium - administration & dosage / Magnesium - blood / Magnesium Chloride - administration & dosage / Magnesium compounds / Male / Microbiota / Microbiota (Symbiotic organisms) / Mitochondria, Muscle - drug effects / Mitochondria, Muscle - metabolism / Muscle, Skeletal - drug effects / Muscle, Skeletal - metabolism / Muscles / Musculoskeletal system / Oxygen Consumption - drug effects / Physical fitness / Physiological aspects / Physiology / Respiration / Young Adult