Of the 12 included studies, 11 were double-blind placebo-controlled; 3 of these were randomised and 5 involved a crossover between treatment and control. The remaining study was a single-blind time series.
The studies were limited by many confounding factors, such as the widespread failure to report Mg status, to control for exercise before testing, or to use crossover designs. There were variations in exercise models, training states and the athletes' ages, and dosages. Other active ingredients were sometimes ingested with Mg. The populations were predominantly male and gender differences were not studied. Only 3 studies measured the typical dietary intake of Mg.
Higher quality studies found no effect of Mg supplementation, regardless of whether the type of performance outcome was strength, anaerobic-lactacid, or aerobic. The strength of evidence was equivocal for peak treadmill speed during an oxygen consumption (VO2max) test. Trained persons appeared to benefit less than untrained persons.