Sarah Blount, Sasha Riley, Kyle M. Edgar, Mark Belio, Andrei Sergeyev, Mohamdod Alzer, Joshua Beaver, Alain Aguilar, Erik D. Hanson, FACSM. University of North Carolina at Chapel Hill, Chapel Hill, NC.

Magnesium (Mg) appears to enhance athletic performance, with acute oral supplementation leading to increases in maximal strength. Alternative Mg application methods have been developed but little data is available as to their effectiveness on altering muscle function. PURPOSE: Compared to placebo, to examine if transdermal magnesium chloride (tMgCl2) increases 1) forearm flexor maximal isometric force and 2) total work performed during a fatigue protocol. METHODS: In a double-blind, randomized crossover design, healthy resistance trained participants (n=40, age 22±3y, 50% female) completed maximal isometric forearm flexor contractions. Participants performed a sub-maximal warm up followed by 2 sets of 3 maximal isometric contractions (Pre) with 1 min of rest between attempts and 3 min between sets. The highest value between both sets was used as the maximal force measure. tMgCl2 or placebo was applied to cover the forearm flexor and absorbed for 60 min, followed by a third set (Post) of maximal isometric contractions. A fatigue protocol consisting of 3 sets of isometric holds to failure at ~50% peak force was then performed. Condition and limb dominance were block-randomized. Data were analyzed using a linear mixed model with time and condition as fixed factors and subject as a random factor using Jamovi 1.6.23 statistical software. RESULTS: For maximal isometric force, there was no interaction (p=0.290) or condition effect (MD = -0.5 kg ± 0.5, p=0.241). There was a non-significant decrease in maximal force 1.2% ± 0.07 over time (Pre: 41.2 kg ± 13.4, Post: 40.4 kg ± 13.4, p=0.07). Independent of condition, 53.8% of the maximal isometric force came from the second set of handgrip contractions, and 41.3% of the max force production came from repetition 1 among sets. During fatigue protocol, time to fatigue was 68.9 sec on set 1, with decreases of 49.3% (p<0.001) and 62.4% (p<0.001) on the subsequent efforts. There was no difference in total time between conditions (MD = 2.1 sec ± 1.8 p=0.240), nor was the interaction significant (p=0.762). CONCLUSIONS: Under the current conditions, tMgCl2 does not significantly alter maximal forearm flexor force or total work during a fatigue protocol. The slight decrease in force may be related to interneural potentiation that does not occur in the third set. Increased tMgCl2 dose or determining absorption rates should be considered in future studies.

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