This question is about Nutrition and Running
Yes, supplemental magnesium may improve exercise performance but only in individuals that are magnesium deficient [ 1 2 1 2 [2]
[1] Zhang, Y., Xun, P., Wang, R., Mao, L., & He, K. (2017). Can Magnesium Enhance Exercise Performance? Nutrients, 9(9), 946. https://doi.org/10.3390/nu9090946
[2] Nielsen, F. H., & Lukaski, H. C. (2006). Update on the relationship between magnesium and exercise. Magnesium research, 19(3), 180–189. https://pubmed.ncbi.nlm.nih.gov/17172008/
[3] Garrison, S. R., Korownyk, C. S., Kolber, M. R., Allan, G. M., Musini, V. M., Sekhon, R. K., & Dugré, N. (2020). Magnesium for skeletal muscle cramps. The Cochrane database of systematic reviews, 9(9), CD009402. https://doi.org/10.1002/14651858.CD009402.pub3