A Magnesium supplement should be part of your pre- or post-workout routine: Magnesium is used in just about every bodily function that allows you to effectively exercise and build muscle, which includes protein synthesis, muscle and nerve functions, blood glucose control and energy production. Magnesium can ease post-workout soreness and help muscles move smoothly from a contracted to a relaxed state. This is due to Magnesium’s abilities to move blood sugar into your muscles