Magnesium helps to contain normal muscles and nerves functions plays a huge roll in energy metabolism and protein synthesis. Besides that, it helps in a huge way to relieve the muscle stress that that prevent muscle growth and lowers muscle ache. It can even increase strength; the results from a scientific study shows that athletes that took magnesium supplements had an increase in leg strength.
Many people who train with weights have difficulties sleeping after an intensive workout, often this is because of the reaction of the body to the stress of repairing the damage that has been inflicted. Magnesium helps to reduce that stress, and brings the body to a more beneficial state to sleep. And because you improve sleep quality, magnesium not only gives you better recovery during sleep but also gives you better preparation for the next day - mentally and physically - for the next training.