Magnesium is interesting. A lot of these vitamins and minerals interact, in ways many doctors have forgotten. Magnesium is essential for calcium metabolism, so I often recommend it for anyone who takes calcium. It does help with muscle cramps and many take it for insomnia. Magnesium isn't a miracle drug, any more than Vitamin D, but it is a necessary mineral, and people do really notice improvements with muscle soreness. If cramps are the main issue you have, some people swear by magnesium malate - the malic acid in it may also help with sore muscles.