I got this from Dr. Mercola's website. He wrote a blog entry in the American Journal of Clinical Nutrition. He writes:
"Interestingly, Shelton [I need to find out who this is] wrote about it in a book nearly 70 years ago:
It ws known to the ancients that 'sunshine feeds the muscles.' Today every athlete employs sunbathing as a regular part of his or her training. For it not only adds to the size and qualities of the muscles, it increases the calcium in them and adds to their enduring powers. The firmness of the athletic muscle requires calcium in considerable amounts. Such muscles contain far more calcium than flabby ones. After exercise their calcium content is diminished.
Muscles subjected to proper sun exposure grow larger, firmer, and have their contractile powers enhanced even without exercise, due partly to the increase of lime in them, and partly to improved nutrition in general."