Melatonin is a naturally occurring hormone that is secreted from the pineal gland from the brain. It is suppressed from stimuli from light into the eyes and activates from darkness.
This supplement is usually given to older people since our pineal gland secretes less melatonin as we get older , down to 20 % . However, it is quite commonly used as a supplement for people with sleeping problems.
For athletes for such high amounts of muscle stimuli , energy supplements and mentally straining activities that may hinder the secretion of melatonin melatonin is also used.
Another protein that is a precursor of melatonin is tryptophan. Trytophan can be found in chicken/ turkey meat.
Most of our joints, muscles and the brain recovers is from sleep. So if you are an athlete or a body builder make sure you have enough sleep to recover and repair your muscles for your next training session. The hormone that is secreted for muscle growth is called growth hormone (somatotropin).
Nearly fifty percent of GH secretion occurs during the third and fourth NREM sleep stages. (1)
(1)^ Mehta A, Hindmarsh PC (2002). “The use of somatropin (recombinant growth hormone) in children of short stature”. Paediatr Drugs 4 (1): 37–47. PMID 11817985.