Exercise stimulates the release of growth hormone (HGH), as does the natural circadian (sleep) ryhthm. Growth hormone increases lean mass, reduces adiposity, and improves bone density. Erythropoietin (hormone) increases the rate of red blood cell (RBC) production. The increase in RBC's improves oxygen consumption, reduces fatique, and improves endurance capabilities.

 
Adiposity: the quality or state of being fat. 

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