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1.
The type of muscles that develop as a guy transitions from teen/young adult to full fledged man. It is accompanied by a gain in strength and usually happens between the ages of 26-28. Man muscles aren't bigger, but they are rock hard and will allow men to beat much "stronger" young men in things like arm wrestling and give them greater endurance in repetitive hard labor.
You think Bryce Harper is a good player now? Just wait until he gets his man muscles! or Now that LeBron James has his man muscles the rest of the NBA doesn't stand a chance.
by scrapple000 May 02, 2013
 
2.
The muscle in the forearm that gets ripped as a result of jerking-off to often.
Damn!!!! Look at his arms! That boy spends to much time alone working on his man-muscles.
by hawkgal January 22, 2011