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.

When some little bitchboy is acting like a little tiny pee pee poo poo baby and messing up the group plans.

The muscle in the forearm that gets ripped as a result of jerking-off to often.