Sentence:  Too often a beginning bodybuilder has to do his training secretly either because his parents do n't want sonny-boy to `` lift all those old barbell things '' because `` you 'll stunt your <WSD>growth</WSD> '' or because childish taunts from his schoolmates , like `` Hey , lookit Mr. America , whaddya gonna do with all those muscles ( of which he has none at the time ) '' ? 
Meaning of the word marked with <WSD> tags:  (biology) the process of an individual organism growing organically; a purely biological unfolding of events involved in an organism changing gradually from a simple to a more complex level