Periodic Muscular Growth in Humans
Disuse and lack of exercise are actually exceedingly new problems when considered on an evolutionary scale.  The bigger evolutionary pressure for the last few million years has been not starving to death, therefore not maintaining expensive muscle fibers unless they were absolutely necessary.

I haven't found any evidence of previous musculature effecting growth, but I'm going to look into it more (only some quick pubmed searches), and edit this answer.  If someone else knows more immediately, please feel free to answer.