Here's a study that makes you wonder:
Mechanism of work-induced hypertrophy of skeletal muscle.Goldberg AL, Etlinger JD, Goldspink DF, Jablecki C.
"Back in the early 70â?²s researchers quickly realized that if you took a rat and had him walk downhill on a treadmill or induced tension overload by putting a muscle on stretch (eccentric contractions) that they could do all sorts of nasty things to try and blunt muscle hypertrophy but it did not stop muscle hypertrophy from occurring: they removed their pituitary so they could not produce GH or IGF-1, castrated them so they could not produce testosterone, removed their thyroid, or just didnâ??t feed themâ?¦despite this punishment, the rats still had increases in muscle hypertrophy in their legs .
In his research, Dr. Goldberg noted, â??Maximal tension development leads to increases in muscle hypertrophy. Unlike normal developmental growth, work-induced hypertrophy can be induced in hypophysectomized (rats that canâ??t produce GH) or diabetic animals. This process thus appears independent of growth hormone and insulin as well as testosterone and thyroid hormones. Hypertrophy can also be induced in fasting animals, in which there is a generalized muscle wasting.
Thus muscular activity takes precedence over endocrine influences on muscle size. The increase in muscle weight reflects an increase in protein, especially sarcoplasmic protein, and results from greater protein synthesis and reduced protein breakdown."
This seems totally out of the box. Of course, they didn't say at what extent muscle protein synthesis occured, which should be quite minimal compared to a rat with both its balls...