when i was bodybuilding, i combated all the constipation from eating my fucking bodyweight in proteins with natures candy:
PRUNES
theyre cheap (especially farm fresh prunes, theyre so fucking cheap and so good for you its a steal), INSANELY good for you, and make you shit like a swiss train. i was buying big tubs of prunes to eat every week for like $2 at the farmers market, eating like 15-20 prunes every night right after dinner, and i could shit out half a cow the next morning.
im also quite familiar with opiates and their effects on muscles. potassium, magnesium, and manganese - of which prunes are LOADED - are excellent for that.
last resort: milk of magnesia (chalky shit u buy at a pharmacy). prepare to shit your brains out (you will experience dehydration and loss of nutrients from this).