I believe he should start out with 2 on 1 off. I mean, if that's too much, then switch to 1 on 1 off.This is definitely due to overstressed loading. It happens with pumping too much for too long of a period under high pressures.
You can back off with a day on, day off routine so the body can restrengthen. You can even do a 2 days on, 1 day off just to give the tissues a chance to recuperate a bit more.