I don't know what to think of this. One wonders whether the load and rate of exertion are controlled for. If I know I am going to have to work out 5x/week, I sure as he'll don't go as hard on day 1 as I would if I had a whole week to recover on a 1x/week regimen. Maybe 5x/week is still overall more load, and that's why it works, but taking the time to do this week after week is also tricky. Not to mention, there's periodization to control for too. If all of the participants had been doing something closer to 1x/week per body part before the study, the 5x/week regimen had an unfair advantage purely due to novel metabolic and neuromuscular challenge.