This topic for the garillionth time.
The amount of times you train a muscle depends on your goal and what program your following. Obviously if you’re after general fitness, don’t have many days to train or don’t want to train often, then you’re going to probably be using a full body or upper-lower program, in which case you’ll be training each muscle group two or three times per week.
However, if we’re talking about the most ideal way to train for size, we’re talking about bodybuilding training, not all programs that literally build the body. I say this because several times in the past when I discussed this topic, some people have actually gotten angry with me and acted as if I insulted their best friends or family members, and exclaimed, “What are you trying to say, you can’t build a body or get big doing other programs other than split routines?”
So I’ll discuss bodybuilding training because that seems to be the form of training many fitness writers are referring to when they try to discredit body part splits or low frequency training. Because of the nature of a body part split, a high volume can be done per muscle group and the frequency is once every 5 to 7 days.
What many of these MPS-obssessed coaches and writers don’t mention is that just because there’s an increase in MPS, it doesn’t mean there’s an increase in actual growth.
Second, they write and think as if nothing is going on with specific muscle groups when they’re not trained specifically, even though there is plenty of overlap during the course of a five- to-seven day training period. I’ve used these examples over and over again. If I train chest on Monday, and then two to three days later train shoulders and triceps, i have trained chest, shoulders, and triceps twice considering dips might be used for triceps and the shoulder and triceps are used on both days, obviously. If I do stiff legged deadlifts for leg day, and then two to three days later train back, I have hit my back twice, once specifically, one with less stimulation.
And as Lonnie said, there must be something else besides MPS going on considering bodybuilders have done fine just training each muscle group once per week. Even with quads not getting much more overlapping stimulation, there have been people who developed impressive quads training them directly once per week, with little else stimulation.
Anyway, without all this being explained, the proof is right in front of everyone’s faces: pro bodybuilders having the most heavily muscled bodies while not following the advice of the great fitness sages who never stepped on a stage or looked like a bodybuilder. At least Brad Schoenfeld competed and I believe he has stated that bro splits are just fine.