https://training-conditioning.com/news/when-to-do-full-body-workouts-splits/

*NOTE*

[My (TK:) comments are injected in bold italics to make logical points]

Which is better? That depends on three questions only you can answer:

1. How often you want to train.

2. How much training experience you possess.

3. How intense each session is.

TK: Anyone who trains – regardless of age, experience, training day schedule – should train HARD to get results, whatever that hard is.

Here’s how to figure out the best approach for you.

If You Lift 2-3 Times a Week using Full-Body Workouts

Some research shows that training muscle groups twice per week is better than doing so once per week, even if the total amount lifted is the same, according to a November 2016 review in ​Sports Medicine.

One explanation for this could be multiple increases in what’s called “muscle protein synthesis.” After you lift weights, this process — which tells your body to build muscle — is elevated for a period that lasts between one and two days, according to a June 2015 review in ​Sports Medicine. Training the muscle two or more times per week will spike this twice instead of once.

Not all research says that twice a week is better than once a week, though. Another review, published in December 2018 in the ​Journal of Sport Sciences, found that the effect on hypertrophy was similar whether a muscle group was trained once, twice or three times a week — as long as those 10 to 20 sets were done.

TK: If you train hard to create muscle overload, proper recovery between workout sessions is mandatory to accrue results. That could mean anywhere from 24 hours (two days) to 96 hours (four days). On that, that may mean only the two or three sessions in a typical 7-day week.

If You Lift 4 Times a Week using Either Split- or Full-Body Workouts

If you perform a routine that splits your body in half — maybe one upper-body and one lower-body workout - or a workout comprised of pushing exercises and another with pulling exercises — you can hit every muscle group two times a week.

You could also do four full-body workouts per week as long as the workouts are spread out or you don’t train your muscles in exactly the same way.

“Total-body training on a daily basis [can mean you] don’t allow proper recovery between training days,” Jason White, Ph.D., associate professor and director of performance sciences at Ohio University, tells LIVESTRONG.com. Giving yourself at least one rest day between full-body training sessions is necessary for your muscles to recover.

TK: There is no way one can PROPERLY recover from four full-body workouts in a 7-day period if they are truly working hard. Understand the conventional 7-day week is not a good fit for a lot of smart trainees because it does not accommodate the biological stress-recovery formula. Along with that is the commitment to work, school, and family commitments that result in many who 1) try to jam their training into the 5-day work week or 2) need to use the weekend to schedule at least one training session. Either way it can hinder proper recovery and adaptation due to too much exercise stress from training sessions scheduled too close to each other.

So, if you want to train full-body, either use my suggestions above regarding the two or three days options or schedule a full-body session every 3rdday. For the latter, that could conflict with one’s set weekly life routine because it would mean the scheduled training days would vary over a three-week period (and disrupt that pre-set work, school, and family schedule), but would allow adequate recovery time between sessions. Here you go:

M – Th – Sn - W – Sa – Tu – F – and back to M to repeat the same sequence.

If You Lift 5-7 Times a Week Using Different Body Part Splits

“Splits are more for people who desire increased frequency,” White says. That keeps you in the gym on a near-daily basis and allows you to hit the high volumes you want to hit for those muscle groups while still allowing recovery days before the next time you hit them.

One other benefit of adding sessions is that it’s often easier to get more total volume from spreading the sets out: You’ll get pretty tired doing 15 sets of 10 reps in a row, so the weight might decrease, or you may not be able to finish all your reps. When you’re doing just 5 sets, for example, you’ll likely be able to lift a greater total in each of the three sessions, resulting in more total weight lifted throughout the week.

TK: Yikes. I’m still flabbergasted by the love affair with “total volume.” If that was so important for obtaining great results, what exactly is the magic “total volume” goal? Is it 30 sets per muscle group? 50? Is it 250 reps? 500? On that, if more volume is purportedly better, why not aim for 100 sets per week or 2,000 total reps completed. See, it’s gray area; subjective; unscientific and based on one’s “feel” and totally ignores the proven research that supports a minimal amount of stress to elicit the maximum potential adaptation. Like prescription medicine, a specific dose is needed to obtain the desired response. Too little won’t cut it and too much can be deadly. Exactness is needed and in resistance training it is mostly a minimal amount of it that is best.

So, to elicit the stimulus for increasing strength or building muscle, focus on high intense efforts (safely achieving momentary muscle fatigue) and use a minimal number of sets (1 to 3). The more you do the more you are 1) hindering recovery ability and 2) unnecessarily taxing your muscles. Regarding the number of reps, that can vary depending on one’s goal (pure strength, power, hypertrophy). It’s  not about achieving an arbitrary “total rep number” at the end of the week but working those sets – whether they consist of low (3-5), moderate 8-12), or high (20+) reps – to the limit in each reasonably scheduled training session.