The best split for building muscle and getting jacked may just be no split at all.
"Back and Bis", "Chest and Tris", "Leg Day", "Shoulders and Arms"... there are countless variations of the above, and I've probably tried most of them in the search for the perfect muscle-building training split. But what if the perfect training split isn't a split at all?
Full body workouts are often dismissed as best-suited for beginners, but there's some compelling research suggesting that it might be worth rethinking our approach to how we structure the training week.
The Aim of the Training Session
Some things seem so obvious that we never really examine them, and the actual goal of an individual training session may well be one of those things. The goal of a training session, at least in the context of building muscle, is to stimulate an increase in muscular protein synthesis (MPS). This protein synthesis is the mechanism by which our body builds muscle tissue. It's that simple, but that important if muscle mass is the goal.
In the course of daily life, muscle protein is routinely being both broken down and built up. All things being equal, these rates balance out in the body's never-ending search for homeostasis. In order to build muscle, we need to tip the scales in our favor (no pun intended), and we do so by applying a stress (resistance training) that convinces the body of the need for more muscle tissue. The resultant adaptation is the increased rate of MPS.
This singular fact is the one aim of a program aimed at building new muscle; everything else we associate with training is subservient to its effect on MPS. That means that while rep schemes, rest periods, total volume, relative intensity, even how "sick your pump is" are all means to an end, but not the end itself. If swole is the goal, MPS is how you get there. And in order to take a critical look at the merits of both split and full body routines we may need to consider killing some of strength training's sacred cows along the way.
Full Body vs. Split
While I'm sure most readers are familiar with the definition and the concept of each of these training methods, I'd like to take a minute to set up and examine an even comparison. For the sake of our discussion, take a look at the following training plans.
Both are built around a four-day training week; the first using a full body approach, the second following a common body part split. The exercises included are identical, and while it may not perfectly represent what you—or even I—would actually choose, it allows for a head-to-head analysis.
Let's assume a pretty standard three sets of 10 for all working sets (planks excepted). By using identical exercises we can theoretically adjust for total volume (sets x reps x load... more on why this may only be a theoretically even playing field later), as well as any variation in individual exercise effectiveness. In fact, this is exactly how some of the research conducted was set up.
We'll revisit the strengths and weaknesses of each approach in more depth in a moment, but for now, try mentally walking yourself through each training day and week. I'll be honest, that leg day scares me a bit, and machismo aside, the goal of a training session is an increase in MPS, not the inability to walk (and brag about it on social media).
The Drawbacks of Full Body Training
Two major objections are typically raised by those concerned with the efficacy of a full body training plan: DOMS, and the general feeling that you're just not doing enough work for each muscle group during a given workout.
Delayed Onset Muscle Soreness is muscle soreness that sneaks up on a lifter a day or two after their training session. Theorized to be the result of micro-tears within the muscle tissue, it can make training the same muscle group a tough ask. While the concern is valid, three counters are worth mentioning.
The first is that while DOMS may be uncomfortable, it doesn't seem to actually reduce force output except in particularly extreme cases.
The second is anecdotal; as someone who's tried a fair amount of full body training I can say that I quickly adapted to the new stimulus and after a week or so felt as ready for each workout as I have on any body part split.
The third counter is hypothetical; while the total training volume for each muscle group remains constant, by spreading the work out over four days instead of one the trainee is subjected to less specific muscular stress in a given workout, thereby limiting local soreness.
Anyone who came of lifting age on a body part split (hand goes up) got used to a feeling of exhaustion following a workout. That feeling of "I can't lift my arms" combined with the subsequent muscle soreness became a badge of honor, and for many of us began to be equated with progress. As referenced earlier, a leg day you could walk away from wasn't much of a workout, right?
If we drop these ingrained assumptions for a moment and remind ourselves (again) that the goal of a training session is not fatigue, is not soreness, but is instead an uptick in MPS, then the goal shifts. We no longer need to annihilate a muscle group (sorry magazine headlines), we simply need to stimulate it enough to flip that chemical switch and trigger new muscle growth.
We'll look at the research on this in a bit, but for now, let's look at some of the drawbacks a body part split may offer.
The Drawbacks of the Body Part Split
Despite potentially being the single most common approach for lifters looking to build muscle, there are some distinct drawbacks to body part split training. While these clearly don't mean that it can't be an effective approach to organizing the training week, ignoring them is intellectually irresponsible.
Intensity & Total Volume
Take another look at the two example training weeks outlined above, and specifically at that absolute monster of a leg day to start the week. Here's the menu: front squat, deadlift, leg press, Romanian deadlift, walking lunge, hip thrust, leg extension, and leg curl. I'm pretty well conditioned to some terrible workouts, but by the time those walking lunges roll around, I'm probably stuck reaching for a lighter pair of dumbbells than I would be if I were a little fresher. In reality, that effect probably begins with the deadlift and is further compounded as the workout progresses. Lighter weight means less total volume, and while total volume is not the goal (again, muscle growth via increased MPS is the goal), multiple studies link total volume to increased hypertrophy.
Skewed Volume Split
So "Leg Day" sucks... I did some quick math and my best guess is that I'd wind up somewhere near 64,000 pounds of total work. Oof. That "Shoulders and Abs" workout? A little under 15,000 pounds. That's less than a quarter of the total weight lifted. And while I'm a fan of waving intensities and volumes (undulating periodization), that seems a little too skewed.
The Myth of the Isolation Exercise
Let's take another look at the body part training split, but this time from the perspective of the trainee's shoulders. The program says those get trained on day five, but the reality is fairly different.
"Leg Day": those front squats require a good amount of anterior shoulder work, both deadlift variations will tax the posterior head, and anyone who's really pushed the weight on a walking dumbbell lunge is keenly aware of the shoulder and trap working.
"Chest Day": another "day off" for the shoulders, minus the bench press, incline presses, machine press, and tricep dip.
"Back & Biceps": big day for the back of the shoulder, as it's involved in every last one of the pulls and rows. The good news is it can probably relax a bit during the curls.
"Shoulders & Triceps": are we really training shoulders for the first time? And are we able to effectively target all three heads of the deltoid? As written, this workout—while pretty standard—only targets the anterior and medial heads of the shoulder.
In essence, a split training routine has some full body training effects, but because they're largely unintentional the potential benefits may be minimized.
What the Research Says
I looked at a total of seven studies measuring differences in hypertrophy among experienced lifters. Studies were selected for being relevant, recent, peer-reviewed, using well-trained subjects, and measuring hypertrophy (as opposed to strength). The studies compared different training frequencies (per muscle group), and almost all of them were standardized for training volume (weights, sets, and reps). The trainees had on average between one and five years of training experience, and were primarily in their early to mid-twenties. Measurements of hypertrophy including circumference measurement (considered an indirect measure) and direct diagnostic imaging techniques (a direct measure of muscle). The researchers involved are essentially a "who's who" in the field, and include some fairly well known names like Brad Schoenfeld and Bret Contreras.
Of the seven studies conducted, a total of five showed greater hypertrophy in the full body training programs than in the body part split programs. In one study the participants saw an average of 38% more muscle gain over the course of the study.
The remaining two studies were split; one found no substantial difference in hypertrophy rates between the full body and split routines, while the second found that the body part split increased muscle growth rate slightly vs. the full body training group.
As compelling as the evidence in favor of full body training is, it's far from definitive. While all of the studies trained muscle groups once per week on the "low frequency" plan (body part split), the "high frequency" groups ranged in frequency from twice per week to five times per week, depending on the study. Additionally, different muscle groups were measured, population sizes tended to be in the twenties, and study length was typically limited to a few months. As with all research, when you get into the weeds, you seem to find more questions than answers, and while that's part of the fun (a close reading of the researchers involved in the studies reveals a number of them keep coming back for more), it can leave a bro just trying to build some muscle scratching his head.
A Possible Mechanism for The Difference
If full body training really can help advanced lifters not only build muscle, but build more muscle than the traditional bodybuilding splits most of us grew up on, our first hint as to why comes from the terminology in the research itself. While study participants were in fact divided into split routines and full body routines, the researchers refer to the training groups as low frequency and high frequency.
It may all come back to MPS, and to how long it keeps the rate of MPS elevated.
As a new trainee, just about anything builds strength and muscle. Let's be honest: for most of us, that first year in the gym was filled with some pretty stupid stuff, and yet we grew like weeds. In addition to the hormonal cocktail that is a teenage boy's blood (sorry ladies, not so much your blood), some of that comes from how long the uptick in MPS lasts. As a new trainee, I can bench on Monday and expect to see increased muscle protein synthesis for days afterwards, maybe even a week. That means my body part split is just fine; by the time the effects wear off I'm about to hit another bench workout.
For more advanced trainees however, this window of time shortens to closer to 24 hours. If I bench on Monday morning, by Tuesday afternoon my chest is done building more muscle. Wednesday, Thursday, Friday... all just lost time.
The full body workout offsets the shortened window of increased MPS by basically reopening the window more frequently. The graphs below don't represent any actual data, but are meant to be illustrative of the aforementioned concept.
This is far from a perfect representation of the mechanisms behind muscle growth, but the images—as well as the ideas they represent—are striking.
The reason this may work is that while training volume is a critical ingredient in a muscle-building program, MPS is either increased or it isn't. Any work done beyond the stimulus threshold is likely going to waste. That would mean that the key to an effective full body training plan would be to reach the stimulus threshold and then stop, conserving energy for both the rest of the workout and the next day's training.
One final note: all of the studies I looked at kept volume consistent. Sets, reps, and loads were the same across both groups. But it seems fair to assume that by the time your eighth exercise rolls around on leg day you're not putting as much into it as you would if it's the first of second leg exercise of the day (as it was in our example full body program). The increased weights used and the resultant uptick in volume might just be enough to further enhance hypertrophy. I haven't seen any research into this (it would be a hard variable to isolate), but the mechanism and theory is sound.
But What About Bodybuilders?
The sport of bodybuilding is essentially a contest to see who gan build the biggest muscles. And at a rough estimate, more than 90% of bodybuilders I've spoken to follow a split routine. This is a pretty heavy dose of anecdotal evidence, and worth considering. A few thoughts worth keeping in mind:
Correlation does not equal causation.
There may be a substantial role played by pharmacological aids.
Many modern body part splits actually target individual muscles multiple times per week.
What's That Mean for Me?
The research I read is compelling, but not definitive. Still, anecdotal evidence continues to come in on the side of the full body training plan. Pat Davidson's MASS and MASS 2 are both full body plans, and every coach I've worked with in the past few years has written a variation of a full body training plan for me as their best bet to help me put on a few more pounds of muscle. And with more than twenty years of training experience under my belt, I've seen better results in terms of both strength and size with some of these plans than anything I've done in years. Having said all of that, I see three potential paths for you to take:
If you're currently seeing tremendous progress on a body part split, stay the course.
If you're brand new to lifting weights, find something you like and work hard at it. You'll grow regardless provided the effort is there.
If you haven't given full body training a chance, and if you feel like you could be making better progress—or if you just want to play lab rat and see what happens—give it a go.
And for anyone looking for any help or direction with either approach, I'd love to hear from you and see if I can be of service.
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