Training volume and frequency are currently hotly debated. For good reason, as these are fundamentally important considerations for the design of a training program. Over the last year, several studies have reported surprising and seemingly conflicting results. One study says higher training frequencies improve muscle growth, the next says they don’t. One study suggests the optimal training volume is as high as 45 sets, the next says doing more than 10 sets is counterproductive and reduces your gains. Here I’ll lay out a theory that makes sense of all these findings.

Let’s look at all studies so far that found detrimental effects of higher training volumes compared to lower ones.

2 Studies by Barbalho et al. (2018, 2019) find that when training a muscle only once per week and trying to train to true momentary muscle failure, the optimal training volume is only 5-10 sets per week. Groups doing 15 and 20 sets per week achieved worse muscle and strength gains.

Amirthalingam et al.’s 2017 German Volume Training study showed better gains in strength and size with 5 instead of 10 sets of their primary exercise per workout. The total set volume per workout was around 9 in the medium volume group compared to 14 in the high volume group.

Heaselgrave et al. (2019) found a trend for an optimal training volume of 18 sets per week for the biceps: groups training with 9 and 27 sets achieved worse overall strength and muscle development. The medium and high volume groups trained their biceps twice per week, so the high volume group performed 13-14 sets per workout for the biceps compared to 9 sets for the medium group.

The common interpretation of these studies is that they show there’s an upper limit of training volume you can do in any week. But were they really training with too much volume…. or too little frequency? Total volume was not that extreme in any of these studies. It was only 5-10 sets per week in the Barbalho et al. studies and below 30 sets in the other 2 studies. In contrast, Radaelli et al. (2015) and Schoenfeld et al. (2019) both found overall greater muscle with 45 compared to 30 sets per muscle per week, which in turn led to greater overall muscle growth than doing 15 sets per muscle. The difference with these studies is that they trained each muscle 3x per week, so the 30-set groups were still ‘only’ doing 10 sets per muscle per workout.

Together, these results suggest that productive training volume is limited to 9-13 sets per muscle group per workout. The exact optimal volume likely depends on the specifics of the training program, in particular how close to failure you’re training, and individual factors like genetics.

It makes sense that you can only stimulate so much muscle growth in one workout. The body’s adaptive capacity is limited. Evolutionarily speaking, it also wouldn’t make sense for the body to morph into The Hulk after a single day of extreme manual labor. Adaptations are only desirable against stresses that repeat over time.

There’s also a limit to the amount of quality volume you can do in a session. The accumulation of neuromuscular fatigue and muscle damage can reduce performance, muscle activation and mechanical tension further and further with each extra set. Not to mention mental fatigue and dwindling training motivation.

As a result, after doing about 10 sets you may not be able to increase muscle protein synthesis (MPS) further anymore. Research in rats supports that several anabolic signaling pathways and MPS plateau around the 10-set mark: see the figure below.

Source

Continuing to train after this point may result in negative protein balance as you only further increase muscle protein breakdown levels without stimulating more muscle growth. The increased muscle damage may also delay net muscle protein synthesis, so if you train again too soon afterwards, you may end up in negative protein balance over time and lose muscle mass.

A maximum productive training volume per workout would also explain why some but not other studies find benefits of higher training frequencies. Most of the studies that find benefits of higher training frequencies are in trained lifters with higher training volumes. Conversely, there are many studies where training frequency does not seem to matter independent of training volume and these studies are mainly done with training volumes below 10 sets per week. I think enough data are available now that the interaction between training frequency and volume can be formally analyzed in a meta-analysis to verify this. James Krieger has already unofficially reported such a trend.

Practical application

If productive training volume is indeed limited to 9-13 sets per muscle group per workout, this has major implications for training program design and exercise science.

The traditional bro split where each muscle is trained once a week with a very high volume is most likely suboptimal. Higher training frequencies should be employed with higher training volumes.

Training volume should be considered on a per-workout basis, not just on a total weekly basis. Bench pressing 3x per week with 10, 5 and 3 sets per session may have worse results than doing 6 sets each session.

Researchers should carefully consider both training volume and frequency when trying to study either and contextualize their results accordingly.

Training volume should be optimized with training frequency in mind, not separately. Even if someone should theoretically handle 30 sets, it may not be a good idea to do it if they’re only training 2x per week.

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