Are full-body splits best for muscle growth?

Take-aways

1. All else being equal, training a muscle group more frequently may lead to more muscle growth.

   1. Practically, try training each major muscle group at least twice a week and up to 4-5x/week if you seek best results for that muscle group.

2. Don’t forget that compound movements will provide stimulus for a variety of muscle groups at once, contributing to weekly frequency.

3. This effect may be mediated by better performance across the week or via more frequent increases in muscle protein synthesis.

Training frequency refers to how often an exercise/muscle group is trained across the week. For instance, if you’re doing two upper-body and two lower-body days a week, each muscle group would be trained 2x/week.

A question arises. What frequency is best for muscle growth? What split should you be following? This is what a meta-analysis by the good folks over at Stronger By Science tried to answer.

Thirteen studies were included in the analysis. Studies needed to be volume-equated to be included.

Here’s what they found.

When frequencies were simply categorized into “higher” and lower”, higher frequencies resulted in significantly more hypertrophy, though the effect size was statistically “trivial” (d = 0.11; 95%CI: 0.07-0.16).

When frequency was instead viewed as a continuous variable (from a muscle being trained 1x/week to 6x/week, above), a positive linear relationship emerged. Each additional day of frequency led to 22% more growth, on average.

Finally, it’s worth noting that the positive effect of frequency is generally larger in the upper- vs lower-body, greater in untrained vs trained lifters and more meaningful with lower- vs higher- volumes.

Why?

A few different interpretations can be formed as to why higher frequencies lead to more muscle growth. The first is that spreading the training for a given bodypart across the week leads to a higher workload. As we’ve previously discussed on the newsletter, volume load does appear to be predictive of muscle growth stimulus. So, if by spreading out the work for a given muscle across the week, we can accumulate more tonnage, this may be positive for muscle growth.

It may also have to do with the molecular processes underlying muscle growth. Whenever you train a muscle group, you increase the rates of muscle protein synthesis, the process through which muscle is built. Importantly, this increase is relatively short-lived, generally only lasting for 48-72 hours at the most. So, if you train a muscle more frequently across the week, you may spend more time in a state of elevated muscle protein synthesis.