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Your optimal training frequency will depend on your genetics, lifestyle, etc. As a rule of thumb, though, higher frequencies – to a point – will allow you to do more weekly volume for a bodypart while still recovering between sessions. For muscle growth, frequencies of 2-6x/week are usually optimal. Use trial and error to determine the muscle group training frequency that allows you to do the most weekly volume while still recovering, and you will have found what your optimal frequency is. From there, using slightly lower frequencies can be helpful for preventing the build-up of staleness across multiple mesocycles, while slightly higher frequencies can be useful for functionally overreaching and maximising volume and growth short-term, but usually aren’t sustainable.

Why is frequency important?

The primary reason why frequency is important is because the relationship between muscle growth and per session volume (hard sets/bodypart) is likely that of an inverted-U.

As the volume in a session increases, up to a point, the growth stimulus (usually measured via Muscular Protein Synthesis) from that session increases. However, at a certain point, the growth stimulated plateaus. Past that point, net growth will potentially even begin to reduce (e.g. rhabdomyolysis, in extreme circumstances).

If you recall from my article on volume, weekly training volume (hard sets/week/bodypart) has a positive relationship with growth, provided you can recover. Thus, once weekly volume has been determined, it becomes a matter of distributing volume across enough sessions to maximise net weekly growth – which is the sum of the growth incurred in each session (and breakdown across the week).

Importantly – the U-shape of the relationship implies that the first few sets of a session for a bodypart are also the most stimulative of muscle growth. As sets are added, the marginal hypertrophic stimulus decreases, until it eventually becomes 0 and finally increasingly negative.

When should I train a bodypart again?

How much growth volume induces is only one part of the equation. What will determine how often and when you should train is the fatigue induced by training and how long it takes you to recover from it.

As per session volume increases, fatigue will also increase. However, fatigue will increase in a manner that is likely closer to linear in nature (i.e. the first set will add about as much fatigue as the 2nd, and the 2nd as much as 3rd) than stimulus.

Because of this, a session with 10 sets will grow you more than a session with 5 sets – provided that amount of volume is on the left side of the graph – but will also fatigue you much more, such that the trade-off between stimulus and fatigue is an important consideration. Not only that, the amount of fatigue induced and your ability to recover will be the bottleneck/rate-limiting step for you to train again productively. In other words – intuitively enough – if you do more volume, you’ll want to wait more time before you train that bodypart again. The more volume you train a bodypart with in each session, the longer you will have to wait for it to recover and to train it again, and vice versa. Therefore bodypart splits “work” relatively well – the amount of weekly volume you’re able to accumulate is still reasonable, even if frequency is low.

What does the evidence say, anyways?

Over the past few years, there have been two meta-analyses –studies where you combine the results of several studies to be able to draw more robust conclusions – with regards to muscle growth and training frequency.

The first found that, on a volume-equated basis, (i.e. if the amount of sets, reps and weight used are the same and the only difference is frequency) training a muscle group twice a week was superior to training it once a week. However, no significant effect of higher frequencies was found.

The second found that, on a volume-equated basis, training a muscle group more often was better for muscle growth. The marginal benefit of additional frequency was larger for the upper body than the lower body, larger for untrained lifters than trained lifters and larger for lower volumes than higher volumes.

There’s a third in-house meta-analysis by James Krieger, but that one is behind a paywall, so I’ll omit it from this discussion, but read it if you’d like.

Based on these findings, it seems that, even on a volume-equated basis, there is either no difference between lower and higher training frequencies for growth, or there is a benefit in favour of higher frequencies.

Importantly, this analysis was on a volume-equated basis. It does not account for the extra stimulus one would accrue from being able to lift heavier/do more reps due to being less acutely fatigued intra-session and/or being able to do more sets/week/muscle group.

A practical perspective

Training frequency is important for muscle growth. However, it is not as influential as training volume for growth and is often more impractical than manipulating load. Let me explain – higher frequencies/muscle group/week can only be used if you’re training quite often already. In addition, using very high frequencies also extends training time – indeed, if you’re training 5 different bodyparts in the same session, you’ll probably need to spend some time warming up for each, and the systemic fatigue from training lower body, for example, will “spill over” and somewhat elongate rest periods for the rest of that session. One strategy to counter this is to train lower body at the end of a training session, but that suffers from a meaningful drawback – training it last will also likely reduce how much growth it induces.

Moreover, while very high frequencies do allow for recovery from higher volumes than lower frequencies – I’ve gone as high as 200 sets total in a week very near failure on the week before a deload before – they also wear you out like nothing else can. Most people I’ve spoken to – myself included – have reported feelings of burn-out, psychological staleness and amotivation following several mesocycles of high frequency training. In my experience, it’s mostly due to how high volume it is. Most sessions looking rather similar and training very frequently are smaller but notable contributors to feelings of burn-out.

As such, if you are in a position where you can train often enough to even consider it (i.e. you have enough free time to train as often as ~5-10 total sessions/week), I would recommend periodizing frequency. Here’s a sample example of how I would periodize frequency: