Training frequency is one of the variables one must consider when building a program for muscle growth, and it refers to how many times per week you train each muscle group. It might not be as important as training volume, but the two are intrinsically connected, as frequency will determine how you distribute your weekly volume for each muscle group. When done correctly, manipulating frequency will improve the relationship between training stress and recovery, so that you get the most out of each session (not doing too much or too little) and have an adequate recovery time until you train that muscle group again.
A common gym practice is to train each muscle group once per week (twice for biceps and triceps), with high volumes per session (15+ sets per muscle group). However, in recent years, higher-frequency training has been gaining popularity. Therefore, the purpose of this article is to analyze the data on the impact of training frequency on hypertrophy and, based on that, give some practical applications.
Before we take a look at some of the studies on the topic, let me state that all the individual studies referenced in this article are volume-equated. In other words, in each study, the participants in both the higher and lower frequency groups did the same total weekly volume (i.e., the same number of sets per muscle group). For example, if a study compares two groups, one using a frequency of once per week (F1) and the other using a frequency of three times per week (F3), both will do the same weekly volume. For 15 sets per muscle group per week, the subjects from F1 will do those 15 sets for a given muscle group in just one session, while the subjects from F3 will divide the 15 sets into 3 sessions and do 5 sets for a given muscle group in each session (15/3=5).
This is important because, by keeping the volume between the two groups equated, the only variable that’s different between groups is training frequency. Otherwise, the higher frequency would typically also do more volume. If this happens, and the results show that the higher frequency group gained more muscle, we don’t know for sure whether it’s because of the higher training frequency and/or the higher training volume.
Now, let’s take a look at some of the available data. I gathered seven individual studies (all randomized control trials), one systematic review, and two meta-analyses (a study of individual studies on the same topic).
First, two of the studies showed superiority for higher training frequencies: the first  compared a frequency of 3 vs. 1 time per week for the quadriceps and 3 vs. 2 times per week for the biceps and triceps. This study found that training each muscle group 3 times per week resulted in greater gains, specifically for the biceps (and approaching significance in favor of 3 vs. 1 for the quadriceps). The second  compared a frequency of 5 vs. 1 time per week for the quadriceps and 5 vs. 2 times per week for the biceps and triceps and found that training each muscle group 5 times per week resulted in greater gains, specifically for the biceps and quadriceps.
Despite these two studies giving superiority to higher training frequencies, most research I came across found no significant differences between higher and lower frequencies on hypertrophy [3-7]:
One study  comparing a frequency of 2 vs. 1 time per week showed no differences between frequencies, but a potential benefit for the higher frequency group.
Two studies showed no differences between frequencies, but a potential benefit for the lower frequency group: the first  compared a frequency of 3 vs. 2 times per week, and the second  compared a frequency of 6 vs. 3 times per week.
Finally, two studies showed no differences whatsoever between different training frequencies: the first  compared a frequency of 2 vs. 1 time per week for the deltoids and quadriceps and 4 vs. 2 times per week for the biceps, and the second  compared a frequency of 5 vs. 1 time per week.
Now, let’s see what the meta-analyses and systematic review tell us about the impact of training frequency on hypertrophy.
The first meta-analysis  looked at 7 studies (5 were volume-equated) and concluded that training each muscle group at least 2 times per week might be superior to one time per week. However, the authors couldn’t draw conclusions for higher frequencies (e.g. 2 vs. 3+).
The systematic review  looked at 28 studies (12 were volume-equated) and supported the conclusions of the earlier meta-analysis, stating that frequencies of 2+ times per week might be better than 1 time per week. They also added that frequency potentially plays a secondary role in hypertrophy and, given the importance of volume, you can use higher frequencies to increase your weekly volume.
The final meta-analysis  looked at 25 studies (13 were volume-equated) and concluded that, on a volume-equated basis, frequency has a negligible impact on hypertrophy and that you can choose based on your preference. However, when volume is not equated, it seems that frequency has a greater impact as it generally allows for more volume. This supports the view of the authors of the previous systematic review that you can use higher frequencies to increase weekly volume.
Given all this data, I think it’s safe to assume that the number of times you train each muscle group per week doesn’t play a huge role in hypertrophy. However, it seems that training each muscle group at least 2 times per week is better than training just once. Therefore, training each muscle group at least 2 times per week seems to be a good idea in most situations for most people. Unfortunately, there’s still not enough data to know whether higher frequencies (3+) are better and, if they are, at what point it becomes detrimental.
As suggested in the systematic review  and meta-analysis , training frequency can be used as a tool to increase your weekly volume, which seems to be a more important variable for hypertrophy. Generally, higher frequencies will allow for greater weekly volumes and probably better “quality volume” per session. To illustrate this last point, consider these two scenarios:
Scenario 1: On Monday, you do 4 sets of bench presses, 4 sets of incline dumbbell bench presses, 4 sets of weighted push-ups and 3 sets of cable flyes (total weekly volume for the chest: 15 sets).
Scenario 2: On Monday, you do 4 sets of bench presses and 4 sets of incline dumbbell bench presses, and, on Thursday, 4 sets of weighted push-ups and 3 sets of cable flyes (total weekly volume for the chest: 15 sets).
In scenario 1, once you get to the push-ups (and then the flyes), your pecs will probably be very fatigued from all the pressing (assuming you’re doing every set close to failure; make sure that's the case!), and, because of that, your performance in those exercises will be far from optimal. In scenario 2, by doing the push-ups and the flyes another day, you will perform those exercises while your pecs are still “fresh.” Your performance will probably be much better, and you’ll be able to lift more weight and/or do more reps per set. That extra volume, accumulated over time, can make a difference.
Now, you might be thinking: “Why not split the 4 exercises into 4 sessions and do one exercise in each session? That way you’ll always do each exercise fully fresh and get the most out of it.” In theory, that can totally work. However, as you increase your training frequency, you must pay more attention to your recovery. It’s paramount that whatever training frequency you choose, you make sure your muscles and connective tissue have enough time to recover between sessions. There’s no point in increasing your training frequency if you cannot recover from session to session.
The last point I want to make is that, as with training volume, there’s likely to be individual variability to higher training frequencies, meaning some people can handle it better than others and will have better results. The only way to find that out is to experiment with different frequencies and per session volumes and see what works best for you.
You should probably train each muscle group at least 2 times per week; choose based on your weekly volume, recovery capacity, and preferences.
You can use frequency as a tool to increase weekly volume and perform more “quality sets” each session.
Whatever frequency you choose, make sure you train a given muscle group only when it’s recovered from its previous session.
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