The Best Look at Training Frequency for Muscle Growth Yet
Only have a second? Check out the takeaway below. Have 5 minutes? Check out the rest of the newsletter.
TRAINING TAKEAWAY: On the group level, frequency does not seem to influence muscle growth at a given training volume. However, if increasing frequency results in meaningful improvements in training performance for an individual, it may result in more muscle growth.
The optimal training frequency for muscle growth has been subject to a lot of debate. Some experienced lifters advocate for performing the week’s volume within 1-2 sessions, while others prefer to split volume up over more sessions per week. A new study by Neves. et al. provides novel insight on this topic.
Background
The theoretical grounds for higher frequency training seem intuitive, particularly in trained individuals. This is due to acute elevations in myofibrillar muscle protein synthesis (mMPS), which is a potential proxy of muscle growth (1, 2). All else equal, with more "area under the curve" for mMPS one could plausibly suspect greater muscle growth. In trained individuals, spikes in mMPS following a training session seem to return to baseline more rapidly than in untrained individuals. This difference could highlight a potential advantage of higher frequencies: staying in positive net protein balance for more time throughout the week.
There is another compelling argument for higher frequencies based on performance. Consider an example with 12 weekly sets prescribed for the biceps. Total performance (defined as volume load: sets x reps x load lifted) will often be superior by breaking up those sets into separate sessions (e.g., three sessions with four sets each) versus performing all 12 sets in one session. Over time, these differences in performance could lead to greater hypertrophy.
However, relying on proxies of applied outcomes can be misleading. When looking at the applied data, a well cited meta-analysis by Grgic and colleagues can be summarized succinctly: frequency does not meaningfully influence muscle growth when weekly set volume is equated. The authors made multiple comparisons of studies examining different training frequencies that boil down to the fact that not much is going on, especially when direct measurements of muscle size are used (e.g. ultrasound, MRI).
However, one critical limitation of this research is that there are few within-participants designs. As we’ve discussed before, since each participant serves as their own control, these designs control for individual differences in factors like nutrition, sleep, stress, and previous training history. Thankfully, the new study by Neves et al. rectifies this limitation and provides the best look at training frequency to date.
Study Overview
Neves et al. employed a simple yet elegant design to investigate frequency's effects on muscle growth. Twenty-four trained men completed an 11-week training study following a thorough 4-week familiarization period. The researchers randomized participants into one of two overarching conditions: volume load equated or not volume load equated. To avoid confusion, I will refer to these conditions as the "flexible" and "restricted" progression groups for the rest of the newsletter as I feel these terms better describe what's going on.
After the initial randomization, the participant's limbs were randomly assigned to a low (one session per week) or high (three sessions per week) frequency protocol. Each limb completed a linearly periodized unilateral leg press program (moving from 12RM to 8RM load over time) and performed nine sets per week. Unfortunately, rest periods between sets were not specified. Before and after the 11-week training program, quadriceps cross-sectional area (CSA) was evaluated by magnetic resonance imagining. For participants in the flexible progression group, both limbs were allowed to progress independently. However, in the restricted progression group, the high-frequency limb was required to equate their average load to the low-frequency limb and perform the same total number of repetitions.
For example, if the low-frequency limb performed nine sets with an average load of 100kg and a total of 108 repetitions, the high-frequency limb was required to match that even if their performance allowed for higher loads and/or more reps. Typically, higher frequency training allows for greater training performance and thus greater volume loads. Since this element of frequency was removed in the “restricted” group, this design essentially isolates training frequency itself. This protocol comes with the limitation that proximity to failure (RIR) and load (% of 1RM) were almost certainly not controlled. That said, having both groups in the same study can help to account for the other's weaknesses.
Importantly, this design rectifies many of the limitations of previous research investigating the effect of training frequency on muscle growth:
Within participants design
High quality measure of muscle size
Trained participants
Equates set volume
Tests the inherent performance benefit of higher frequencies vs. frequency itself
Results
Following the training program, no significant frequency x time interaction was observed for gains in quadriceps CSA for either progression condition (p = 0.310). So, in general, the frequency in which a limb trained with didn’t seem to influence gains in muscle size. However, the authors reported a significant moderate effect size of 0.63 [0.21 - 1.10] comparing the changes in muscle size of the high and low frequency limbs in the flexible progression condition (p<0.05). The type of effect size that was calculated is called Cohen’s dz. This value is what's called a signal-to-noise effect size that is used to primarily quantify the consistency of a change rather than the magnitude of a change. When calculating a more typical magnitude-based effect size, we get d = -0.14 [-0.94 - 0.65], indicating a non-significant trivial difference between training frequencies.
This distinction helps to illustrate the main takeaway from this study: higher training frequencies don’t seem to offer an inherent meaningful advantage. This is evidenced by the fact that the restricted progression group saw essentially no difference between frequencies when volume load was equated (d = -0.01 [-0.81 - 0.79]).
However, higher training frequencies allow you to perform less sets under fatigue, consequently improving overall performance. In support of this point, the higher frequency condition in the flexible progression group performed ~16% more total volume load than the lower frequency condition. While the magnitude of the difference between frequencies in gains of muscle size in the flexible group would be considered trivial, they tended to favor higher frequency training. Overall, this provides some indication that the superior performance may have led to better outcomes.
The analysis I would have loved to see is a correlation between the difference in volume load between frequencies and the difference in gains in muscle size between frequencies. I suspect that individuals who fatigue heavily after a set to failure likely benefited considerably from higher frequencies. For these individuals, higher frequencies would allow for substantially higher total volume load. On the other hand, lifters that can easily maintain performance across multiple sets may not need a higher frequency. Moreover, I’ve heard anecdotes that some lifters take quite a few sets to “build momentum” within a training session. This could potentially help identify those who would benefit from lower frequencies. Looking at the individual data, this seems plausible as some individuals definitely benefited from the higher frequencies more than others.
Practical Applications
Overall, this study does an excellent job highlighting the potential effects of frequency on muscle growth. On the group level, this study supports the findings of Grgic et al. that frequency doesn’t seem to meaningful change outcomes when weekly set volume is controlled. However, on the individual level, the logistical benefits of higher frequency training may allow some lifters to perform considerably better and accumulate more total volume load. For some, this could lead to superior hypertrophy.
While determining the optimal training frequency for muscle growth on an individual level is an art as much as it is a science, I’ve provided a systematic approach to manipulating frequency that I hope can be useful.
