Women are sorely underrepresented in exercise science. There’s a variety of reasons for this, but one of the more pervasive causes is a misunderstanding of the impact of female biology. Let’s cover some basics.
The menstrual cycle involves a follicular phase, followed by ovulation, followed by the luteal phase. During these different phases, hormonal profiles can vary substantially.
As a result, exercise scientists have long assumed that the phase of the menstrual cycle participants are in will confound any research they conduct. Not only was it assumed that performance in the gym would be impacted, but the resulting size and strength gains would be influenced by the phase of the menstrual cycle participants were in, too.
Unfortunately, alongside other issues, this misunderstanding has translated to social media platforms, where popular influencers will frequently recommend the practice of “cycle-syncing” – or, simply put, the practice of periodizing training based on menstrual cycle phase.
The science on the topic is, to put it bluntly, quite weak. A systematic review by Colenso-Semple et al sought to review all existing meta-analyses and systematic reviews looking at the influence of menstrual cycle phase on both acute performance and gains in size and strength.
The results of existing meta-analyses and systematic reviews are mixed at best. Performance in the gym isn’t consistently better or worse in a certain phase of the menstrual cycle. Similarly, there’s insufficient research to support the idea that training should be cycle-synced for best gains. The two studies that most strongly supported the notion of cycle-syncing had several issues (1, 2).
First, like many other studies on the menstrual cycle, the studies didn’t properly validate that subjects were in the intended menstrual cycle phase. In one study, an elevation in body temperature was used as a proxy. In the other, it was assumed that the follicular phase and luteal phase would span precisely days 1-14 and days 15-28, respectively. Neither of these assumptions is always accurate – combine this with relatively small sample sizes, and it becomes relatively likely that we’re dealing with false positive findings, particularly given the direction the overall body of research is pointing.
Still, we unfortunately don’t have much research actually measuring hypertrophy from cycle-synced vs non-cycle-synced training approaches. To better inform our understanding, we can turn to a recent study by the same authors on muscle protein synthesis rates from lifting weights during the follicular vs luteal phase.
As a reminder, it’s commonly hypothesized that you’ll see greater muscle hypertrophy in the follicular phase compared to the luteal phase, due to higher estrogen and lower progesterone levels.
The authors confirmed female participants’ menstrual cycle timing through several months of menstrual cycle history and using blood testing to compare actual hormonal levels with predicted hormonal levels based on cycle phase.
Then, when estrogen and progesterone were at their highest, respectively, participants completed a standardized resistance training workout. For the following 6 days, myofibrillar protein synthesis rates were measured.
Contrary to popular belief, protein synthesis rates were similar when the workout was performed in either phase. While this is only a single study, it comports well with a previous investigation by Miller, which also found similar protein synthesis rates.
So, where does all this science leave us, practically?
On average, there’s no reason to train differently based on menstrual cycle phase. However, one common theme in this body of research is variability. The duration of phases vary. The symptoms experienced in each phase by different participants vary. As cliché as it may sound, “listening to your body” is likely the way to go here. Set up a consistent training program but remain flexible and autoregulate based on how you’re feeling that day. Over time, you may learn that you tend to perform better or worse in different parts of your cycle; for the time being, this is all the cycle-syncing you need to worry about.