'Cycle-Syncing': Fact or Fiction

Research Writer: Sophie J.

Editor: Linette Borges

It has been well-established that hormones play a crucial role in maintaining our body’s balance, or in the more appropriate scientific terms, homeostasis (Campbell & Jialal, 2022). The maintenance of which allows our bodies to perform all life sustaining functions, most notably that of reproduction. Reproduction is heavily influenced by a slew of hormones that work to fertilize, and eventually, enable the formation of an embryo.

From Kissow et. al. (2022).

The intricacies of the menstrual cycle have long been studied, but so far scientists have distinguished 4 main ‘phases’; first the menstrual phase, then the follicular phase, the ovulatory period and the luteal phase. The main hormones of interest across the cycle include estrogen and progesterone, which fluctuate relatively predictably within an individual throughout their cycle. Across the follicular phase, especially in the late half, estrogen peaks. Whereas, in the luteal phase, specifically mid-luteal, progesterone peaks. However, it is important to note that each phase may be variable in length and hormonal profile, as large inter-individual variations are more common than uncommon among those menstruating (Kissow et. al., 2022). These differences can include anything from length of the entire cycle, length of phases, hormone levels and psychological welfare throughout phases. 

From Kissow et. al. (2022).

However, the scope of these hormones is not limited exclusively to the reproductive system. Estrogen specifically has been found to bind to receptors in muscle and engage an enzyme called 5’ AMP-activated protein kinase (or AMPK). This causes a cascade of events that eventually targets satellite cells, whose presence around muscle is thought to be indicative of protein anabolism, or muscle growth (Kissow et. al., 2022). On the flip side, progesterone has been proposed to catabolize or breakdown protein, creating an effect that works against that of estrogen (Colenso-Semple et. al., 2025). 

From these hypotheses, it has been proposed by some parties that athletic training structure should reflect hormone levels. That is to say that, females should capitalize on these hormonal fluctuations to build their training program and activities across the cycle in accordance with whichever hormone is present. The question is, is this a valid methodology for female athletes?

The resounding answer to which, in the literature to date, seems to be ‘we don’t know’. For instance, a recent study conducted out of McMaster by Colenso-Semple et. al. (2025) finds no muscle mass response differences across the entirety of the cycle with resistance exercise. Whereas, a group of studies discussed by Kissow et. al. (2022) finds that training during the estrogen-rich follicular phase enhances muscle mass in leg muscles of females. 

One of the largest issues contributing to the lack of clarity on the subject, remains that the female body is extremely complex; especially in physically active populations. Among active females, the prevalence of conditions like anovulation (lack of ovulation) and luteal phase-related hormonal deficiencies falls around 30%, and that doesn’t even account for the large percentage of young females taking contraceptives to exogenously alter hormone levels (Thompson et. al., 2020). Additionally, some studies fail to quantifiably determine the phase in which their participants are exercising, others combine contraceptives with non-contraceptive participant groups, and more did not test participants at all points throughout their cycle (Thompson et. al., 2020). 

So the question no longer becomes, is cycle syncing valid, but rather what standardized methodologies must we employ to establish a baseline for menstrual phase-related research?

Due to the lack of standardized processes for the methods by which the menstrual cycle is studied, there can be little investigation into its specific impacts in a way that is both reliable and reproducible in the scientific community. Therefore, if you ever find yourself listening to someone telling you the benefits of cycle-synching for your resistance training protocols, take a moment to consider that the scientific community has yet to come to a consensus on how to properly study the subject.

References 

Campbell M, Jialal I. Physiology, Endocrine Hormones. [Updated 2022 Sep 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538498/

Colenso-Semple, L. M., McKendry, J., Lim, C., Atherton, P. J., Wilkinson, D. J., Smith, K., & Phillips, S. M. (2025). Menstrual cycle phase does not influence muscle protein synthesis or whole-body myofibrillar proteolysis in response to resistance exercise. The Journal of physiology, 603(5), 1109–1121. https://doi.org/10.1113/JP287342

Kissow, J., Jacobsen, K. J., Gunnarsson, T. P., Jessen, S., & Hostrup, M. (2022). Effects of Follicular and Luteal Phase-Based Menstrual Cycle Resistance Training on Muscle Strength and Mass. Sports medicine (Auckland, N.Z.), 52(12), 2813–2819. https://doi.org/10.1007/s40279-022-01679-y

Thompson, B., Almarjawi, A., Sculley, D., & Janse de Jonge, X. (2020). The Effect of the Menstrual Cycle and Oral Contraceptives on Acute Responses and Chronic Adaptations to Resistance Training: A Systematic Review of the Literature. Sports medicine (Auckland, N.Z.), 50(1), 171–185. https://doi.org/10.1007/s40279-019-01219-1