You Could Be Training Against Your Hormones Every Month, and Exercise Science Is Only Now Catching Up
The global femtech market hit $66.2 billion in 2025 and is projected to reach $255.5 billion by 2035, with cycle syncing apps and hormone-tracking wearables leading the surge. The science driving the trend, though, is moving slower than the marketing. A major Karolinska Institutet trial expected to be published in 2026 could reshape what people actually know about training with their cycle.
The premise is straightforward: the four phases of the menstrual cycle create distinct hormonal environments that may shift energy, strength, endurance and injury risk. The harder question is whether tailoring workouts to those phases actually delivers meaningful results.
How Your Hormones Change Across the Month
Cycle-based training divides the month into two main windows anchored by ovulation. The follicular phase, running from day 1 through roughly day 14, is when estrogen rises and most women report higher energy and motivation.
The luteal phase, days 15 to 28, is dominated by progesterone, which researchers have long flagged as catabolic and potentially disruptive to muscle contractions during hard efforts.
A December 2025 narrative review in Frontiers in Endocrinology confirmed estrogen’s role in substrate metabolism, cardiopulmonary function and thermoregulation during exercise, with aerobic performance tending to run higher in the follicular phase.
A 2022 randomized controlled trial by Kissow et al. in Sports Medicine found that concentrating resistance training in the follicular phase produced greater gains in muscle strength and volume than luteal-phase training, currently the strongest objective evidence for phase-based strength periodization.
Where the Cycle-Syncing Science Gets Complicated
The picture gets murkier from there. A 2023 umbrella review from McMaster University in Frontiers in Sports and Active Living examined the full body of available meta-analyses and systematic reviews on the topic and concluded it’s premature to say hormonal fluctuations meaningfully influence acute strength performance, pointing to poor and inconsistent methodology across studies as the main driver of conflicting conclusions.
The January 2026 FENDURA project, published in the European Journal of Sport Science, measured modest differences in ventilation, heart rate and perceived exertion between phases in trained women during endurance work, but its authors concluded overall session demands were not substantially altered in any single phase.
Researchers broadly agree on one root problem: women have historically been excluded from exercise science research, leaving thin data and wide individual variation. That’s part of why the Karolinska IMPACT trial matters. The rigorous randomized controlled trial wrapped data collection at the end of 2025 testing whether cycle-based periodized training improves aerobic performance in trained women. Results are expected in 2026.
Why Injury Risk Gets Its Own Conversation
Elevated estrogen around ovulation increases ligament laxity, a documented ACL risk factor. A March 2025 review in Sports Health found the link between cycle phase and ACL injury risk is real but complex, with inconsistent findings across studies. The review notes that neuromuscular coordination may matter as much as ligament flexibility, meaning strength and technique likely play a larger role than timing alone.
What This Means for Your Own Cycle-Based Workouts
The most defensible takeaway right now is practical. A February 2025 qualitative study in Frontiers in Sports and Active Living found recreational women consistently perceived energy, motivation and strength as highest in the late follicular phase and around ovulation, with a clear drop after. That subjective experience holds up even where the lab data is mixed.
The Harvard Apple Women’s Health Study noted in a May 2025 update that women who exercise regularly show lower all-cause mortality than male counterparts at equivalent activity levels.
The translation for most people: consistency still beats perfect periodization. If adjusting intensity around your cycle helps you show up and train more consistently, the science supports that approach even if it doesn’t yet fully explain why.
This article was created by content specialists using various tools, including AI.
