Research over the past 40 years has explored whether hormonal shifts across the menstrual cycle affect strength, fatigue and recovery. That work has filtered into gyms and social media as simple rules like “take it easy during your period” or “push hard mid-cycle.” The menstrual cycle is driven mainly by estrogen and progesterone, which rise and fall each month and influence how many women feel, move and recover.
Many fitness professionals divide the cycle into four stages:
– Week one: menstruation (bleeding)
– Week two: leading up to ovulation
– Week three: after ovulation
– Week four: before the next period
Trainers often suggest lifting heavier or taking it easier depending on the phase. But what does the science actually show?
Strength and timing: what studies say
A 2024 review searched decades of studies to see how cycle phases influence muscle strength. From 707 studies the authors examined, 22 met strict criteria (regular cycles and clear phase-based strength measurements). On average, women performed slightly better in week two, when estrogen is rising, but the differences were small and varied widely between individuals. Many effects were observed in lab settings or among trained and elite athletes, where tiny margins matter.
Another 2024 study found no meaningful difference in muscle protein synthesis — the process of repairing and building muscle — across cycle weeks. In short, the body is capable of building muscle at any point in the month.
Why cycle syncing is popular
Despite limited and inconsistent evidence for meaningful performance gains, cycle syncing appeals because it offers a framework for adjusting training to how women actually feel across the month. For many, syncing is less about “hacks” to maximize gains and more about using hormonal patterns to guide expectations and manage energy.
Practical adjustments across the month
Workouts combine strength, cardio and mobility, which makes them adaptable to small changes across the cycle.
– Week one (menstruation): Estrogen and progesterone are at their lowest. Many women report cramps, migraines, heavy flow and very low energy, which can reduce exercise tolerance. Reproductive endocrinologist Natalie Crawford advises against pushing to exhaustion during this week; lower-impact or lower-intensity sessions are often more appropriate.
– Week two (pre-ovulation): Estrogen rises while progesterone stays low. Many women feel more energetic and focused. Trainers like Ana Mendes note this phase often supports higher-capacity training — longer runs, HIIT or heavier lifts — because estrogen can help the heart and muscles work more efficiently.
– Weeks three and four (post-ovulation into the luteal phase): After ovulation, estrogen drops and progesterone rises. This is often a maintenance period: some women maintain power and tolerance, others notice reduced performance. Mendes typically recommends lighter loads, slower pacing or more restorative sessions for those who feel a dip.
Irregular cycles and symptom-guided training
Most research assumes regular cycles, but 14–25% of women have irregular periods, and people in perimenopause can experience sudden changes. For these women, strict calendar-based cycle syncing is difficult.
Hormone and wellness coach Emilia Villegas suggests tracking symptoms — energy levels, sleep quality, mood, anxiety and night sweats — rather than relying purely on dates. Symptom patterns can guide training adjustments and also signal excessive training stress. If periods become irregular, it may indicate the need to reassess recovery, nutrition and workload.
The bottom line
Current evidence indicates that the ability to build muscle and strength is not confined to a specific week of the menstrual cycle. Long-term progress depends on consistent training and recovery more than on timing workouts to a particular phase.
Cycle syncing isn’t a guaranteed way to boost muscle gains, but it can help people set realistic expectations, manage fatigue and train more sustainably. “It’s about listening to your body and adjusting what you do,” says Crawford. “Any exercise is better than none. And it’s OK if cycle syncing isn’t for you.”
Mendes follows a similar approach: on low-energy days she doesn’t cancel sessions, she modifies them — reducing load and increasing repetitions, for example. Understanding recurring shifts in energy can help women train smarter, avoid burnout and stay engaged.
Edited by: Zulfikar Abbany