Science Says It's Time to Rethink Cycle Syncing for Strength Training
The idea that women should tailor their workouts to different phases of their menstrual cycle has gained momentum in recent years, fueled by claims that hormonal shifts can enhance strength, muscle growth, or resilience to fatigue. The premise sounds intuitive: during the low hormone phase (early follicular phase), when estrogen is in play, the body is thought to be in a more anabolic, muscle- and exercise-ready state. In the high hormone phase (luteal phase), when progesterone peaks, anabolic resistance is believed to increase, warranting adjustments and accommodations in training.
But a recent publication in The Journal of Physiology challenges this widely accepted narrative. Prominent muscle physiology researchers found no meaningful differences in muscle protein synthesis or breakdown across menstrual phases in response to resistance training. Simply put, muscle adaptation to strength training appears unaffected by hormonal fluctuations. Yet cycle syncing has become a prominent topic in cultural conversations about fitness, amplified by many voices on social media.
While many women feel different at various points in their cycle, the idea that workouts should be structured around hormonal changes is more rooted in popular belief than in scientific evidence. If the data doesn’t support these claims, what should guide training decisions instead?
Exercise Matters, Not Hormones
Researchers recruited 12 naturally menstruating women and used rigorous methods—including blood hormone analysis, urinary ovulation tests, and muscle biopsies—to accurately determine their menstrual cycle phases. Participants completed two separate six-day resistance training protocols: one in the late follicular phase (high estrogen) and one in the mid-luteal phase (high progesterone).
Each participant trained one leg in each phase while keeping the other leg untrained as a control. This within-subject design allowed the researchers to directly compare how muscle protein synthesis (MPS) and myofibrillar protein breakdown (MPB) responded across menstrual phases. The use of stable isotope tracers and unbiased metabolomics provided a detailed look at physiological responses that extend beyond simple performance markers, ensuring the most precise measurement of muscle adaptation.
(Photos: The Journal of Physiology)
Resistance training significantly increased muscle protein synthesis, but menstrual cycle phase had no impact on muscle protein metabolism. Whether participants trained in the follicular or luteal phase, their muscles responded in the same way. In the follicular phase, muscle protein synthesis rates measured 1.52 percent per day in the trained leg. In the luteal phase, rates were 1.46 percent per day in the trained leg— a difference too small to be statistically significant.
Likewise, whole-body protein breakdown showed no meaningful variation between phases, indicating that progesterone does not accelerate muscle protein degradation as some have suggested. Researchers also analyzed blood samples using metabolomics and found no evidence of phase-specific metabolic changes relevant to muscle adaptation.
These findings align with previous research suggesting that hormonal fluctuations throughout the menstrual cycle do not significantly impact strength or endurance performance. While small studies have occasionally hinted at phase-based differences in exercise capacity, larger and more rigorously controlled trials have repeatedly failed to confirm any meaningful effects.
Notably, only about 12 percent of women have a textbook 28-day cycle with ovulation precisely on day 14. Given this variability, relying on cycle phase to structure training routines is impractical.
What This Means for Women Who Lift
The key takeaway? Your menstrual cycle phase doesn’t determine your training results. If you’ve been hesitant to lift heavy weights during certain phases, you can let go of that fear. These findings reinforce what exercise scientists have suspected for years: menstrual cycle phase does not meaningfully affect muscle protein metabolism in response to resistance training. Hormonal fluctuations may influence subjective factors like mood or energy levels, but they don’t dictate whether your training will be effective.
Instead of worrying about whether it’s the “right time” to strength train, women should focus on evidence-based principles: progressive overload, adequate protein intake, and recovery. The key to long-term progress in the gym isn’t timing workouts to hormonal fluctuations—it’s consistency over weeks, months, and years.
Decomplicate Training
The idea that women need to train differently at different times of the month creates unnecessary complexity. Fitness should be about consistency, progressive overload, and good recovery—not micromanaging hormones. Cycle syncing’s popularity is largely driven by theory rather than solid scientific evidence. While some women may feel stronger or more energetic at certain times of the month, attributing this entirely to menstrual cycle phases overlooks more significant factors such as nutrition, sleep, and overall training experience.
Additionally, the idea that cycle syncing can be applied universally ignores the fact that menstrual cycles are highly variable. Some women have irregular cycles, while others use hormonal contraceptives that significantly alter hormone patterns. This further complicates any broad recommendations about training based on cycle phase.
There is also no evidence that adjusting nutrition based on cycle phase provides any meaningful benefit. Research suggests that hormonal fluctuations vary widely between individuals, making generic diet and exercise recommendations based on the menstrual cycle unreliable and potentially misleading.
This study also highlights why women should not be excluded from exercise science research due to concerns about hormonal variability. Historically, premenopausal women have been underrepresented in sports science studies, often because researchers worried that fluctuating hormones would confound results. However, this research suggests that menstrual cycle phase doesn’t meaningfully impact key markers of muscle adaptation.
Practical Applications Through Your Cycle
A well-rounded training plan should focus on long-term progress rather than short-term hormonal shifts. While cycle syncing suggests structuring workouts around hormone phases, the reality is that most symptoms—like bloating, cramps, lower back pain, fatigue, or low motivation—only last several days, not an entire 28-day cycle. That means adjusting your sessions when needed based on how you feel, not overhauling your routine. Here’s how to train smarter:
- Stick to a structured plan. Your muscles adapt best with consistent training. Don’t change your whole program based on hormones—follow a well-designed plan and tweak as needed.
- Adjust for symptoms, not the calendar. Feeling sluggish or crampy in the days before your period? Swap heavy lifts for lighter resistance, mobility work, or active recovery. Modify a session or two, not the whole month.
- Menstruation: your strength may surprise you. Some feel stronger, others prefer to dial it back. There’s no one-size-fits-all rule—listen to your body and adjust accordingly.
- Use high-energy days to your advantage. When you feel good, push hard. Lift heavier, train with intensity, and take on more challenging workouts.
The latest research doesn’t support cycle syncing for strength training—your muscles respond to resistance exercise whether you’re in the follicular or luteal phase. That said, hormonal shifts can affect energy levels, recovery, and how you feel in the gym. Some days, you might feel strong and unstoppable; other days, not so much. That’s normal. Adjust as needed, but keep sight of the fundamentals: train consistently, eat enough protein, get quality sleep, and prioritize recovery.
Instead of waiting for the “perfect” time to train, focus on what keeps you progressing. Strength is built in the long run, not in perfect alignment with any given day of the month. Show up when you can, train with intent, and trust that the work will add up.