For years, it has been speculated that the menstrual cycle might influence strength-training adaptations. The belief that certain phases of the cycle—particularly the follicular phase when estrogen is at its highest—could provide an advantage for muscle growth has led to the rise of cycle-based training programs. Proponents of this approach argue that women should train more intensely during the follicular phase and focus on recovery during the luteal phase when progesterone is higher. However, new research published in The Journal of Physiology challenges this assumption and suggests that these strategies may be unnecessary.

A recent study from researchers at McMaster University explored whether different phases of the menstrual cycle impact how women’s muscles respond to strength training. Specifically, they looked at two important processes: how the body builds muscle protein and how it breaks down muscle tissue. The study carefully tracked women through their natural cycles and had them do resistance exercises during two key phases: the mid-follicular phase (when estrogen is at its highest) and the mid-luteal phase (when progesterone peaks). The researchers then monitored muscle-building activity for several days afterward to see if the body’s response to exercise changed depending on the cycle phase.

The researchers found no noticeable differences in how women’s bodies built muscle or broke down muscle tissue between the two phases of the menstrual cycle. In other words, the body’s ability to build muscle stayed steady, no matter where participants were in their cycle. This goes against the common belief that certain phases are better for muscle growth. Lead researcher Lauren Colenso-Semple, PhD, summed it up well, saying, “We saw no differences, regardless of cycle timing.”

This study challenges previous assumptions about cycle-based training, which were largely based on limited research and anecdotal reports. Some earlier studies had suggested that training in the follicular phase might be more effective due to increased estrogen levels, which were believed to have anabolic properties that could enhance muscle growth. However, many of these studies lacked rigorous menstrual cycle tracking methods, leading to inconsistencies in their findings. The latest research provides a more comprehensive examination of the topic, using best-practice methodologies to ensure accurate cycle phase identification.

What the Research Means to Health and Exercise Professionals

The implications of these findings are significant for health and exercise professionals working with female clients. Given the prevalence of misinformation, particularly on social media, some women have been led to believe that they need to structure their training around their menstrual cycle to maximize results, often leading to unnecessary stress and rigid programming. This research suggests that such an approach may not be necessary and that women can train effectively at any point in their cycle. Instead of adhering to a strict cycle-based training plan, clients should focus on maintaining consistency and progressive overload in their workouts.

Although the study found no physiological differences in response to resistance training between cycle phases, it is important to acknowledge that some women experience symptoms such as fatigue, bloating and mood changes at different points in their cycle. While these symptoms do not affect muscle protein synthesis, they can influence motivation, energy levels and overall exercise performance. For this reason, it is essential to take an individualized approach to training, allowing clients to adjust their intensity based on how they feel rather than on predetermined cycle phases. Some women may naturally feel stronger and more energetic during certain parts of their cycle, while others may struggle with low energy and discomfort. It’s also worth noting that only a small percentage of women—about 13%—have a consistent 28-day cycle, which introduces another level of complexity in trying to organize a training program around an inconsistent schedule. Rather, encouraging clients to listen to their bodies and adjust their training intensity accordingly can help them maintain consistency without feeling pressured to follow a rigid schedule.

Educating your clients about these findings can also help dispel myths surrounding cycle-based training. Many fitness apps and social media influencers have promoted the idea that women should alter their workouts based on their menstrual cycle, often citing studies on animals as evidence. However, this new research provides strong evidence that such an approach is not necessary for muscle growth and that resistance training can be equally effective at any time during the cycle. By sharing this information with your clients, you can help them feel more confident in their training and reduce the anxiety associated with cycle-based programming.

Rather than focusing on cycle timing, encourage your clients to prioritize other factors that play a critical role in strength and muscle development. Sleep quality, nutrition, hydration and stress management all have a far greater impact on training outcomes than hormonal fluctuations throughout the menstrual cycle. Encourage your clients to track their overall well-being rather than fixating on specific cycle phases. If a client experiences low energy or discomfort during certain parts of their cycle, adjusting the intensity, incorporating more recovery time or modifying exercises can be helpful strategies.

Ultimately, this research highlights the importance of taking an individualized approach to training rather than a one-size-fits-all model based on menstrual cycle phases. Women can train effectively and make progress in strength and muscle development regardless of where they are in their cycle. The key takeaway for health and exercise professionals is to support clients in building consistent, sustainable fitness habits that align with their personal needs and goals. By focusing on overall well-being and flexibility in training, rather than adhering to a cycle-based structure, you can help your clients achieve long-term success in their strength-training journey.

This study represents a significant step forward in understanding the relationship between the menstrual cycle and resistance training. While more research is always valuable, the evidence presented here provides strong support for the idea that cycle syncing is unnecessary for muscle growth. Moving forward, you can use these findings to create more effective, evidence-based training programs that empower women to train confidently at any time of the month.