Menstrual Cycle Considerations for the Personal Trainer

Do you really need to train women based on their menstrual cycle phase?

Personal trainers should be well-versed in the effects of the menstrual cycle on women’s exercise performance. Women constitute a significant portion of most personal trainers’ clientele, so understanding how hormonal fluctuations influence training outcomes is essential. The participation of females in sports has dramatically increased over the years. In elite competition, the Tokyo 2020 Olympic Games were the first to reach a 49 % proportion of female participation (Oester, 2024).

Understanding the physiological effects of sex hormones on exercise response, like other variables such as sleep, nutrition, temperature, stress, etc, is crucial for sound program design. This article explores historical and recent research to guide trainers in tailoring exercise programs to individualize women’s exercise programs better.

History

Until the National Institutes of Health Revitalization Act of 1993, researchers in the United States were not obligated to include women in research (Stachenfeld, 2018). This is because the menstrual cycle was cited as too challenging to study, leading to women being excluded or included without consideration of the menstrual cycle’s influence on exercise response (Johnson, 2009).

Before this, most research, including exercise science, focused mainly on males. The NIH Act sought to ensure that health research was equally applicable to females and males, with females represented in study samples (Stachenfeld, 2018). Research on the menstrual cycle and exercise response has increased steadily over the last twenty years, with a recent explosion in the previous five years. 

Methodological Considerations on Menstrual Cycle and Exercise Research:

One of the biggest challenges in menstrual cycle research is verifying menstrual cycle phases due to high inter- and intra-individual variability (Janse, 2003; 2019). For example, within the same woman, progesterone levels fluctuate widely during the mid-luteal phase (Janse, 2003).

Furthermore, the terminology used to describe the different phases of the menstrual cycle often varies between studies (Janse, 2003). For example, the term ‘follicular phase’ could refer to one of three distinct parts of the follicular phase (Janse, 2003).

In a review of the methodological quality of menstrual cycle and exercise research, only 44% of the selected studies measured the actual concentrations of estrogen and progesterone (Jansen, 2019). The review recommends improving the quality of future menstrual cycle research by combining three verification methods. Verification should also be done at rest, as exercise increases estrogen and progesterone concentrations (Jansen, 2003).

Although many women experience variations in their cycles, the menstrual cycle is conveniently allocated 28 days. Many women do not have a cycle that fits within this time frame. In physically active females, especially athletes, 30-50% can experience ovulatory disturbances without abnormal symptoms.

To give evidence-based exercise recommendations throughout the menstrual cycle,  it is paramount to verify if participants are experiencing a regular ovulatory menstrual cycle at the time of testing and verify the menstrual phase with a combination of testing (Janse, 2019).

Next, we’ll discuss three recent reviews.

The Effects of Menstrual Cycle Phase on Exercise Performance in Eumenorrheic Women: A Systematic Review and Meta-Analysis 

This recent study concluded that an individualized approach should be taken rather than drawing exercise guidelines for all women (McNulty). The authors found a considerable variation in findings between studies, with too trivial differences in the menstrual cycle and exercise performance.

Surprisingly, of the 51 randomized control trials included in the meta-analysis, 42% were classified as low-quality studies, due to inadequate cycle phase identification and verification, non-homogenous participant groups (ranged from sedentary, to healthy, to physically active to elite athletes), and large variation in the type of performance outcome measured.

The authors recommend that coaches consider women’s training status and are aware of the phases of the menstrual cycle. 

Current evidence shows no influence of women’s menstrual cycle phase on acute strength performance or adaptations to resistance exercise training

This recent review analyzed the current evidence of the menstrual cycle on strength performance and adaptation to resistance training (Colenso-Semple et al., 2023). They didn’t find high-quality evidence to support creating a specific resistance training program based on the cycle phase. 

They cited a lack of methodological quality in the research. They aren’t saying the menstrual cycle does not affect performance. Many women report many symptoms. Instead, no evidence exists to recommend a completely different routine during menstrual cycles. 

Ultimately, they recommended that coaches tailor their programs to the individual. For some, this could mean a change in programming during certain cycle phases. For others, it could mean a slight shift in intensity or volume for the first days of menstruation. The researchers suggest that the menstrual cycle is a variable to consider in exercise programming, along with nutrition, fatigue, sleep quality, stress, injury, motivation, and program enjoyment. 

Effects of Follicular and Luteal Phase-Based Menstrual Cycle Resistance Training on Muscle Strength and Mass (Kissow et al., 2022)

A research review on the effects of follicular and luteal-phase resistance training on muscle strength and mass discussed multiple studies showing greater strength in the follicular phase for both untrained and trained women. These findings seem contradictory to more recent reviews on the subject. This may be where the cited methodological inconsistencies come into play. 

Regardless, it is still essential to look at the findings that show a difference in performance based on the cycle phase. The bullet points below are results from several randomized control trials cited in the review paper.

• Quadriceps maximal isometric strength in follicular vs luteal (40% improvement vs. 27%, respectively)
• Quadriceps maximal isometric strength in follicular vs luteal (32% improvement vs. 13%, respectively)
• Quadriceps maximal isometric strength increased by 2%-7% after follicular phase
• Greater increase in quadriceps muscle diameter than luteal phase-based training (9% vs. 6%, respectively)

The data from these studies show that the quadriceps specifically saw greater adaptations in the follicular phase. What about other muscle groups? Another study with a similar design examined the elbow flexors but found no difference in adaptations between cycle phases.

The review agrees with other reviews that an individual approach is essential due to the considerable inter-individual variation of the female menstrual cycle. Yet, the authors say it may benefit female athletes with a regular menstrual cycle to adjust their training schedule to focus on resistance training during the follicular phase.

If performance might be better during the follicular, should resistance training be skipped or minimized during low estrogen phases?

The suggestion to focus on resistance training only during the late follicular phase of peak estrogen is made on the premise that high estrogen benefits positive muscle adaptation. This has led to speculations that women should only focus on resistance training during the week when estrogen is the highest. 

We know that there is a high variability in women’s cycles, even broad hormone fluctuations day by day. Removing two or three weeks of resistance training out of the month seems counterintuitive if the goal is to build strength and muscle. 

And for what? Because studies showed the quads were 10 or 20 percent stronger in an isometric strength test during the follicular phase that was only verified with calendar tracking? A recent study on the menstrual cycle phase and muscle protein synthesis and breakdown in response to resistance training found no difference in the menstrual cycle phases (Colenso-Semple, 2024).

It has been established that overall training volume and progressive overload are among the primary drivers of muscle adaptation. Training only when estrogen is highest reduces the training window dramatically.

Until a long-term study shows that women who only resistance train in the follicular phase see the same adaptations as women who train during their whole cycle, with training modifications when needed, we simply cannot recommend that they only train during their follicular or late-follicular phase.

Effect of menstrual cycle on VO2 Max

In an older review, VO2 max was not affected by the menstrual cycle. These findings suggest that menstruating female athletes competing in strength-specific and intense anaerobic/aerobic sports do not need to adjust for the menstrual cycle phase to maximize performance (Janse, 2003). 

The author adds that most studies with hormone verification and electrical stimulation to ensure maximal neural activation found no change in muscle strength and fatigability over the menstrual cycle.

Few studies have been done on this topic. However, A recent study tested 10 women with a submaximal test followed by several VO2 max tests during the early follicular, late, and mid-luteal phases (Ekberg, 2024). While it is good that the researchers distinguished specific points in the respective phases, they only verified the menstrual cycle with a calendar tracking app rather than a combination of tests, as recommended by other researchers. 

The study found no significant differences in VO2, heart rate, RER, fatty acid oxidation, and carbohydrate oxidation, indicating similar aerobic capacity despite hormonal variations. Researchers recommend larger sample sizes and better cycle verification in future studies. These findings can be used for planning aerobic events.

Perceived Impact of the Menstrual Cycle on Exercise Performance

One crucial factor to consider during the menstrual cycle for exercise performance are symptoms, primarily fatigue. One review on this topic found that women experienced fatigue in both phases of the menstrual cycle, as shown by the mixed results in the literature (Pereira, 2020). The author believes the mixed results across studies may result from methodological discrepancies (Pereira, 2020).

One recent meta-analysis showed that the menstrual cycle does not impact the aerobic exercise rate of perceived exertion (RPE). The author writes that although acute RPE is not affected by cycle phases, future studies and practitioners should pay attention to the impact of RPE session by session throughout the MC (Prado, 2024).

Despite some research showing mixed results, 55% of premenopausal women who exercised regularly stated that their menstrual cycle affected training and performance (Bruinvels, 2016). These women reported heavy bleeding and iron deficiency, which suggests that fatigue may be higher in iron deficiency related to heavy bleeding. 

In another study, of the nearly 200 elite female athletes not on hormone control, 77.4% reported adverse side effects during their menstrual cycle, primarily during days 1-2 of menstruation (Martin, 2018). Another study of 186 Danish elite female athletes found that 13% reported that negative symptoms sometimes caused them to not participate in or complete the scheduled training (Oxfeldt, 2020). 

An extensive and up-to-date review on the topic found even though current findings are inconclusive regarding the impact of the menstrual cycle on objectively measured performance, of the 39 studies assessed, 3-100% of women report negative symptoms that they believe affect their performance. This high variability may be explained by the study designs and language used (Oester, 2024).

Exercise professionals should pay attention to these results. The main takeaway is that exercise programming should be flexible during days of negative menstrual symptoms.

Conclusion

In conclusion, the menstrual cycle (MC) can cause adverse symptoms in exercising females, such as fatigue, heavy bleeding, and iron deficiency, which many women report as impacting their training. Research indicates that these symptoms may negatively affect training for some women, particularly during the first days of menstruation. 

However, the degree to which specific MC phases affect exercise performance appears insignificant. Methodological inconsistencies, variability in hormone verification, and limited study designs can lead to limitations in many studies on this topic. 

While some evidence suggests possible strength advantages during the follicular phase, the overall impact of the MC on strength and aerobic performance is insignificant when other training variables are considered. 

Women’s strategies for managing exercise during the MC vary significantly. Some choose to skip or reduce training during heightened symptoms, while others prefer to modify intensity, volume, or exercise type. This variability highlights the importance of personalized and flexible programming. 

Trainers should remain informed about the physiological and psychological effects of the MC, encouraging open communication to tailor programs to individual needs and preferences. Ultimately, empowering women to adapt their training based on their experiences fosters better performance, adherence, and overall well-being.

References

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