If you’ve ever wondered why the same workout feels easy one week and impossibly hard the next – or why training suddenly seems to stop “working” despite doing everything right – you’re not alone.

Most coaches, and many athletes, feel reasonably confident interpreting performance and recovery data. They understand training load, progression, fatigue, and adaptation. They know how to look at relationships between external performance outputs, internal responses, subjective perception, and recovery metrics.

Yet even as awareness of female-specific physiology has expanded in recent years, in large part due to the influential work of Dr. Stacy Sims, a critical gap remains.

That gap isn’t simply knowing that menstrual cycles or perimenopause and menopause matter. It’s developing true physiological literacy: the ability to understand how female physiology may show up across life stages, and to integrate that understanding into everyday training decisions.

Physiological literacy means recognizing normal cycle-related variability without overcorrecting. It means adjusting expectations and training intelligently during perimenopause. And it means interpreting performance and recovery data through a sex-specific lens.

In short, it is the skill of placing data in biological context, and it may be one of the most important competencies modern coaches can develop.

The Menstrual Cycle

Let’s start with the menstrual cycle.

If you’re an athlete in your reproductive years, or a coach working with female athletes in any capacity, this section is for you. If you’re navigating perimenopause or menopause, we’ll get there next.

While awareness of the menstrual cycle in sport has grown significantly in recent years, awareness alone is not the same as literacy. Knowing the names of the phases is different from understanding how physiology may show up during them, and how to adjust interpretation and training decisions accordingly.

For reference, the graph below provides a refresher on the phases of the menstrual cycle. Here, though, the focus is less on textbook definitions and more on what matters in training, data interpretation, and practical decision-making.

The Follicular Phase: Often a More Stable Window

The follicular phase begins on the first day of menstruation and extends through ovulation. For many athletes – especially those who do notice cycle-related variation – this can be one of the more stable and predictable windows of the month.

In practical terms, some athletes report better tolerance for high-intensity work, more repeatability in hard sessions, and a greater sense of responsiveness during this phase.

This does not mean the follicular phase is universally “better,” nor that every athlete experiences meaningful fluctuations across the month. But for athletes who do, this window can be especially useful for benchmark testing and key performance assessments.

This can also help coaches and athletes distinguish between true fitness gains and changes in fitness expression – a distinction that matters throughout this conversation. Meaningful adaptation can be occurring even when performance expression varies across the month.

The Luteal Phase: More Variable, and Often Overgeneralized

The luteal phase follows ovulation. For some athletes, it brings subtle changes in perceived exertion, recovery, thermoregulation, or tolerance for repeated high-intensity work. For many others, it does not meaningfully affect training or performance.

That individuality matters.

Importantly, we do not subscribe to the popularized idea of rigid “cycle synching,” which often takes these concepts too far, portraying large portions of the month as inherently problematic and raising an impractical question: How would we effectively train female athletes if nearly half the month were considered suboptimal?

Instead, we advocate for awareness over prescription.

Physiological literacy allows coaches to validate changes when they are real, without imposing unnecessary adjustments on athletes who are minimally affected or unaffected.

It is also worth noting that when challenges do arise, they often cluster toward the end of the luteal phase, rather than across the phase as a whole.

The “Challenging Window” – and the Difference Between Adaptation and Expression

Many women identify a “challenging window” that often begins in the late luteal phase and may extend into the first day or two of menstruation. For some, the pattern becomes clearer over time as training and recovery data are tracked across multiple cycles.

During this window, some athletes may find they cannot produce the same outputs, that familiar efforts feel more costly, perceived exertion rises, and recovery or readiness scores decline even when training load has not changed.

Importantly, this does not necessarily mean fitness has declined or that the training plan is failing. Rather, it may reflect female-specific physiology influencing the expression of fitness (that is, the ability to access that fitness).

This distinction is one of the most important practical concepts coaches can understand.

Practical Strategies for Athletes and Coaches

Physiological literacy does not mean rigid cycle-based programming. It means informed flexibility.

Whether you’re an athlete managing your own training or a coach supporting others, these strategies can help translate awareness into action:

• Track patterns across multiple cycles. One month tells you very little. Look for repeatable trends over time.
• Benchmark consistently. If you notice cycle-related variability, try to schedule key fitness tests or repeat sessions in the same phase – often the follicular phase – to make comparisons more meaningful.
• Avoid overreacting to short-term dips. A harder-feeling workout, elevated resting heart rate, or lower HRV during the late luteal window does not automatically mean lost fitness or ineffective training.
• Plan key efforts strategically when possible. While race dates are rarely flexible, understanding personal patterns can help guide the timing of important sessions and recovery.
• Remember that adaptation (or fitness gains) and fitness expression are not the same. You can be building fitness even when it temporarily feels harder to access.
• Most importantly, not all women experience meaningful cycle-related changes. The goal is not to assume they are happening, but to recognize them when they are.

Lastly, physiological literacy is not about limiting female athletes. It is about helping them understand their biology so they can train with greater confidence.

Note for Coaches, Refer When Needed: If cycle-related challenges are significant – or if there are red flags such as loss of the menstrual cycle (a red flag for LEA/REDs) or highly painful or irregular cycles without medical evaluation – involve appropriate professionals. Sometimes medical assessment is warranted, and targeted support can make a meaningful difference.

The Perimenopause/Menopause Transition

Perimenopause typically begins in the forties and represents the years leading up to menopause, which is defined as 12 consecutive months without a period. During this transition, hormonal patterns become less predictable before eventually settling into a new baseline.
Unlike the menstrual cycle, where patterns may repeat month to month, perimenopause is often characterized by fluctuation without the same consistency. From a coaching perspective, this is where physiological literacy becomes especially important.

Common Performance and Recovery Shifts

Not every athlete experiences significant disruption during this transition, but many do. Commonly reported changes include higher perceived exertion at familiar workloads, less predictable recovery, sleep disruption, shifts in mood or motivation, and greater variability in performance and recovery metrics.

Importantly, these changes can leave athletes and coaches feeling as though training is no longer working. In many cases, however, this does not reflect failed programming. It reflects a meaningful physiological transition that can alter how fitness is expressed and how data behaves.

One of the most important messages for athletes in this stage is this: progress is still possible, but it may look less linear than it once did.

Practical Strategies for Athletes and Coaches

As with the menstrual cycle, physiological literacy in perimenopause is about informed flexibility, not rigid rules.

Here are some strategies athletes and coaches may consider:

• Reset baselines as physiology changes. Use recent data as reference points rather than comparing to personal bests established many years earlier.
• Use consistency as a success marker. When metrics become noisy, maintaining regular training, preserving intensity tolerance, and avoiding forced reductions due to illness or injury can signal that training load remains appropriate.
• Delay judgement when signals are mixed. When performance, recovery metrics, and athlete feedback do not align, resist the urge to immediately adjust the program. Allow additional time and collect more data before concluding that training load needs to change.
• Use recovery metrics to gauge readiness, not just to judge training load. Remember that recovery data reflects global stress – including hormonal changes, sleep disruption, and life demands – not just training.
• Broaden the definition of progress. Help athletes recognize gains beyond personal bests, including resilience, consistency, confidence, and the ability to navigate harder training weeks while remaining engaged in sport and long-term goals.
• Normalize the experience. Many athletes struggle quietly during perimenopause. Naming what may be happening can reduce frustration and help restore confidence in the process.

Most importantly, recognize that perimenopause and menopause are not athletic endpoints; they are transitions.

With appropriate support, many women continue to train, race, and perform at high levels well into midlife and beyond, sometimes taking on challenges that exceed those of their younger years. In 2023, Canadian Mel McQuaid became the first professional woman to race the Ironman World Championship in Kona at age 50 – a powerful example of what’s possible when physiology is understood, respected, and trained alongside rather than against.

Note for Coaches, Refer When Needed: When it is unclear whether changes in performance and recovery are related to perimenopause or to other factors, involve appropriate providers who can help differentiate possible causes and support the athlete accordingly.

From Awareness to Literacy

Female athletes do not need softer training, lower expectations, or rigid rules tied to biology. They need informed coaching.

Physiological literacy helps replace frustration with understanding and overreaction with perspective. It helps coaches distinguish adaptation from expression, interpret data within biological context, and support athletes through both cyclical variation and life-stage transitions without losing sight of long-term development.

Whether navigating menstrual cycles or the perimenopause/menopause transition, the principle is the same: performance does not exist in isolation from physiology.

The goal is not perfect prediction. It is better interpretation.

And that is not just better coaching. It is better sport.

 

*Aside: Why the Research on the Menstrual Cycle Still Looks Inconclusive*

If you read the scientific literature on the menstrual cycle and performance, you’ll often see the same conclusion: evidence is inconclusive. Many systematic reviews have not found a consistent performance decline associated with menstruation.

At first glance, that might suggest the menstrual cycle has little impact on athletic performance. But the story is more complicated.

Two major issues have historically limited how well research captures what athletes actually experience.

First, studies have often looked at the wrong time window. Many have focused on the days of active bleeding (the early follicular phase), assuming this was the period most likely to impair performance. Yet many athletes report their most difficult training days in the late luteal phase (that is, in the days leading up to menstruation). If research measures the wrong part of the cycle, meaningful effects can easily be missed.

Second, population averages can hide individual responses. Menstrual cycle effects are highly individual. Some athletes experience noticeable fluctuations in performance, recovery, and perceived effort, while others notice very little change. When these athletes are grouped together in research studies, the average response can appear minimal, even if a meaningful effect exists for a subset of individuals.

Together, these limitations mean that real, repeatable patterns experienced by individual athletes can be difficult to detect in traditional study designs.