Women and Running: Physiological Specifics and Challenges

In 1967, Kathrine Switzer famously entered the Boston Marathon using the initials 'K.V. Switzer.' When race officials realized a woman was running their marathon, one physically tried to rip her bib off. She finished the race. Nearly sixty years later, women make up over half of road race participants. The revolution has indeed happened, but specific considerations—physiological, cultural, and safety-related—remain, and they deserve to be understood rather than ignored.

Real Physiological Differences, Often Misunderstood

On average, women have a VO2max that is 15-30% lower than men's—due to factors like lower hemoglobin levels, a smaller heart, and a higher body fat percentage (essential for reproductive function). This isn't an opinion; it's basic physiology.

However, these raw numbers obscure important nuances. The gap narrows significantly among trained athletes. Crucially, women appear to have specific advantages in ultra-endurance events: better fat utilization, more consistent pacing, and a fatigue resistance that leads to the performance gap between men and women shrinking as race distance increases. In events over 200 km, some women can compete with top male athletes. From what I've read, this is a fascinating area of ongoing research.

The issue isn't the physiological difference itself, but its interpretation. For decades, these differences were used to exclude women from competition. We can acknowledge biological differences without using them as an argument for hierarchy—it's simply a matter of intellectual honesty.

The Menstrual Cycle: A Factor, Not a Fait Accompli

Long a taboo subject in sports, the menstrual cycle is finally receiving real scientific attention. And the findings are more nuanced than what we sometimes read.

The cycle, averaging 28 days, is broken down into phases with distinct hormonal profiles. The follicular phase (roughly days 1 to 14), with rising estrogen, appears more favorable for intense efforts for some women. The luteal phase (days 15 to 28), with increasing progesterone, is associated with a higher core body temperature and an increased perception of effort.

However—and this is crucial—individual variability is enormous. Some female runners report no noticeable effects. Others experience significant fluctuations. World records have been set in all phases of the cycle. The mistake would be to generalize, in either direction.

What seems clear is the benefit of tracking your cycle to understand your own patterns. Several apps allow you to cross-reference training data with your menstrual cycle. This isn't about prohibiting yourself from running at certain times, but rather about intelligently adapting your training—scheduling the most demanding sessions during the most favorable times, when possible.

RED-S and the Female Athlete Triad: The Silent Danger

RED-S (Relative Energy Deficiency in Sport) is a serious health problem that primarily affects female runners (though it can affect male runners too). The core issue is that caloric intake doesn't meet the demands of training, leading to a chronic energy deficit.

The consequences cascade: menstrual cycle disruption (amenorrhea), weakened bones (stress fractures), hormonal imbalances, a paradoxical drop in performance, chronic fatigue, and mood disturbances. It's an insidious vicious cycle because the initial signs—weight loss, amenorrhea—are sometimes perceived as «normal» or even desirable within a sports culture that values leanness.

Let's be clear: losing your period is not a sign of optimal training. It's a red flag. Any dietary changes for a female runner should be supervised by a healthcare professional who is aware of the risks of RED-S. I am not a doctor, but this seems like a topic where risks should not be taken.

Iron: An Underestimated Issue

Female runners are particularly susceptible to iron deficiency. Menstruation, combined with red blood cell destruction from foot strike impact and sweat losses, creates a significant drain. It's estimated that up to 30% of female endurance runners experience iron deficiency, with or without anemia.

Symptoms are often mistaken for overtraining: unusual fatigue, a drop in performance, disproportionate breathlessness, and impaired recovery. A simple blood test, including ferritin levels (not just hemoglobin), can make all the difference. This is a check-up every regular female runner should consider doing at least once a year.

Safety: An Issue That Shouldn't Even Be One

It's impossible to discuss women and running without addressing safety. Surveys are clear: a majority of female runners have experienced verbal harassment while out for a run, and many modify their habits as a result—avoiding solo runs, steering clear of certain times, or sharing their GPS location.

This is a reality that impacts the sport, and it shouldn't be minimized. The problem isn't women running alone—it's that certain behaviors make this fundamental freedom risky. Community initiatives and safety apps are making progress, but there's still a long way to go.

Remarkable Historical Progress

The history of women in running is a story of exclusion followed by astonishing catch-up. The women's marathon didn't become an Olympic event until 1984—in Los Angeles. The 5,000m in 1996, the 3,000m steeplechase in 2008. When you consider it, these dates are incredibly recent.

Concurrently, records have fallen dramatically. The women's marathon world record dropped from 3h 40m in 1964 to 2h 09m 56s (Ruth Chepngetich, 2024). And according to my readings, this progress isn't over—some physiologists believe women have not yet reached their biological ceiling in endurance, simply because they've had less time and fewer resources.

Check out age groups to see how performance evolves over time, regardless of gender.

Adapt Training, Don't Limit It

The central message: women don't need «lightened» training. They need informed training—which takes into account the menstrual cycle when relevant, monitors iron and calcium levels, is vigilant for RED-S signals, and incorporates strength training to compensate for a higher risk of certain injuries (patellofemoral pain syndrome, ACL tears).

Unisex training plans work for many female runners, but they can be optimized by integrating these parameters. And the running industry—still largely male-dominated in its leadership—has every reason to accelerate this consideration.