More Than a Bad Day: How the Menstrual Cycle Shapes Performance

On paper, the session should have been straightforward. Molly had been given a set of paces by her coach, a speed she had hit many times before. But halfway through the workout, something felt off. Her legs felt heavier than usual, the pace slipping despite the effort she was putting in. 

“I’d try to hit the paces and just couldn’t,” she says. “Then afterwards I’d realise, ah, that’s why. I’m on day 27 of my cycle.”

For Molly, running has shaped much of her life since she first joined her school cross country team at the age of 12. She went on to join Chelmsford Athletics Club, training through her teenage years before continuing to run competitively at university. She still structures much of her routine around training. “I’m definitely not your average twenty-something-year-old,” she laughs. “I don’t really drink. I’d rather get up early and run.”

But in recent months, Molly has become increasingly aware that her performance can fluctuate depending on where she is in her menstrual cycle. “There’s a really big difference to how my training feels depending on where I am in my cycle,” she says. “I definitely struggle in the luteal phase. Physically I don’t feel as strong and the paces feel harder.”

The luteal phase, which occurs in the days before menstruation, is when the hormone progesterone rises significantly. For Molly this is often when training sessions feel the most challenging. “If a session is really hard, I’m more likely to give up,” she says. “Normally I’d grind it out, but if I’m on day 26 or 27, I’ve definitely sacked off sessions because it was hard and I just couldn’t be bothered.”

Molly’s experience is far from unique. For years, female athletes have been expected to train according to research conducted largely on male bodies, with hormonal fluctuations rarely considered in training programmes. But now the menstrual cycle is beginning to receive the attention it deserves.

The menstrual cycle is a repeating pattern of hormonal changes, typically divided into four phases: menstruation, the follicular phase, ovulation and the luteal phase. Across these stages, levels of oestrogen and progesterone rise and fall.

According to the science, hormonal fluctuations mean that the body is never in exactly the same state throughout the month. But how those hormonal shifts affect athletic performance varies widely between individuals. Add in the stresses of training and sports, and these differences can become more pronounced, with some athletes experiencing large swings in performance and feeling depending on the phase of their cycle, while other athletes actually feel very little difference day-to-day.

An individual approach is important.

Despite the wide-ranging impact of the menstrual cycle, it has historically been overlooked within sports science. Running coach Scott Coller says that awareness of the menstrual cycle is becoming increasingly important when working with female athletes. Coller, who has been coaching runners ranging from first-time marathoners to competitive club athletes for three years, says it is an important consideration for his female athletes.  “It’s always a question I ask when onboarding athletes,” he says. “It gives me an idea of how much they feel their cycle plays a role in their training.”  

For Coller, the goal is not to overanalyse hormonal fluctuations but to create an environment where athletes feel comfortable discussing them.  “There are so many variables at play,” he explains. “I’d rather open the conversation and let the athlete tell me if they think their cycle might be influencing how they feel. I never want to make assumptions. It’s more about awareness.”

“It’s known that during phases of the cycle the body needs different nutrients, taps into different energy sources and even hydration needs can change,” Coller explains. “From a coaching perspective those things are crucial to consider.”

However, he emphasises that every athlete’s experience is different. “Of course every woman experiences the cycle differently, but even small considerations in training can make a difference.”

As a male coach working in a field still dominated by men, Coller believes there is also a responsibility to ensure female athletes feel supported. “Coaching is still an industry dominated by men,” he says. “So as a male coach I think it’s my responsibility to address these topics early and revisit them regularly.”  

Ultimately, he says, the goal is simple, “it’s about giving female athletes the best possible chance to succeed.”

For many athletes, the differences between phases are subtle but noticeable.

Erin has been running for over a decade and is currently training for her third marathon. Like Molly, she has become increasingly aware of how her cycle influences her training. “My cycle definitely makes it harder sometimes,” she says. “The week before my period I always feel more tired and less motivated to run.” 

Occasionally, cramps stop her from running entirely. “Sometimes the pain prevents me from going out,” she says.

But the experience isn’t always negative. In fact, Erin says racing during her period can sometimes feel surprisingly empowering. “I actually feel quite strong when I’m running on my period,” she says. “If I run well when I’m on it, it feels like even more of an achievement. I feel quite strong, both physically and mentally.”

Like many athletes, Erin tracks her cycle and adjusts her expectations accordingly. “I don’t necessarily change my training completely,” she explains. “But I listen to my body more and cut myself a bit more slack.”

Training around the menstrual cycle can also raise practical questions that are rarely discussed. While preparing for last year’s London Marathon, Erin found herself worrying about something she had never previously considered. “I was really stressed about the logistics,” she says. “Like whether they have sanitary products around the course. I don’t think they do, but surely they should.” 

Even in sports dominated by women, conversations around menstruation can remain surprisingly absent. Isabella, a 21-year-old university netball player, says the topic rarely surfaced during her years playing competitively. “You’d think netball would be the perfect place to talk about it because it’s a predominantly female sport,” she says. “But it never really came up.”

For Isabella, the impact was often psychological rather than physical. “I definitely felt less confident in my shooting when I was on my period,” she says. “Confidence is really important when you’re playing in a match.”

There were also practical anxieties during matches. “When you’re playing you can’t just focus on the game,” she explains. “You’re also worrying about your period leaking through your netball dress or having to run off court to change your pad.”

She believes that conversations about menstrual health should begin much earlier, particularly within school sport. “PE sessions would be the perfect place to talk about it,” Isabella says. “Both men and women need to hear the conversation.”

In elite sport, athletes have also begun speaking more openly about the issue and shedding light on what was once considered a taboo topic.

Scottish distance runner Eilish McColgan has spoken about the unpredictability of racing across different phases of the menstrual cycle. Writing in a column for BBC Sport, she explained how the experience can vary dramatically from month to month. “Some months it’s manageable. Other months it’s unbearable,” she wrote. “There’s no telling which version of me you’re going to get.”

At its worst, the sensation can make running feel almost impossible. “The only way to describe it,” McColgan added, “is that my legs feel like they have been replaced with concrete blocks. And that a screwdriver is carving out the Taj Mahal around my ovaries.”

This honesty from elite athletes has helped open a conversation that, until recent years, was rarely discussed at the high level of sport. Instead of viewing the menstrual cycle purely as a barrier to performance, many experts now frame it as a key indicator of overall health. For athletes, losing a menstrual cycle can be a warning sign of insufficient fuelling and low energy availability, both of which can increase the risk of bone stress and muscle injuries. 

Now, instead of shying away from their cycle, many athletes are starting to work with it by monitoring their cycles and look for patterns in order to adapt to the differing effects of each stage of the cycle.

Molly now tracks her cycle through the Garmin app and the training platform Wild AI, which allow her to take hormonal fluctuations into account when planning her sessions. “I try to run more on feel now,” she explains. “Sometimes I’ll miss a pace and only afterwards realise why.” Understanding these patterns has helped her approach training with greater insight and perspective. “It just helps you give yourself a bit more grace.”

Rather than something to ignore, the menstrual cycle is increasingly being recognised as valuable feedback about how the body is functioning. 

“It’s your superpower, not your weakness,” says Dr Georgie Bruinvels, on the Pacey Performance Podcast. “It’s a feedback system, if you listen to it and work with it rather than trying to ignore it or fight it, you’ll be a much more resilient and successful athlete in the long run.”

For athletes like Molly, the menstrual cycle is no longer something to ignore, but something to understand and work with. 

“It affects half the population,’ she says. “So it makes sense that we should actually be talking about it.”