Separating Fact from Fiction for Female Athletes—with Dr. Stacy Sims

When it comes to coaching female athletes there's an abundance of myths and misconceptions. Physiologist Stacy Sims sets the record straight.

When it comes to female-specific training and performance, Dr. Stacy Sims has been leading the charge in recent years to help educate athletes and coaches about the many differences that exist between male and female physiology. Coaching female athletes using protocols and practices that have only been researched on men can lead to poor performance, injury, illness, and burnout. Yet many of these protocols and practices still exist.

In this video, Dr. Sims talks through five of the most popular misconceptions that she still sees coaches and their athletes adhering to. They include:

  • Exercising in a fasted state
  • Linking menstrual irregularity or amenorrhea with “good” body composition
  • Avoiding racing during certain times of the menstrual cycle
  • Placing too much trust in data from wearable devices (which are largely based on male-derived data)
  • Believing being lighter is better and/or chasing a specific race weight

RELATED: Maximizing the Physiology and Performance of the Female Athlete

By understanding the science behind female physiology, training, and performance, coaches can be better equipped to get the most from the female athletes they work with, and, in turn, these athletes gain greater enjoyment from their respective sports and are far more likely to reach their potential.

Video Transcript

Emma-Kate Lidbury  0:04

So Stacy, when it comes to the rise of female-specific physiology and research, you have been leading the charge in the past five to 10 years. And a lot of the work you’ve done and underscored has shown just how different the female body and female physiology is. And for really a very long time, female athletes have simply followed the advice and protocols that have been designed and tested on men. Now this is changing rapidly. And we’re going to talk through some of the popular misconceptions that coaches really need to be aware of when working with female athletes, the first of which is working out in a fasted state. Can you explain to us why this can be problematic for female athletes?

Should female athletes exercise in a fasted state?

Dr. Stacy Sims  0:38

We know from research that women do better in a fed state. And it comes down to a couple of things. One is in the brain for women. So in the hypothalamus, there are two areas that are sensitive to nutrient availability, especially carbohydrate availability, but in men, there’s one. It’s called kisspeptin neurons. So when women start to exercise in a fasted state, one, we have to question why because women are already maximally fatty-acid adapted by the nature of sex differences within the mitochondria. Women have more of the proteins required for using free fatty acids. And by the nature of metabolism, women go through blood sugar and then tap into fatty acids, whereas men do blood sugar or glycogen, then fatty acids. And when we’re looking at the fasted state itself, and we’re exercising in a fasted state, it sends a signal to the hypothalamus that, “Hey, wait a second, we’re in a low energy state.”

And so if we don’t have enough calories coming in to actually do this exercise stress, then we don’t have enough calories to adapt to it. As a matter of fact, we need to start conserving. So we know after four days of this perturbance, we start to see a decrease in our thyroid function. We also see an increase in sleep issues with poor architectural aspects of sleep. And if we continue down this track, then we get into full low-energy availability and we see menstrual cycle dysfunction.

Why address menstrual cycle dysfunction?

EK  2:05

So up until fairly recently, I’d say within, like, the last five to eight years, a female athlete losing a period was deemed to be a sign that she had reached a good body composition. Why should coaches be concerned if their athletes have lost their period or are experiencing some kind of menstrual irregularity?

Dr. Stacy Sims  2:21

So when we look at body composition, we often see amenorrheic athletes who don’t have ideal body composition. It’s not necessarily about having more lean mass and less body fat. It’s about how is your body being robust to actually ascribe to and accept that exercise stress, that training load, adapt to it, and keep progressing. So a menstrual cycle and that regular bleed phase is really important from a sign of health and a sign of the body being able to adapt to training loads.

One of the first tell points is a change in the bleed pattern. So if we see that the bleed pattern shortens or lengthens—and this is after two cycles—and the athlete will know that, then this is a, “Okay, wait a second, that probably was anovulatory, so I need to talk to my coach about pulling back a little bit or putting in a few more recovery days so that I can get my brain and everything back in sync so that I can continue to have ovulatory cycles.”

Does the athlete’s cycle affect race performance?

EK  3:16

I think it’s worth noting that many women hate to race at certain points in their cycle, and certainly when they’re bleeding. What advice do you have for coaches when it comes to planning racing around an athlete’s cycle?

Dr. Stacy Sims  3:26

So we know that there’s a difference between performance and training. So there is a way that you can leverage the menstrual cycle to improve training adaptations. But when you look at performance on the day, there’s actually no negative day in the menstrual cycle to perform at your best because we see more psychological aspects that come into play.

If a woman has heavy menstrual bleeding, or really uncomfortable cramping, and she knows that her A race is going to fall on the day of her period—because she’s aware of that from tracking her cycle—there are things that she could do to put into place to eliminate that aspect.

So when we’re talking about performance, we want people to understand that in that low-hormone phase, it’s a perfect time to nail it. Especially if we’re looking at trying to train for and peak for an A race. Don’t be afraid of where you are in your menstrual cycle.

Is wearable device data reliable for females?

EK  4:16

Now, when it comes to wearables, I know you’ve got some good opinions here. I mean, wearables are everywhere right now. Right now we can’t get away from them. What should female athletes be aware of when it comes to using and interpreting this data?

Dr. Stacy Sims  4:29

You need to make it more ecologically valid. Because when we look at the algorithms that are used to drive these wearables, they’re based on male data, so they don’t take into account the effects of hormones. We know that there’s an immune system change to pro-inflammatory after ovulation. We know that there’s an autonomic nervous system change after ovulation, where we see a decrease in our heart rate variability, increase in our resting heart rate, increase in our respiratory rate, we see changes in our sleep architecture.

And if you’re relying just on the data from wearables, it’ll look like your athlete is either getting sick or isn’t adapting to training. What we need to be aware of is we need to be able to compare wearable data from the luteal phase to the luteal phase, or week three of the oral contraceptive pill to week three, so that you’re doing an adequate comparison. Follicular [to] follicular, luteal to luteal, or OC week to OC week, so you can actually see the progression.

So when we’re looking at the wearables, you need to use it as a tool. So you can have an idea—being aware that things change after ovulation, and have that conversation with your athlete, knowing where they are in their menstrual cycle to make it ecologically valid—until we can get more robust algorithms that take into account female physiology.

Is lighter better when it comes to performance?

EK  5:46

A lot of endurance athletes are prone to think that lighter is better when it comes to performance. How can coaches help athletes who might be stuck in this model of thinking?

Dr. Stacy Sims  5:56

There was a really big study that came out last year or the year before that was looking at female endurance runners and bodyweight and power-to-weight ratio, and found that those who settled in a normal BMI without any kind of restrictive eating or out of low energy availability, had normal menstrual cycles, were actually faster and responded better to training. When you put that weight category on, and you’re saying, “Hey, I have to stay at this particular weight or reach this particular weight to supposedly race well,” we do see that there’s an impediment in performance and training adaptations. Because women end up in a subclinical low-energy availability state. So that isn’t necessarily coming up with all the red flags that we usually see with low-energy availability of hormone dysfunction [or] putting on body weight, but we see it as sitting on the low end of normal for iron, the low end of normal for hormone ranges, but [women] just aren’t responding to training.

Some coaches say that their athletes are non-responders, but it’s not a non-response, it’s the fact there is still not enough energy coming in to support what the body needs to adapt. So one of the biggest things I’ve been able to do with so many female athletes is take that weight restriction off. And we see that they can actually perform better, they can adapt better, they have better sleep, better recovery. And it goes so much further than what you look like on the race course or what your weight is on the race course. The more robust you are to stress, the better you are at the back end of a race, which is where it really counts.