Menstrual Cycle Impact on Training and Performance

I know I'll be getting a lot of grief from male athletes for this one. After all, as if we're not getting chicked often enough in races!...

Don't shoot the messenger!!

Highlights

- How your menstrual cycle impacts your training and performance
- How to time your races against your menstrual cycle for peak performance
- How training can impact the frequency and duration of your cycle
- How severe calorie deficiency can lead to stress fractures
- How contraception pills can help you train better and strengthen your bones
- My recommendations on how to train to be ready to race at all times

Biology 101

As most of you already know, there are 2 "primary" hormones that differentiate men from women: Estrogen and Progesterone.

Estrogen

What many people don't know, is that Estrogen, in addition to controlling the development of sexual characteristics and development related to pregnancy, also plays important roles in bone protection, blood coagulation, menstrual cycle functioning, cholesterol production, and salt and water retention. 

In fact, the concentration of circulating Estrogen in the blood is the single most important determinant of bone mineral density in women.

Estrogen deficiency caused by Amenorrhea (missed period as a negative consequence of large training volume) is the most significant risk factor for osteoporosis (bone fragility) and stress fractures among active women). 

ATHLETE IMPLICATIONS: Estrogen also influences pulmonary function, body temperature, fat metabolism and blood plasma volume (therefore fluid retention and hydration), all critical aspects for endurance sports.

We're going to delve into the impact of Estrogen on training and performance later...

Progesterone

Progesterone is one of the primary hormones involved in preparing the female body for the conception of a newborn. It has multiple functions both in terms of preparing vital organs for the fertilization of the egg as well as gestation.

However, in addition to these important functions, Progesterone has been shown to be involved in a number of other physiological functions. 

Progesterone:

- Acts as anti-inflammatory and helps with immune response
- Regulates gall bladder activity
- Normalizes blood clotting, circulating zinc and copper levels, cell oxygen levels
- Increases the usage of fatty acids (fat) as a source of energy, raises glycogen stores and reduces lactate - all have obvious implications for athletes which I discuss further below
- Plays an important role in the signaling of insulin release and pancreatic function, thereby impact risk of developing diabetes

Your Menstrual Cycle and how it affects your training and performance

Let's start with the basics:

The menstrual cycle is typically 28 days long and is divided in half by ovulation on day 14:

- The first half of the cycle is called the Follicular Phase

- The second half is called the Luteal Phase.

ATHLETE IMPLICATIONS: Each of these phases has hormonal and physiological characteristics which have a significant impact on your training and performance, as I explain further down.

The Follicular Phase starts with menses (period) - following menses, Estrogen rises, peaking around day 14, right before ovulation. A burst of Estrogen at the end of the phase causes a surge in luteinizing hormone to initiate ovulation. Progesterone stays low

The Luteal Phase starts at ovulation - Progesterone rises, Estrogen drops and rises again towards the middle. The increase in Progesterone causes an increase in body temperature (to prepare for egg fertilization). If fertilization does not occur, both Estrogen and Progesterone drop quickly, triggering the onset of menses.

Source: www.sciencebasedmedicine.org/

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A note on bloating and PMS:

Why do you sometimes feel bloated during your cycle: high concentration of Progesterone during the Luteal Phase (phase 2) affects fluid balance, causing you to lose water and electrolytes. The rapid drop in Progesterone at the end of the phase (if egg is not fertilized) results in excess premenstrual water and electrolyte retention, creating that bloated feeling.

What causes PMS and what can you do about it: PMS is a series of uncomfortable symptoms triggered by the rapid drop of both Estrogen and Progesterone at the end of the Luteal Phase when the egg is not fertilized. 

The cramping during PMS is thought to be caused by the hormone prostaglandin, which is produced by the uterus and causes it to contract (the cramping). Birth control pills and anti-inflammatory drugs (such as Ibuprofen) can reduce cramps by inhibiting prostaglandin. 

A note on Ibuprofen and other over the counter anti-inflammatories: as I mentioned earlier, these drugs inhibit prostaglandin. But you have to be aware that prostaglandin plays a big part in the health of your gut lining, and inhibiting prostaglandin puts people at risk of deterioration in gut health and creates the potential for gut leakage (and it doesn't take long for that to happen).

Only limited research has been conducted on the effects of exercise on PMS (assign blame as you wish) - but whatever research was done did yield significant results supporting the theory that exercise does reduce PMS symptoms (results varied among individuals).

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So the impact on performance then?!

Well as I alluded to earlier, the Estrogen/Progesterone cycle influences:

1- Basal Body Temperature

2- Metabolism (utilization of fat vs. glycogen as fuel)

1- Impact on body temperature and its effects on training and performance

The chart below illustrates the change in your "Basal Body Temp" during the cycle. Basically, your Basal Body Temp is the temperature your brain considers to be "normal" and does not trigger either sweating to bring it down or shivering (for e.g.) to raise it.

As you can see from the chart, your Basal Body Temp rises gradually during days 14 to 24 (Luteal Phase), with a sharp "spike" around day 25.

Remember the hormonal chart above? This coincides with the gradual rise followed by a "spike" in Progesterone during that same period of time.

In effect, what is happening is that Progesterone is triggering an increase in your Basal Body Temp in preparation for the possible fertilization of an egg.

So on days 6-14 for example, a body temp below 36.2C is considered "normal", while on days 20-28, a body temp of 36.6C or higher is considered "normal". The difference may only be 0.4C, but that has big implications!

ATHLETE IMPLICATIONS:

The Hypothalamus in your brain acts as your "thermostat", regulating body temperature. When it detects a sudden rise in body temperature above your Basal Body Temp, it triggers sweating to cool you down and bring the body temp back to Basal.

What causes this to get triggered? It could be ambient temperature (walking in hot weather), exercise (active muscles producing heat as a bi-product), etc.

Now your muscles need that stable body temperature to continue functioning. I won't get into the chemistry of why that happens, but many have experienced how heat impacts ability to exercise. 

AND, your muscles don't really care that your Basal Body Temp is being adjusted upwards in preparation for the fertilization of an egg. They want the temperature to be "stable goddammit !!! What's all that about letting it rise to 36.6C or 37C ??!".

But here's the problem:

Days 1-14: Basal Body Temp is low - if body temp goes above it, that triggers sweating and cools it back down. Muscles are happy.

Days 14 onwards: Basal Body Temp is now high - sweating doesn't happen until body temp rises above the new, "now higher", Basal Body Temp. Muscles are NOT happy!

And muscles not happy = feeling horrible during training and lower performances = heat exhaustion...

And it's not just muscles: when exercising in heat, increased thermal strain comes with greater cardiorespiratory strain:

1. Sweating causes loss in blood plasma volume

2. Which causes a lower stroke volume (how much blood the heart pumps with each "beat")

3. Which leads to less oxygen to muscles

4. Which means that the heart has to beat faster to compensate

==> this is what we call cardiac drift: your HR rises by 3 to 5 bpm for every 1% body weight lost from dehydration

Of course, this can be averted with proper hydration - and now you can see why I'm always banging the table about hydration :-)

And who's the culprit behind all this: well it's Progesterone, because it is the one telling the Hypothalamus: "hey buddy, I'm preparing for egg fertilization, so don't you dare trigger sweating until the body temp reaches this new higher number!"

And here's another interesting piece of info: both Estrogen and Progesterone affect women's breathing during exercise. In fact, Progesterone has been shown to increase breathing and severity of asthma symptoms as well as the "Rate of Pereceived Exertion" or RPE (how much effort you "feel" you're putting out).

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A couple of side notes on this whole Basal Body Temp thing:

Head Adaptation: by training sporadically in moderate heat, your body becomes more efficient at sweating. In other words, it teaches your body to start sweating earlier at ALL body temperatures. This is one way to deal with this issue if you must train or race during those peak Basal Body Temp days.

Oh and by the way, as some of you may know, the reason your doctor has you monitor your body temp if you're trying to get pregnant is exactly because of this whole mechanism: a rapidly rising Basal Body Temp means that Progesterone is rising and ovulation is about to happen - perfect timing to conceive a future athlete!

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2- Impact on metabolism

Let's start with some general information which I'm sure female readers will love and male readers will hate.

Ok let me put it out there once and for all: women are better equipped for endurance racing than men "metabolically". Again, don't beat me up for it boys! Women have a better fat metabolism period.

In fact, if you were to look at average finishing times in running races between men and women, you will see the difference shrinking as the distance increases.

As a matter of fact, in 2002 and 2003, Pam Reed won the 217km Badwater ultramarathon, posting the fastest time overall, beating all the men.

If you would like to know more about this inspiring athlete, read her book: The Extra Mile.

You want further proof? Here are the differences between men and women for the world record over increasing distances:

- 5,000m: 11.0%
- 10,000m: 10.8% 
- Marathon: 8.5%
- 100km: 5.5%

Spot the trend there?

Studies have shown that women rely more on fat as fuel then men. A number of studies have shown that female athletes on average use 75% more fat than male athletes at efforts between 65% and 70% of VO2max (aerobic efforts).

Additional training further increases the number of mitochondria (cellular power plants) in muscles, thereby assisting in fat utilization (in both men and women). This type of training has to be specific to fat adaptation tough.

Of course, there's a catch: as you burn more fat, you burn less glycogen (the carbohydrate stores in your liver and muscles). And that's a good thing! Because while women are better at burning fat than men, they have lower glycogen stores to begin with.

Again, diet and training influences how much glycogen you can store, but still, no amount of training and diet can bring women's carb-storing capacity in line with men's.

So forget carbo-loading at races ladies! It doesn't do much! But still come along, we enjoy your company ;-)

In fact, relying heavily on carbs in your diet will teach your body to burn more carbs, but since you have a lower ability to store carbs in the first place, you could be leaving your naturally given fat-burning potential on the table!

And because of the higher fat utilization / lower glycogen utilization in women, the rate of muscle breakdown is lower, and you can recover quicker from workouts... (fantastic, just what we male athletes needed)

So what does all this have to do with the Menstrual Cycle?

Estrogen is partly responsible for higher fat utilization as fuel in women - when male rats are given Estrogen, they utilize less glycogen and have higher circulating fatty acids (indicating an increase reliance on fat as fuel). In fact, those same studies have shown that injecting these male rats with Estrogen increased their endurance.

Lance probably knows better, but wouldn't Estrogen be cheaper than EPO?

So this means that any heavy-training-induced drop in Estrogen level will affect your fat metabolism.

But it's not that clear-cut I'm afraid: Female athletes have shown an even higher level of fat utilization and lower lactate during the Luteal Phase, when Progesterone is high. 

So it seems that while Estrogen does provide women with a better fat metabolism then men, Progesterone is what maximizes that ability.

ATHLETE IMPLICATIONS:

That creates a bit of a dilemma right? We have 2 conflicting pieces of information now:

- Race during the Follicular Phase (phase 1) because low Progesterone keeps your Basal Body Temp low, ideal for your muscles to function well

- Fat metabolism peaks during the Luteal Phase (phase 2) when Progesterone is high.

What to do then?

While no significant studies have been conducted to explore these 2 conflicting phenomena, observations have shown that the best performances were reported during the early days of the Follicular Phase, and the worst during the Luteal Phase. 

In other words, expect to perform well when Estrogen is dominant and worse when Progesterone is dominant.

It seems that your body's temperature is more critical to your performance in endurance races than the "marginal" increase in fat utilization induced by Progesterone.

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So my personal take on how to structure training would be as follows:

- Improve your overall fat-adaptation so you can burn more fat in both phases

- Make sure you add some heat acclimatization into your training to "teach your body to start sweating earlier at all Basal Body Temps"

- Make sure you include higher-intensity training to develop glycogen storage capacity

==> This should equip you optimize your body to deal with any condition:

- If race falls during the Follicular Phase (phase 1): your Basal Body Temp is low (optimal), your fat metabolism has been increased through training, and while you do use a little glycogen, you have more of it since you trained to increase its storage capacity.

- If your race falls during the Luteal Phase (phase 2): your heat adaptation allows you to start sweating earlier despite the higher Basal Body Temp, the high Progesterone levels will make you more fat-efficient anyway, and you can tap into those glycogen stores to put the hammer down in the last few Kms!

General Note: in my opinion, specificity in training is key not just to get fitter and faster but also to stay healthy, injury-free, save time and avoid burnout. 

A training program with good specificity will capture the adaptations needed to work "around" your menstrual cycle and enable good performance throughout the month.

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How does heavy training affect the cycle and what can you do to fix it?

What does heavy training do to the cycle and your overall well-being

As we discussed at the beginning, low levels of Estrogen caused by excessive training without adequate caloric intake significantly increase risks to bone density.

Bone Mineral Density peaks for both sexes around age 30, but the "female peak" is lower than the "male peak". This means that female athletes need to be a lot more careful with how much pressure they put on their bones (e.g. increases in run volume). 

This becomes even more critical if irregularities in the menstrual cycle are observed (risk of low Estrogen), and this why your doctor would be asking you to take Vitamin D and Calcium supplements (importance of Vitamin D in bone health was discussed in a previous blog here).

Furthermore, heavy training shortens the Luteal Phase (phase 2), followed by cycles without ovulation and finally cessation of menses (amenorrhea), related to constantly low levels of Estrogen and Progesterone, where levels of Estrogen would be similar to post-menopausal women.

And once again, Estrogen is that gives women the metabolic "edge" through higher fat utilization. Lower Estrogen starts to give that advantage away. Combine that with lower glycogen storage capacity, and you can guess the impact on training and racing.

So what can you do?

Research has shown that this hormonal imbalance is not because of the stress of exercise but rather because of severe caloric deficit. 
Some studies have shown that women who exercise heavily but fuel well (pre, during, post) prevent amenorrhea.

One way to help increase bone density in active women with menstrual irregularities: oral contraceptives, which increase Estrogen and regulate the cycle.

However be careful, different pills have different concentrations of Estrogen / Progesterone, and some of them "cycle" the ratio 2-3 times during each menstrual cycle.

One additional word of caution: check iron levels if heavy bleeding occurs regularly during menses.

A special thanks to Dr. Jason Karp whose book Running for Women was an important source of information for this article.

Happy training!

T