Should Female Athletes Bother Tracking Heart Rate Variation?

Should endurance athletes bother measuring heart variability?

Yes.

Does heart rate variability fluctuate throughout the menstrual cycle?

Yes.

In today’s blog, I am going to share with you the importance of heart rate variability measurement (HRV) and how the menstrual cycle can affect those readings.

By reaching the end of this blog you will understand:

1. The meaning of HRV
2. What do HRV measurements indicate in terms of training
3. How the menstrual cycle can affect these readings
4. How to interpret HRV measurements with these factors such as the menstrual cycle in mind

What is HRV?

Heart rate variability is the measure of inter-heartbeat variation over a given period of time.

So, what does that mean?

In simpler terms, by measuring your HRV you can find out the time period between each heartbeat, and how it varies over time. Even if your heart beats 70 times in one minute, it is unlikely that there is one second between each heartbeat.

It is measured in milliseconds, such a small measurement that can have a lot to say but is also dependent on a number of factors.

Measuring your HRV can tell you how adaptable your body can be! It is controlled by an important part of the nervous system called the autonomic nervous system (ANS).

This system is broken up into two mechanisms called the sympathetic and parasympathetic nervous system.

These systems should work in harmony together to react or relax in certain situations. For example, it may instruct the body to react to situations such as an argument with your partner, a happy surprising event, or even running to catch the bus.

However, constant signals to react with little signals to relax can lead to an imbalance of the autonomic nervous system and overuse of the parasympathetic nervous system (the flight/fight system).

Therefore, given that HRV is controlled by the autonomic nervous system, it is easy to see how an imbalance in this system can affect HRV.

Should I have a high or low HRV?

HRV is a measurement that will consistently change over time due to a number of factors.

For example, athletes, males, and younger people will typically have higher HRV in comparison to everyone else. HRV is also a measurement that will decrease with age and may decrease if you have an illness/injury.

It is widely accepted that in general, having a high HRV is a sign of a well-functioning nervous system that can easily adapt to change. It also accepted that having a low HRV may be a sign of a fatigued nervous system.

However, there are times when it is normal to have a low HRV, for example during high-intensity exercise HRV lowers as there is an increase in sympathetic activity to raise heart rate.

However, post-exercise the relaxation response will later decrease heart rate and increase HRV.

Here is a graphic to help you evaluate your HRV more effectively:

RHR: resting heart rate    HRV: heart rate variability

A high HRV is usually a sign that you are adapting well to training, have good cardiovascular fitness, and are sufficiently recovered.

So, as you can see, reading your HRV measurements can show you a lot about your current training, fitness, and recovery.

However, imagine something working that’s behind the scenes that could affect female athletes’ readings of HRV, and for some, that’s the menstrual cycle.

How Does the Menstrual Cycle Affect HRV?

The menstrual cycle contains fluctuations of the hormonal profile’s oestrogen and progesterone.

Progesterone stimulates the sympathetic nervous system (fight or flight) which decreases HRV and increases resting heart rate, and as we can see from the graphic above, both of those measurements indicate signs of accumulated fatigue.

Therefore, during your luteal phase (where progesterone is high) you may evaluate these readings as negative. You may think you aren’t adapting to your training or that your recovery is working.

In reality, it may just be your hormonal profile decreasing your HRV.

So, what about the rest of your menstrual cycle?

During the follicular phase, progesterone is low, therefore studies have found that parasympathetic activity is higher in the follicular phase. This can allow for higher measurements of HRV.

Whereas sympathetic activity is increased during the luteal phase, and causes HRV to lower.

What should you do with this information?

You may read this blog and think, if HRV is so tricky to read, should I even bother tracking it?

The answer is yes.

Here are some tips to make tracking your HRV more accurate:

1. HRV trends should be evaluated over time. Similar to the way we track weight loss/ weight gain, you shouldn’t take daily readings as black and white as there are so many factors that can affect readings. Try not to fixate on one high reading or one low reading, instead calculate your average readings over a longer period of time such as a week/month.
2. Take HRV readings first thing in the morning as the nervous system has had a chance to recover overnight and there are very few external factors increasing sympathetic activity at this time.
3. Don’t assess this measurement by itself. Using other measurements such as resting heart rate, sleep, and others such as training can help paint a bigger picture of what’s going on inside your body.
4. Use trustworthy and reliable technology. Wrist monitors typically do not give accurate measurements of HRV. Some elite athletes may have access to electrocardiograms (ECG), however a more accessible and reliable option is heart strap monitors.
5. Tracking your menstrual cycle alongside HRV can help you keep track of another variable that may be affecting your HRV readings.

Should you track HRV?

This question can be simply answered with another question, how much time do you have?

HRV can be a very useful and insightful variable to help optimize your performance and recovery. 

However given it’s high dependability on various factors, its important to remember that all individual measurements are not black and white. You must evaluate the bigger picture.

Take Home Message

• HRV measurements can be affected by the hormonal fluctuations that occur during the menstrual cycle. 
• Progesterone increases sympathetic activity which in turn reduces HRV.
• This means that during the follicular phase your HRV readings may be higher (low levels of progesterone), and during your luteal phase your HRV readings may be lower (high levels of progesterone). 
• One reading of HRV should not be assessed by itself. Trends of HRV taken over a longer period of time should be assessed, in conjunction with other measurements such as heart rate, training load, and sleep quality.

Are you looking for a way to enhance your performance and get the most out of your training?

We can help!

Our Personalised Strategy in our free eBook about The Female Athlete is designed to help you get the most out of your training, while saving time and money. It dives into detail on topics such as "How to Cycle Sync your Training to Your Menstrual Cycle", "Relative Energy Deficiency Syndrome", and more!

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References

1. Bai, X. et al. (2009) ‘Influence of the menstrual cycle on nonlinear properties of heart rate variability in young women’, American Journal of Physiology-Heart and Circulatory Physiology, 297(2). doi:10.1152/ajpheart.01283.2008.

2. Brar, T.K. (2015) ‘Effect of different phases of menstrual cycle on heart rate variability (HRV)’, JOURNAL OF CLINICAL AND DIAGNOSTIC RESEARCH [Preprint]. doi:10.7860/jcdr/2015/13795.6592.

3. Tenan, M.S. et al. (2014) ‘Changes in resting heart rate variability across the menstrual cycle’, Psychophysiology, 51(10), pp. 996–1004. doi:10.1111/psyp.12250.

4. Yazar, Ş. and Yazıcı, M. (2016) ‘Impact of menstrual cycle on cardiac autonomic function assessed by heart rate variability and heart rate recovery’, Medical Principles and Practice, 25(4), pp. 374–377. doi:10.1159/000444322.