Heart Rate Variability (HRV) And The Menstrual Cycle
In this post, we cover a few insights derived from recent research on HRV and the menstrual cycle, including a journal paper just published by Patricia Doyle-Baker and her group at the human performance lab, University of Calgary, using HRV4Training.
This is the first study ever to monitor HRV daily during the menstrual cycle to understand the impact of different phases of the cycle on autonomic activity (which is crazy if you ask me, considering that it's 2019). Anyhow, we are glad HRV4Training made it possible to finally collect real life data with high compliance and I hope this write up will be useful to better analyze your own data or your athlete's data, so that you can include an additional piece of information in the decision making process.
In literature, the relation between menstrual cycle and HRV is investigated to understand if the menstrual cycle can act as a confounding factor when analyzing HRV data, for example because of changes during the different phases of the cycle that would require to interpret the data differently. The first potential confounding effect of the menstrual cycle brought up in literature is at the population level, so for analysis that look at sex differences in HRV features. This is not really something too relevant in our case, as we always stress that data should be analyzed at the individual level, with respect to your historical data, and not compared to others (Aubert et al, heart rate variability in athletes). Many studies in literature have shown that regulation of the ANS is modified during the menstrual cycle, hence the need to further investigate the relationship with our marker of parasympathetic activity, rMSSD.
A second and more relevant aspect, tightly coupled with what just discussed, is that if different phases of the cycle have an influence on autonomic activity, then even at the individual level HRV data might be affected by the cycle phase, which should be accounted for when we look at our data. HRV analysis in women may be inconsistent if HRV cannot be considered stable across the menstrual cycle or if the expected differences are not accounted for. This can be an issue as interpretation may lead to inappropriate conclusions.
What do we know?
An increase in sympathetic drive or decrease in parasympathetic activity after ovulation is possible because studies have consistently shown an increase in metabolic rate in this period (Tenan et al, Changes in resting heart rate variability across the menstrual cycle). Most results suggest therefore that the follicular phase is characterized by enhanced vagal activity while the luteal phase by enhanced sympathetic activity, as often highlighted by increased heart rate and reduced HRV across the cycle.
This relationship has been shown in most studies in literature, despite the fact that we do have some inconsistencies (studies showing the opposite relationship or a lack of relationship - we will discuss this in the next section). We can derive the following high level view:
- Follicular -> More parasympathetic
- Luteal -> More sympathetic
This means that most studies have also shown a consistent increase in heart rate and reduction in HRV across the cycle (different metrics reported in various papers, for example rMSSD and HF, both representative of parasympathetic activity).