Why your hormones are not a side issue in endurance training

You know that route well. Same route, same effort, same conditions, but everything about it feels completely different. Heart rate is higher than the training load justifies, legs are heavy, and the watch says recovery looks fine.

This is not a bad day or a fitness question. It is oestrogen and progesterone operating on an internal schedule that most training plans have never accounted for. Here is what is actually happening.

One note before proceeding: the typical 28-day cycle is a statistical average, and cycle length ranges from 21 to 35 days in women with regular periods. What follows describes the hormonal pattern, rather than a fixed day schedule.

What oestrogen and progesterone are actually doing

The menstrual cycle is governed mainly by two hormones: oestrogen and progesterone. Neither stays steady. Both rise and fall in a predictable wave pattern throughout the cycle, affecting energy metabolism, thermoregulation, muscle repair, connective tissue, and the autonomic nervous system. These interactions affect many of the signals that wearables use to estimate recovery, readiness, and strain.

The follicular phase: rising oestrogen and fuel availability

The follicular phase starts on day one of menstruation and ends at ovulation. Oestrogen rises steadily while progesterone stays low throughout. Some research suggests oestrogen may promote fat oxidation during endurance exercise, though findings across studies are not uniform. Some studies have reported higher HRV and lower resting heart rate during parts of the follicular phase compared with the luteal phase, which may show up as improved recovery scores on Garmin or WHOOP.

Ovulation: the hormonal peak

A surge in luteinising hormone (LH) triggers ovulation. Peak oestrogen is observed at this point, while progesterone remains low and begins its substantial rise only after ovulation. Some women report feeling stronger or finding hard workouts more manageable around ovulation, although responses vary considerably. Body temperature rises after ovulation as progesterone increases, a shift detectable on a basal body temperature chart.

A 2017 meta-analysis by Herzberg et al. found significantly increased ACL laxity during the ovulatory phase compared with the follicular phase, coinciding with peak oestrogen. The overall strength of that evidence is graded low, and whether it meaningfully increases injury risk in practice remains debated. Wearable data cannot capture this.

The luteal phase: progesterone changes the equation

After ovulation, progesterone rises sharply and becomes the dominant hormone. This is the phase most runners notice most clearly, and the one most visible in wearable data.

Baker et al. (2020) showed that progesterone elevates core body temperature by approximately 0.3-0.7℃ from baseline. That shift means the body has to work harder to stay cool during training. Heart rate at the same pace will be slightly higher, particularly toward the end of the luteal phase and more pronounced in warmer conditions.

The luteal phase is where hormonal effects on wearable data are most apparent. Many women see reduced HRV, elevated resting heart rate, increased skin or body temperature, and lower recovery scores, all without any change in training load. Sleep may also suffer, with more nighttime awakenings or reduced sleep quality.

Menstruation: reset, not shutdown

From a hormonal perspective, menstruation is the beginning of the cycle, not the end. Oestrogen and progesterone are low, and the conditions of the follicular phase begin to return. For some athletes, menstrual symptoms are the primary challenge. For others, menstruation is simply another week of training.

Menstruation is also an important health marker. Changes in cycle length or loss of menstruation can be important indicators of low energy availability and possible RED-S (Relative Energy Deficiency in Sport). In that context, the cycle becomes a physiological performance measure rather than something separate from training.

Individual variation matters more than any phase chart

Some athletes notice clear changes in recovery, effort, sleep, and performance across the cycle. Others notice almost none. Hormonal patterns provide context but do not determine outcomes. Training history, sleep, nutrition, life stress, environmental conditions, and overall health remain large factors. The most useful approach is to treat cycle tracking as another data source rather than a performance prediction.

What wearables are actually measuring

No current consumer wearable measures oestrogen or progesterone directly. What devices can monitor are the downstream effects: skin temperature, HRV, resting heart rate, respiratory rate, and sleep architecture. Those signals do reflect real hormonal influences, which is why recovery scores after ovulation tend to differ from those in the follicular phase.

The bottom line

Hormones affect physiology more reliably than they affect performance. Wearables can now track changes in body temperature, heart rate, HRV, and recovery metrics across the cycle with increasing confidence. How those physiological changes translate to race results is more complex and more individual.

Understanding the menstrual cycle is not about finding a universal training strategy. It is about understanding why heart rate, HRV, body temperature, and perceived effort may fluctuate, and interpreting your own data in that context rather than treating every variation as a problem to fix.

Quick answers

Does the menstrual cycle affect heart rate during running?
Yes. Progesterone in the luteal phase raises core body temperature by approximately 0.3-0.7℃, which increases the cardiovascular demand of running at a given pace. Heart rate at the same speed may read higher than in the follicular phase, with no change in fitness. The effect is more pronounced in warmer conditions.

Why do WHOOP or Garmin recovery scores drop in the second half of the cycle?
The luteal phase typically produces lower HRV, higher resting heart rate, and elevated skin temperature. Wearables interpret these physiological signals as incomplete recovery. They are registering real hormonal effects, not training errors. Tracking multiple cycles helps distinguish a hormonal pattern from a genuine recovery problem.

Can wearables track hormone levels directly?
No current consumer device measures oestrogen or progesterone directly. Devices measure downstream effects: skin temperature, HRV, resting heart rate, and respiratory rate. Several companies are developing tools to infer hormonal shifts from these signals, but direct hormonal measurement is not yet available in a validated consumer product.

What is RED-S, and how is the menstrual cycle connected to it?
RED-S (Relative Energy Deficiency in Sport) is impaired physiological function caused by insufficient energy availability relative to exercise demands. Changes in cycle length or loss of menstruation can be important indicators of low energy availability and the development of RED-S. Any significant change in cycle regularity warrants attention, particularly in athletes who have increased training load or reduced food intake.

Does the menstrual cycle increase injury risk?
Evidence suggests that ACL laxity increases around ovulation, coinciding with peak oestrogen levels. A 2017 meta-analysis found this effect, though the overall quality of the evidence is graded as low, and the clinical significance is debated. There is no established protocol for modifying training based on the cycle phase to prevent injury.

This article is part of the site’s female athlete tech coverage. For tested product recommendations across wearables, recovery trackers, and heart rate monitors, see the best wearables for female endurance athletes.

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Last Updated on 24 July 2026 by the5krunner