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Sleep and resting heart rate across your cycle

By Chris Ayers 6 min read

If you wear a watch or a ring to bed, you have probably seen your resting heart rate drift up and down over a month with no change in training to explain it. Part of that drift is your cycle. The pattern is small, it is real, and it has been measured with wrist and ring sensors in more than one study.

Sleep is a different story. The studies disagree, and I would rather show you the disagreement than pick a side.

Resting heart rate: a small, repeatable pattern

One clear measurement came from a 2017 study in Scientific Reports. Researchers put a wrist sensor on 91 women for 274 ovulatory cycles and recorded pulse during sleep. Pulse rose 2.1 beats per minute in the fertile window compared with the menstrual phase. Mid-luteal pulse was 1.8 beats above the fertile window and 3.8 beats above the menstrual phase. Put simply, lowest during your period, climbing through the middle of the cycle, highest in the second half.

A 2024 study in the Journal of Biological Rhythms found the same low point with a ring instead of a wristband. It followed 116 healthy women, split into two age groups (18 to 35 and 42 to 55), for one cycle each, with home ovulation (LH) tests. “HR was lowest during menses in both groups.”

A 2019 paper in the Journal of Medical Internet Research, from the same research group as the 2017 study, used a bracelet again. In 237 women wearing it at night, the phase shifts in wrist temperature, heart rate and breathing rate were all significant. The same paper cites earlier clinical work showing that nightly basal temperature rises 0.28 to 0.56 C after ovulation, and that resting pulse, breathing rate and heart rate variability also run higher in the luteal phase. That study was built to predict fertile days, which is not what Ferrabelle is for, so I am borrowing only its physiology.

Three datasets, two kinds of sensor, one shape. Your heart beats a few times more per minute in the second half of your cycle than in the first. If you have ever stared at a recovery score on day 22 wondering what you did wrong, this may be the answer. Nothing.

Sleep: the evidence does not agree

The 2024 ring study looked for a sleep effect and did not find one. In the authors’ words: “No significant menstrual cycle changes were detected in wearable-derived or self-reported measures of sleep efficiency, duration … or sleep quality.” What did change was mood, which was more positive around ovulation, and physical symptoms, which showed up during menses.

The FENDURA project, published in the Journal of Sports Sciences in 2025, found something else. It followed 58 female endurance athletes for a full year, logging symptoms, sleep quality, readiness and resting heart rate. “Perceived sleep quality was lower during pre-bleeding compared to bleeding days.” Symptom severity was higher on bleeding days than on other days, in every group, and more severe symptoms went with worse sleep and lower physical readiness to train.

Why the difference? I can only point at the obvious ones. One study watched a single cycle in healthy volunteers, with a ring and a daily sleep rating. The other watched athletes for twelve months with a diary, and its sleep finding compares the days just before bleeding with bleeding days, which is a narrower question. Both could be right about the people they studied. I do not know which one is right about you, and I would be suspicious of anyone who claimed to.

Reading your own numbers

The practical lesson from all of this is about the comparison you make, not the number itself. A resting heart rate of 58 means nothing on its own. A resting heart rate of 58 when your own usual is 54 means something, and it means less if you are on day 22 than if you are on day 3.

That is why the Fe Score compares your resting heart rate and heart rate variability with your own 30-day baseline, not with a population chart. When either one is well off your usual, a short line under today’s score says by how much. Today’s score is free; the score history is part of Pro.

The numbers can come from your wearable through Health Connect. Ferrabelle only reads from Health Connect and never writes to it. It reads resting heart rate, heart rate variability, sleep sessions and more, and the raw values never go to an AI provider or a partner. As the accuracy page puts it, “If you connect a wearable, its nightly temperature and heart-rate signals feed ovulation detection where your device provides them.” The validated wearable accuracy numbers are still coming, and I will not quote one here until they exist.

A few things worth doing with what you now know.

This is general information, not medical advice. Talk to your doctor about your own health.

Ferrabelle is in a closed test on Google Play right now. If you want to try it, you can join at ferrabelle.com/testers.

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