Same Workout, Different Numbers: Exercise HR Across Your Cycle

Same route, same pace, same playlist. But your watch shows a different heart rate than it did two weeks ago. You don't feel like you're working any harder. Here's what the research actually says about why the number moves.

By Go Go Gaia Team July 13, 2026 9 min read

Quick Answer: Does Exercise Heart Rate Change With Your Cycle?

A 2021 study of endurance-trained women found that heart rate during identical high-intensity interval workouts ran about 2 to 3 beats per minute higher in the late-follicular and mid-luteal phases than in the early-follicular phase. Perceived exertion (RPE), meaning how hard the effort felt, stayed essentially flat across all three phases.^[1] Same workout, same effort, a slightly different number on the chest strap.

The pattern isn't universal. A review of submaximal, steady-state exercise found no consistent cycle effect on heart rate or RPE at all,^[3] and a separate study on untrained women found perceived effort ran higher specifically during menses.^[2] The honest summary: exercise heart rate can shift with cycle phase, especially in higher-intensity, trained-population studies, but it isn't a rule that applies the same way to every workout or every person.

Educational content about published research, not medical or training advice. For personal training questions, talk to a coach or your doctor.

Wearables make heart rate impossible to ignore. Every run, every spin class, every set gets a number attached to it, and eventually you notice the number doesn't always match the day. You finish a workout that felt completely normal and your average heart rate reads a few beats higher than the same workout two weeks ago. Nothing about the route, the pace, or how you felt was different.

A handful of exercise physiology studies have actually measured this, and the pattern they find is more specific and more limited than most fitness content implies. This page reports what the studies measured: heart rate at matched exercise intensity across cycle phases, and how that compares to how hard the exercise actually felt. It isn't a guide to changing your training. It's a look at what's happening on the chest strap and why the number and the feeling don't always move together.

For general guidance on training with your cycle in mind, see our cycle syncing app guide. This page stays narrower: the heart-rate mechanism itself, not what to do about it.

The Study: Same Intensity, Different Heart Rate

The clearest data point here comes from a 2021 study published in the International Journal of Environmental Research and Public Health.^[1] Researchers had 21 eumenorrheic, endurance-trained women complete a high-intensity interval running protocol, eight 3-minute bouts at 85% of their maximal aerobic speed, in three separate cycle phases: early-follicular (days 2 to 5), late-follicular (one to three days before ovulation), and mid-luteal (five to nine days after ovulation). Researchers confirmed phase with a three-step method combining calendar tracking, urinary LH testing, and blood hormone panels, not just counting days on a calendar.

The workout itself never changed. Same intervals, same target pace, same recovery periods. What changed was the heart rate response. Average heart rate during the high-intensity bouts came in at 167.3 beats per minute in the early-follicular phase, compared to 169.9 beats per minute in both the late-follicular and mid-luteal phases, a gap of roughly 2 to 3 beats per minute. The difference between early-follicular and late-follicular was statistically significant, and the overall model showed cycle phase had a measurable effect on heart rate across the three phases.

The same study measured rating of perceived exertion (RPE), the standard 1-to-10 or 6-to-20 scale athletes use to rate how hard an effort feels. RPE stayed flat. So did oxygen consumption, carbon dioxide production, and breathing frequency. The researchers' own conclusion was direct: sex hormone fluctuations across the cycle weren't large enough to disrupt the body's overall response to high-intensity exercise, but heart rate and minute ventilation stood out as the two variables that did shift, enough that the study's authors suggested heart-rate-based training programs should account for cycle phase.

Why the Number Moves But the Effort Doesn't

Heart rate and perceived effort usually track together. Push harder, your heart rate climbs, and it feels harder. That's the whole premise behind heart-rate zone training. So a gap between the two, where the number rises but the feeling doesn't, is worth explaining.

The leading physiological explanation ties back to progesterone. In the luteal phase, progesterone rises and has a thermogenic effect, meaning it raises resting core body temperature by roughly 0.3 to 0.5 degrees Celsius.^[4] A warmer starting point means your cardiovascular system has to work a little harder to move blood and manage heat during exercise, even at an identical workload. That extra cardiac effort shows up as a higher heart rate. Our wearable-tracking explainer covers the same temperature mechanism as it applies to resting heart rate. This is the exercising version of that story.

Perceived exertion doesn't rise the same way because RPE isn't purely a readout of heart rate. It draws on breathing effort, muscle sensation, and central nervous system signals, a different set of inputs than the ones driving a few extra heartbeats per minute. Researchers don't have a fully confirmed explanation for why the two decouple here. What the data shows is that they can move independently, and in this study, they did.

Worth knowing: this is a population-level pattern from controlled studies averaging results across many people and many sessions. It describes what researchers found when they measured heart rate and effort side by side, not a signal to read into any single workout on your own watch.

It's Not Universal: What Other Studies Found

The endurance-trained study above is the most detailed data point, but it isn't the whole picture, and stacking it against other research is where the honest complexity shows up.

A widely cited 2003 review in Sports Medicine looked broadly at submaximal, steady-state exercise, walking, cycling, and running at a constant, moderate pace, rather than high-intensity intervals.^[3] Across that body of research, oxygen consumption, heart rate, and RPE mostly showed no consistent cycle-phase effect. The review's broader conclusion was that regularly menstruating athletes generally don't need to adjust for cycle phase to perform well, though it flagged that prolonged exercise in hot conditions during the luteal phase can add extra cardiovascular strain, tying back to the same temperature mechanism.

A 2023 study took the opposite angle and found the opposite result. Researchers tested untrained women on a graded cycling test and found RPE was significantly higher during the early-follicular phase, which for most participants overlapped with menses, than during ovulation or the mid-luteal phase.^[2] Perceived recovery after the test was also lower during menses. That's a reversed pattern from the endurance-trained study, in a different population doing a different kind of test.

Put together, three things seem to matter for whether a cycle-phase effect on heart rate or RPE shows up at all: how trained the participants are, whether the exercise is high-intensity intervals or steady submaximal work, and whether menses itself, rather than cycle phase generally, is part of what's being measured. None of the studies agree on a single clean rule, and that disagreement is itself the accurate finding, not a reason to round it off to something simpler.

What This Looks Like on a Wearable

Translate the research to a smartwatch screen and the practical version is small: on some days, for some people, the same workout might read a couple of beats per minute higher than it did a couple of weeks earlier, without feeling any different. Plenty of other things move exercise heart rate: sleep, heat, hydration, caffeine, illness, training load. A shift of 2 to 3 bpm tied to cycle phase is a minor input in a noisy signal, not a dominant one.

Cycle-detection features on devices like Oura and Apple Watch don't use exercise heart rate to place you in a phase, and for good reason: a workout heart rate bounces around with pace, terrain, and weather in ways an overnight resting reading doesn't. Our HRV and resting heart rate explainer covers the metrics wearables actually lean on for that.

Go Go Gaia pulls in exercise heart rate data from connected wearables like Apple Watch, Oura, and Garmin, and logs it alongside the cycle phase you're tracking. That's the extent of it: the numbers sit next to each other in your history so you can look at your own workouts over time if you're curious. The app doesn't interpret the pattern or suggest changing how you train around it.

The Short Version

Strip the research down to what's actually established:

In one study of trained women doing high-intensity intervals, heart rate ran about 2 to 3 beats per minute higher in the late-follicular and mid-luteal phases than in the early-follicular phase, at identical workloads.
Perceived exertion stayed flat across all three phases in that same study. The workout felt the same even though the heart rate number didn't match.
The likely driver is progesterone's thermogenic effect, which raises resting core temperature and adds a small cardiovascular load during the luteal phase.
Other studies on steady-state exercise or untrained populations found no effect, or a different effect entirely. The pattern depends on training status, exercise type, and which phase is being compared.

None of this changes what a workout should look like. It's a description of a small, real, and inconsistent physiological pattern, not a set of instructions.

Frequently Asked Questions

Educational information based on published research. Not medical or training advice.

Does your heart rate really change during a workout depending on your cycle phase?

In one study of endurance-trained women doing identical high-intensity interval workouts, heart rate ran about 2 to 3 beats per minute higher during the late-follicular and mid-luteal phases compared to the early-follicular phase, a difference the researchers found statistically significant. The exercise intensity, pace, and effort were the same across phases. Only the heart rate number moved.

Why doesn't perceived effort (RPE) match the heart rate number?

In that same study, rating of perceived exertion stayed essentially flat across all three cycle phases even as heart rate shifted. Researchers haven't pinned down exactly why cardiac response and effort perception decouple this way. One idea is that perceived exertion draws more on central factors like breathing effort and muscle sensation than on heart rate itself, so a few extra beats per minute don't necessarily register as harder work.

Does this pattern show up in every study?

No. A widely cited review of submaximal, steady-state exercise found no consistent cycle-phase effect on heart rate or RPE at all. A separate study on untrained women found the opposite direction, with perceived effort running higher specifically during menses. The exercise type, intensity, and whether someone is trained or untrained all seem to change what shows up.

Which cycle phase shows the highest exercise heart rate?

In the endurance-trained study, the late-follicular and mid-luteal phases showed slightly higher heart rate than the early-follicular phase during high-intensity intervals, a gap of roughly 2 to 3 beats per minute. That's a specific finding from one study population and one type of workout, not a rule that applies to every phase, every workout, or every person.

If my smartwatch shows a higher workout heart rate one week, does that mean something is wrong?

Not necessarily. The research above describes a population-level pattern averaged across many workouts and many participants, not a rule for reading a single day's number. Sleep, heat, hydration, caffeine, and training load all move exercise heart rate too, often by more than a cycle phase does. A single reading isn't enough to draw a conclusion from.

Can wearables use exercise heart rate to detect cycle phase?

Not really, and most don't try. Cycle-detection features on devices like Oura and Apple Watch rely mainly on overnight skin temperature, with resting heart rate and HRV as supporting signals, because those are measured under stable, controlled conditions. Exercise heart rate bounces around with pace, terrain, and heat, which makes it a poor standalone signal for placing you in a cycle phase.

Does Go Go Gaia track exercise heart rate?

Go Go Gaia pulls in exercise heart rate data from connected wearables like Apple Watch, Oura, and Garmin, alongside the cycle phase you're tracking, so you can see your own workout numbers next to where you are in your cycle. It logs the data. It doesn't tell you what your numbers mean or suggest changing anything about how you train.

Your workout heart rate, next to your cycle.

Connect Apple Watch, Oura, or Garmin and see your exercise heart rate logged alongside whatever else you're tracking, phase by phase, cycle by cycle.

See Your Own Data

Connects with Apple Watch, Oura, and Garmin.

References

Rael B, Alfaro-Magallanes VM, Romero-Parra N, Castro EA, Cupeiro R, Janse de Jonge XAK, Wehrwein EA, Peinado AB. Menstrual Cycle Phases Influence on Cardiorespiratory Response to Exercise in Endurance-Trained Females. Int J Environ Res Public Health. 2021;18(3):860. doi:10.3390/ijerph18030860
Delp M, Chesbro GA, Pribble BA, Miller RM, Pereira HM, Black CD, Larson RD. Higher rating of perceived exertion and lower perceived recovery following a graded exercise test during menses compared to non-bleeding days in untrained females. Front Physiol. 2023;14:1297242. doi:10.3389/fphys.2023.1297242
Janse de Jonge XAK. Effects of the menstrual cycle on exercise performance. Sports Med. 2003;33(11):833-851. doi:10.2165/00007256-200333110-00004
Goodale BM, Shilaih M, Falco L, Dammeier F, Hamvas G, Leeners B. Wearable Sensors Reveal Menses-Driven Changes in Physiology and Enable Prediction of the Fertile Window. J Med Internet Res. 2019;21(4):e13404. doi:10.2196/13404