How pregnancy exercise affects HRV and resting heart rate over time

Podcast episode originally published on March 22, 2022

Pregnancy exercise changes heart rate variability, resting heart rate, and recovery in ways that have rarely been tracked continuously. In this episode of the WHOOP Podcast, Dr. Shon Rowan of West Virginia University School of Medicine joined Dr. Kristen Holmes, Global Head of Human Performance, Principal Scientist at WHOOP, and Emily Capodilupo, Senior Vice President of Research, Algorithms, and Data at WHOOP, to explain what a first-of-its-kind WHOOP study found when active women were followed before pregnancy, through pregnancy, and into postpartum.

The discussion explains why pregnancy research has lagged for decades, what current exercise guidance actually says, how HRV and resting heart rate change across pregnancy, and why exercise duration may matter more than workout intensity.

For the full discussion, hear Rowan, Holmes, and Capodilupo in Episode 165 of the WHOOP Podcast on Spotify.

Why has pregnancy exercise research been so limited?

Pregnancy exercise research has been limited because pregnant women have long been excluded from clinical studies, even when that exclusion leaves clinicians and patients with weak guidance. Rowan argues that the protection model has often produced the opposite of clarity, because the field ends up relying on guesswork, outdated advice, and retrospective observations instead of prospective data.

That gap is one reason this WHOOP study mattered. Rowan and his collaborators designed it around women who were already exercising, then followed them before pregnancy, during pregnancy, and after delivery. That approach let participants serve as their own controls. It also avoided prescribing exercise inside the study, which helped the team work within Institutional Review Board limits while still collecting continuous wearable data. In the end, 38 women enrolled, and 18 completed the full study with enough data to analyze. Rowan said all 18 remained physically active throughout pregnancy, and all delivered at term.

The design solved a problem that standard pregnancy studies often cannot solve. Instead of a single lab visit or a few snapshots from a Holter monitor, the researchers could see day-to-day changes in HRV, resting heart rate, and activity over months. WHOOP later published a summary of those findings in Pregnancy Study Shows Benefits of Exercise, Useful Trends in HRV & RHR, while Rowan noted that the underlying paper appeared in a BioMed Central journal.

Rowan put the broader evidence problem in stark terms:

“If you look at even drug studies that are out there, it's something like 98% of drugs approved have had no pregnancy data.”

That statistic helps explain why exercise guidance during pregnancy still feels inconsistent. When research is thin, cultural advice fills the gap. Family members, internet searches, and even clinicians can end up repeating rules that are decades out of date.

What you should take away

• Pregnancy research has historically excluded pregnant women, which has left major evidence gaps in exercise guidance
• The WHOOP study followed women who were already active, allowing each participant to serve as her own pre-pregnancy control
• Thirty-eight women enrolled, 18 completed the full protocol with enough data, and all 18 delivered at term
• Continuous wearable data can reveal trends that short, one-time measurements often miss

What does current guidance actually say about exercise during pregnancy?

Current guidance supports regular exercise during pregnancy for most healthy pregnancies, and the old heart-rate myths are outdated. Rowan walked through how the recommendations from the American College of Obstetricians and Gynecologists have changed over time, moving from rigid restrictions toward a more practical, exertion-based approach.

He highlighted several milestones. In 1985, the first formal committee opinion on exercise during pregnancy appeared. By 1994, the old advice to keep heart rate below 140 beats per minute had been removed. In 2002, guidance shifted toward recommending about 30 minutes of moderate exercise on most days. Rowan said the 2017 guidance continued that direction, recommending exercise three to four times per week at a moderate level and using perceived exertion rather than a hard heart-rate ceiling. Current ACOG guidance on physical activity and exercise during pregnancy and the postpartum period reflects the same overall approach.

Even so, outdated advice still circulates. Rowan described hearing patients told not to lift more than 10 pounds or 25 pounds, not to vacuum, or not to start moving if they were previously sedentary. He also noted that many people still worry too much about heart rate or temperature without accounting for context. His practical guidance was less dramatic and more useful: stay hydrated, keep your body cool, and use common sense around exertion.

Rowan summarized the mismatch between current recommendations and older myths this way:

“That whole idea of, ‘Do not let your heart rate get above 140,’ was 1985. 1994, that was removed. It's been removed since 1994, and yet we still hear that all the time.”

This is also why generic search advice can be frustrating. Terms like “moderate exercise” sound simple, but they are hard to apply if nobody explains what moderate feels like in real life. Rowan described it as effort where you know you worked, but you are not wiped out and lying on the floor recovering for 10 minutes.

Rowan goes deeper on outdated exercise myths and ACOG guidance in the full episode over on Spotify.

What you should take away

• Current pregnancy exercise guidance relies more on perceived exertion than on strict heart-rate cutoffs
• The old “stay under 140 bpm” rule was removed decades ago, yet it still shapes advice many people hear
• For most healthy pregnancies, regular movement, hydration, cooling, and common sense matter more than arbitrary lifting limits
• Pregnancy does not automatically rule out starting a reasonable exercise routine if you were previously inactive

What happened to HRV and resting heart rate during pregnancy in this WHOOP study?

In this study, HRV generally fell and resting heart rate generally rose through much of pregnancy, then both trends reversed about seven weeks before delivery. That late-pregnancy reversal is the finding Rowan found most interesting, because previous studies using short monitoring windows had not captured it.

To understand why the result stood out, it helps to define HRV clearly. Heart rate variability measures the variation in time between heartbeats. In everyday terms, higher HRV often reflects a system with more flexibility and readiness, while lower HRV can reflect added physiological strain. If you want a deeper baseline on the metric itself, see HRV 101: Insights From the WHOOP Podcast.

That framework makes the pregnancy pattern easier to read. The body is taking on extra cardiovascular work as pregnancy progresses, so a drop in HRV and a rise in resting heart rate are not surprising. Rowan said the cohort showed that same broad pattern seen in earlier trimester-based studies. What changed with continuous monitoring was the resolution. Instead of averaging an entire trimester, the team looked week by week and found an inflection point roughly 50 to 56 days before birth.

Rowan described the timing this way:

“When you actually broke it down by week, it was somewhere around 50, 56 days prior to delivery, we saw a complete reversal.”

From that point forward, HRV started rising and resting heart rate started falling, and the pattern continued into postpartum. Rowan also described anecdotal cases where participants noticed a sharp shift in their data before a missed period and before a positive pregnancy test. He was careful not to treat that as a diagnostic claim. WHOOP is not a medical device, and the episode did not present WHOOP as a pregnancy test. What the study does suggest is that personal baseline data can reveal very early physiological changes that people may otherwise miss.

The seven-week reversal later became an important thread in broader WHOOP pregnancy research, including Episode 197 on HRV and preterm birth. In this earlier Rowan cohort, though, the key point was simpler: continuous tracking revealed a repeatable pattern that short, intermittent monitoring had missed.

Holmes and Rowan unpack the seven-week inflection pattern in the full episode over on Spotify.

What you should take away

• HRV tended to decline and resting heart rate tended to rise through most of pregnancy in this cohort
• The study found a reversal roughly 50 to 56 days before delivery, with HRV rising and resting heart rate falling
• Continuous wearable monitoring made that week-by-week reversal visible in a way older snapshot studies could not
• Early shifts in personal baseline data may help people notice physiological changes sooner, but WHOOP does not diagnose pregnancy

Can exercise during pregnancy improve postpartum HRV and recovery?

This study suggests that continued exercise during pregnancy can support better postpartum cardiovascular trends, and exercise duration may matter more than intensity. Rowan said the women in the cohort wore WHOOP for at least 12 weeks after delivery, which gave the team a usable postpartum window instead of stopping at birth.

One of the most interesting findings was that postpartum HRV exceeded pre-pregnancy baseline in the cohort. Rowan framed that as evidence that women may preserve, and in some cases improve, fitness through pregnancy when they keep moving. That finding pushes back against the assumption that pregnancy automatically erases training progress.

Rowan stated the central result directly:

“Women in our study had a higher HRV in their postpartum period than they did in their pre-pregnancy period.”

The exercise pattern mattered too. Rowan said the data suggested that total minutes of exercise were more strongly associated with improved postpartum HRV than intensity was. That is a practical result. It means the upside may come from staying consistent and accumulating activity, even when harder sessions become less appealing or less comfortable later in pregnancy.

That conclusion fits the rest of the cohort profile. Participants included powerlifters, CrossFit athletes, cyclists, marathon runners, and women whose main goal was simply to stay active. Many adjusted their training as pregnancy progressed, and Rowan said monthly surveys showed that people often reduced how hard they were pushing while still keeping movement in the routine. He did not present the answer as “train harder.” He presented it as “keep doing something.”

That approach also aligns with personal stories WHOOP has shared elsewhere, including WHOOP Pregnancy Data: Trends in Resting Heart Rate, HRV, Strain, Sleep & More, where pregnancy-related changes in resting heart rate, HRV, Strain, and sleep were tracked over time.

If you want to hear Rowan explain why minutes mattered more than intensity in this cohort, go to the full episode over on Spotify.

What you should take away

• Postpartum HRV was higher than pre-pregnancy baseline in this cohort of active women
• The data suggested that exercise duration mattered more than workout intensity for postpartum HRV improvements
• Consistent movement during pregnancy can coexist with scaled-back training intensity
• Pregnancy does not automatically mean losing all of your hard-earned fitness

How can WHOOP data support pregnancy monitoring and future research?

WHOOP data can help define what normal pregnancy physiology looks like over time, and that may eventually improve how trends are interpreted by researchers and clinicians. Capodilupo and Holmes both argued that the real value of wearables here is scale plus continuity, because pregnancy, postpartum, perimenopause, and menopause all involve long arcs of change that are poorly captured by occasional office visits.

That was the bridge from Rowan's initial study to broader reproductive health research. In Episode 165 of the WHOOP Podcast, Capodilupo described new survey work designed to include people trying to conceive, people who were pregnant, people in the first 12 months postpartum, people entering perimenopause, and people who were postmenopausal. The goal was to define normal first, then identify patterns that may deserve closer attention. Rowan added that the same research gap exists in menopause care, where many women are still told that symptoms are simply part of life rather than something worth measuring carefully.

Capodilupo explained the research goal this way:

“We want to understand, first and foremost, what does normal [...] look like? And then over time, what can we start to see about what's not normal?”

The conversation also raised an important caution. Rowan said he would be careful about asking pregnant people to monitor a possible preterm-birth trend on their own, especially if that creates anxiety that could itself affect physiology. His preference was a clinician-facing model, where a care team could be alerted to a meaningful pattern without asking the patient to stare at every fluctuation. That is a useful distinction for any wearable feature tied to pregnancy. WHOOP can surface trends. Clinical interpretation still belongs in a medical setting.

Since this episode aired, WHOOP has expanded on the same research direction in Understanding Pregnancy with New Research and Pregnancy Insights. That later work built on the same core idea introduced here: if you can observe enough pregnancies continuously, you can ask better questions about timing, symptoms, exercise, sleep, and postpartum recovery.

Capodilupo explains the larger reproductive health research agenda in the full episode over on Spotify.

What you should take away

• WHOOP data is especially useful for longitudinal research because it tracks physiology continuously across months
• Capodilupo and Holmes framed the next step as defining normal pregnancy, postpartum, and menopause patterns at larger scale
• Rowan cautioned that pregnancy trend alerts should be interpreted carefully and ideally with clinician involvement
• WHOOP can reveal trends that lead to better questions, but it does not replace medical care

The bottom line

• Pregnancy exercise research has been limited for decades because pregnant women were often excluded from prospective studies
• In Rowan's WHOOP cohort, HRV generally declined and resting heart rate generally rose through most of pregnancy
• The study found a repeatable reversal about 50 to 56 days before delivery, when HRV began rising and resting heart rate began falling
• All 18 women in the final analyzed cohort delivered at term and remained physically active throughout pregnancy
• Postpartum HRV in this cohort was higher than pre-pregnancy baseline, suggesting that fitness can be maintained or improved through pregnancy
• Exercise duration appeared to matter more than intensity for postpartum HRV in this study
• WHOOP can help people and researchers see long-term physiological trends that short snapshot studies often miss
• Pregnancy trend data is most useful when it supports better conversations with a clinician, because WHOOP is not a medical device

Frequently asked questions about things discussed in this episode

How does WHOOP measure HRV during pregnancy?

WHOOP measures HRV during sleep and compares nightly values with your personal baseline, which makes pregnancy-related trend changes easier to spot over time. In this episode, HRV was one of the main signals that fell through most of pregnancy and then rose again in the weeks before delivery.

What does WHOOP track besides HRV during pregnancy?

WHOOP tracks resting heart rate, sleep, Strain, and Recovery-related trends that help put pregnancy physiology in context. In Rowan's study, resting heart rate rose for much of pregnancy and then declined around seven weeks before birth.

What does WHOOP data suggest about exercising during pregnancy?

WHOOP data in this study suggests that continued activity during pregnancy was associated with better postpartum HRV, and total exercise minutes mattered more than intensity. The cohort was made up of women who were already active, so WHOOP should be used as trend context alongside clinical guidance.

Can WHOOP tell you that you are pregnant?

WHOOP can reveal baseline shifts that some people notice before a missed period, but WHOOP does not diagnose pregnancy. Rowan described participants who saw their data change before a positive test, yet the episode did not present WHOOP as a pregnancy test.

What does WHOOP show after delivery?

WHOOP showed that postpartum HRV in this cohort rose above pre-pregnancy baseline, which suggests that fitness was maintained or improved for many participants. Rowan said the pattern continued through the postpartum monitoring window of at least 12 weeks.

What does WHOOP do for pregnancy research?

WHOOP supports pregnancy research by collecting continuous wearable data before, during, and after pregnancy at a scale that traditional studies often cannot match. Capodilupo described using that kind of data to define normal physiology across trying to conceive, pregnancy, postpartum, perimenopause, and menopause.

What does WHOOP do when pregnancy trends change unexpectedly?

WHOOP shows personal trends, but care decisions still belong with a clinician because WHOOP is not a medical device. Rowan said a clinician-facing alert model would be more useful than asking pregnant people to monitor every fluctuation on their own.

For pregnancy, the clearest value of WHOOP is seeing HRV, resting heart rate, sleep, and activity trends early enough to ask sharper questions through each trimester and into postpartum.