For decades, pregnant women were told to take it easy. Don't raise your heart rate too much. Don't lift anything heavy. Sit down, rest, and "save your energy for labor."
I call BS on all of it.
Here's the problem: labor is the most physically demanding event most women will ever experience. And somehow we've convinced an entire generation of moms that the right way to prepare for an endurance event is to do less.
If you've been active your whole life and you're scared you'll have to give it all up for nine months, I want you to hear this loud and clear: you probably don't.
And if you've never been much of an exerciser and you're wondering if pregnancy is even a safe time to start? Also good news. For most women, it absolutely is.
In this post, we're going to dig into:
- The outdated myths about pregnancy exercise (and why they stuck around so long)
- What the current research actually says about safety
- How active moms can keep training, with smart modifications
- How beginners can ease into a pregnancy-safe routine
- Why your pelvic floor needs to be part of this conversation
This is your permission slip to stop tiptoeing around your own body. Let's get into it.
Myth #1: "Don't Raise Your Heart Rate Above 140 BPM"
If you were pregnant (or alive) in the '90s, you probably heard this one. The "140 bpm rule" has been floating around for so long that a lot of providers still repeat it without realizing where it came from.
Where it actually came from: a small 1985 study that monitored fetal heart rate during maternal exercise and noted some temporary dips (called bradycardia) when moms exercised at very high intensities. This idea emerged from research that found that, in some cases, fetal heart rate dropped below 110 bpm when pregnant people exercised with a peak heart rate of 180 bpm.
That's it. One small study, decades ago, became the foundation for a blanket rule applied to every pregnant woman regardless of fitness level.
What the research says now: Heart rate alone isn't a reliable way to gauge exertion during pregnancy, because your resting heart rate naturally increases during pregnancy, which means judging exercise intensity via typical heart rate metrics isn't always reliable. Newer studies on fetal heart rate response have shown mixed and largely reassuring results, including one study where exercise that raised maternal heart rate to an average of 176 bpm showed virtually no concerning changes in fetal heart rate.
A number on your watch isn't the gold standard. How you feel is.
Myth #2: "If You Were Active Before, You Have to Scale Way Back Now"
This is the one that makes my blood pressure rise (pun intended).
Runners get told to switch to walking. Lifters get told to drop the weights entirely. CrossFitters get side-eyed at every box in America the moment they announce a pregnancy.
What the research says: ACOG, the American College of Obstetricians and Gynecologists, has explicitly addressed this. ACOG advises that pregnant women who were previously very active, including running and jogging, can continue their level of activity, discussing any specific concerns with their OB provider.
For higher-intensity training specifically, vigorous-intensity exercise completed into the third trimester appears to be safe for most healthy pregnancies. The caveat is that competitive athletes require closer attention to avoiding overheating, staying hydrated, and maintaining adequate caloric intake to support fetal growth.
There's also reassuring data specific to running. A large international study of runners found that moderate-intensity exercise is generally accepted as likely safe during uncomplicated pregnancy and should be encouraged, even though high-impact activity hasn't been studied as extensively as other forms of exercise.
If you were a runner, lifter, or cyclist pre-pregnancy, the default assumption should be continuation with modification, not abandonment.
Talk to your provider, listen to your body, and adjust as needed. But "I have to stop everything" is not the evidence-based starting point.
Myth #3: "Starting a New Workout Routine During Pregnancy Is Risky"
This myth keeps women on the couch who would genuinely benefit from moving more, and it's backwards.
What the research says: Pregnancy is actually one of the best times to start, according to the official guidance. Obstetric care providers should encourage their patients to continue OR commence exercise as an important component of optimal health, and women who haven't had healthy activity habits before pregnancy are encouraged to use this time as a starting point.
The benefits aren't small, either. Regular exercise during pregnancy is associated with a decreased risk of cesarean delivery, faster postpartum recovery, lower glucose levels for women with gestational diabetes, and help in preventing preeclampsia.
The current recommendation for most healthy pregnant women is at least 2.5 hours of moderate aerobic activity per week, spread throughout the week, working toward 20 to 30 minutes most days.
You don't need a "before" fitness level to qualify for a "during" routine.
Walking, prenatal yoga, swimming, stationary biking, and bodyweight strength work are all excellent starting points, and your provider will likely be thrilled, not worried.
Myth #4: "Strength Training Is Too Dangerous While Pregnant"
This myth has deep roots. For a long time, lifting weights during pregnancy was avoided due to concerns about injury and possible fetal heart rate changes related to the Valsalva maneuver (holding your breath while bearing down), but it was largely precautionary, not evidence-based.
What the research says now: The guidance has shifted toward encouraging strength work as part of a well-rounded routine. ACOG's updated committee opinion reflects current literature showing both aerobic and strength conditioning exercises should be encouraged before, during, and after pregnancy.
The key modification isn't whether to lift. It's how. This is where breath mechanics matter enormously (more on that below), and it's also where a lot of women benefit from working with a pelvic floor physical therapist to learn how to brace and breathe under load without creating excessive downward pressure.
Strength training isn't off the table. The Valsalva hold-your-breath-and-grind approach might be. But learning to exhale through effort keeps lifting on the table well into the third trimester for most women.
If you're someone who likes structure (raise your hand if you're a recovering type-A athlete), this is exactly the kind of thing a platform like ZonalFit is built for. Programming that adjusts for trimester, flags high-impact or supine work after the first trimester, and adapts your loading as your body changes.
The Part Almost Nobody Talks About: Your Pelvic Floor
Here's where my PT brain takes over.
Every time you lift, run, jump, or even sneeze, you create intra-abdominal pressure. During pregnancy, your body is already managing a growing uterus, shifting hormones (hello, relaxin), and a core that's being asked to do more with less.
The old fear was that exercise (especially core or pelvic floor work) would make things worse: more diastasis recti, more pelvic floor dysfunction, more "damage."
What the research says: A randomized controlled trial specifically tested this. Researchers had pregnant women complete a 12-week abdominal and pelvic floor muscle exercise program during pregnancy and measured the gap between their abdominal muscles (the inter-recti distance, or IRD) afterward. The result? Abdominal and pelvic floor muscle training during pregnancy had a negligible effect on the IRD, meaning it didn't make diastasis recti worse.
Even more importantly, research on diastasis recti itself shows that the condition isn't really a strength problem you "exercise into existence." During pregnancy, abdominal muscles and connective tissues stretch as the uterus expands, aided by hormones like relaxin and estrogen, and some degree of separation is expected for nearly all women by the third trimester. Pelvic floor physiotherapists are specifically trained to develop exercise and movement strategies that support optimal physical function through pregnancy and prepare the body for birth.
Your core isn't fragile. It's adapting.
Training it correctly, with proper breath mechanics and pressure management, is part of how you prepare for the demands of labor, not something to avoid out of fear.
So... Who Should NOT Be Exercising?
I'd be doing you a disservice if I didn't mention this. Evidence-based doesn't mean ignoring red flags.
Certain conditions do warrant caution or modification, including bleeding, preeclampsia, severe anemia, certain heart or lung conditions, and placenta complications. If you're carrying multiples and at risk for preterm labor, your provider may also recommend a different approach.
This is exactly why every pregnant woman, athlete or beginner, should have a conversation with her OB or midwife about her specific situation before starting or continuing a routine. It's especially important for athletes and those with health conditions to consult with their physician and undergo a clinical evaluation before continuing an exercise program.
This isn't fear-mongering. It's just... medicine. Get the green light, then go train.
If You're Already Active: How to Keep Going
You don't need to start over. You need to adjust.
Reframe intensity. Instead of chasing a heart rate number, use perceived exertion and the "talk test." Can you hold a conversation? Good. Gasping for air? Back off.
Watch the heat. Thermoregulation is one of the few areas where the research consistently flags a real concern. One study on high-intensity running during pregnancy found that pregnant women can likely run safely for up to 35 minutes at 80 to 90% of their max heart rate in environments below 25°C (77°F), so summer training plans may need an indoor or early-morning pivot.
Shift your strength focus. As your center of gravity changes, prioritize stability and controlled tempo over max lifts. Exhale on exertion. Don't hold your breath and bear down.
Build in your fuel. Vigorous training, especially for athletes, requires close attention to hydration and adequate caloric intake to prevent the weight loss that can negatively affect fetal growth.
If You're Starting From Scratch: How to Ease In
You don't need a perfect plan. You need a starting point.
Start with walking. It sounds simple because it is. Walking is consistently named as one of the safest and most accessible ways to meet activity guidelines.
Add 10 minutes before you add intensity. Build duration first. Most guidelines point toward working up to 20 to 30 minutes of moderate exercise most days of the week as a realistic, sustainable goal.
Get curious about your pelvic floor early. You don't need to wait until something feels "off" to learn how to brace, breathe, and move with intention. This is the foundation everything else builds on.
Pick something you'll actually do. Prenatal yoga, swimming, a stationary bike, bodyweight circuits: the "best" exercise is the one that fits your life and that you'll keep showing up for.
The Bottom Line
Pregnancy isn't a 40-week pause button. It's training camp for the biggest physical event of your life, and the research increasingly backs that up.
If you've been active, you likely don't need to stop. You need to adjust intensity, watch the heat, and train your breath and pelvic floor alongside everything else.
If you're new to working out, pregnancy can be a genuinely great time to start, with the right guidance and a green light from your provider.
Either way, your body isn't fragile. It's capable. And the more you train it with intention now, the more prepared you'll be for labor day.
Want a head start on training for birth like the athletic event it is? Come find me on Instagram @the.pt.birth.nerd for evidence-based pregnancy and postpartum education, or reach out about working together in Kansas City, Overland Park, or virtually.
If you want programming that takes the guesswork out of training through pregnancy, adjusting automatically as you move through trimesters, I helped review the pregnancy programming for ZonalFit, a strength training platform built around your changing biology.
Frequently Asked Questions
Is it safe to exercise while pregnant?
For most healthy, uncomplicated pregnancies, yes. ACOG encourages both aerobic and strength conditioning exercise before, during, and after pregnancy. Certain conditions warrant caution or modification, so every pregnant woman should talk with her OB or midwife about her specific situation before starting or continuing a routine.
Do I have to keep my heart rate below 140 bpm during pregnancy?
No. The 140 bpm rule traces back to a small study from the 1980s and was never meant as a universal limit. Your resting heart rate naturally rises during pregnancy, which makes heart rate an unreliable way to gauge intensity. Perceived exertion and the talk test are more useful: if you can hold a conversation, you are likely working at an appropriate intensity.
Can I keep lifting weights or running if I was active before pregnancy?
Usually, yes, with modification rather than abandonment. ACOG advises that previously active women, including runners, can continue their level of activity while discussing specific concerns with their provider. The main adjustments are managing heat, hydration, and adequate calories, and learning to exhale through effort instead of holding your breath under load.
Is it safe to start a new workout routine during pregnancy?
For most healthy pregnancies, pregnancy can be a great time to start. Walking, prenatal yoga, swimming, stationary biking, and bodyweight strength work are all excellent starting points. The general recommendation is at least 2.5 hours of moderate aerobic activity per week, working toward 20 to 30 minutes most days, with a green light from your provider.
Does exercise during pregnancy cause or worsen diastasis recti?
A randomized controlled trial of a 12-week abdominal and pelvic floor exercise program found a negligible effect on the gap between the abdominal muscles, meaning training did not make diastasis recti worse. Some abdominal separation is expected for nearly all women by the third trimester. Training the core correctly, with proper breath mechanics and pressure management, is part of preparing for labor.
Sources & Further Reading
- American College of Obstetricians and Gynecologists. Committee Opinion 804: Physical Activity and Exercise During Pregnancy and the Postpartum Period. Read on ACOG.org
- Sperstad, J.B., et al. Pregnant women may exercise both abdominal and pelvic floor muscles during pregnancy without increasing diastasis recti abdominis. Indexed on PubMed.
- Bø, K., et al. "Cool Mama": Temperature Regulation During High-Intensity Interval Running in Pregnant Athletes. Indexed on PMC.