Heavy Lifting During Pregnancy Is Safe—Now We Have Evidence
The Fear-Based Restrictions
If you're pregnant and interested in continuing strength training, you've probably been told to back off the intensity. Use lighter weights. Avoid lying on your back. Don't hold your breath during lifts.
Not because there's evidence these things cause harm—but because there's been no evidence proving they're safe.
Current clinical practice guidelines recommend moderate-intensity resistance exercise during pregnancy but typically discourage high-intensity training due to theoretical concerns:
The Valsalva maneuver (breath-holding during heavy lifts) might reduce cardiac output and limit fetal perfusion
Supine positioning might compress the vena cava and restrict maternal and fetal blood flow
Heavy loads might... do something harmful (the concern is vague because the evidence doesn't exist)
For women who participate in strength sports—powerlifting, Olympic weightlifting, CrossFit—these restrictions are frustrating. Backing off to "moderate intensity" means abandoning the training that maintains their strength, performance, and identity.
An online survey of 679 women who lifted at least 80% of their one-repetition maximum during pregnancy found that those who maintained their training intensity had a 51% reduction in pregnancy and delivery complications compared to those who reduced intensity to follow current guidelines.
But survey data can't tell us what's happening to the fetus during heavy lifts. Until now, no study had directly assessed fetal well-being during high-intensity resistance exercise.
The First Direct Assessment
Researchers at the University of Alberta published the first study examining maternal and fetal cardiovascular responses to high-intensity resistance exercise during pregnancy in the British Journal of Sports Medicine.
They recruited 10 healthy pregnant women (average 26.4 weeks gestation, range 22-31 weeks) and 10 healthy non-pregnant controls. All participants had at least 2 years of resistance training experience and were capable of lifting more than 50 pounds for 10 repetitions in the back squat, bench press, and deadlift.
The study had two visits. Visit 1 was a conservative strength testing session to determine each participant's 10-repetition maximum (10RM) for each exercise. Visit 2 was the experimental protocol.
What They Actually Tested
Visit 2 included:
Baseline measurements of maternal heart rate, blood pressure, glucose, lactate, fetal heart rate, and umbilical blood flow
Treadmill warmup and stretching
Four sets of barbell back squats: 70%, 80%, 90% of 10RM with free breathing, then 90% of 10RM using the Valsalva maneuver
Three minutes of rest between sets
Immediate post-exercise assessment of fetal heart rate and umbilical blood flow
The same protocol repeated for bench press (in supine position) and deadlifts
For the Valsalva maneuver sets, participants were instructed to take a breath, brace their core, hold their breath during the repetition, and release after completing the movement.
Maternal heart rate was monitored continuously throughout. Fetal heart rate and umbilical blood flow were assessed via Doppler ultrasound immediately before and after each exercise.
The Results: No Fetal Distress
Weights lifted were similar between groups: At 90% of 10RM (equivalent to >75% 1RM), pregnant women lifted:
Squats: 51.5±7.3kg (113 lbs)
Bench press: 34.2±4.6kg (75 lbs)
Deadlifts: 59.0±13.2kg (130 lbs)
Non-pregnant women lifted:
Squats: 57.6±8.8kg (127 lbs)
Bench press: 32.2±5.9kg (71 lbs)
Deadlifts: 61.2±10.5kg (135 lbs)
The differences were not statistically significant. Pregnant women in their second and early third trimesters were lifting just as heavy as non-pregnant women with similar training backgrounds.
Maternal heart rate increased appropriately: Heart rate peaked during the Valsalva sets:
Squats: 137±8 bpm
Bench press: 111±10 bpm
Deadlifts: 131±9 bpm
There were no concerning cardiovascular responses. Heart rates were within expected ranges for the intensity of effort.
Fetal heart rate remained stable: No fetal bradycardia was observed at any point. Fetal heart rate did not change from pre-exercise to post-exercise across all exercises:
Squats: p=0.639
Bench press: p=0.682
Deadlifts: p=0.847
Umbilical blood flow remained normal: Umbilical blood flow metrics—including systolic/diastolic ratio, resistive index, and pulsatility index—remained within normal ranges throughout all exercises:
Squats: p=0.642 (resistive index)
Bench press: p=0.287
Deadlifts: p=0.614
This held true even during supine bench press and when using the Valsalva maneuver.
What About Pregnancy Outcomes?
Nine of the ten pregnant participants completed the postpartum follow-up questionnaire (one was lost to follow-up). All babies were born healthy:
Average gestational age at delivery: 39.5±1.3 weeks (all at term)
Average birth weight: 3433±375g (7.6 lbs, within normal range)
No NICU admissions
No pregnancy complications: no pre-eclampsia, gestational hypertension, or gestational diabetes
The most common maternal symptoms during the study were transient and mild:
Light-headedness (2 pregnant, 2 non-pregnant)
Mild pelvic pressure (2 pregnant, 0 non-pregnant)
Mild low back pain or sacroiliac joint discomfort (2 pregnant combined)
No symptoms were severe enough to stop the exercise.
Why This Matters
This study is the first to directly assess fetal well-being during high-intensity compound movements in pregnancy. Previous studies of resistance exercise in pregnancy typically used light loads (1-20 lbs) or resistance bands. Few examined compound, multijoint movements like squats, bench press, and deadlifts.
The findings provide empirical evidence that:
High-intensity resistance exercise is well tolerated by both mother and fetus in healthy, trained pregnant women during the second and early third trimesters
Supine positioning during bench press does not cause fetal distress when exercise bouts are relatively short (~90 seconds per set)
The Valsalva maneuver during heavy lifts does not compromise fetal heart rate or umbilical blood flow in this context
Pregnant women can maintain training loads similar to their non-pregnant counterparts well into pregnancy
The Limitations
This was a small study (n=10 pregnant women) examining acute responses to a single session of exercise. Rare complications could have been missed.
All participants had at least 2 years of resistance training experience. The findings may not apply to women who are new to lifting or who are initiating training during pregnancy.
Participants were beyond 20 weeks of gestation (average 26 weeks). The study doesn't address first-trimester training or training into late third trimester.
The exercise bouts were relatively short—about 90 seconds per set. Longer duration high-intensity work hasn't been studied.
Participants lifted up to 90% of 10RM, which is approximately 75-80% of 1RM. The study doesn't address true maximal or near-maximal lifting (>85% 1RM) during pregnancy.
Despite these limitations, this study provides foundational data using direct physiological measures of maternal and fetal health.
What This Means For You
If you're a pregnant woman with resistance training experience who wants to continue training at higher intensities, this study provides evidence to support that choice.
The absence of evidence is no longer a reason to back off.
If you're a healthcare provider counseling pregnant patients, these data can inform evidence-based recommendations rather than precautionary restrictions based on theoretical concerns.
If you're a strength coach working with pregnant athletes, you can program compound movements, higher-intensity loads, and natural breathing patterns (including Valsalva when appropriate) with confidence that these are well tolerated by healthy, trained pregnant women.
The Future of Pregnancy Exercise Research
This study opens the door for more nuanced research on resistance training during pregnancy:
Does training throughout the entire gestational period show similar safety?
Can women safely initiate high-intensity resistance training during pregnancy if they're new to lifting?
What are the responses to true maximal or near-maximal loads (>85% 1RM)?
What are the long-term benefits of maintaining strength training intensity throughout pregnancy?
Until now, pregnancy exercise guidelines have been limited by lack of empirical data. This research provides novel information on near-repetition maximum lifting and acute variables including intensity for pregnant women engaging in resistance exercise.
The message is clear: for healthy, trained pregnant women, high-intensity resistance exercise—including compound movements, supine positioning, and the Valsalva maneuver—is well tolerated by both mother and fetus.
Source: Moolyk, A.N., Wilson, M.K., Matenchuk, B.A., Bains, G., Gervais, M.J., Wowdzia, J.B., & Davenport, M.H. (2025). Maternal and fetal responses to acute high-intensity resistance exercise during pregnancy. British Journal of Sports Medicine, 59, 159-166. https://doi.org/10.1136/bjsports-2024-108804
