CrossFit and Powerlifting During Pregnancy

Pregnancy raises hard questions about training, especially weight lifting. Cautious voices warn against heavy loads across those nine months. But is that advice grounded in solid evidence, or is it outdated myth dressed up as medical counsel?

The picture is more nuanced than the warnings suggest. Traditional guidelines have long cautioned against lifting over 11kg, citing occupational studies that link such work to potential harm. Yet the evidence behind those claims is surprisingly thin — categorised as low to very low in certainty — and an occupational setting is a world away from controlled, fitness-focused lifting.

The usual concerns

Alongside the fear of heavy loads, a few specific worries come up again and again:

• Pelvic floor stress. There's a belief that lifting increases the risk of urinary incontinence in pregnancy. The combined effect of pregnancy and heavy lifting on the pelvic floor is still uncertain, and the research is evolving.
• Blood pressure. Prenatal guidelines caution against the Valsalva manoeuvre — the body's natural response to a heavy load — over concerns about a sudden rise in blood pressure. Some small studies suggest Valsalva may not cause adverse outcomes, but these mostly involved relatively low loads. Its effect during genuinely heavy lifting needs more study.
• Supine exercises. Lying flat is discouraged from around 16 weeks due to possible compression of the vena cava and aorta, which could reduce fetal oxygen supply. A recent review found that while compression does occur, most people show no symptoms of hypotension. The evidence on whether supine work causes harm remains inconclusive.

Evidence-based fear, or industry guesswork?

Many of these guidelines aren't rooted in research that proves heavy resistance training, Valsalva or supine work are inherently dangerous. They err on the side of caution, which is understandable given how delicate pregnancy is.

Challenging an overly conservative guideline usually takes two steps. You can't start with randomised controlled trials, because ethics boards won't approve a study of something believed to be seriously harmful. So the first step is uncontrolled cohort studies: find people who have already chosen the "risky" behaviour and observe the outcomes. When several observational studies keep failing to find the expected harm, ethics boards become more willing to greenlight controlled trials.

Research spotlight

Prevett C, Kimber ML, Forner L, de Vivo M, Davenport MH. Impact of heavy resistance training on pregnancy and postpartum health outcomes. Int Urogynecol J. 2023 Feb;34(2):405-411.

This 2022 cross-sectional survey collected data from 679 people who lifted at least 80% of their one-rep max during pregnancy, using a 60-question survey covering sport history, reproductive history and training characteristics before, during and after pregnancy. Participants had to be at least 18 and to have trained above 80% of 1RM while pregnant.

Key findings:

• 85% kept lifting heavy (with or without modification) until delivery.
• 24% maintained pre-pregnancy training levels throughout.
• Most did Olympic weightlifting (72%) and supine exercises (71%); only a minority used Valsalva (34%).
• 37% experienced urinary incontinence during pregnancy.
• 89% returned to lifting at around three months postpartum.
• Pregnancy or delivery complications were reported by 34% during and 20% after pregnancy.
• Complication rates were largely no different between those who used Olympic lifting, Valsalva or supine work and those who didn't.
• Rates of gestational hypertension, pre-eclampsia and gestational diabetes were below general-population values.
• Those who kept pre-pregnancy training levels had fewer complications than those who cut back.

Because the study is observational, it can't prove that the training caused the outcomes. But the results are notable: they suggest heavy lifting, Valsalva and supine work aren't as dangerous as once believed. This paves the way for controlled trials, though we still can't say with certainty that the existing guidelines are too cautious.

Coaching your client

Help your client make an informed decision by explaining that research is starting to push the boundaries of what's considered safe in pregnancy. Plenty of people keep lifting heavy while pregnant — but your client needs to do what's right for them, factoring in how they feel and their current skill level. Recognising signs of overexertion, such as dizziness, shortness of breath or pain, is essential.