Feb 8 / Amy Snelling

CrossFit & Powerlifting during pregnancy

Pregnancy is a time of profound physical and emotional change, and for many women, it raises critical questions about fitness routines, particularly weight lifting. Common wisdom and cautious voices often warn against the risks of heavy lifting during these delicate nine months. However, is this advice grounded in solid scientific evidence, or is it a case of outdated myths masquerading as medical counsel?

Recent studies paint a more nuanced picture. While traditional guidelines have long cautioned against lifting over 11kg, citing occupational studies linking such activities to potential adverse effects, the actual evidence supporting these claims is surprisingly thin – categorised as low to very low in certainty. The context of these studies – occupational settings – is vastly different from the controlled environment of recreational or fitness-focused weightlifting. Below is FASTER trainer Hope showing her journey through pregnancy while simultaneously lifting!

In addition to the concerns previously raised about heavy lifting during pregnancy, there are several other factors that have sparked apprehension:

  • Stressing the Pelvic Floor: There has been a belief that weightlifting could potentially increase the risk of urinary incontinence during pregnancy. However, the combined impact of pregnancy and engaging in heavy weightlifting on urinary incontinence and other pelvic floor disorders remains a topic of uncertainty. Research in this area is still evolving, and a comprehensive understanding of the relationship is yet to be established. ·     
  • Increased Blood Pressure: Prenatal physical guidelines caution against the Valsalva maneuver, which is the body's natural response to lifting a heavy load. This caution arises from concerns about a sudden rise in blood pressure. While some small-scale studies have indicated that the Valsalva maneuver during pregnancy may not be associated with adverse outcomes, it's crucial to note that these findings are primarily based on lifting relatively low loads. The impact of this maneuver during more intense weightlifting routines remains an area that warrants further investigation. ·     
  • Supine Exercises: Performing exercises in a supine position (lying flat on the back) is discouraged from around 16 weeks of pregnancy due to the potential compression of the vena cava and aorta, which could lead to hypotension and reduced fetal oxygen supply. However, a recent review of existing evidence suggests that while compression does occur, the majority of individuals do not exhibit symptoms of hypotension during such exercises. Despite this, the overall evidence regarding whether exercises in a supine position are linked to adverse outcomes during pregnancy remains inconclusive, and more research is needed to establish a definitive stance on this matter.

Evidence based fear or industry guess work.

In the world of pregnancy and exercise, it's important to understand that certain guidelines aren't necessarily rooted in concrete research that definitively proves activities like heavy resistance training, employing the Valsalva maneuver, or engaging in supine exercises are inherently dangerous for both the expectant mother and the developing fetus. Instead, these recommendations tend to err on the side of caution, which is completely understandable given the delicate nature of pregnancy.  

When it comes to challenging established medical guidelines that might be overly conservative, the process is usually a two-step journey. It's often not feasible to kick things off with randomized controlled trials since ethics boards are naturally risk-averse and unlikely to approve a controlled study involving a treatment believed to have significant potential harm.  

The initial step in reevaluating an overly cautious recommendation often involves uncontrolled cohort studies. These studies seek out individuals who have already made the conscious choice to engage in behaviors deemed risky, and researchers observe the outcomes of their voluntary actions.  

When researchers conduct several observational studies on a specific subject, consistently finding that an activity considered perilous doesn't seem to result in the expected adverse effects, ethics boards tend to become more receptive to greenlighting controlled studies on that topic.  

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. doi: 10.1007/s00192-022-05393-1. Epub 2022 Nov 4. PMID: 36331580.   

A 2022 cross sectional survey did exactly this by collecting data from 679 individuals who lifted at least 80% of their one rep max during pregnancy to explore if they were at a heightened risk for adverse birth outcomes, adverse fetal outcomes, or pelvic floor dysfunction.  

Researchers recruited lifters to complete a questionnaire consisting of 60 questions, including sport history, reproductive history, pregnancy health outcomes and pre-pregnancy/pregnancy/postpartum aerobic and resistance training characteristics.  

Participants needed to have engaged in resistance training during pregnancy with loads exceeding 80% of 1RM and to be at least 18 years old.

Summary of main findings

• 85% continued to engage in heavy weightlifting (with or without modification) until delivery.
• 24% maintained pre pregnancy training levels throughout.
• The majority engaged in Olympic weightlifting (72%) and supine exercises (71%), whereas only a minority reported using the Valsalva maneuver (34%).
• 37% experienced urinary incontinence during pregnancy.
• The majority (89%) of respondents returned to weightlifting at around 3 months following delivery.
• Pregnancy or delivery complications were reported by 34% during, and 20% following pregnancy.
• Prevalence of pregnancy and delivery complications were largely not different between those who engaged in Olympic lifting, Valsalva maneuver, or supine exercise, compared with those who did not.
• Rates of gestational hypertension, preeclampsia and gestational diabetes were below prevalence values for the general population.
• Those who maintained pre pregnancy training levels experienced less pregnancy and delivery complications than those who reduced their training.

Since this type of study is observational in nature, causation between the people’s behaviours in the study and their outcomes cannot be established.   However, the results are certainly of note because they suggest that heavy lifting, use of Valsalva and supine exercises are not as dangerous as previously believed. Whist this will pave the way for more studies and controlled trials, we still can’t say with absolute certainty that existing guidelines are too cautious.

Coaching your client

When it comes to coaching your client, you can help them to make an informed decision by relaying that research is beginning to push the boundaries on what is considered safe exercise during pregnancy.  

And while there are many individuals who continue to engage in heavy lifting during pregnancy, your client needs to do what is best for them and how they feel, factoring their current skill level. Recognising signs of overexertion, such as dizziness, shortness of breath, or pain, is crucial.  
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