In our Bliss Baby Yoga training courses, we generally advise against stronger abdominal activation during pregnancy. Since our approach is considered and, as much as possible, based on the latest research, in this blog, we thought it time to review a question that often arises in prenatal exercise practice: to crunch or not to crunch?
The pregnant uterus can expand up to 500 times its original size and consequently the abdominal muscles become stretched as the pregnant belly grows. This can explain why back pain is a common complaint for up to 70% of pregnant people – the stretched abdominal muscles are potentially compromised and not so easily recruited when performing movements of exertion.
A key reason we recommend the avoidance of strong abdominal activation is due to the changes in posture that occur during the antenatal period. The weight of the heavy uterus shifts the belly and centre of gravity forward, creating a deepening in the arch of the lower back – what is known as lumbar lordosis, or a ‘banana back’ shape.
This can shorten the lower back muscles resulting in pain and tightness. Therefore, focus on postural alignment will help the pregnant student lengthen their lower back and draw the weight of the expanded belly back towards the spine.
Activating the “TA” Transverse Abdominus
In exercise physiology this activation of the abdominal muscles is known as ‘pulling in’ and chiefly recruits the deep layer of abdominal muscles, the transversus abdominus or ‘TA’.
In yoga, one way we activate the TA and support the posture is by having a pregnant student practise a safe version of the Cat-Cow exercise. Instead of arching or dipping the back in the ‘Cow’ movement of Cat-Cow stretch, the student maintains a neutral spine (neither arching nor rounding), drawing the weight of their baby towards the spine, away from the floor.
Plank Pose in Pregnancy
If the student practises a Plank Pose during pregnancy they need to be strong and experienced enough to maintain good alignment so as not to risk common ‘dipping’ in the lower back, potentially straining the back muscles. That’s why we do not consider Plank Pose a key prenatal posture; many pregnant students are beginners and may not have the control and awareness to maintain good postural form, especially as the increasing weight of the baby adds extra challenge for the compromised abdominal muscles.
We go so far as to list this as a contraindication in our Introduction to Prenatal Course as most students will experience this dipping in the second half of pregnancy. As an alternative, try bringing them back to all-fours and into the Pregnancy Cat pose mentioned previously.
Abdominal Crunches?
And what about ab crunches, are they safe to do? These abdominal exercises involve the student lying on their back and raising their head and shoulders off the mat to engage the rectus abdominis muscles. These are the large ab muscles – or ‘6-pack’ – that run parallel to the spine.
In yoga we don’t generally practise ab-crunches; it’s an exercise found in Pilates and strength-based training. Rather than crunches, one of the most effective yoga poses to engage the rectus abdominis muscles is Navasana, The Boat Pose.
Since Navasana involves quite a lot of exertion of the rectus abdominis we have long argued that if you have your pregnant student do this pose they may strain their back and potentially increase the chances of / cause diastasis recti. Diastasis Recti Abdominus (DRA) occurs in many pregnant people when there is a separation of the rectus muscles, which can mean less support for the lower back.
But is it true? Does activation of the rectus abdominis muscles worsen or cause DRA?
Diastasis Recti and Abdominal Activation in Pregnancy
The latest research from a study in 2025 published in The Journal of Physiotherapy shows that regardless of whether a pregnant person activates the TA (TrA) or rectus abdominis (RA) there is no increase in risk for DRA.
But I would suggest that a key caveat is how we practise exercises like Navasana that engage the rectus abdominis. If an abdominal exercise is performed poorly the pregnant student risks causing / exacerbating back pain, remembering that postural alignment and integrity of the abdominal muscles are compromised during pregnancy. Not to mention the lack of space for the pregnant belly in this pose, that means the back is further compromised.
Backing up my caution are recommendations detailed in the recent publications Exercise and Physical Activity During Pregnancy and Postpartum and The Active Female. Offering an all-important evidence-based perspective, these texts are co-authored by experts in the field of antenatal physiotherapy, sports science and obstetrics. These experts advise avoiding or proceeding with caution those exercises which ‘overload the lower back’. This is very vague!
So, we must use some more specific guidelines about how to engage the abdominals detailed in these texts and see how these apply to Navasana in order to ensure no injury is caused.
Proceed With Caution
This brings us back to how abdominal exercises are performed. Reinforcing our prenatal yoga perspective that we discuss in our Online Prenatal Yoga Teacher Training, where we counsel adapting postures depending on the phase of pregnancy, Szumilewicz and Santos-Rocha suggest that:
When selecting the exercises for abdominal muscles, the stage of pregnancy should be taken into account. A large uterus will certainly hinder the abdominal muscle shortening during contraction. A growing fetus takes up space in the abdominal cavity. Therefore, in the high pregnancy, it is rational to limit the movements which additionally will reduce it, like in crunches. Nevertheless, it is the uncomfortable feeling of a woman in a given exercise that should be an indicator for its elimination or modification.
It follows that Navasana is not an ideal posture for late pregnancy; the legs need to be brought close to the abdomen as we move into hip flexion which as mentioned earlier, is not a comfortable or easily achievable action at this stage of pregnancy.
In summary, check in with the individual student as to what feels comfortable for them when performing movements like Navasana that actively engage the abdominal muscles. Always focus on correct postural alignment to avoid increasing/ causing lower back pain and strain. And moderation and awareness are the key, in line with advice from five professional pregnancy organisations to avoid ‘Excessive Abdominal Exercise’ (from a 2021 Systematic Review).
References
Exercise and Physical Activity during Pregnancy and Postpartum, ed. Rita Santos-Rocha, Springer, 2022 https://www.dropbox.com/scl/fi/8jfmlpi96b48u1o9a1n8i/978-3-031-06137-0.pdf?rlkey=z60j9iuvqzomvtfkg20uvjmyt&dl=0
The Active Female, eds. Jacalyn J. Robert-Mcomb, Mimi Zumwalt, Maria Fernadez-del-Valle, Springer, Springer 2023.
‘Transversus Abdominus and Rectus Abdominus Activation Exercised do not Alter Inter-Recti Distance in Pregnant Women: A Randomised Trial’, Cabral et al., 2025 https://www.dropbox.com/scl/fi/50ptu0kr9chp3v8qrk6ir/1-s2.0-S1836955325001109-main.pdf?rlkey=p4jbj41nz58vnqprhl9da0yvy&dl=0
‘Professional Exercise Recommendations for Healthy Women who are Pregnant: A Systematic review, Rudin et al., 2021 https://www.dropbox.com/scl/fi/gmmsoufq08rr1egg1llxq/rudin-et-al-2021-professional-exercise-recommendations-for-healthy-women-who-are-pregnant-a-systematic-review.pdf?rlkey=o8efxoum1b4gv1flzrfk8m6be&dl=0
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