- Jenni Davies
What is Safe Exercise During Pregnancy? Does One Guideline Fit All?
Is the general advice for pregnant women to keep exercise “gentle and low impact” (i.e. walking, swimming, pre-natal pilates, pre-natal yoga) correct? This is very safe advice and absolutely appropriate for those who have never exercised before getting pregnant. However, if you’re used to exercising 5-6 times per week at high intensity, or for long durations or lifting heavy weights, being told to suddenly stop doing what you really enjoy, or need to do for maintenance of your fitness, sanity, social life or any other reason it’s not advice that you want to hear.
As most people who regularly exercise know, there are multiple wonderful side effects to being active:
Increased feeling of well-being
Improved mental health
Decreased risk of cardiovascular disease
Decreased risk of diabetes/gestational diabetes
Decreased risk of blood pressure problems
Maintenance of a healthy weight, strength, endurance and fitness
So how much exercise is safe in pregnancy?
Research into this area is increasing all the time, but has ethical constraints due to the pure fact we are dealing with pregnancy and the formation of a new little life that no-one (quite rightly) wants to put at risk. Therefore the research is not totally definitive. We do have sufficient quality evidence though to say that the guidelines, as written above, are overly conservative and are generally based on “old school” theories rather than the current evidence base.
What we do know from the research is that:
For normal weight women with single, uncomplicated pregnancies aerobic exercise for 35-90 minutes, 3-4 times/week is perfectly safe (1)
In these same women, the same rate of exercise does not cause premature births or babies of low birth weight
It also significantly lowers the incidence of caesarian sections, increases the rate of vaginal births and lowers the rate of gestational diabetes and blood pressure issues
Lifting heavy loads (greater than 20kg more than 10/day) can increase the risk of preterm birth (Runge et al, 2013 in a study looking at lifting heavy loads during the working day – not specifically during a single exercise session)
Women with a higher BMI (body mass index) before they get pregnant are at greater risk of pre-term birth, gestational diabetes and other complications than those within normal BMI limits, but when an appropriate exercise programme is undertaken during pregnancy (30-60 minutes of aerobic exercise, 3-7 times/week), these risks are significantly decreased. (3)
We don’t yet know what the upper limit of exercise intensity is. General advice by the American College of Obstetricians and Gynaecologists (ACOG) (4) and Sports Medicine Australia (SMA) (5,6), is that exercise kept to being moderately intense (on the perceived rate of exertion scale (7) you’d say what you were doing was “somewhat hard”) is safe throughout pregnancy.
In terms of research of this upper limit, it’s sparse. Szymanski & Statin (2012) identified that 30 minutes of strenuous exercise in the second trimester of pregnancy was well tolerated by both the mother and baby in both active and inactive pregnant women. However, a number of studies showed that women who continued to exercise vigorously during the third trimester were more likely to deliver infants weighing 200–400 g less than comparable controls. This was not significant enough to increase the risk of foetal growth restriction (ie birth weight under the 10th percentile) (8, 9,10,11) but both ACOG and SMA still recommend that you should not exercise intensely more than 3 times/week in the third trimester.
Warnings to avoid overheating during pregnancy are well established and there is good research evidence that there is an increased risk of neural tube defects (that occur in the first trimester) from significantly increasing your core temperature. This research was related to hot tubs, saunas and fevers (12). According to ACOG there is little chance of exercise increasing core temperature to this dangerous range however they do suggest keeping well hydrated, wear clothing that allows heat to dissipate and be sensible with environmental heat – whether that be due to room temperature (hot yoga), outdoor temperature (ambient heat) or humidity.
Body changes during pregnancy:
Hormone changes increase the laxity in your soft tissues and joints. This is a brilliant reaction that allows your body to accommodate to the growing baby and eventually give birth. However, if you have had previous injuries, especially to the back or pelvis, (but also shoulders, hands and feet), or if you are naturally hypermobile, you need to be aware that certain exercises will challenge your stability a lot more during pregnancy than normally. Asymmetrical exercises are a prime example – lunging, one-legged yoga poses, impact work, quick changes of direction can all lead to a feeling of weakness or pain. Having said this, it is very individual. Research has shown that the degree of extra movement available in the joints is not related to the amount of pain you suffer. Some people just feel it more than others. Pregnancy is not the time for trying to increase flexibility though - maintain and work through movements, especially yoga type movements/postures, to gain the strength benefit rather than flexibility.
Body weight increase – 10-15kg is normal – secondary to increased breast tissue, increased bodily and amniotic fluid and growth of the baby and placenta.
Change in body weight distribution and body shape
Alteration in posture due to a change in your centre of gravity secondary to changing body shape
Increased resting heart rate
Decreased maximal heart rate
Lower blood pressure
Higher nutritional needs
Stretching of your abdominal muscles with potential “separation of the abdominals”. This occurs in nearly all pregnancies to some degree and can compromise your ability to stabilize your trunk. This in turn can lead to musculoskeletal issues such as back and neck pain, pelvic pain, less efficient movement patterns etc. To minimise the “separation” it is advised to avoid abdominal crunches/curl ups, double leg lifts, plank and any other really heavy abdominal exercises. For a more detailed explanation of this please read the "Abdominal Separation" blog here.
Effect of these changes to your body and your exercise programme?
Everybody responds differently to pregnancy and you just can’t pick who is going to sail through it and who is going have difficulties. You may have been fit and healthy and doing everything right before pregnancy but end up feeling rotten and unable to exercise for the full 9 months (like I did) or you may not be in good shape at all before the first pregnancy but completely blossom and feel the best you’ve ever done in your life (like my friend did!). Yep, I felt conned.
For most people, at some point in their pregnancy, if aware of their body, they will feel their own limitations creeping in and find that they need to adapt their exercise programme accordingly. That may be due to discomfort, fatigue, lack of heart rate adaptation to exertion, shortness of breath with exertion or multiple other causes. Listen to your body and respect the changes.
Specific exercises to stop or modify:
Exercises to stop:
Plank, side plank, abdominal curls or twists, double leg lifts when lying on your back, exercises flat on your back after 16 weeks, exercises on your stomach once you start to “show”
Any sport or exercise that involves the risk of impact to your abdomen – contact martial arts, boxing, soccer, hockey, rugby, skiing, water skiing, basketball, mountain biking,
Scuba diving, sky diving
Hot yoga or similar
Exercises to modify:
Deadlifts, asymmetrical work (in some people), seated leg press, TRX, pilates, yoga
Heavy weights – although the research was not done directly on heavy weight lifting as an exercise programme, it was done on repeated lifting of heavy weights at work, and demonstrated a higher risk of having a pre-term baby (2). SMA, in their latest position statement (5), advise to only lift body weight or light weights at a sub-maximal intensity. In short, we don’t have sufficient research to be able to definitively advise an upper safe limit for weight lifting, so I would advise to progress with caution.
Stop exercising and get medical advice if you experience any of the following:
Dizziness and/or nausea
Shortness of breath that is not related to the intensity of your activity
Swelling of the face, legs, abdominal area
Fluid or blood loss vaginally
Decreased foetal movements away from exercise (there are often decreased movements during exercise)
Pelvic Floor exercises during pregnancy:
I often get asked whether you should be training your pelvic floor muscles during pregnancy or whether this will make the birth more difficult due to making them too tight.
The simple answer is, yes, you should be training them. The significant word in this answer is “training” not just strengthening. A well-trained muscle is able to efficiently contract AND relax. Yes we want you to have a strong effective set of pelvic floor muscles to support the pregnancy and help you to recover more quickly postpartum, but it is also essential that they are able to also fully relax and lengthen.
Good training involves both contraction and relaxation and the more you get the feel of both aspects, the more control you will have both during pregnancy - using the pelvic floor contraction before and during lifting/carrying - and during birth when your body is wanting to contract but you need to physically relax to allow the muscles to safely stretch.
Normal healthy pregnancy is to be celebrated and accommodated in normal life. It is no longer a “fragile condition” that needs caressing and protecting.
We now have sufficient evidence to say that the traditional advice of keeping exercise "gentle and low impact" during pregnancy, is overly conservative. Programmes should be tailored to the individual dependent upon personal circumstances.
If you have a normal, healthy single pregnancy with no previous health conditions or pregnancy complications, then you are safe to continue your normal exercise routine taking into account the modifications or certain exercises to stop (as written above).
If you are used to exercising at high intensities the best advice based on the most current research is that you are able to continue safely for up to 30 minutes during the 2nd trimester and for 3x/week in the third trimester but there is a risk of your baby being of lower birthweight compared to normal, however this doesn't appear to fall into a serious low birthweight category. Talk with your Obstetrician/care provider so that they are aware of your exercise programme and can monitor you more closely.
If you are used to lifting heavy weights (> 20kg), there is no research specific to exercise programmes at this point, but there is research looking at occupational lifting which carries a higher risk of having a pre-term baby. Proceed with caution, listen to your body, stabilise well pre-lift using pelvic floor, deep core and "spread the load" throughout your body. Also ensure that you have great technique to minimise risk of injury.
If you have never exercised before and want to start a programme now to minimise the risk of complications during pregnancy and birth, start gently - as per the traditional advice - with walking, swimming, pre-natal pilates/yoga, gentle weights programme etc.
If you have a multiple pregnancy or any complications, it does not necessarily rule exercise out, but you need to get advice from your Obstetrician or GP to get clearance and specific guidelines. Once you have this, I can work with you to establish an appropriate programme.
Remember that this is a time of great change in your body both mentally and physically. Respect these changes and listen to your body. Each person reacts individually so don't compare what you are doing to anyone else. This is a time for maintaining a programme rather than setting personal bests. The exception to this being if you are starting an exercise programme for the first time ever, in which case you will build up slowly and conservatively following the same guidelines above.
Finally, remember that if you are used to exercising but have a rough first trimester with enforced time off, you will restart your normal programme at a lower level then you left off at - in the same way you would had you been on a long holiday or been sick.
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Runge SB, Pedersen JK, Svendsen SW, Juhl M, Bonde JP, Nybo Andersen AM. Occupational lifting of heavy loads and preterm birth: a study within the Danish National Birth Cohort. Occup Environ Med 2013;70:782–8
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