|Just back from the gym, Week 35.|
Exercise During Pregnancy.
(1) In General
(2) What I've Done (already posted)
(3) What I Wish I Did
Clearly pregnancy is a time of dramatic anatomic change for all women. But which changes become most physically significant and noticable, and when are vastly different depending on genetics, a woman's baseline level of health and fitness, and the work each woman continues to put in to maintain her fitness during pregnancy. No wonder a one size fits all approach doesn't work!
The American College of Ob/Gyn (ACOG) used to promote a one size fits all approach saying that pregnant women should avoid allowing their heart rate to exceed 140-150 bpm while exercising. That was the main guideline. Many fit women found that they were barely breaking a sweat with a heart rate of 140 and felt extremely limited by this arbitrary cut off. In recent years, the guideline has changed to a more subjective recommendation to keep your exertion level such that you could carry on a conversation while exercising. This guideline acknowledges that this cut off will be different for every woman. For some, this may be a brisk walk on a flat surface even in the first trimester. For others, it may mean continuing endurance endeavors such as marathons but reducing intensity (speed) up until even the third trimester. My personal bias is that even this guideline is probably a bit conservative, but when you are talking about maintaining the health of a completely helpless fetus, it seems reasonable to be conservative. What do I mean by a bit conservative?
Even staying conversational is not much of a work-out for most fit women. Better than being limited to 140 bpm, but still not all that hard. I liked a description I saw indicating that a conversation in full sentences may mean you are not working hard enough (to improve/maintain fitness), but only being able to utter one word sentences indicates one is working too hard (to be safe for fetus). So somewhere in between (3-5 word sentences?) is probably the sweet spot b/t exerting oneself and not risking any degree of fetal harm. I do wonder though if short intervals at a slightly higher intensity might be reasonable? The US Department of Health and Human services in their 2008 physical activity guidelines for pregnant women note that "vigorous intensity aerobic exercise in pregnant women has not been studied carefully and that women who have not been exercising before pregnancy should not begin vigorous exercise". But what of those who were exercising vigorously and regularly prior to pregnancy?
Again, every woman needs to make her own decisions and I am not an obstetrician or exercise physiologist. This is not medical advice. But my personal belief (which I assume you care about, otherwise you wouldn't be reading this) is that there is no need for woman to freak out if they have slightly increased intensity (even a bit of huffing and puffing, but not breathlessness) for short (30s-1 min) intervals in the midst of an otherwise "conversational" cardio session. There is some data to support this, but the studies are small, so it's hard to draw firm conclusions.
Am J Obstet Gynecol. 2012 Sep;207(3):179.e1-6. doi: 10.1016/j.ajog.2012.07.021. Epub 2012 Jul 20.
Strenuous exercise during pregnancy: is there a limit?
For example, a 2012 study published in the American Journal of Obstetrics and Gynecology evaluated 45 healthy, normal weight women with uncomplicated pregnancies (15 non-exercises, 15 "regularly active" and 15 "highly active") with a peak treadmill test b/t 28-32 weeks gestation. Interestingly, the mean age of the women was between 32-34, slightly older than the average pregnant lady. Regularly active women were defined as those who exercised at mild to moderate intensity 20 minutes per session at least 3 days weekly and highly active women were defined as those who vigorously exerted themselves at least 4 days weekly- the vast majority of these women were runners. The women then essentially underwent the equivalent of a cardiac stress test on the treadmill- they started on the treadmill at 3.0 mph with 0% grade and the incline was increased by 2% every 2 minutes until it reached 12%. Then- for the women who were ready for more- the speed was increased by 0.2 mph every 2 minutes. Women stopped when they reached "volitional fatigue", a clearly subjective measure defined as the "limit beyond which a participant no longer desired to continue the protocol". While subjective measures have their short-comings, I actually like this measure in this instance. It takes into account the variability from woman to woman- what is "hard" for one person may not be "hard" for another based on physical and mental stamina/endurance. The "keep it conversational" measure of exercise during pregnancy in general, is similarly subjective, which I think is fine.
They measured the women's peak heart rates, ratings of perceived exertion, and EKGs. They measured fetal well being at rest and immediately after exercise with uterine and umbilical artery Doppler data, fetal heart tracings, fetal heart rates and biophysical profiles. Interestingly, there were no differences in perceived exertion by the women in the different groups- they all felt they were strenuously exerting themselves and peak heart rates were similar- but not surprising the highly active group exercised an average of 22 minutes as opposed to 12 minutes in the non-exercising group (meaning they got to higher inclines and paces). Without going into too much detail (please feel free to read the paper), 5 of the women in the "highly active"group had transient fetal heart rate decelerations and mild alterations in uterine and umbilical artery Doppler indices immediately after exercise. However, fetal well being was reassuring in all the woman (exercisers and non-exercsers) as measured by fetal heart tracings and overall biophysical profile. The authors conclusion is that the findings of decelerations and changes in umbilical and uterine artery measurements in the 5 highly active women might be concerning, though it is hard to say given the small numbers and the fact that the more clinically relevant findings of biophysical profile- likely a better indication of fetal well being- were still normal. Note that these woman were nearly maximally exerting themselves- much more exertion that traditionally recommended during pregnancy- thus my takeaway is that intense but nowhere near maximal exertion is likely totally fine. While this was not specifically tested, I suspect these ladies were well beyond conversational when they called uncle on the treadmill test- the fact that they were estimated to be near 80% max heart rate supports this.
The authors reference a similar study in 6 Olympic caliber pregnant (23-29 week) athletes, showing fetal bradycardia when exertion exceeded 90% of max heart rate (Br Journal Sports Med, 2012). Again, this exertion is SIGNIFICANTLY more than recommended during pregnancy, and for most athletes significantly beyond what they usually achieve in non-pregnant max training. Again, for me this validates the idea that moderate and even intermittently vigorous exercise during pregnancy has no untoward consequences for fetus and certainly is good for mother. Very intense exercise approaching 80-90% max heart rate should be saved for postpartum.
So, those are some thoughts on exertion level, from a strictly cardio perspective. But what about other....sensations? How do you know when a sensation is new "pregnancy normal" vs a reason to stop exercising? Pregnancy is wrought with new sensations that the female athelete- generally in tune to her body- will notice starting as early as week 5. The female athlete will not be one of those (crazy) ladies who don't know they are pregnant until the third trimester or even delivery (how someone could be so out of touch with their body is beyond me!). I personally felt all kinds of non-painful, non-bothersome, but totally new to me sensations b/t week 6-9. I didn't think much of them but then they stopped one day. I called my doc who informed me I was probably feeling increased blood flow in the ovary and uterus, normal to feel it, and normal to stop feeling it at some point. Crazy!
Then of course, at some point the sensations come back in other forms- pressures, whooshes, mild discomforts- goodness knows what all of these feelings represent. It takes weeks and weeks before there are any clear cut fetal movement type sensations but eventually there are clear cut kicks, punches and other discrete fetal movements, and then (still relatively new to me) the uterine contractions! And hiccups, the crazy fetal hiccups! With all these sensations, that change from week to week, how on earth does a woman know whether it is okay to keep exercising?
I made up my own rule that I didn't read anywhere, but it has served me well thus far and I plan to continue to follow it. I decided early on that any sensation or mild discomfort that I feel during my every day activities when I'm NOT exerting myself is fine to have while I AM exerting myself. Braxton-Hicks contractions occur with some frequency when I'm walking, therefore I don't worry if they happen when I'm running or biking.
Beyond fall risk activities, which are obvious no-nos (horseback riding, downhill skiing), are there other specific activities that need to be carefully considered or even flat-out avoided? As far as I can tell there are two broad categories of activities that probably should be avoided in the 2nd and 3rd trimester as baby gets bigger 1) activities that require you to be flat on your back for extended periods of time (can decrease fetal blood flow due to positioning of uterus and the vena cava) and 2) activities that increase intra-abdominal pressure and can cause/worsen diathesis recti. I believe diathesis recti deserves its own post which I will get to eventually. This became a huge concern for me for a few weeks and there is a serious lack of resources about this topic. So stay tuned for that.
I think this post is long enough. I'll leave you with a couple Exercise During Pregnancy Resources:
1. Helpful book on the (scant) data on exercising during pregnancy.
Good website with educational blog posts and weight training ideas for the pregnant woman.