20 weeks / Body Temperature Regulation

Today I am about 20 weeks and 3 days pregnant, I am right at the halfway point! Last week she was moving like crazy, I was even able to see the kicks through my skin! Pretty cool! I was a lot more active last week than this week, I was running and even trying to do some speed work, however I think I over did it just a little. Over the weekend I had a lot of aches and pain in my calves and my hip. I think the most logical explanation for this is that my joints just aren't used to the extra body weight. during the first trimester I only put on about 5 pounds, but I'm still early in the second trimester and I've already put on about 10, so that's a lot of weight coming on really fast and so there hasn't been much time for my body to adapt. So this week I decided to take it easier, I haven't done any running, just weight lifting, yoga and elliptical. Today I am planning to take a step class which is high impact but I feel good today so I think it'll be fine. Next week I plan to start easing back into running. I am signed up for a race at the end of February and will probably also do one in March so I need my body to hold itself together! 
While I'm on the topic of exercise I'd like to mention some more adaptations to exercise and pregnancy. Two  adaptations to exercise in a trained person is that they will sweat sooner, and they will sweat more, when I say more I mean more than they did prior to habitual training, or more than an untrained person. So who's going to need to drink more water during exercise, the trained athlete or the person just starting an exercise routine?  The trained athlete would need to replenish water more because they are losing more through sweat. Why is this important? Sweating is our body's way of maintaining a cooler core body temperature, if we sweat sooner and more then our body is more efficient at cooling itself.  (Side note for competitive athletes: Training in a hotter environment furthers this adaptation, although you have to take it easier as your body gets used to the heat you will be better off when you compete in a cooler environment because your body will be more efficient at dissipating heat).  Now let's look at pregnant women. Some people worry about the pregnant woman overheating during exercise and in turn causing damage to the unborn baby.  I'm not arguing that this is not a concern at all, I'm just going to give you some information that should make that concern less prominent.   This information again, comes from the book "Exercising Through your Pregnancy" by James F. Clapp III. M.D. In his studies of pregnant women he found that "Starting very early in pregnancy, these women's resting body temperature fell dramatically and continued to fall progressively throughout the remainder of pregnancy." Therefore getting rid of excess heat, as during exercise, would probably not be a problem for these women. It seemed that "their ability to get rid of heat had improved so much due to adaptations during pregnancy that the women had to increase their heat production to stay warm when they weren't active!" I can say that has definitely been my experience, it surprised me because everyone always talks about being so hot when pregnant but since I've been pregnant during these cold months, unless I'm active, I am just freezing all the time.  So what does all this mean? 

1. Pregnancy lowers the body's set point for sweating, meaning you sweat sooner. Increased skin blood flow creates the pregnancy "glow", the skin is already warm so the sweat evaporates immediately.
2. Pregnant women breathe 40 - 50 percent more air which improves her ventilation but also increases her ability to get rid of heat through the air she exhales.
3. Increase in blood volume and body weight/mass improves a pregnant woman's ability to deal with extra heat. Increased blood volume maintains skin blood flow, and the weight gain "buffers any increase in heat production by progressively increasing the amount of tissue to heat by 5 - 10 percent in early pregnancy and by 20 - 25 percent near term." Meaning that "at term a pregnant woman can generate about 20 percent more heat without raising her body temperature because there is about 20 percent more tissue to keep warm."

So when looking at these adaptations to exercise and pregnancy separately you can see how they are important but I think you can also see why it might be best to already have that adaptation in place prior to pregnancy by developing an exercise habit before you become pregnant and then of course carefully maintaining it during your pregnancy.