Running During Pregnancy … (WHY am I SO SLOW?)

Lately, running has been an exercise in extreme frustration for me.  For the past two weeks, I’ve had the more typical symptoms of pregnancy (food aversions, cravings, fatigue, etc.) so it hasn’t surprised me that I’ve been low on energy, but what has surprised me is how difficult running has been for me in other ways.  For a few weeks now, I’ve struggled to catch my breath while running (I’ve never had asthma before, but from what I’ve heard from others, I’ve been experiencing something very similar to a mild case of it) and over the past couple of runs, my legs have been incredibly tired in a way that has reminded me of my horrible 12 mile experience, when, due to inadequate water intake and horrible nutrition, my muscles simply gave out on me around mile 7.  It’s been incredibly frustrating, especially since just over a month ago I was clocking some of my fastest times and convinced I was on my way to Boston.  Okay, well, maybe not THAT fast, but I was feeling pretty proud of my 34 minute 5k!  Now, I’m doing well to average a 15 minute mile and keep from walking during a 3 mile run.  WHAT IS GOING ON HERE???

A few days ago, I decided to find out.  Following the thoughts of my friend Michelle who thought my difficulty breathing might be pregnancy related, I googled “shortness of breath first trimester” and found an excellent article that my husband (a nurse) kindly summarized for me, using small non-medical words.  In case anyone else was interested, I thought I would share his summary, here.  If you’re pregnant and experiencing shortness of breath, muscle fatigue and overall crumminess any time you have to get out of a supine position on the couch, this might be why:

The hormone progesterone (produced in high levels during pregnancy) increases a pregnant woman’s sensitivity to carbon dioxide (CO2.)  This sensitivity causes the body to work harder to expel CO2 from the system.  One of the most efficient ways our bodies expel CO2 is in the form of exhalation.  As a result, progesterone increases the rate of respiration (the number of breaths taken per minute) by up to 50% during pregnancy.

Even when just sitting on the couch, a pregnant woman will take more breaths per minute than she would if she were not pregnant.  When engaged in aerobic activity, the muscles require more oxygen, thus producing more CO2.  In order to keep these levels of CO2 low, the woman’s respiratory rate increases even further.  This can cause extremely rapid breathing as the body struggles to blow off the increased levels of CO2 caused by exercise. 

Another change caused by progesterone in the expecting mother’s body is the increase in blood volume.  As previously mentioned, when engaged in aerobic exercise, the muscles need more oxygen.  Oxygen is carried to the muscles by hemoglobin, present inside the red blood cells.  During a pregnancy, blood volume levels rise and the number of red blood cells per unit drops.  You can think of it like salt water.  If you take a tablespoon of salt and put it in a cup of water, the water will taste salty.  Add a gallon of water and the water tastes less salty, even though the same amount of salt is present.  Similarly, when pregnant, progesterone raises the amount of plasma (the liquid content of the blood), thus diluting the red blood cell count and causing hemoglobin concentration to fall (this is why many pregnant women struggle with anemia.)  In this diluted state, muscles are not getting the amounts of oxygen they were before the rise of progesterone levels.  This decreases muscle function and leads to early fatigue.

In many ways, the newly pregnant athlete is experiencing changes in her body that affect her in a way very similar to the changes experienced when an out-of-shape person first begins to exercise.  Her muscles are fatigued from the dilution of red blood cells (which decreases the amount of oxygen reaching her muscles) and she experiences shortness of breath and increased respiratory rate due to the increased levels of progesterone.  Consequently, her performance may diminish.

I’m not discouraged.  The way I figure it, this will be excellent conditioning!  Jon’s theory is that the more running (shuffling) I do in my current oxygen-depleted state, the more efficient my muscles will become.  I also read somewhere that as a result of the heart muscles pumping more blood, exercise during pregnancy can assist in improving the cardiovascular system.  So although I may barely scrape by under the time limit for the Flying Pig Marathon in May, by this time next year I’ll be ready to breeze through a 100 mile ultraOr at least run a slightly faster marathon.  One or the other.

I’m reminded of something I wrote after my horrible 12 mile run (I love the fact that blogging allows me to look back and be encouraged by lessons I’ve learned in the past, long after I’ve forgotten them.  Another reason why I blog.)…

There is no failure in this journey.  Every single run, whether it’s a 15 minute run, or a 20 minute run/walk, or a personal record setting sprint, is an achievement.  Every single time I get out there and go the distance, I’ve accomplished something.

Amen to that.  Borrowing a line from John Bingham:

Waddle on!


Categories: Running, Running through Pregnancy

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6 Responses to Running During Pregnancy … (WHY am I SO SLOW?)

  1. maggsworld says:

    The research and loving support you have in understanding the changes to your body and finding possible benefits is encouraging. And inspiring.

  2. Mrs. Parunak says:

    Fascinating! I knew about the blood volume thing, but I never knew about the CO2 thing, which explains a lot. People often worry about me when I’m pregnant. because I get out of breath doing ordinary things like carrying a basket of laundry up the stairs. NOW I can tell them why (and that it’s not a big deal).

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  4. cbug says:

    Whew. Thank you for this! Finally makes sense. I have spent a few hours googling for information on *why* this happens. And most of the information is focused primarily on acceptable intensity, as if a sudden significant drop in performance was irrelevant. I understand that it’s real and that there is a reason for it, but without understanding the dynamics, it’s maddening. I’m in the first trimester and my pace has increased about 1.5 – 2 minutes per mile. I finally decided to strap my HR monitor back on and see what was up, assuming that my HR had just been skyrocketing quickly. In fact, it turns out that my “high” intensity HR (the rate I could only sustain for a minute or two during the 7w run) was actually the heart rate that I could previously sustain comfortably for 30 – 45 minutes. Maddening, I tell ya. Thanks for the clear information. Craving finally satiated. :)

  5. Pingback: 7 Quick Takes – January 20 | Rina Marie

  6. Jen says:

    Thank you for this! I’ve been really frustrated with my running thinking I was just out of shape; this puts it all into perspective!

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