Low Blood Sugar and Exercise

On Monday, I had what I think was an episode of low blood sugar (hypoglycemia) after exercise.  This is apparently common in people with diabetes.  I don’t have diabetes, but I am insulin resistant and do have elevated blood sugar at times.

Monday I went to training.  I did the elliptical to warm up and then went to do strength training with my trainer.  On several exercises, we upped the weight so it was a little more intense than usual.  I do this as a circuit where I do one set of each exercise, usually with no rest between exercises except walking to each place.  I had my heart rate monitor on and I usually will stop and rest 30 seconds or so if my heart rate is above 140 or so.

On Monday, I noticed that I soon felt really tired.  Resting for 30 seconds or a minute to get my heart rate down didn’t help.  I also started feeling shaky and nauseated.  Finally, about halfway through the third set of exercises, I told my trainer that I was done.  I went out to the reception area where my husband was waiting for me.  Normally, we then go out to the car.  But, I felt like I couldn’t possibly walk out to the car.  I sat down at the table and my heart rate quickly came down.  But, that didn’t help.  I still felt shaky and nauseated and was worried that I would faint.

At some point, I realized that my symptoms would fit with what I had heard about as low blood sugar.  I’ve never really experienced it to that extent before, but it seemed to fit.  I recalled that I hadn’t eaten much that morning.  I had a Kind bar about 3 hours before exercising (about 15g of carbs).  Then, right before we went to the Y I had a cheese stick (no carbs) and a small piece of dark chocolate (9g of carbs).  At that point, once I thought about that, I had my husband go to the vending machine and he got me a Zbar which had 12g of carbs.  A little after eating that, I started feeling better.

While I can’t be entirely sure, I think my problem was low blood sugar.  While I don’t eat totally low carb, I do eat lower carb than most people.  I usually end up averaging about 100g of carbs a day (70 or 80 net carbs).  I think I need to pay attention to my carbs before exercising particularly on the more intense days when I am seeing the trainer.

I read some articles about eating before exercise for people with diabetes, which gave me some ideas.  So, this morning I tested my blood glucose when I got up.  It was at 94.  Then I had a Quest bar (chocolate cookie dough for breakfast) for breakfast.  Then, right before leaving for the Y I had a sandwich.  I used 2 pieces of 100% wholegrain sprouted grain bread (28g of carbs) with 2 ounces of turkey and a piece of Weight Watcher pepper jack cheese.  Normally I wouldn’t eat that much carbs early in the day (I often go a week or two without eating any bread, although I do sometimes eat it and do eat some other grains).  When we got to the Y, my blood sugar was at 124, which made sense given what I had eaten.

I went in, did the elliptical and then did my training session.  I did not feel awful during it.  A couple of times my heart rate went over 140 and I rested for 30 seconds or so, but all went well.  When it was over, I didn’t feel nauseated or awful.  I did test my blood sugar, which was just over an hour after I had had the sandwich.  My blood sugar was 90.

Blood sugar

That is actually really low for having eaten a sandwich an hour before.  So this really reflects how much exercise had lowered my blood sugar. I knew that exercise lowers blood sugar and diabetics are often told to exercise to help control blood sugar. I just hadn’t thought that it might lower blood sugar so much that I might become hypoglycemic.  If my blood sugar was 90 today after having about 30g of carbs at lunch, then it was probably much lower on Monday when I had had much lower carbs that morning than today I had 26 Monday including breakfast, versus 52 today including breakfast. From a net carb standpoint (carbs less fiber) it was 17 Monday versus 30 today.  So, chances are my blood sugar on Monday was well below 90 when I got finished exercising and may have gone below 70 to hypoglycemia.

And, I do remember there have been some times that I’ve finished at the Y and felt shaky and a little sick but never as bad as this last Monday.  I suspect that was on days when I hadn’t eaten much.  So, I’ll be watching this much more carefully going forward.


  1. says

    Wow, what an episode! Sorry that happened to you, but glad you figured it out!
    It’s interesting that your BG reacts so quickly, and so much, to carb intake and exercise. I wonder why that is. Anyway, great job figuring it out. I have kind of a weakness for those Quest bars, especially since they started selling them recently at my Trader Joe’s! It’s a constant battle, buy, don’t buy, eat, don’t eat. 😛
    Wendy recently posted…What I Ate WednesdayMy Profile

    • says

      sorry, my “why that is” is a mechanical question. I get that you basically answered this saying it is likely due to insulin resistance for you. I’ll check out the links you posted. Interesting topic.
      Wendy recently posted…What I Ate WednesdayMy Profile

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