Does high intensity exercise make your BGs increase 9 to 12 hours later?

Hey everyone! I have a question that has been bugging me for quite a while: does high intensity exercise make your BGs skyrocket 9 to 12 hours after? I first noticed this when I got my CGM: some nights were off. But I couldn't figure out why. Then I started to pay really close attention and I notices that when I first begin a new exercise or do the same activity at a higher intensity, I skyrocket 9 to 12 hours later (then the next day I am low all day). Does anyone else notice this trend? I just began to connect the two together, and I wanted to verify my hunch with someone else out there who has noticed this. How do you combat this? I hate to increase my basal since I am stilil unsure that exercise is truly at fault. Plus, it is affecting my overnight BGs, so I'd rather go high than low until I figure it out. I'll keep watching on my own now since I have an idea about what's causing these occassional high BGs overnight, but any help would be appreciated!!

Huh, that's strange. I do high intensity exercise 5-6 days a week and I haven't noticed anything like that. When do you exercise? And when do you eat your meals? Are you eating a big medium-high glycemic meal at the end of the day and then overcorrecting? I had problems with recurring lows until recently (when I lowered my basal rates. The thing with lows is that the more frequently they occur, the worse they get. I'll definitely be interested to hear what this is once you figure it out.

Exercise can do funky things to blood sugar.  During a workout your muscles release glycogen, which is stored glucose.  As your muscles get used to a workout they're more efficient and don't affect blood sugar as much.

Sheri Colberg wrote a must have book called "The Diabetic Athlete" that outlines how different activities affect blood sugar and how to counteract the effect.  For $30 you can also do Gary Scheiner's online class on exercise.  In addition to writing "Think Like a Pancreas" he's an exercise physiologist.

I actually have the opposite problem of what you experience... sky high blood sugars right after high intensity workouts (especially anaerobic stuff like lifting weights) then a big drop in the middle of the night.  Only things activities that give me a nice, steady reduction in insulin are swimming laps and walking.  

@ Elie: it occurs most often when I increase the amount of exercise. For example, I walk 3.5 miles per day, but I added jogging a few miles per day (on sporadic days) to the mix a few months ago. I noticed the occasional nighttime highs at that time but didn't make the connection. In the last few weeks, I increased to 3.5 miles jogging (still on sporadic days) in addition to my daily walks, and on the days that I jog, I noticed the high nights on my CGM. Still not sure 100% if my hunch is right, but I'll keep watching and post my findings!

@ Jennagrant: Thank you for all the information! I'll definitely check them out!

hey Christa I can't think of any kind of physiological reason this would happen, and would bet that there is something other than the exercise itself causing the highs

hey Christa I can't think of any kind of physiological reason this would happen, and would bet that there is something other than the exercise itself causing the highs


I recently read Sheri's book. It's a great book, but I don't think it answers this question. Sometimes high intensity exercise releases epinephrine, which raises sugar levels. However, as far as I know that doesn't explain the problem Christa is describing. Really, high intensity exercise should be lowering your blood sugar as it increases metabolism for several hours. It could very well be that Christa needs to adjust basal rates. That is, maybe Christa lowered her basal for her high intensity workouts but didn't realize that she should only lower it for a several hour period, say, 7-8 hours tops. I'm not sure this explains the lows the next day, but maybe those are the result of overcorrecting..I have no idea.

I have a similar problem in that I go high during/after exercise and then drop anywhere from 2-24hours later. It was recommended to me by a dietitian to try eating something like peanut butter and fruit before hand to stable my blood sugars during but also lessen/prevent a low later. I also reduce my insulin at the snack prior to working out and do not correct at the meal following (I tend to work out before dinner) so that when my blood sugar is naturally coming down after my body relaxes I don’t have too much insulin in my system at the same time.

It’s not a prefect science no matter what anyone tells you - you just gotta try things out, eliminate “fixes” until you find one that works for your body :slight_smile:

As an avid exerciser, having lived with T1d for 45 years I am relieved to see these thoughtful, helpful and more informed comments on this forum. today is my first day on this website. thank you for taking the time to share your insight and knowledge. I will attempt to do the same at some future date.

I do high intensity exercise 3-4 times a week and low intensity about 2-3 times a week. In both cases I had to figure out my insulin and nutrition information to get the right balance and reduce low’s and high’s. For me, on my high intensity days I do not wear my pump during exercise but check 2-3 times and update my CGM. I also drink a half cup of whole chocolate milk. When I am done, I eat a full meal with more protein to cover my night lows. My low intensity days include a basal reduction, checking throughout exercise, and eating a meal but not loaded with as much protein. Keep trying…you will learn what your body needs:)