Unusual very high BGs after 8 mile road bike ride

I am hoping some of you experienced T1 diabetics who exercise might be able to give me some insights on this new phenomenon I am having. Usually, of course, exercise brought my BG down and I had to carry juice or glucose tabs. These last 4 months (I am 65 years old but generally healthy) my BG goes out of control after medium intensity exercise. I ride my bike to work usually 2 times each week. My Endo thinks it may be a hormonal change and I will have my cortisol checked next week.
Your experience or ideas are appreciated. I’m attaching my reading from this morning when I road 8 miles to work on an asphalt path in 74 degree weather. Of course I over-reacted and took to much Humalog afterward.

Did you have any carbs on board when you started your ride? Or perhaps you had a particularly heavy meal the previous evening? I notice that my BG can spike up similarly during a run if my previous evening meal is particularly heavy in carbs/fat/protein than my normal meal.

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What are the times of the ride? Looking at the BG trace, I wasn’t sure the start and stop time.

Are you sure it was medium intensity? Heat could be a factor. The same speed and distance that is easy in cool weather will be much harder in hot weather, and will make your body feel like it is working harder.

What are you doing with your basal during the ride?

Are you eating before the ride?

Morning stuff is tricky, because you body might be responding to waking up in addition to the ride.

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I had this same issue when I was training for a triathlon many years back. Exercise lowers your sugar and your insulin resistance so sugars can jump around more quickly.
What I discovered is that low sugars cause a glycogen dump much quicker when I’m exercising.
It will happen in the low 80s. Instead of the low 60’s. Once that happens I would go super high then super low in pretty fast succession. I learned to not allow my sugar to go low and it prevented the highs too.
I would not start till I was over 130. As I start dipping under 100 I would consume carb gel like gu or something similar.
The carb gels have a slow absorption so it gives you a more even and steady level throughout your ride. It also prevents your liver from dumping glycogen.
It seems counter intuitive but it did the trick for me.

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Thanks Timothy, Eric2, and Trying,
My biking timing was between 7:15 to about 8:15 this morning. This morning I had only whole wheat toast and black tea.
My situation does not seem to vary that much with what I ate the night before, though I had some high BG overnight.
My typical breakfast is high protein with eggs and sausage with salad most days. Along with coffee and whole cream.

Regarding medium intensity, I have learned to back off my biking speed as I think adrenalin was kicking in. But this morning it really jumped.
Coming home it did not jump so perhaps it IS related to the dawn effect compounding the BG rise.

I think I will try Timothy’s suggestion of trying to prevent the glycogen dump of glucose by starting with my BG over 130 and keeping it above 85.
I will look for a carb gel to use rather than glucose tabs.

Thanks all! Rob

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I’m 64, and having similar experience with biking. BG used to always drop with aerobic exercise (I used to run, but then: arthritis), but now as often as not it goes up, though nothing like as high as you’re seeing (I’m currently at a 5.8 A1C, so I’m starting from a pretty low avg. to begin with). I always understood that high intensity exercise would raise it while slow-steady aerobic would not, and that’s always been the case for me, except for riding in very cold weather. Like you I’m wondering if aging and hormonal changes have something to do with it. I’ll be interested to hear what you learn about your cortisol levels.

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It is not uncommon for me, at all, to develop highs while exercising.

Its my body kicking out sugar and adrenaline to help me perform well.

Here’s the catch 22 - when I am performing very well and enjoying myself, I tend to go high. I feel really good in my body when this happens, so I think that my body is performing as it should - outputting appropriate amounts of energy for me to perform well.

I might have flatline data all day, then start skiing at night and see it jump from flatline 100 to 400 within 15 min, like clockwork. That happens when I’m skiing like a champ and I feel like I can do anything. Its the days when kids cheer for me from the chairlift - when I’m taking jumps and skiing through heavy terrain like a mountain goat.

This doesn’t typically happen from biking, but it does from x-county, even more reliably than downhill.

When I go for a moderate-intensity run, if I have any IOB I drop but if I run first thing in the morning with no insulin and no carbs, I stay completely flat. Well, I recently decided to see how fast I could run one mile, so I did it first thing in the morning with no insulin, and I had a significant spike. I normally see an increase in blood sugar with other exercise, but never running. I definitely think it was the higher-intensity/adrenaline that caused the spike.

Thanks darkandstormy. I might try biking in the morning with no breakfast and see how that does. The dawn effect is pretty strong in my body even after just coffee. Of course I will need to bring some food or carb gels in case I have a drop.

I also have a strong dawn effect and sometimes it wakes me up. It’s a good sign that your adrenal glands are working.

I appreciate everyone’s help. I have not had an Endocrinologist so not sure how much my new Endo will be able to help. I will respond with my blood test results in about 10 days. But regarding Dawn Effect, it is SO much stronger than it ever was. Last night my BG was perfect yet about 15 minutes before I was able to get my breakfast on the table it shot up over 140 from 108. I am having to double the amount of Humalog I am taking. I would appreciate other’s experience and discussion!

All of this will be very difficult to deal with if you don’t see consistent patterns.

If you get up at the same time everyday (you may have to do this), and see the same pattern reliably, then you need to bump up the basal insulin delivery 2 - 4 hours prior to officially waking up. If you take shots, you may need to split the dose of basal insulin into one before bed and one in the morning (a higher dose). This will provide some overlap between the two injections and hit you with a bunch of insulin in the morning.

Patterns change over time. So, you might see this behavior for a few months, then it might disappear. That’s not uncommon. Patterns typically last 2-3 months, for me, before adjustments are necessary.

Seems like you are an adrenaline-rich human lately. You are kicking a lot of sugar out of your liver and/or producing a lot of adrenaline. Thats ok. It means your organs are operating the way they should.

QUESTION: Do you feel good right now? Like, do you have a lot of energy and highly productive mornings?

mohe0001 and Timothy, Here is my BG of 105 after 2 hours and driving to work, not biking. (I did have a snack when I got to work after this BG).
I do wake up consistently at the same time and take my doses between 5:15 and 6 a.m. I’ve learned to try to take my doses first thing on getting up but when my BG is perfect, like this morning, I often delay which was a mistake. I am in some work and home stress which may be adding on to hormone changes. Drinking more wine than usual, probably 6 glasses a week…SMILE. I feel generally very good but not as energetic and focused in the mornings. I can feel the adrenaline rush in the mornings and after bike rides which does not “feel good”.
Yes, my pattern has significantly changed over time. I was getting lows at night but large dawn effect before breakfast so I stopped taking a Lantus evening dose and added it all to the morning. So I think I must concentrate on getting some insulin started perhaps BEFORE I come down to the kitchen, then monitor the BG direction for further coverage.

Hi all! Just want to post some good news and thank you for your suggestions. This morning I had NO spike of BG after my bike ride.
As you can see from my screenshot, I still have insulin working in my system and the prediction (the black circle) would have been a low, but the exercise and morning rise kept it normal. These are some things I did to help:

I started the morning with a BG of about 64 but still took insulin
I took my Lantus right away upon getting up
I took Regular insulin rather than humalog, and that lasts longer for me
I ate a smaller breakfast than usual, but low carb with coffee
I watched my BG along the ride from 7:10 to 8:05.
Hopefully I can continue to match this good result!


Great to see. It’s all a game of trial and error.
You are working uphill on daily injections so that result is not easy to achieve. I moved to a pump and find it much easier to make small corrections. However the pump can be an albatross sometimes.
I took a pump vacation for 2 months and my sugars were all over the place. I have not had a significant low in two years. Maybe my cgm plays a bigger role than my pump but still. I found long term insulin tough to manage.