Exercise and controlling BG

How do Type 1, pump using, CGM members control their BG from falling while exercising OR skyrocketing AFTER exercise? As usual I’m trying all different approaches to keeping my BG in range before and after exercise but wow, is it hard!

I have tried suspending my pump when my BG is 110-120 and that hasn’t helped me from having hypoglacemia, even with taking O.J. to class with me. Today I went into a class with a 135 BG. I suspended my pump, fearing I’d go very low which I started to do, 20 minutes into the exercise I was at 117, going down at 110 took a couple gulps of O.J. Class ended I turned my pump on again. Twenty minutes later I was at 223! Gave myself 3 units of humalog from my pump and increased my basal from .87 to 105%for 2 hours! Finally, after 1- 1/2 hours my BG started to drop to 206. At 2 hours after having given myself the insulin and the 2 hours of having the basal at 105. my BG was 188! Still not in the “normal” range.

I’m thinking maybe next time I’ll NOT suspend my pump but lower my basal to .50%, for the duration of the class returning it to it’s normal setting after the class. Such frustration with all this!

I turn down my basal to 60% two hours before I start exercising. Also I try very hard not to have any insulin-on-board from previous meals when I’m working out. I find if I start at about 130 or so I shouldn’t have any problems. I’ve even had workouts where I stay pretty flat all the way through. (By no means every time!)


I turn down my basal to 50%, but don’t completely suspend basal (otherwise I skyrocket and get high ketones and feel sick about an hour after finishing). I also set the temporary basal to start at least an hour or an hour and a half before exercise and end at least a half hour before exercise is over.

It hasn’t been perfect (I do sometimes go a little low or a little high), but it’s been the best combination I’ve tried and does often result in pretty flat lines through exercise.

Also, no insulin on board at exercise start (if there’s IOB, I will eat enough glucose tablets or other fast carbs to “use it up” before starting).

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I am a walker so this is not a huge issue for me but when I was running, I like the others here reduced basal rate at least 2 hours before running. It’s all about timing and a lot of experimenting with good record keeping. Good luck.


All of this depends greatly on what you are doing and your personal circumstances.

I would start with a number of questions about your situation.

  • What kind of exercise is it?
  • How many times per week are you exercising
  • How long are the sessions?
  • Describe the intensity - hard? medium? easy? Is your heart pounding? Or just slightly elevated? Also, is the exercise intensity consistent throughout the class, or does it change throughout the class?
  • What is your current fitness level?
  • What type of diet are you on in terms of carbs - low carb? medium carb? high carb? About how many carbs per day is normal for you?
  • Do you have access to your pump and carbs during your exercise?
  • What time of day are you exercising and how close to meals is it? How soon after a meal do you exercise and how soon do you eat after you are done?

It’s a bunch of questions, but the best way to manage it really depends on your situation, so that’s where we have to start.

I’m not on a pump so I’m not sure how helpful I will be, but before I exercise I look at my numbers and do one of two things;
if I’m high, I leave it alone. I see how the exercise affects me before correcting.
If I’m anywhere from 150 or below and it’s going to be a long exercise routine like walking even just a mile or so, I eat something like an 18g carb granola bar. This usually keeps me from dropping which is what I worry about if I’m walking in town. I always keep fruit snacks on me too.

If I end up high after my workout for whatever reason, I usually eat a small snack of some sort of protein which I bolus and correct for. I usually eat after a workout regardless of my BG though, just because I end up hungry. lol I hope this helps some!

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Basal adjustments takes 1-2 hours to take effect as @Michelle43 mentioned above. The book “Think Like A Pancreas” mentioned this too. Something to keep in mind when doing basal testing. Also, Keep this in mind when adjusting basals for exercise.

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Thanks to all of you who answered and helped with some great suggestions on BG and exercise! I plan on using them. You’ve all been so helpful!


I am so thrilled to report that taking the suggestions many of you gave, reducing my basal to 50% or 60%, 1-2 hours before my exercise (cardiac, strength and resistance class) WORKED for me! I am cautiously optimistic, as I know that next time I may not get this result and that’s the fun of having diabetes, right?

Anyway, I reduced my basal to 60%, had a slice of toast with peanut butter, started the class at 178 BG, first few minutes it climbed, then proceeded to drop, 150, 106, 89, at this point I drank 6 oz. of O.J. At the end of the class my BG was 122 and leveled off at 116! NO extreme low or extreme high!

Thanks again all of you who offered your help in this!


I love success stories!

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I have found that during my routine exercise session my BG will drop from50-70. So I get my BG up to someplace in that range and do nothing else. It seems to work most of the time. After the exercise, I adjust as necessary to bring it in range.

Hi Jeff21. Let me get this straight your BG usually drops 50 to 70 points, exercising, correct? So you try to get your BG up to the 175 range before starting exercise?

This is all good to know. Thank you Jeff21!

Correct. Sorry I confused.

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Cellular uptake of glucose during exercise can happen independently of insulin. The uptake of glucose during exercise - caused by the contraction of muscles - is complex and involves a variety of signaling molecules. For simplicity, we can refer to it as the “contraction mediated pathway”.

If you do not adjust your insulin amounts during exercise, the combination of the insulin’s effect on blood glucose, combined with the contraction mediated pathway, will be greatly amplified.

But there is no need to be resigned to always having a huge BG drop. Adjustments to insulin levels and well-timed carb intakes can allow your BG to remain relatively flat.

There is no one-size-fits-all solution that works the same for everyone. The exact amounts and timing of it depends greatly on your particular circumstances. If you would like to work though the specifics of it, we can do that.

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Yes, I agree with you. But my system doesn’t always respond the same way, so this keeps me ok even if my BG goes UP during the exercise session. I probably depends on where my BG is at the time as well as the recent food history. Too complex for my small mind. This seems to work for me and keeps my A1C near 7.0-7.2.

This is what I do with insulin while doing exercise, it works for me, no idea how it works for others.

First you need to decompose exercise in two categories, aerobic exercise (running, walking etc.) and other type, weight lifting, climbing etc.

For the the aerobic exercise (I run), I lower the basal by 50%, which for me means turning it off, I am at 0.025u/h and my pump does not go any lower. On very long runs (over 4hours) I do 1 hour 0.025 and 0 the next and so on. I start my runs at about 100/0.80 and finish in the same range. On long runs I eat carbs every hour, and I usually do the same rule for boluses, cut them by 50%.

For other exercise, which is intense, but short, such as climbing in my case, I do not change a thing and, for example if I am a bit high before exercise, say 140, I will actually bolus 1unit (as I would do otherwise).

For the bloodsugar after the exercise, there it is a wee bit more tricky. For intense sports, I do not change a thing. But for endurance sport, it depends on the intensity of the exercise, which I measure by heart rate. At a low heart rate, the body burns fat, and I can run 3 or 4 hours without any change to my bloodsugar after exercise. On the other hand, when I run at a faster heart rate, the body also eats glycogen and it will replenish its reserve later, so I need to lower my basal and boluses up to 6hours later.

All this works well for me, my A1c are around 5.


Good detailed advice. The 100 number makes sense to me but I’m puzzled about the 0.8 number. Did you intend to write the equivalent mmol/L number or does the 0.8 refer to a basal rate in your pump?

I mean 80mg/dL of sugar and 100mg/dL (the normal for a non diabetic being 110 to 80). Apologies for the lack of clarity…

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OK, so not to be a kill joy, but just to be realistic - this is one of the most difficult things I deal with. Some things to consider might be: 1.) Are you doing anaerobic (tends to increase BG) or aerobic exercise (tends to decrease BG); 2.) How much exercise have you done lately (have you depleted all the glycogen in your liver that might contribute to rapid BG rise? If so, you might be more likely to get severe lows). This probably isn’t that helpful. I view it as kinda a crap shoot. Gotta watch very closely and use caution if your data is goofy.

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