Managing BGs During Intense Exercise

Hey folks, (T1D, CGM and Pump). I’m exercising 4-5x per week, typically cardio – 50 minutes interval training and lifting 2x per week. I am having trouble figuring out the right way to maintain my BG’s during exercise. What are you folks doing? What are you eating? I’m lowering my basal to 50% but obviously need to do more.

All ideas welcome.


When are you lowering your basal? I also lower mine to 50%, two hours before I start the workout. I also try to have zero insulin on board (meaning it’s at least four hours since my last bolus). I do pretty well in this regime.

We’re all different, of course, but I have found that, for me, it’s far more important to make sure, as @Michelle43 said, to try and have zero, or as little as possible, insulin on board when you start your workout than it is to reduce basal rate. That assumes, of course, that your basal is well-tuned. You may still have to lower basal. I don’t, at least not now – it seems that nearly all exercise (even cardio) results in somewhat higher BGs around an hour after I stop. On the other hand, with even 1u of remaining bolus insulin on board (and sometimes even as little as 0.5u), my BG promptly plummets after 15-20min of any type of exercise.


Thanks Michelle. My endo who is also diabetic recommended reducing nasal 1/2 hour before workout and eat a protein meal.

Do you eat before you work out? If so, what?


Thanks Thas. Good points.

I have a carb/protein meal 45min to 1hr before workout. I delivery only 50% of insulin in my pump. After workout, temporary basal rate of 70% for 3 hours. That usually works good for me. My workouts are usually 1 hr. doing cycling or kickboxing classes.

Thanks Luv… I’ve tried that @ 30minutes before but I crashed just before the end of the work out. I’m gonna try pushing it back a bit more. I’m vegan so I have to work a bit harder to get the protein I need.

Maybe even 1 hr. How about a protein smoothie with a banana or something like that?

I think I’ve had a similar experience to Thas. I don’t do a whole lot of intense Cardio, but I go rock climbing 2-3 times a week followed by strength exercises for climbing which are basically pullup pushup style exercises.

I’m using MDI but I find I have to actually give a bolus before I exercise or my BGL go high. Depending on a persons interpretation of high I guess, but I usually find if I don’t do this it raises to around 10 mol/ml or 180 mg/dl. Which for me, given I haven’t eaten, is unacceptable.

However, the exception to this is if I go climbing not long after eating, where I still have insulin on board from my lunch. In these instances I find I don’t need to give any bolus.

I’ve read in the past that this has something to do with the fact often your body releases glucose to deal with higher intensity exercise, which normally would be combatted by your own insulin production. However, in a type 1 diabetic this means higher Blood glucose if you have no insulin on board. I’m not sure if IOB somehow supressess this response or just means deal with the glucose.

I actually prefer to excercise when it’s been at least 3-4 hours since I’ve eaten, I don’t really find I go low, but again i don’t really do long distance cardio or anything like that so it’s usually an hour of climbing. I then like to eat after that, and I always have to reduce my bolus to carb ratio after exercise.

When I was doing warm up (15 minutes) followed by intervals (20 minutes) and the 45-60 minutes lifting, I used to reduce my basal by 50-70% 1 hour before starting or setting my pump to my basal profile called “training”. If trending upward before or under I just bolused a small amount, if trending downward I adjusted with small sips of regular soda. I did some tests and found out that each sip of soda would equal approximately 1 gr of carbs (I sipped and spitted into a measuring cup). Trending downward meant 5 gr carbs or sips, plummeting meant 10-15 sips or gr carbs maybe more. Regular soda being fluid makes it easy for the body to use, it doesn´t go stale and it´s always easily accessible almost wherever you go. (It has become my trusty friend day and night.)

After lifting I drank a protein shake, finding I almost always had to bolus for it using half my regular I:C ratio.

When eating later on - usually within an hour - I always reduced my bolus to some extent, sometimes also reducing basals for 2-3 hours, but all this was always dynamic based upon numbers, trends and experience.

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Siri… sounds like this really works for you. I hear you regarding the soda. I’m using the little cans of Apple juice which have 20g C but I’m not getting as granular as you are re: sips. I have a bunch of questions.

  1. My schedule is “complicated" so I’m having trouble finding something that works. looks like this;

Day 1. 5 minute stretch >Cardio - 50 min> 15 min stretch
Day 2 5 minute stretch >Cardio - 50 min> 15 min stretch
Day 3: same stretch routine> Hybrid Cardio - 50 min and either lower or upper body circuit ~ 30 min
Day 4: lift - 30 min
Day 5 lift 30 min

So, given the above, how would you approach this for pre- post- and lows?

  1. Do you follow the same regimen for cardio days?

  2. What pump are you using? are you just going into bolus settings and changing your I:C ratio? and then changing it back?

  3. Why bolus with the protein shake?

Sorry for all the questions but I’m trying to better understand what you do and why?

I’d second what’s been said about not having any IOB and lowering basal well ahead of time. A small amount of insulin goes a really reeeeeally long way when doing moderate to heavy exercise. This is an advantage if you’re trying to knock down a stubborn high of course. A brisk 15-minute walk with a little IOB can be amazingly effective.

I’d add that in my experience there’s a considerable bounce-back from an exercise low. Unless I’m seeing sparkles and getting cone vision I generally try to wait it out, see how far it rises within 40 minutes or so after I’ve finished exercising and then treat with carbs as necessary. I find that keeps me from roller-coastering. I’ve always had a semi-irrational resistance to taking carbs before exercising since part of the whole point is to burn carbs in the first place, though I try to be very regular about bike riding and if my BG at the outset requires it I’ll have something in the 15-25 grams range before starting out.

So for the meal pre-exercise are you giving a standard bolus or reducing. I go low when I work out intensely. And I have a similar experience that if I have any insulin on board I crash. I’m finding that if I don’t bolus, I go high after working out but don’t know if its from the meal or a post exercise rise

I’ve been eating a high protein hi carb lunch, cut my bolus in half and then go work out about 30 minutes later. I try to do this at the same time every day.

Thanks so much!

No, I don´t. Like others here have said, pure cardio usually require less insulin while lifting (and sprinting) usually requires some insulin. I would recommend Stephen Ponders book “Sugar Surfing” to get the full use of your CGM when excercising. He preaches a dynamic approach and - if you don´t do this already - he teaches you how to adjust your alarm settings to get warnings beforehand to avoid both highs and lows. It´s really no set answer to your quetsions, the answer is to use the technology and knowledge you have to always do the adjustments you need when needed.

I´m using the Animas Vibe with Dexcom G4 integrated. I use the basal settings and adjust them when excercising, not the bolus settings. The boluses I use are different every time, so I don´t have settings for boluses. My I:C ratio is programmed into my pump,- after excercising I just override the pumps suggestions and do the math in my head based on prior experiences and how the last couple of days have been. I also keep a close eye on my CGM and adjust my insulin/carbs when needed.

Beacuse of experience,- and my guess is because it´s right after lifiting that I need insulin. Lifitng = insulin. Cardio = less insulin.

Thanks Siri… .much obliged

I lower 1 hour before to 50% then go to 70% for three hours post exerices

@drbb totally agree re: having carbs when the goal is to burn them but what do you do to set yourself up for a moderate to heavy exercise regimen then?

Mostly it’s the timing. I maintain a pretty low-carb diet, and as long as I don’t have IOB I can ride pretty hard for 45min-1hr without getting below 70s, depending on where I am at the start. When I struggle with it the most is my homeward ride from work because lunch time is when I usually indulge in carbs (it’s just so much easier if you can have a sandwich!), and I don’t care what they say–my lunch time insulin always seems to have a little kick left in it even 4-5 hours later, so if I’m going to have an exercise-induced hypo that’s when it’s going to happen. I have set a reminder to back my basal down to like 10-20% starting about 1.5hr before leaving, so that helps. Tonight I was <100 when I got to my bike so I had a single glucose tab just in case and between that and the lower basal I’d been running I’m at 109 just after arriving home. Cutting down the carbs at lunch (only half a sandwich!) seems to have made things a lot more stable.

I just do find that, even though the official line is “You can eat whatever you want, just bolus for it!” it’s a LOT easier to manage by keeping carbs to a minimum.

Pre-meal exercise I give my standard Bolus. I will make it clear though I rarely do this, I mostly go climbing after work or go for a walk or run after work. By this time it’s been 4-5 hours since I ate and I have little insulin on board.

The few times I have done climbing within the 2-3 hours after eating I find that if I give my standard insulin regime then my blood sugars actually seem to be pretty stable. I also bolus 2 hours after my meals though for the protein I ate.

So in an instance where I’ve eaten, usually I eat lunch, and then 2 hours after lunch I go climbing. At this point I give about 2 units of novorapid for the protein and I go climb. I did this last Saturday actually and tested an hour after climbing and two afters after climbing and my blood sugar was pretty stable floating around 90 mg/dl.

I wish I could say this works everytime, but much like anything in diabetes I am having to constantly re-evaluate this. I almost always give a pre-bolus before climbing after work. Which assumes I haven’t eaten for at least 4 hours and don’t have a lot of IOB. But I do sometimes find this brings my low after climbing. So it’s a bit of a gamble but given the majority of the time it seems to keep me in a desired Blood glucose range, and given I eat almost immediately after clmbing it’s a gamble I take and it pays off 90% of the time.

I havent really found a consistant approach with standard Cardio yet. I do go for runs occasionally and regular walks, it doesn’t seem to lower my blood sugar, sometimes it does seem to raise it. However, almost gauranteed if I give some insulin before running I will go low.

I don’t eat anything before working out, I find an empty stomach works for me! And I lower my basal 50% for three hours, two hours before working out, so I finish the temp basal when I finish my one hour workout. I rarely go high after this. Occasionally I may go a little low.