Working out with T1D

Does anyone else have trouble keeping their blood sugar consistent while working out? Mine will either go high or will tend to drop depending what I am doing. Also, is it safe to take insulin and then work out while still having acting insulin working? I was told that if you workout with acting insulin it can cause your blood sugar to drop? Just looking for some answers to help manage my blood sugar better while I workout.


I would definitely not take insulin before working out especially if your body body still has some natural insulin. Always always always keep juice on you when you’re working out in case it drops

@chamm hi Courtney, there are a lot of opinions on this, you can do a search if you click the search glass at the top of the page.

Aerobic exercise (think running on a treadmill) tends to lower blood sugar.
Anaerobic exercise (think power lifting) can raise blood sugar in some people.

If you are weight lifting and going high, you’ll have to experiment with insulin and it might be necessary to have some active insulin “on board” when you work out.

Lately I’ve been mixing routines, anaerobic first then jogging out the last 30 minutes. Also and for me, I use a pump and so I can dial back my basal insulin (usually to 20% of normal for 40 minutes before and about an hour after) and my numbers stay pretty stable during and afterwards.

Good luck.

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Exercising with T1D is definitely tricky. I’m a varsity athlete and I still struggle to keep my blood sugar in range during matches. One important thing to figure out (I’m sure there are other people on this site who can give a more in-depth explanation) is whether the exercise is aerobic or anaerobic. Aerobic exercise, such as running or swimming, will cause blood sugar to drop, while anaerobic exercise, such as sprints or lifting weights, will cause blood sugar to go up. My sport, tennis, happens to have elements of both, which makes for some interesting numbers. :slight_smile:
Another important note–dehydration will make blood sugar skyrocket. Make sure to stay hydrated before, during, and after a workout.
If I’m doing aerobic exercise (like going for a run) I’ll usually cut back on my insulin before I do, and if necessary eat some slow-acting carbs. If I’m doing anaerobic exercise I’ll give myself a bit of extra insulin before I start. Everyone’s different, so take some time to figure out what works for you, and don’t be frustrated if it takes a few tries.

Hi Courtney - @chamm, even after living with insulin injections / infusions for over 60 years and living an active life, some say “too active”, I can still be taken by surprise by either “high” or “low” following some activities. and sometimes several hours [6 to 10] after the activity is completed my BG will drop suddenly and significantly. There are a few explanations for this:

  • Our bodies are not [yet?] programed as robots;
  • Aerobic exercise will generally help lower BG levels;
  • Anaerobic exercise will more often cause BG levels to rise - the stress put on the body will signal the liver saying “muscles need food” and the body will get flooded with glucose / glucagon;
  • Residual insulin [active insulin] from a previous bolus can, depending on activity level’ either keep your glucose level [anaerobic exercising] or cause glucose levels to drop, sometimes VERY suddenly.

Personally, I can not always anticipate or recognize when my exercise morphs from what I intended to be a light - moderate workout to a full blown anaerobic experience. My solutions, in the past I set a timer [such as a bike tracker] so I’d stop and do a fingerstick; now, I set alerts on my CGM to let me know audibly when I’m going up or down at certain rates.

Before any exercise I set my pump at a percentage level of less than 100% and when I notice that my exercise level has reached anaerobic, I cancel the temporary reduced basal; if my BGL is dropping I will suspend my pump and eat - my preferred snack for this drop is a protein granola bar loaded with nuts and dark chocolate. My bars give an initial sugar jolt and plenty of prolonged glucose; I also carry a couple of juice boxes in my bag, just in case.

@Dennis excellent!
@chamm Glucose tablets - keep them always with you. I keep my sugars pretty stable now - so exercise bgs are pretty stable. When I used to roller-coaster with my sugar levels, I went low all the time. Now they’re good - but I’ve learned to keep tablets on hand, use my cgm, and to not lower my basal - insulin has a three hour window, if I lowered my basal, I went sky high later. Exercise is key for keeping sugars in range - sleep too, :joy:

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When would you recommend working? Before or After a meal? And how long?

Working out first thing in the morning without taking a bolus has helped me tremendously. Basically the only time I can do cardio without having to both cut my basal and consume carbs if my blood sugar is within a normal range. Having as little insulin on board as possible has been the most helpful for me.

Hi Courtney,
As someone who has lived with T1D for 58 years, I discovered some things about exercise the hard way. Unless you’re going to a very good endocrinologist, you won’t find out that your bg should be between 150 and 250 before exercising. If your bg is above 250 before you exercise, it will be much higher after you exercise. If you are below a bg of 150 before, it’s sure to go down. I’m on a pump & have used the temporary basal function or suspend basal function when I exercise. You’ll either have to discuss this with your endo or experiment on your own. I never leave home with liquid glucose or glucose tabs just Incase I go low.
Hope this helps,


We can file this under everyone is different. For me the trick is in the basal rate (if you pump) and insulin on board. I can work out with high bs but I don’t like to. I’ve been under 120 the last few sessions and ended my workout right at 100. Currently dialing back basal to 25% of normal at 40 minutes before the workout. Cheers good luck

Hi Courtney, I’m pretty new at this but anytime I work out with active insulin in my body my sugar drops like crazy. It still gets low even when I don’t have active insulin, but not Nearly as low as when I do!

Hey Courtney! I definitely agree with that it’s different for everyone. I’m a college athlete and even some practices are different for me. My best advice is try to check it every hour or so and before and after you workout to track trends. Make sure you have food with you in case it drops and talk to your doctor about adding insulin! I was told by mine not too because it drops later but I would check anyways.
Hope that helps!


Thanks for the info! I was a college athlete as well. I was diagnosed almost 3 years ago and it came as a total shock. Since being diagnosed I’ve been getting back into working out a lot so any information related to sports and diabetes is always appreciated! @jenn-lee16