What's up with not exercising above 240 mg/dl?

I’m on a pump and I always bolus when my blood sugar is high because I remember learning that you shouldn’t exercise if you’re high because the body releases additional glucose when you start exercising. But who came up with this mysterious 240 number? Has anyone experiment with exercising at high levels to get their sugar down?

I think it might be time for me to start some experimentation.

Hi Aaron,

Yes this always seemed mysterious to me. I thought that it was for fear of sudden rises in case you had too little insulin in your system. (i.e. fear of going to DKA quickly…)

But I admit that i don’t understand the logic. I have bolused and exercised when I was above 240 mg/dl.

I’ll be curious to see the other responses. I have never noticed a rise in blood glucose when I start exercising (but that doesn’t mean that it doesn’t happen).

I have exercised on bgs over 240, but have only heard of this phenomenon in the last few years and yes I have noticed if I exercise on a 240 and no bolus I can go higher, but… I have also noticed that I can lower my bgs as well, so like always with diabetes it depends upon the day and time, but like I had said I never heard of this until a few years ago when I had started on Lantus and humalog after being on NPH and regular for 35 years.

Kind of funny when I am at this high number and so physically drained I will listen to this advise as I am too tired to exercise. :wink:

I had never heard of this either. when my BS goes over200 I try to walk it off. not too long ago I was up to 350 and I walked half a mile…about all I could do. BS stayed over 250 for the remainder of the day.


I have read a few times “you shouldn’t exercise if your bg’s are above 240” I have walked a few times with my bg’s above 240 and I am still alive and kicking:) Not sure where this “you shouldn’t exercise if your bg’s are above 240” came from.

I recently read that if you still have some insulin on board, then it’s okay to exercise up to 300. If not, then you might be sending yourself to the stratosphere. I think the danger of correcting plus exercise is the possibility of really crashing hard.
But, everybody’s different…but, if I’m in the high 200’s a couple hours after supper, I can easily bring it down to the mid 100’s with an hour walk. But, like Karen said, it’s not easy to get movin’ with a high bg.

I don’t believe 240 is a magic number. Someone was probably writing some guidelines one day and had to pick a number and 240 seemed as good as any.

That’s my theory, anyway.


BTW, I have been known to exercise when my BG is over 240. Sometimes it goes up, but usually it goes down. I don’t use exercise as a substitute for my correction bolus, though. I calculate the correction bolus then take reduce it by 1 unit for each 30 minutes of exercise or cut it in half, whichever is the lower number.

I know that if I disconnect and am in the 80-180 range, my BG will go down but if I start getting in the 250 range, I have a VERY difficult time getting it down without bolusing. A little strange but I know that I am hitting the 250s when exercising, I need to bolus and I can then continue exercising.

Not a good idea to disconnect when exercising. That means you’re getting NO insulin so, about two hours after you’ve disconnected, you’re likely to see a big spike.

I used to disconnect until a CDE pointed out to me that nobody turns off their pancreas when they exercise. (Doh!) Better to reduce your basal or pre-exercise bolus.

Maintaining SOME basal while exercising might prevent you from going high while exercising. As always, YMMV. It takes some experimenting.


Thanks for the replies. I’ll do some tests the next time I’m high and I’ll try and post what happens. I want to explore some really intense exercise and see how quickly I can make it drop, though perhaps I’ll feel so exhausted that I won’t get very far.

What I’ve undertstood is that if BG is above 240 to test for ketones. If ketones are present then circulating insulin is not high enough and you’re likely to produce higher ketones as your system ‘converts fat to glucose’ in order to fuel the exercise. If no ketones are present then its OK to do do moderate exercise which should bring down BG levels but to test frequently.

If BG level is above 300 then you almost certainly have too little insulin and need to use insulin to lower BG before exercise.(and reflect why the level is so high!)

’ I want to explore some really intense exercise and see how quickly I can make it drop’

This might not work, sustained aerobic exercise is what usually reduces BG, whilst anaerobic exercise tends to increase BG. Indeed one tip is to start a long workout with a 30-60 second burst of maximum effort to help prevent hypos

(see Runsweet.com, the section on starting sports for more info on the physiology of exercise and diabetes. Its a site set up by Dr Ian Gallen a British diabetologist an ‘expert’ in diabetes and sport. He first developed an interest when newly diagnosed Steve Redgrave became his patient and needed advice as to how to win his 5th Olympic gold medal in spite of diabetes)

You are absolutely right.Testing for ketones, aerobic on non aerobic is the most important.Every one know himself,what will bring BG up or down. The educator tells our patients this new information but many of long standing diabetic children do not agree!!.At 250 mg with ketonuria, we fear from DKA.

Thanks for the tip about runsweet.com!!


I believe that the BG is only a part of the picture. For me, the type of exercise is equally important. For instance, if I play hockey, no matter what, my BG will rise. It uses muscle and heart power around the same, due it being about equally aerobic and non-aerobic, if not more anaerobic. (Due to my slow pace!) If I rollerblade for the same time, be it 30 min., or 1.5 hours, it normally will considerably lower my BG, both during and after. Especially if I do not lower longterm insulin after the exercise to prevent the phenomonon of low BG in the night, 12-16 hours later. So the effects on BG can be pronounced in an immediate and long term sense.
So, practically speaking, in order to lower BG, aerobic, or cardiovascular exercise has the stronger effect. Try lifting weights, and you will usually increase your BG, due to the release of lactic acid into the blood stream, amongst other things. Even yoga has increased my BG in an immediate sense. (although it can actually improve metabolism in the long term.) Bicycling, basketball, rollerblades, running, etc; all good for quick and long term BG.
Now if we all would cross country ski to work, we would need very little insulin, if any!
Be very careful about taking insulin prior to exercise, as hypoglycemia poses added risk during
exercise. It can sneak up on you unannounced, especially during strenuous exercise, with all the adrenaline and energy pumping through your system. Thats the worst!

there’s no way for energy to get into your cells. your exercising will be very uncomfortable and you will feel weak. noticeably. Exercise needs to be ongoing to stimulate your metabolism. For me, a change in activity/exercise takes a couple weeks to take effect.

Well, I have never heard of this, but my doctor never gave me a number to get to before I excercise and that is what I need advice on. I have too many lows while trying to excercise, even when I suspend my pump. Does anyone know an average number I should be at before excercising?

If my bgs is around 100, I will then eat 20 carbs and that will carry me through for 30-40 minutes of cardio. I am thinking my bgs is around 150-180 for exercise.

Just changing my basal never works for me. :frowning:

Thanks Karen. I am definately going to try that!

I don’t think there is a magic number but if the BG is over 240 because you carb loaded in preparation for exercise, then go ahead. If BG is 240 for an unknown reason or because of a forgotten bolus then one should check to see if there are urine ketones before beginning to exercise. Insulin is needed even during exercise to prevent ketones from being produced in too high of numbers. I think 240 was picked because it should be safe for all but we all know that everyone is different.

I may have strayed a little off topic in my previous reply (not the first time, nor the last,) but i ran across this data, from the Hanbook of Exercise in Diabetes:
"making recommendations on how to adjust insulin and diet for exercise that are broadly applicable
to the type one diabetic population is clearly not feasible. recommendations for treatment modifications need to be tailored to the specific exercise response of each individual. it is equally important to emphasize that whereas therapeautic strategies must be specific to the individual, the vast majority of physically active individuals with diabetes can be adequately controlled by a variety of insulin/diet options and should not feel bound to a single regimen."
it also states that hyperglycemia increases the deleterious effects of exercise on metabolism,
and that too little insulin contributes to ketogenesis and increased hepatic glucose output.
it seems that you shouldnt necessarily exercise with high BG, but that each persons different, and since exercise is such an important part of treating this disease, it can and should be done, given the proper cautions.