Going low when exercising

I would like to suggest set Dexcom G6 alerts to: (1) high at 160 mg/dl, (2) rise rate at 2 mg/dl/min. Once you receive the alert notification, start to walk immediately. If you don’t start walking, you may end up with high BG > 200 mg/dl.

If you plan to walk longer than 1 hour, consider reduce your breakfast bolus units, and set basal to zero at around 160-200 mg/dl for the remaining journey (2 hours+). You may still hit low BG (<80 mg/dl) later. In that case, consume some carbs around 100 mg/dl or so to prevent low BG.

You need practice and find out the best parameters to suit your need. Good luck.

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I agree that 50% or more reduction of breakfast bolus might be the best and easiest place to start. Eating to handle lows is why I got heavier over the years. It was a major learning curve for me to use less insulin. I was just on that low, eat, high, insulin. It was a nightmare. With much less insulin on board, there is much less problems. I did find that I couldn’t just snack anymore. If I wanted a snack, I have to bolus for it. But that also helps with my reduction in calories in. It isn’t worth the effort sometimes.
You can also do a temp basal if it is exercise that is not normal. Most people try and start it an hour or so before starting and extending an hour or so after. But this recommendation come with the statement, “we are all a science experiment “ what works well for one person, might not work well for the next. I have just found experimentation is key. Just keep trying different things until you find what works. It took a lot of pizza before I found what worked best for me. (That was an experiment I loved, as I love pizza!)
And I just carry a tube of glucose tablets when I exercise. Quick, easy, don’t melt and they are not something anyone is just going to snack on! Good luck with your experiments!

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You could experiment with a low or no carb breakfast. Then you could have a much smaller breakfast bolus. My guess is that that bolus is really kicking in while you’re walking rather than while you’re eating. You could even save some of the carbs in your typical breakfast for when you get back when any bolus you take might work more efficiently. I find that first morning bolus takes a long time to really work.


When I get on my exercise bike daily, I try to reduce my bolus for a meal, so I can get on my exercise bike for a full hour. (Doesn’t always work, days can be different) But I also like to get on when I eat a small snack, take a smaller dose and then I know it won’t kick in mostly until after the hour I am on my bike. I deal with more insulin during or after as needed.

For snorkeling I used to reduce my basal 50% a half hour before I started actually snorkeling for a 2 hour time frame. This worked really well for quite a while.

Now I think I am so used to snorkeling and I stay out a lot longer I started climbing half the time when I did that. So I have changed my protocol to eating 15-30 carbs before I start to boost my BG level and not taking a bolus and not reducing my basal at all. Then I take some insulin when I am done because I will start to climb afterwards at some point.


You might try just eating breakfast and heading out within a short time after and before your blood sugar really starts to rise too much. and I would also agree with the person who said try a less carby breakfast but still reduce bolus by 50% and see what happens. It’s all trial and error.


haha how resourceful!! I don’t know what my dog would think about that :smile:

I don’t carry a bag with me, I just try to exercise as light as I can.

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You’ve hit the nail on the head. Every time I go low and need to eat, I kind of think its counter intuitive on the weight. But I tend to over bolus than under because I find it awfully difficult to bring a high BG down as opposed to a low BG up. It could be several hours before a high BG returns back to normal.

Thanks everyone, I’ll try with cutting my bolus down first and see how it works out.

Why not try testing your basal first. Once your basal is correct, generally everything else should fall into place.

Edited to add:

Here are a few other suggestions:

Diabetic Athlete’s Handbook by Sheri R. Colberg

Sugar Surfing by Stephen W. Ponder and Kevin McMahon

Integrated Diabetes has a few articles on exercise/activity at the link below


Dogs need jobs in this difficult economic climate.
I think my dog feels important when he has a job, like “find the kitty,”
or “wear your vest.” PS There are cheaper ones than a this site.


I always set temp basal 90 minutes before exercise. If I’m going for a 1.5-3 hour bike ride,I set the time so that the regular basal rate resumes around 1 hour before end of exercise. This last bit helps from going high later on after exercise. I also agree with other posts, try reducing breakfast bolus more. Sometimes I’ll do 1/2 the normal breakfast bolus plus use a 1 Hour duration. Avoids low during exercise but also avoids high 1-2 hours after.


Thank you to everyone who have contributed to this thread. I have reduced my bolus by 40-50% and set my temp basal to 0% an hour before my walks.

I’ve noticed

  1. I’m not going hypo anymore - I may be able to reduce this even further if i extend my walks.
  2. My sugar after lunch isn’t sky rocketing anymore - this was due to me setting my temp basal to 0% just before my walk and not 1 hour before.

I’ve only tried this for 4 times so far but all looking promising. Thank you.


I have gone through from a similar kind of situation without having exercise but after a few hours of work at the office. In the beginning, I was taking sugar candy but then I started to take 1-2 bananas and honestly, I got much relief. It has natural sugar and also good bad for teeth also.

I also found a perfect sure for numb legs and use it without low sugar levels as well.

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I do find that light prolonged exercise can cause lows. Same thing happens to me when I mow the lawn (walk-behind mower). I usually reduce my meal bolus by a couple of units, and also emphasize fiber to prolong the carb cycle. Nuts or high fiber cereals are a good choice for that.

Similar things happen with heavy exercise (I fence twice a week), and in that case I try to time the meal so that my sugar is either a bit elevated (~150) or rising when I start. In that case I also reduce the basal insulin for the day by 5-10%, since there’s a prolonged effect that can extend for 12-18 hours.


So today I lowered my breakfast bolus , had the same breakfast as i usually do, and went for my exercise. I came home and my sugar level was at 15mmol (about 270 mg), while last week it was in range 5.5mmol ish (around 100mg). The only difference today is I left the house about 10 -15mins later than usual and I suspect I missed the timing with the peak so my sugar wouldn’t come down. How exactly should I be timing this so I don’t miss the peak. And what should I do if I’m running late for my exercise, injecting insulin at that point won’t help.

Rapid insulin starts working in about 30 minutes, but it’s not working very hard in the beginning. it hits its peak action between an hour and a half and two and a half hours. At least that’s been my experience. By 3 and 1/2 hours you don’t have much left working at all. I never had much luck adjusting basal with exercise because things can be so variable and it often created a high afterwards. (I’m not sure if you are adjusting basal as well.) That is, unless the exercise is prolonged like a very active day - then setting a decreased basal is very effective. We have found that timing and adjustment of boluses has been the most effective with exercise.

Exercising right after a meal and bolus is tough. Have you considered doing your walk before you eat?

If you think about athletic competitions, nobody eats right before the event, even non-D’s don’t do that.

Eating 2 hours before exercise is usually the ideal time-frame for a hard effort that needs perfecting fuel (such as a competition).

And eating either 4 hours before the exercise or right after the exercise is good for less intense efforts.

If you eat and bolus right before exercise it is doable, but it just needs close monitoring and corrections.


I don’t think that would work because I walk during the morning so if I had to exercise before having breakfast I’m not sure I can sustain the session on an empty stomach. And I’ll feel miserable exercising hungry.:sweat_smile:

This have the bolus seemed to work for me last week, this week I seem to have a different result. Perhaps my timing is off. My exercise isn’t intense, just about an hour of fast walking.

I also like the idea of bolusing less because I will exercise after a meal.

Should I be already into the walk and getting a fast pulse by the first hour or is it the time I leave the house for my walk in order to stop my BG climbing to the top?

This will be trial and error too because everyone is different. I would think you want to intercept that blood sugar from going high from the lower bolus. On a Dexcom you’ll see blood sugar starting to rise about 20 minutes after a meal so you’ll want to head that off at the pass. Prebolus timing also comes into play, so that is another factor to adjust. Unfortunately there’s no easy answer you have to just see what works for you most of the time.


I’ve been reducing my bolus and finding the sweet spot for the reduction amount. At the moment its about 40-60% and its frustrating that what works on one day does seem to have the same results on another despite having the same breakfast. I guess that’s the unpredictability that comes with D.

Just want to get some opinion on something. After my walk today and yesterday, I came in nicely at 4.6mmol (~80mg), had 3 small chocolate drops and did another 30 mins of aerobic exercise. I was feeling good at the end of the session - no hypo or hyper symptoms. Jumped in the shower and 45mins after measured my BG and it was 8.6mmol (155mg) which was higher than what I was expecting given my 30 min additional aerobic exercise was low impact high intensity and I was sweating by the end of it. I would have liked it to be sitting under 6mmol (100mg). But it went up.

So where did I go wrong? What had caused the increase in BG.

  1. Is my basal setting not strong enough for the window an hour before my BG measurement, I didn’t suspend my basal at all.

  2. Did I not reduce my bolus enough? The fact I came in after my initial walk at 4.6mmol (80mg) suggests that this was a good amount.

  3. Or was it the chocolate I had? I was afraid I would hypo if I didn’t get my sugar up before my aerobic. The amount of chocolate I had was so small I didn’t think this was a factor. I had 3 of these (not packets :smiley:, actual chocolate!)

It does depend how many carbs you consume for a low. 2 carbs from a vegan gummy bear makes me go up about 10 points. But it can make me go up 15 sometimes. There is a delayed reaction to going up to the full amount too. Chocolate has fat which would delay some of the absorption. So you probably need to look at how many carbs are in what you ate.

Hot showers send me though the roof fast. The earlier I take them the more it sends my BG up. I try to take lukewarm showers in the evening so it doesn’t effect my BG level as much. I actually don’t feel well from a hot shower that’s more than a few minutes because my BG wants to climb so fast.