Extreme sensitivity to exercise


My daughter (17) has Type 1, uses Dexcom G4 and Tandem T:slim Pump.

If she has any IOB and moves her little finger for a few minutes, her blood sugar plummets. This is an exaggeration, of course, but it’s how we talk about how sensitive she is to exercise! Some examples:

  • Walking across a parking lot to a store after a recent meal and bolus has sent her dropping very quickly.
  • It’s very rare for us to go on a family walk or something and not have to stop to deal with a “FALLING” alert at some point, even after reducing basal and bolus.
  • She works at a fast food restaurant and being on her feet at the cash register sends her low (this is after reducing her meal bolus – she has to take tabs during her shift
  • Going to the pool…nah, forget it!

This doesn’t seem typical - I don’t get the impression that very light exercise causes problems like this. Or is this more typical than I realize?

One hypothesis is that she is typically far too sedate, so that when she does move, to her body it’s like real exercise! Does that seem reasonable? Does she just need to be more active generally?

Anyway, would appreciate any thoughts anyone has on this.



I was diagnosed april 2018.

Back in the Gym maybe by July 2018 and would drop like a stone afterwards, then that effect just kind of went away. I still have to watch it, be aware but its not like it was.

The same thing would happen if I went on brisk walks with the neighbor and the dog. Now not so much.

My guess is my insulin sensitivity stabilized and is less effected by my activity level because I exercise regularly as opposed to the beginning when like I read exercise increases insulin sensitivity and makes it work more efficiently.

Lets see what some other people have to say, lots of people here at this gosh 50 and 60 times longer then me but I think that insulin sensitivity thing has a much greater effect then activity that burns the sugar off into energy.

Double post what ever, yes I agree with that.

How much cross-checking of CGM with fingersticks have you and your daughter done done before/after exercise?

These sudden deep drops from minor exercise that have been reported on CGM’s, seem to me to be more a result of interstitial fluid “catching up” than an actual deep drop in real bg.

I think modern CGM’s try to model and fit the interstitial fluid history and it’s possible that more exercise will help the CGM learn the properties better?


She needs to adjust both her basal rates and bolus amounts. The Tandem pump can store a bunch of different profiles for basal rates. I have to change between a weekend and work profile, with each containing 6-9 different rates for certain times of the day. Her bolus amounts seems to too much, especially at her job. I don’t go to a gym or workout, but I would personally disconnect my pump if I was going to be working out.

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Just a thought, but how long has your daughter had Type 1? Could it be that she still has some beta cells that kick in? I haven’t been walking this road very long, but the scenario sounds familiar. Now that my honeymoon is over ( sigh) ,although I was blessed to have a relatively extended one, I can now exercise more and I do. Just a thought though.


I agree with all the above, I guess that means there is no easy answer.
But I do want to add

I don’t know if you’ve ever done a basal check but it can be done in 5 hour fasting increments. Because maybe when she’s “busy” she isn’t snacking like she might at home or sitting? So she is adding the exercise drop to maybe a little too strong basal rate?

I do lower my basal by at least 50% from exercise, even walking, if I know it’s something more strenuous like snorkeling for me, I will even start at a higher number to make sure I stay high enough. I will start out a trip to the dentist which makes me drop or snorkeling at about 30 points higher to compensate for a stronger drop in case I didn’t reduce my basal enough.

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I have severe lows with otherwise normal activities, too. My endocrinologist said it was likely due to high metabolism. I find that protein helps, but I’m also one of those people for whom protein raises my blood sugar, so that’s part of it. I drink a glass or two of unsweetened soy milk or, when I was a teenager, I would eat 2 tablespoons of peanut butter before moving about. Doing it before leaving the house seems to work best for me, and also before any activity that requires more energy around the house. I have to test my blood glucose levels a lot more frequently then average, but it’s worth it to avoid the lows and all that goes along with them since they were way more disruptive than the act of just checking my blood sugar. It took a while for me to adjust as a teen, and I still have to deal with people scoffing at how often I need to check or have snacks. But my A1C’s are good and I’ve had type 1 diabetes for more than 15 years now with the same issue, no complications to date, so it seems to be worth it for me. Oh, and I buy Tropicana orange juice boxes in bulk from Amazon and keep them in my supply bags and around the house. Sometimes I have to have a lot of them to prevent or treat lows, and they don’t have any added supplementary vitamin C, so I don’t have to worry about that potentially throwing off my meter. Anyway, I’m sorry she’s having to deal with this. It’s really hard. But, she’s not alone! Hope this helps


Thank you.

Yes, being out of shape makes exercise have more impact. I think that I notice that in myself. But, its more likely that her basals are set too high. I wouldn’t view this as something that is fundamentally part of her body. Its much more likely how her insulin is dosed.

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I just watched this video! Wow!
It is also a good judge of how exercise can make a huge impact on your insulin needs.
Chris Pennell a rugby player


I watched the video. Thanks for posting.

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Thanks to you all for your comments. It sounds like we have some work to do 1) getting her moving a bit more and 2) looking at how we might reduce basals (although basal tests indicate her basals are about right…)

I keep my basal rate off during intensive exercise/running (55 min). I turn it off about 30-40 minutes before I start and keep it off for about an 1 hour after exercise. I also eat a medium/large banana right before I start with some pb ( no bolus) This used to hold me though out the session, I have increased my pace and distance and realized that I was getting low at 45 min.

Now, I noticed that I have to refuel about 30 mins into the workout if running. so not to drop too low that I would have to stop, I eat something sweet before I drop to keep the bg maintained.

Also, keep in mind that there is a lag time between meter and cgm and it could be about 15 to 20 minutes. The reason was that when you are exercising your sugar is rapidly changing and the cgm has to keep up(from the internet) That is a lot of time when you are actively exercising and potentially dropping bg. Once when I was exercising my cgm said 120 and my meter said 80. My meter and cgm are usually on point.

Your basal rate changes all the time for some especially if your daily activities change.

My basal setting is at .55 during the regular day relaxing, but when I am very active shopping or light exercise I drop it about 50%

I use the Dexcom 4 as well with Omnipod
It is trial and error. Keep a easy to process sugar with you.

Good luck

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I assume you are specifically referring to the original Tandem t:slim which integrated with the Dexcom G4.

I would be curious why you are not now on the Tandem t:slim X2, integrated with the Dexcom G6 and running Basal-IQ?

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Good questions - the t:slim is under warranty for another year, so insurance co won’t cover a new one yet (though we want to explore this). We will be moving to G6 soon though.