Adjusting for intense exercise

I recently rejoined a weekly pickup basketball game and have had trouble keeping my BG high enough the past couple of weeks. Last week, I suspended basal about an hour before the game and ate a big bowl of cereal about 50 minutes prior to the game, blousing 10 units, which is about half of what I would normally bolus for that meal. My BG was about 130 and heading up when I started playing, but after the first game (usually play 3-4 games over the course of 90 minutes to two hours), my BG had dropped below 100 (I wear a Dexcom G5). I drank most of a bottle of Gatorade (32 grams of sugar) and ate several cookies. After the next game, I was down in the 80s. I popped a few sugar tabs, and after the final game, I was at 78 and decided I should probably not play another game. Soon after I quit exercising, my BG began to rise. I resumed my basal and my BG continued to rise, hitting close to 200 even after a couple of boluses of around 2 units each. I’m not sure what is happening here. Is it possible that my body is not processing the carbs once I begin the intense exercise, or am I just eating too soon before my workout? Should I suspend my basal earlier to get insulin out of my system sooner? I’m looking for some tips from those who might have figured this out already.

Yes, that is part of it. Your digestion will slow down a lot when you are exercising intensely.

The other part of what you are seeing is that you had a bunch of IOB during the games. The IOB from your meal bolus, plus the fact that your body is not processing the food as quickly means you see the drops during the game. Once you stop playing, all the carbs catch up with you, plus the fact that you have suspended your basal means you see a spike afterwards.

I’d suggest not having the meal so close to the game. Try to give it a few hours at least before you play. And then cut your basal a bit before and treat the dropping BG as needed.

After the last game, immediately bolus to replace the lost basal and prevent the spike.


Lotta different factors at play there (so to speak!). A couple of things jump out at me:

Obviously you know that exercise can supercharge the effect of insulin, but I mean, it can really supercharge it. Might try eating something low- or no-carb so you don’t have any IOB at the start. I’ve experienced severe drops with just a few units onboard; ten is a lot!

I generally find I get considerable bounce-back after an exercise-induced low. I learned a while ago that it works better for me if I don’t treat those but give it half an hour or so to see where it’s going to end up. In this case it looks like you consumed quite a few carbs during the workout, so combined with the bounce-back effect that may explain why your BG ended up spiking. Alternatively, the adrenaline factor may be at work. It’s a known thing that rapid/intense forms of exercise spike your adrenal system, which pushes your BG up rather than down, and the competition factor really kicks that in. So the combination could be causing your BG to spike rather than drop, and it takes a while for the full curve of that effect to peak and clear. (In my case I bike ride, and normally that’s aerobic, sustained exercise that drops my BG, but when I started riding in the winter, I was surprised to find that my BG can actually go up significantly when the temps get far enough below freezing, which I take it is due to the same effect.)

Those are kind of contradictory possibilities, but I think the main thing I’d do is eliminate that pre-exercise bolus from the picture so you can get a clearer picture of how you’re reacting to this particular form of exercise all by itself, and use that as a basis for what you do going forward.

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Very interesting and helpful responses here. I did not realize that intense exercise could supercharge IOB and really hadn’t thought about exercise shutting down processing carbs until I saw the results. Today, I will eat earlier without a bolus and carry Gatorade and sugar pills in case they are needed during the workout. We’ll see how that goes.


I had a Dr tell me that it takes something like 30 chemical steps for insulin to get glucose metabolized into your cells when you’re at rest, and when you’re exercising it takes… one. Not exactly sure of the scientific accuracy—it was a long while ago—but I think the basic idea is correct.

I had another basketball game last night. Ate the cereal with no bolus about an hour before gametime. BG was around 140 when we started playing. It dropped into the 120s, give or take, after the first game. Over the course of the night, I also drank one jar of Gatorade (21 grams sugar) and was able to keep my BG above 100 the entire time. My Dexcom sensor was more than a week old and began to get a little wonky, losing signal towards the end of the night. I bloused about 3 units after stopping play. When I got home and got a signal, the Dexcom said 180, so I bloused a couple more units. After taking a shower, I tested with my Omnipod PDM meter. Dexcom was saying about 200 then. My meter said 250. I’m thinking that loading up on carbs may not be the way to go because I’m spiking after the game. Should I be looking at more sugar and less carbs because the sugar will be used up more quickly? BTW, I’m Type 2, if that matters.

Are you turning basal off for the games?


I did not know that.

What happens if you turn your basal off 1-2 hours before exercise, and don’t take as many carbs? How low would you drop?

I see you mentioned 78 above. Do you ever drop very low if you are not using basal?

I think the large amount of carbs is causing that spike afterward.

I can’t tell that suspending the basal makes much difference, but I have dropped even with basal suspended. I’m wondering what is the best and quickest form of nutrition for keeping my BG high during exercise but hopefully not spiking afterwards. Is sugar alone the answer and eliminating carbs, which seem to just sit in my system during exercise and then spike my BG afterwards.

Keeping your BG high is not what you want. Try to aim for keeping it in range.

Is this like a basketball league, where you sub out every once-in-a-while? Or is it more like pick-up games without breaks on the bench?

How often are you able to test BG and take carbs?

The best way to do this is to check your BG every time you have a break, and treat if needed. Treat not only the number, but the trend. A BG check will give you a much more current value than a CGM, which will have a lag during exercise.

If you are looking for a fast carb, Gatorade Prime is pretty quick. It is a higher sugar version of the normal Gatorade. About 3x more carbs, so you can treat a low very quickly.

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It’s a series of pickup games, usually no more than 10 minutes each with a few minutes’ break between games. If you win, you play again; if you lose, you sit out a game (or maybe two if it’s crowded). Generally, you’ll play 4-5 games over a two-hour period. I’m not trying to stay high, but if I get to 100 or under, I get a little concerned. I’ve been using sugar pills and a lower-sugar version of Gatorade, but not the no-sugar version (21 grams in a bottle).

I would start with these general things and then adjust depending on what you are seeing.

  • Eliminate IOB. Avoid the meal before. Eat maybe 4 hours before you play so the insulin has time to be used up, but not closer than that.

  • Turn off or reduce your basal.

  • Test as much as you can, like between every game. Have your stuff on the bench ready to test. A BG reading will give you a much more current number than a CGM.

  • Use small amounts of a rapid sugar drink to treat a low or an impending low.

  • Look at not only number but also trend. If you are 100 after a game that is fine. But…if you were 120 after the game before, and now you are 100, then it’s a sign that you need a small amount of carbs. Treat not only the number, but the direction. Also, look at your CGM during this so that you can get an idea of the lag.

  • Afterwards, replace lost basal and replenish muscle glycogen with a strong dose of both insulin and carbs. And check frequently after games to adjust as needed.

I appreciate your advice. Will see how it goes tonight.

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For me (T1D), I reduce my basal rate by 90% at least one hour prior to exercise, sometimes two. I also will eat and bolus 50%, but I like to avoid a higher carb meal like cereal, replacing it with some protein like eggs and cheese. Note, that while this generally works well, it doesn’t always, so I have glucose tabs and protein bars available. I use them in a two step process. First the glucose tabs alone to quickly raise my BG, then a part of the protein bar at least 15 minutes after the glucose tabs.

For the situation you are describing here, I typically would have bolused a correction like you, but I would have also raised my basal rate for 1 - 2 hours.

Also, for me, there’s quite a bit of variability. For a long time, I tried to attribute the variability to something I had consciously done (or not done). Then, I discovered dynamic homeostasis - aka the fact that your body is constantly doing many things in the background to keep you on an even keel. That’s when I realized that I can only have general strategies and to use the CGM data to quickly take action when the strategic plan goes wonky.

Last night’s results: ate bowl of cereal at about 5:30 with no bolus. By 7 pm was at 215 BG. I did not turn off my basal but was afraid to bolus with the results I had seen from IOB during exercise in the past. BG dropped during the evening, but only to about 150 before I quit playing. I bolused about 3 units at that time. BG began to rise again so I bolused another 3 units when I got home. Between 9:30 and 10:30 I dropped to 72. I ate a few cookies before bed and topped out at 122 at about 12:30, slowly dropping during the night to around 80 when I got up this morning. I think I may have eaten too early because of the high level I hit by 7 pm. Maybe a little before 6:00 would keep me from going so high but give me enough sugar to not suffer the severe drops I have seen.

That stinks. I spin several times a week and I make sure IOB = 0 when class starts, or it will inevitably spell doom. IN fact, If I start class a little high, I will wait till the middle of class to correct it.

Managed things better last night. Ate bowl of cereal a little before 6, did not bolus and did not suspend my basal. Was about 150 when play began and dropped to about 125 during the night. Bolused 3-4 units when I finished playing. Got up to 163 before that kicked in and pulled me down to 95. Ate a snack before bed and moved back up into the 140s during the night but was in the low 80s when I got up. These are numbers I can live with. I don’t mind being at 150-160 briefly if it keeps me from having to worry about going to low during play. Hopefully, I’ve found a strategy that I can live with.

Definitely eat protein with your meal before the game.