Highs after activity

Hi guys!

I’m newly diagnosed T1D, kind of, I was diagnosed in early March (at the age of 21) and I’m pretty athletic. I run 5-6x a week (3-5mi usually) and do some CrossFit and I also play irish football (similar to soccer) with practice 3x a week and irish dance during most of the year. I was told so many times that my sugar would be low after activity so I’ve been very adamant with testing and that is just not the case at all! I am usually so high after working out and then a few hours later I am low. A few times now, after running or practice, I have been close to 300 (and was around 120-150 before the run) and then a few hours later I am in the 40-60s without eating and just taking some correctional insulin. I am wondering if any athletes have experienced this. It’s frustrating because I want to eat after working out but my sugar is just too high. I left a message with my endo this morning, but really any advice would help! Thanks!


The highs and the lows should both be expected after strenuous or prolonged exercise but there are some methods to control them. I’m my no definition an athlete although at 74 I walk 4 - 5 miles a day and peddle my bike 15 - 25 miles whenever I feel like it. I’m aware of how much energy you must expend and I’d get exhausted watching our granddaughter at many a Feis or Oireachtas.

Do you pump? These highs and lows are easier to manage with a pump, but a similar tactic can be done with MDI. sixty to ninety minutes before a bike ride I lower my basal rate to 30 or 25% and have this lower rate continue for at least a 1/2 hour after I complete the ride. It is more difficult getting this affect when using a background insulin such as Lantus. I test test a few times during my ride and eat if necessary; for hydration [Florida heat] I use a Camelbak with water and also may drink two 20 oz. jars of regular Gatorade mixed [I use the powder stuff] that I sip continuously.

Before the end of my ride, I’ll stop, test and snack and bolus. The purpose of this bolus even if my BG is relatively low is to signal my body [the liver, I believe] to stop producing glucagon which will raise BG. I don’t know the full science of this last step, but it has worked, by much experimentation, very well for me.

Welcome to the world and life of T1D - live fully and you may find yourself, down the road, more healthy than many of your pears.

The difference is between aerobic and anaerobic excersice. Aerobic exercise fuels muscles with oxygen. Such as walking or jogging. Anaerobic such as rugby sprinting heavy lifting etc. Is fueled through glycogen in the muscles to keep the muscles working the liver releases glucagon. This will raise BG so controlling it can be difficult. Test often as soon as it begins to raise above target take a unit of insulin to correct, i use intramuscular sites so it takes less time to work. The later hypos are associated with anaerobic action too its called delayed hypoglycemia. Use glucose tablets to keep in range and test every thirty minutes cor cour hours following intense action. Next time you have a marginlly low BG try doing a sprint and pushups to see if can increase. What ix aerobic and anaerobic may change person to person.

It seems like your pre-workout numbers are a little low. I attempt to keep my exercising bg levels (and the 15 minutes beforehand) around the 180 range. When running or biking I have a fairly preset routine that involves taking a PowerBar gel packet at certain intervals to maintain that 180 level and often times taking it before beginning exercise if I am in the 150 or lower range. That gives me some cushion for dropping bg during exercise. The lows that you are experiencing afterwards are to be expected as well as it doesn’t sound like you are dialing back your correction dosage for the effects of exercise (you will be more sensitive to your insulin afterwards). This kind of routine takes a lot of practice and, even then, odd results will pop up here and there. Just keep at it.

I would not call myself an athlete :), but have always been very regular with my exercise - running, other cardio, moderate weight lifting. I’ve experienced all the things you describe, and have learned how to (mostly) manage it after LOTS of trial and error. I think everyone reacts a little differently to exercise, but I have the same reaction that you do, with highs afterwards. I do have a pump and CGM, which helps make some of this easier. I will say that exercise became more of a challenge for me after going on a pump - dropping so dramatically with exercise that previously I could get through without any lows. My humble theory is that having short acting insulin in your system all the time is part of the reason for that. Anyway… I have also found that the more intense the workout is, the higher I will go afterwards. I’ll try to summarize my ‘rules’ for exercise here:

  1. Like someone else mentioned, I decrease my basal rate by 50% for 30-60 minutes before I exercise. This is MOST important when I’m doing any prolonged cardio (especially running), which sounds like most of what you’re doing.
  2. I also need to modify any bolus I take if it will be within 3-4 hours of exercising. For example, if I’m going to exercise at 5 pm, then any bolus I take from 1 pm after needs to be modified, so that I don’t have too much insulin on board. The more on board, the more dramatically I will drop during exercise (which just sucks to deal with), and then the more dramatically I will go up afterwards. I usually use about 50% of my correction factor (if I need one) and/or 50% of my bolus for whatever I’m eating during this time frame. If I need a correction factor AND I’m eating, then I usually decrease the whole dose by ~50%.
  3. As far as a goal BG to start exercise with, I’m usually ok if I’m at least ~120, AS LONG AS I’ve done the previous steps, to avoid having too much insulin on board when I start exercising. I’ve also found that I can start with a much lower BG when I exercise first thing in the morning (because…no recent bolus to manage…) vs. later in the day.
  4. I maintain my basal rate at 50% less during exercise. Sometimes, 75% less, if I think I’m more prone to dropping, based on the intensity of the exercise.
  5. As soon as possible after exercising, I increase my basal by 75% for 1.5 hours. THIS IS KEY FOR ME!!! It has mostly eliminated the dramatic highs I was otherwise experiencing.
  6. As others have said, be prepared for a drop in your BG - mine happens right around 4 hours after exercise. I either take a little less insulin with whatever I eat after exercise to try to minimize this drop, or sometimes just have a little snack around that time when I can tell that I’m dropping.

Of course what you eat in the few hours before you exercise will absolutely affect your blood sugar during exercise. Making sure to have a balance of carbs, protein, and fat can help.

Yes, so many rules and steps and details and planning! It’s frustrating, and hard to not just be able to pick up and go. It takes a lot of work and experimenting to figure it out, but you’ll get there, and you’ll figure out how your body works and what kinds of tweaks you need. Nothing can replace the benefits of exercise, especially with type 1, so keep at it. Let me know if you have any specific questions!

As stichar mentioned and I should have put in my post since it looks like you use a pen as well but I always wait until 3 hours after a bolus (pen) dosage because any exercise effects are dramatically increased during this time period for me. It’s sort of a pain but I’d rather focus on my exercise session and not worry about a big drop during it.

Thanks everyone, this is such learning experience and I seriously appreciate all of your responses. I’ve changed my insulin to carb ratio in the mornings and it seems to be helping- but of course there are so many things that seem to influence blood sugar!

Thanks again!

Thanks for the tips, @Stichar. I just came across this thread after noticing increasingly high BG’s after my runs. Typically I will start with between 120-150 and end at 250-300. I have never had this with any other form of exercise (cycling, weight lifting) before - it’s just started since I began long distance running. But anyways, it is good to know its normal, albeit still frustrating.

I agree with everyone here.

After Crossfit exercise, blood sugars are up because your body is releasing glycogen to your muscles as designed. Manage it with a small amount of Humalog if necessary after your anaerobic workout.

With cardio though (running, biking, ice hockey), my blood sugar could be at 200+ afterwards and I will leave it alone because in the next few hours it will drop sharply. That post aerobic burn is really evident when you see your numbers do this.

I am new to the post-workout high, so thanks for your input, Alan.

So far, I have been dumb and bolused immediately when I saw the 250 after running, only to crash later. The last time I ran, my bg was actually okay after I was done (120). So, I took a shower, prepared a meal, checked again, and it was at 280. Very frustrating, but I guess I will just have to keep playing around with it to find what works for me. Annoying when you think “Oh, I should start running more - that will be good for me!” and it completely wrecks your blood sugar measurements for the whole day.

I completely understand Courtmart. A CGM will help you understand what is going on before, during and after your workouts. Don’t get frustrated. Exercise is good! You just need to find the right pre and post number that matches what you are going to do. I like to go into running with a high 100 number to cover me for the 45-90 mins of time I am going to be doing it.

Any competitive swimmers out there? My daughter goes high during a meet. 4 to 5 swims only 30 - 60 seconds long of primarily anaerobic effort.


I have the same issue, though very inconsistently. I run 7-10 miles five days per week, and generally witness a steep drop in BG (e.g., from 200 to 75) during activity with a sharp increase (e.g., 75 to 400) after my run is over. Generally, I have found that the extent of this depends on the time of day during which I am exercising. It’s just knowing yourself that helps.

@jillianmarron This is an issue that I have been experiencing lately as well. I am a high school athlete who runs on my school’s cross country team. We usually run anywhere from 4-7 miles 5-6 days a week, and I too experience high around 250-300 right after I run but anywhere from 3-4 hours later find myself crashing low. I have recently gotten the Dexcom CGM and it has helped SO much. I highly HIGHLY recommend it, not only for running:) It’s very frustrating to deal with big swings like that, and with the trend graphs that the CGM shows you, it can alert me at whether I’m trending up or down before I exercise which helps determine whether or not I should eat something beforehand. I hate carrying around all of my blood glucose checking supplies (meter, poker, test strips) with me when I run because they get cumbersome, but on shorter runs I can usually just grab my Dexcom and a snack and go! Plus, when I’m on a run and want to avoid stopping to check my blood sugar, I have confidence knowing that my CGM will alarm if I go too low and need to eat something or if I start going high (that anaerobic glycogen that matthewgates mentioned). Hope this helped:) Good luck on your future running endeavors!

what do you do if you start going high? Do you take a fast acting insulin to get back down?

I am an Irish Dancer too, and I experience a similar situation as you. I am always in a normal range before dancing, in the 300’s right after, and then low a few hours after I’m done. What I usually do is test frequently while I’m at dance class and if I have a high reading, I take a correction. I have also found it helpful to eat a snack with protein, as opposed to a snack with a lot of sugar, before dance to help me power through and keep my BG in check. Talk to your Dr. to see if they have any recommendations for you. Good luck with your dancing and running!

Normally if I notice I’m going high after activity, I will wait 30-60 minutes to see where my blood sugar goes. If I’m still high after waiting, then yes I’ll correct with fast acting insulin. If I started running with blood sugar levels that were already high, I’m likely to still be high after exercising. In this case I would do something like a half correction after I stop running, then check frequently for the next 3 hours (this is where a CGM comes in handy). Hope that helps:)

and I completely agree with alyssarothman4! High protein snacks with some carb (but nothing fast acting) about an hour before exercising helps a lot with preventing lows during and after.