Type one on MDI and rigorous workouts

My question is for type 1 and MDI. Any of you out there do rigorous workouts and how do you prepare before to not go low?

I am a avid mountain biker and I typically ride intensely for 1-1 1/2 hours.

Right now I am on a pump so I adjust my basal about 30 minutes before my workout but sometimes still go low after about 1 hour of mountain biking.

I may have to switch back to MDI’s due to a job/career change.

I also go backpacking from time to time and that is a all day deal and have a basal program for that.

So how do you deal with this type of activity? Do you keep a steady intake of sugar??


There are a few possible ways, but it is a bit more tricky with MDI.

What type of basal will you be using?

You can either time your basal injections so that it will be wearing off at the time you start your exercise, or basically just feed the basal throughout the workout.

If you need to feed the basal, it’s best to take small bits frequently so you don’t spike. Don’t feed the entire hour or two right when you start. Instead take a little bit at start, and then frequently feed it a little bit every 10-15 minutes throughout the workout.

On the plus side, if you feed the basal you will have a steady intake of carbs, which will provide fuel for your workout.

I’m on a pump not MDI; however, when I play golf, I always take energy bars and a bottle of Gatorade which I usually need to offset lows.

I have been off MDI for years but I was around 25-30 lantus at night.

For a lot of people, Lantus does not last 24 hours. So if you have figured out your Lantus duration, you might be able to time your run in the evening to be at around the same time as your Lantus is wearing off. That would basically be like running with your basal turned off.

For me, Lantus lasts 18 hours. So if I took it at 11pm at night, I could run with almost zero basal starting at 5pm the next day.

As an MDI person, I think the most important question for strenuous activity is: do you use a CGM?

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As a skier, I take new data at the start of the season, as a baseline, without making any changes. I think I kick a lot of adrenaline and glycogen when I’m excited to ski, thus I tend to run high - downhill and X-country. But, that changes over time, like once I’ve exhausted my glycogen, I will tend to bottom out. The one consistent thing is that BG is HIGHLY variable. It is very difficult to manage and I need to keep a close eye on my Dexcom.

Some days it will just go back and forth between 400 and 30, 400, 30, 400, 30, with very little time spent in range. I try to have my basals set perfectly before starting the season so that I know what is the result of abnormal exercise and can best judge a happy medium for my basals that allows me to survive wild swings.

You may, eventually, need a pump. But, honestly, a CGM is vital.

I have a freestyle libre

I thought this would be a huge problem when trying MDI, but I dont notice activity lowering my blood sugar nearly to the level it did using a pump. At least with Levemir this is the case, I have heard Lantus is suspectible to lows due to accelerated absorption from activity. On a pump I always have to lower my basal rates if I am going for a long walk, out in the heat or doing any other kind of activity. I would always plummet the minute I started to run or play sports unless I lowered my basal hours in advance. I dont find the problem nearly as bad on Levemir and a bit of peanut butter and fruit before sports or exercise is often enough.

i have been on mdi and the pump
When i was on mdi I would eat a banana if less than 150 when i started and I was doing 45 min to an hour on treadmill running/jogging. Every 30 min I would check and if heading low I would eat a hammer gel. pre cgm

Now i am on the pump and cgm i am trying to figure out the best way to not get low. I went to the health club and did 30 min on bike and a few weights and walked home about 15 min.
I started at 230 (over eating pre exercise snack) and did a partial bolus 50%
and when I got home I was 74.

So now i will try 25% bolus on on pre exercise snack)

I haven’t tried adjusting basal. any suggestions?

For low to medium intensity running, turn it off right when you start, or a little before you start, like 30 minutes before. Just experiment with it.

Take a few carbs right when you start to prevent the initial drop.

For very high intensity runs - like race effort, or all-out effort - you will probably need to leave your basal going.

Thanks , will try it.

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I do a 20-25% basal 30mins before but after an hour of mountain biking I usually have to take in some sugar. I use either Gatorade drink or the energy tabs work well too

Good to know. I pretty much always tank after an hour of mountain biking with a 20-25% basal 30 mins before I start. It seems the increase adrenaline and activity counter act at first but then I head for a low if I don’t catch it on time🤷‍♂️

When I work out, one full hour of pretty intense (for me) exercise, I lower my basal rate to 40% for three hours. I start the temp basal TWO hours before I exercise. I don’t eat for four hours before the exercise. If I start at a good pre-exercise BG, say 130 to 150) I usually don’t go lower than 25-30 points. My Dexcom makes this much easier. This takes lots of trial and error!

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I agree, this takes a lot of trial and error. I am older and used to do Body Pump. Sometimes, I would have to leave 15 minutes into it as I would drop like crazy. I lowered my temp basal, but not 2 hours before…more like 30 minutes. I finally gave up as I just could not get it right. This is really good advice, I will have to resume BP and try your recommendation. This might just work for me too!! Thanks, Adam, for asking a question I have wondered about. Thanks, MIchelle, for some logical advice.

My 13 yr old son is T1 and a competitive cyclist. Both road and mountain biking. Right now is MTB season. He is currently MDI but hoping to get a pump soon to better manage his training. We find we really need to look back the past 48 hours to attempt to predict what will happen during the ride. He eats a high carb meal before he rides and gives a half bolus. Then he waits till he is at least 160 before he goes. If he isn’t going up in time, he might have 10g fast carbs - like gummy bears - to push him up. Once on the ride, he has a gel every 45 minutes no matter what his BGL unless it is really high - over 200. We have found that doing this will reduce the chances of going low later that night or right away on the next day’s ride. If he doesn’t then he likely will go low really quickly on the next day’s ride. He rides very intensely and pushes himself super hard. I encourage you to keep track of what you do on your rides and always look 48 hours back. It takes up to 48 hours to replenish glycogen stores in your muscles and liver which is your first fuel for exercise. If you haven’t managed to do that well, likely you will go low fast. Keeping an active amount of glucose available in your blood stream when you ride will help recovery later. Oh, and always a high carb recovery shake (milk with extra protein powder) with no correction and a half correction on the meal post ride. Sorry, lots of info, hope it helps. We are finding the Long Acting insulin very difficult to manage with his riding and I feel like it is a constant experiment. His training log reflects distance, time, avg HR and amount of long acting to try and sort it all out and it’s a work in progress. Also he has a Dexcom so he can keep track on the ride. Good luck!