Exercise and Insulin Sensitivity

Recently, i have posted on my swimming thread about how i have had to make tweaks and changes in both my basal rates as well as my ICRs.

it seems that my body is becoming more insulin sensitive. i would not have noticed this if the changes werent significant. i would have waited for patterns to emerge over the course of a week or so. but, i had continued to crash into the low 40s regularly and have found myself eating a lot of yummy correction foods (cookies, malt balls, juices,etc).

i am surprised by this b/c it did not happen to me last year when i began swimming regularly. but just these past few weeks, my insulin needs have continued to drop. i keep amazing records for my own benefit to see my BGs and what i eat and how i respond to what i’ve eaten. i write down everything. literally. :wink:

well last week i was hooked up to a “trial” Dexcom run for one week. (although i think i will get about 10 days out of it, which coincides with my next endo appointment)

since i have had the dexcom, i have been able to short stop some crashes as well as see patterns much faster than just by keeping my BG logs.

has anyone else noticed that their body’s need for insulin has been changed by their exercise routine? i know that a lot of you (or your active children) do lowered temp basals for over-night. i have never needed to do this. my over-night BGs are always steady and in target.

but what i mean to ask is have you noticed that the more fit you are, the less insulin you need?


Absolutely. Doesn’t even seem to take that much exercise to cause an overall drop.

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Yes, DM, I have definitely experienced what you’re describing.

My gym membership started up again on April 1st, and I’ve been swimming a few times this week. My overall numbers have been significantly better. I respond faster to the insulin, and I need less of it. My whole management system works better when I’m working out regularly. This is in spite of the fact that I’m fairly active anyway.

I have had some lows during the night, but usually only the night after a swim. Other nights, my overnight sugar levels are so perfectly flat :slight_smile:. I expect after a couple more weeks of swimming, I’ll drop my Tresiba dose by 1 unit. I’m not ready to drop it yet.

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when you say that you respond faster, so you mean that you dont need much in terms of pre-bolusing? i ask b/c i used to do a 20 minutes pre-bolus, and now if i wait more than 10 minutes i crash within 1/2 hour.

when you say you need less insulin, are you refering to your bolus insulin (I:Rs ) ???

Yes. Especially after exercising or the day after exercising. My Humalog kicks in faster and peaks faster.

Yes, but I’ll eventually need less basal too. I think this happens for a couple reasons (my own thoughts though, not scientific). I think as I get more fit, I’ll gain muscle and lose some fat. Both of those things will make me more insulin sensitive. This is in addition to the more immediate effects I see from exercising (as stated above).

So I’ll need to increase my insulin to carb ratio (meaning more carbs per unit of insulin) and my correction factor may be affected too (less noticeable here though for me).

This kind of stuff probably varies a lot from person to person. You may not see as pronounced of a difference because you’re so lean :wink:

There is a reason you are seeing that! Beside the reasons for increased sensitivity during and right after exercise that I mentioned here ==> How exercise increases the effect of insulin and carb usage

There is a reason it affects you the whole time. Really cool stuff, I will post it later.


For myself, this follows any exertion beyond everyday normal activity, not just general improved fitness. If I go on an all-day strenuous bike ride or all-day hike, even with lowered basal for the duration, I’ll run low all the next day and often the day after as well. Probably a combo of what @Eric has been posting about, and needing the time to refuel (or not refueling sufficiently), plus not knowing about the connection with increased insulin sensitivity, so taking the same bolus/basal as usual, compounding the problem.


I have not noticed any long term trend of increased insulin sensitivity because my activity level has not really changed much since I got diagnosed. I was active before and am still at about the same activity so I don’t have a good way to compare.

I have noticed the short term increased insulin sensitivity after heavy exercise which is usually reflected in the I:C ratio for 24-36 hours afterward as well as dropping BG under basal and no morning BG rise the day after heavy exercise. What I’ve noticed more is the opposite effect when not active: If I spend a few days basically sitting around being lazy or if I am behind the wheel for a few days in a row on a long driving trip I need more insulin to stay in range, both basal and bolus.

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this is something that i have noiticed, too. i dont tend to run low at all the day of the exercise; its the days that follow that i trend low. especially when i work out back to back days and then take a day off.


Me, too…which leads me to think I don’t replenish enough.

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Yes absolutely!

are you talking about carb replenishment?

Yep! I have no idea how to estimate how much I need after exercise. :muscle:t3:

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after 2 hours of swimming laps, i refuel with 32gms carbs and 32 gms protein. i drink these shakes called BOOST Glucose control; i think they are made by Nestlie. i get them from Amazon and buy them by the case. i drink 2 of them right after i get home from my swim (about 1/2 hour after my shower) and i bolus for 1/2 of the total amount of carbs. i like the Chocolate Sensation flavor best.

and thats before dinner.

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I have no idea where you are with your current understanding as this was posed in April of last year or if my own idea is bunk, but could this maybe be a result of reduced body weight as well? I know you’re as slender as one can be, but any chance a few pounds could’ve been the difference between your prior and later experiences?

I’m throwing it out there because my endo throws the same comment out there every time I see her if I’ve lost weight. She’ll tell me to keep an eye on my basal rates as her concern is my overall insulin needs will change in relation to my weight loss. I’m always a little embarrassed when she clearly is not concerned because it usually means my current weight puts me back in the very safe category (aka,the “you’re packing in those pounds so let’s put the cracker down” category).

I digress. :grin: So is there a chance that in addition to the more immediate decrease in insulin needs as a result of physical exertion, there’s also an overarching decrease in insulin needs when there’s also been weight loss? … I ask as I polish off my cracker. :thinking:

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not as far as i am concerned. since i hadnt been exercising, i have put on about 4 pounds !!! (of course, thats to be expected :wink:

Yes, as a general rule, the less you weigh, the less insulin you need (and yes, of course there are a million other factors beside weight).

Basal metabolic rate (BMR) is how much energy your body uses, for basic functions like breathing and keeping warm, no activity.

It does not take as much energy to keep a smaller person going.

A lot of initial calculations for new diabetics still use the person’s weight to come up with a starting point for their basal insulin and total daily dose and all of that. They don’t send you home from the hospital without some ballpark of insulin needs. So a lot of it is based on weight.

Is that what you are asking?

Here is stuff you didn’t ask!

For you, Nicky, with no activity, your BMR if you were to do nothing but lie around all day, and do nothing, would be about 1250-1300 calories per day.

Add activity and you - DN - get up to about 1940-2100 calories burned per day.

It’s different for everyone of course.

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:thinking: Can I ask how you’re getting that, or should I just leave it alone??

Or that??

Yes, that was what I was asking. So how much are we talking here?? What’s a didfeeemce of 5 lbs to a basal rate? Or 10?? How often would I be considering a change?

There are a bunch of calculations, based on weight and body fat percentage, and activity and your general metabolism, and all of that. And also how much you are eating is going to be a huge factor!!

So of course, these are general rules and there is a large variation for everyone.

But in general for a T1, the range is about 0.23 to 0.45 total units per day per pound. So if you lose 4 pounds you might use about 1 unit less total per day, if everything else stays roughly the same.

And the general rule is that about 50% of your insulin is basal, so if you are only asking about basal, it would be roughly 1/2 of that amount. But that 50% rule is kinda silly.

I have been feeding you workouts for 7 months, talking to you about your basal needs and insulin usage, and paying attention. I know a lot about you by now. :wink: