Impact of exercise to BG level

A bit like most things T2 everyone is different and reacts differently. Exercise can lower your BG however its down to the intensity, I find higher intensity will actually raise my BG and then will lower post exercise, whereas low intensity will reduce BG whilst I am active and continue to be lower in general. Trial and error is the best thing, see what works for you.

Any and all exercise raises my BG.

We are all different, so it depends, but exercise that is more stressful (i.e. produces more stress hormones) (e.g. anaerobic things such as sprints, weights, etc.) will tend to cause the liver to release more glucose than is being used while you exercise, less strenuous exercise (e.g. aerobic) will produce fewer stress hormones, so less hepatic glucose production than is being used by the exercise. The fact that the more stressful types of exercise also tend to last/are carried out for shorter durations doesn't help this effect either.

Everyone is different in terms of what their bodies consider "stressful", and this also changes as you do more exercise and your muscles become more efficient, this means that what may have previously produced a rise in BG may no longer do so (though outright anaerobic exercise likely still will do, though exercise habituation apparently also makes the liver more reluctant to release glucose, so YMMV.)

No matter what you do, your liver will eventually run out of glycogen to turn into glucose, but it depends on how long you exercise for as to whether you ever reach this point and see the effect - I find 1h30 - 2h (of cycling) is the turning point. Some people get a post-exercise rise in BG, this is because the liver is still releasing glucose but you've stopped exercising, doing some aerobic exercise towards the end of an exercise session can reduce/eliminate this effect (or go beyond 1h30-2h and it will no longer be a problem.)

Pre-event stress can cause liver glucose production even if the exercise you're undertaking would not on its own (or at other times - e.g. training for a half-marathon of things like that) produce a rise.

Muscular insulin sensitivity is raised for up to 48h after exercise, so BG levels should be lower/flatter (or potentially go low overnight post-exercise if you take insulin/other BG reducing drugs). I find my foot-on-the-floor vanishes after exercise and then comes back gradually over a couple of days.

As those before have said, you will have to monitor what happens to you as we all vary, with different starting points, metabolisms etc.

For me I try to get a 20-30 minute 'brisk walk' in after I have eaten breakfast or lunch each day to counteract the effects and dampen the peak, (I have LADA, but treat with diet and exercise with metformin, no insulin).

When I eat breakfast, (a few blueberries and Greek yogurt), and then start working straight away, my BG goes higher than on days off when I go out straight after and use my muscles for a bit. I don't do the gym or more strenuous exercise, as I have found that even after doing a big tidy up, gardening or more heavy lifting etc my BG does go up.

In time you will find what works for you to get the balance of healthy heart/body/mind etc and decent BG - good luck @jmckirgan

(Jessie Inchauspé (Glucose Goddess) does push the science that at least 10 minutes of exercise/muscle use after eating will help reduce the effects of what you have eaten, and in my experience she's correct).

I believe exercise has a different effect on people depending on how strenuous the exercise is relative to their fitness level. If the exercise causes adrenalin (AKA Epinephrine) to be released - fight or flight/physical exertion hormones - then their BG will go up in the short term.


If the exercise level is moderate relative to fitness - i.e. if the body does not respond to it as if it was a stressful event, then BG should decrease in the short term. This is a graph from my Libre 2, modified with image editing software, which illustrates how moderate exercise can reduce BG levels after a meal. This was a meal delivery from an Asian restaurant, and the rice portion was generous. Usually I wouldn't eat all of the rice but as I was wearing a CGM I decided to experiment. I weighed the cooked rice and added a few grams to estimate the carb content of the vegetables in the meal. The meal was very high in carbs, over 3 slices of bread worth, but as you can see, going for a long walk around 30 minutes after eating, once digestion got well underway, actually reduced my BG levels at a time when they would likely rise to very high levels. To my mind this illustrates how exercise can impact BG levels in a positive way.

EDIT - Included the word Epinephrine as an AKA for adrenalin

Melgar said:

Many things have an effect on blood sugars, exercise is definitely one of them: food; temperature; stress; illness; time of day, the list goes on. For me I can go either way, up or down, if I have not eaten then my blood sugars can fall just going for a walk. The type of exercise matters. In short the more stress you put your body under the greater it will impact your blood sugars. Weight lifting will raise your blood sugars in the short term. I lifted some logs a few weeks back and my blood sugars shot up to 15 mmol/Ls from a baseline of 6 mmol/Ls. Low level exercise over a long period will raise your blood sugars, for instance a 5k slow jog will raise BS. A sprint over 50 meters will definitely spike your blood sugars. It depends on the type of exercise and how your own body copes with the physical stress. A cgm would help you understand how your own body deals with phyisical stress. We are all different. Ed for typing error.

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I find that watching my local team Bournemouth raises my BG!

Having eaten virtually no carbs all day, my BG rose into the 8s as we made our comeback from 0-2 down with 15 mins left to get it back to 2-2 and very nearly win the game at the death.
Even watching on the TV when we played Burnley away last weekend also pushed up my BG. similar effect in previous matches.

Must be the adrenaline..

Melgar said:

even a very slow jog would stress your body significantly and the result would be higher blood sugars

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Thank you, just the reason I need to Not take up running lol.

Do you have your HRV for the same time period - I'm not sure how good HR itself is as a proxy for stress hormone production (the half-life of which is apparently very short - on the order of a couple of minutes.) I'm also not sure how good HRV would be, would be interesting to see if there is a correlation.

In Response said:

I assume this question is in response to my HR graph.
I have no idea what a HRV is but I had not intended to use my graph to illustrate stress hormones. I was using it to illustrate short sharp exercise which is intensive enough to raise my heart rate for 5 to 10 minutes with fast recovery.
Given I was climbing, you may think my stress and adrenaline was high but as I was on a top rope (rather than leading - taking the rope up with me), I was more confident than usual as a fall would not drop me very far.

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Yes, sorry for not quoting you directly.

HRV is heart rate variability. I wasn't suggesting you were stressed in the conventional sense in which it's used (as in psychologically worried) but rather your elevated heart rate indicates you were doing "work". For others reading, both psychological stress and physical stress (i.e. doing work) increase stress hormones, which raise BG due to hepatic glucose production.

You mentioned that you had a gradual rise over the course of the evening, I was simply wondering if your HRV remained lower than usual (with low HRV indicating more stress, higher less stress) despite your HR dropping back quickly, and therefore whether this might act a decent proxy for "stress" that generates an increase in BG.

Yes, exercise is definitely one of the many metabolic variables that can definitely affect your BG levels, at the time, and over time. What the effect is for you can only be experienced and tracked by you, to determine the extent of the effect for you. And, yeah, this can change over time as all those metabolic variables can.

But kind of exciting experiencing and tracking the effect of exercise?