How Exercise Affects Blood Sugar Levels

One subscriber to my articles recently asked me how exercise and nutrition affects blood sugar. He thought it was going to be a short answer, and boy, was he wrong. So I decided to turn it into 2 articles: one to talk about how exercise affects blood sugar levels, and the other to talk about nutrition. If you’re a diabetic, pre-diabetic, or know a diabetic (or if you’re just a geek who wants to impress others with their knowledge), this article will be particularly helpful to you.


Original source: here.

How Exercise Affects Blood Sugar 

For the longest time, it’s been said that exercise lowers blood sugar, but that’s not the complete truth.

Exercise only lowers blood sugar when:

  • The exertion is sufficiently high
  • The duration is sufficiently long.

You have to cross a certain intensity threshold for exercise (this applies to both endurance exercise as well as resistance exercise) to have a blood-sugar lowering effect. Your exercise has to be moderate to strenuous to affect your blood sugar levels. How intense is that? That’s at least 60% of your maximal heart rate. How do you figure out your maximal heart rate? It’s approximately 220 minus your age. So if you’re 50 years old, your maximal is 170 beats per minute. 60% of 170 is 102. So your heart rate must rise above 102 in order for your exercise to have any kind of blood sugar lowering effect.

In other words, people frequently ask me during my speaking engagements “is walking enough?” The answer is “usually no.” If one person is extremely out of shape, and walking gets that person’s heart rate to 60% of his/her maximum, then yes, it’s enough. But for most people, walking, no matter how fast doesn’t quite get their heart rate that high. More intensity is needed.

If you don’t know how to count your heart rate, or don’t feel like doing arithmetic while exercising, the low-tech way to figure out if your intensity is sufficient is the “talk test.” Your exercise should be intense enough that you can’t put together more than 3-4 words without taking a breath. If you can easily carry on a conversation while exercising, the intensity is lacking.

I guess what I’m saying is stop slacking. Don’t be a lazy bum. Don’t baby yourself. Either push yourself hard enough, or hire someone to do so (may I suggest my company?)


The other part to blood sugar lowering is duration.

In a person who does not have diabetes or pre-diabetes (in other words, a healthy person), when s/he starts exercising (again, assuming exercise is of at least a moderate intensity), the body releases adrenaline, and other hormones that break down the stored sugar in the muscles and the liver, and release it into the blood. But not to worry. Because simultaneously, the body also releases a tiny bit of insulin to prevent blood sugar from rising. The net effect is no change in blood sugar.

The dynamics of a diabetic or a pre-diabetic are a bit different. Because of problems with insulin, when this person starts exercising moderately or intensely, there is nothing to counterbalance the blood sugar-raising effects of adrenaline. So for the first few minutes of moderate to intense exercise, blood sugar actually rises. But if the exercise is prolonged enough (that is, more than 10-15 minutes) blood sugar then starts to fall. So if a diabetic was to run after the bus, blood sugar will be high. But if the diabetic was to run a mile to the bus stop, blood sugar would be lower.

It is generally recommended that if you’re a diabetic, and your blood sugar immediately before exercise is over 9.4 mmol/l, don’t exercise until your blood sugar falls below that. Why? Because again, in the first few minutes of exercise, stress hormones will raise blood sugar even higher.

It can get even more complicated in diabetics taking certain medications (specifically those belonging to the class of sulfonylureas. Examples are Glucotrol, amaryl, and diabenese). These medications stimulate insulin release. So for these folks, insulin during exercise may be too high, and blood sugar may end up falling too low.


So now that we’ve talked about how exercise affects blood sugar levels in the short term. Now let’s talk long-term.

In the long-term, there is a net reduction in blood sugar through exercise.

Although when talking about the long-term, there is a difference between strength and endurance training.

Though they’re both effective at lowering blood sugar, strength training appears to have a slightly better effect on blood sugar lowering.

As I showed in a newsletter from a few weeks ago (this one), one of our clients, Mandy was a diabetic, and used to do a lot of cardio to control her diabetes. And while it worked at first, eventually, it stopped working. Strength training had a better effect, and resulted in more sustained reductions in blood sugar, to the point where her doctor took her off some of her medications.

If you’d like help figuring out how to use exercise to control your blood sugar, you can apply here.

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