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Dear Diabetes: Heavy Exercise

The DX explains how strenuous exercise may affect the body

Dear Diabetes:

I have type 1 diabetes. Why does heavy exercise like weightlifting or intense cardio affect my blood sugar differently than other activities?

Most doctors would agree that exercise is good for you, especially if you have diabetes. Not only does it burn glucose, but according to the American Diabetes Association, physical activity also makes your body more sensitive to insulin – both of which help lower your blood sugar. So why can particularly intense physical activities like weightlifting or nausea-inducing sprints sometimes make your blood sugar go up instead of down?

The answer has to do with glucose, a type of sugar that circulates in our blood so that our muscles and organs can use it as fuel. Some of this blood glucose comes directly from food, but our bodies also store glucose – in the form of glycogen – in our muscles and liver, and release it as needed. Such is the case when our blood sugar levels shift while we’re exercising.

Your body first uses the glucose that’s circulating in your bloodstream, but sometimes, it’s not enough. Serious exercise, like lifting weights or sprinting, requires more glucose than gentle-to-moderate exercise, like walking or riding your bike around town. Think of a car: It takes less gas to drive at 20 miles per hour than it does to do 70 on the highway.

The result? If you need more glucose than is available from your blood, your body releases a boost of adrenaline. The adrenaline stimulates your liver to break down stored glucose (glycogen) and release it into your bloodstream so that it’s available for your muscles to use.

Here’s the catch: In order to absorb that boost of glucose, you need insulin, a hormone made by the pancreas that enables your muscles to suck up the extra fuel. But when you have type 1 diabetes, your body doesn’t make insulin – so instead of going to your muscles, the extra glucose just builds up in your blood. Rather than dropping, your blood glucose starts to rise. What’s more, the less insulin you have circulating in your blood when you start exercising, the more dramatic the rise can be – which is one of the reasons why it’s not a good idea to exercise when your blood glucose is too high. (High blood sugar is usually the result of too little insulin.)

As if that’s not enough to deal with, when you stop exercising and your level of adrenaline drops, your liver and muscles will start replenishing their stores of glucose that you used while you were at the gym. This can happen up to 8-12 hours after you finish exercising, and is one of the reasons that your blood glucose can suddenly drop hours after you’ve left the gym, which can be scary and even dangerous, especially if it happens while you sleep.

It’s enough to make you want to forswear exercise altogether and eat low-carb snacks on the couch, but that would make you miss out on the many positive effects of exercise, like lowering cholesterol and strengthening your heart. Instead, work with your doctor to figure out the type of exercise you enjoy and the effects it will have on your blood glucose – and always make sure you’ve got your glucometer, insulin, and some fast-acting carbs at hand.

© 2012 The DX: The Diabetes Experience

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  1. Anyone
    June 25th, 2014, 7:29 PM

    yes I would wholeheartedly agree with that article…except I would add that the body can produce and release glucose without adrenaline, and does so during weight-lifting in order to cycle that fuel back to the muscles. Except, like it said, the body needs extra insulin to make that happen. Most average exercisers don’t workout intensely enough to induce an release of adrenaline.

    1. The DX Editors
      June 26th, 2014, 9:48 AM

      Thank you for your input!