How high blood sugar stands in the way of getting fit

When you first start exercising after being a couch potato for too long, it’s excruciating. You can’t breathe. You’re drenched in sweat. And every muscle in your body hurts. But the good news is, eventually, you’ll build up your aerobic capacity and it will get easier.

After a while, aerobic exercise starts to alter your muscle fibers. It makes these fibers more efficient at using oxygen while you exercise, which makes exercise feel a little less excruciating. Exercise also promotes the growth of new blood vessels, which helps deliver more oxygen to your muscles. All this leads to a higher level of aerobic fitness.

But there could be something standing in your way if you’re trying to improve your aerobic fitness level — high blood sugar.

New research shows that higher-than-normal blood sugar levels hamper your body’s ability to adjust to aerobic exercise, making it harder for the people who need it most.

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High blood sugar blocks your muscles from adapting to aerobic exercise

Researchers from Joslin Diabetes Center just discovered that high blood sugar makes aerobic exercise even more of an uphill battle than it is normally…

In their study, researchers tested the impact of high blood sugar on the aerobic fitness of mice. They induced high blood sugar in one group of mice by feeding them a junk food diet, and they induced high blood sugar in another group of mice by altering their bodies to produce less insulin.

Both groups of mice then performed an aerobic exercise training protocol where they ran in wheels in their cages. These mice ran over 300 miles by the time the study was over. But their aerobic exercise capacity didn’t improve as much as mice with normal blood sugar levels. Why?

When researchers looked at the muscles of these mice, they found that their muscles weren’t adapting to aerobic exercise the way muscles typically do. Normally, regular aerobic exercise causes muscles to remodel themselves. Like I mentioned earlier, muscle fibers change, and new blood vessels develop to get more oxygen to your muscles.

But in the case of mice with high blood sugar, this just wasn’t happening. Researchers think that’s because high blood sugar modifies the “extracellular matrix” proteins in the space between the muscle cells, where blood vessels are formed. This prevents the muscle changes that normally occur.

Researchers also found that high blood sugar seemed to impair communication in something known as the “JNK” signaling pathway. This pathway acts like a molecular switch that tells muscle cells to adapt to either aerobic exercise or strength training. In the case of mice with high blood sugar, this pathway signaled to the mice’s muscles to adapt to strength training even though they were doing aerobic exercise, which means their muscles weren’t prepared for the type of exercise they were undertaking.

Researchers decided to follow up on this research in mice with clinical tests in young adults. They found that those with higher blood sugar levels after ingesting glucose had the lowest aerobic exercise capacity.

“Looking at how their muscles responded to a single bout of typical aerobic exercise, we also saw that those with the lowest glucose tolerance had the highest activation of the JNK signaling pathway, which blocks aerobic adaptations,” says study researcher Sarah Lessard.

Aerobic exercise is still worth it if you can stick with it

If you have high blood sugar, you may be thinking, “What’s the point in doing aerobic exercise then? Maybe I should just throw in the towel.” But that would be a big mistake…

High blood sugar or not, people and mice who do aerobic exercise still experience benefits. In fact, in this study, mice with high blood sugar still reduced fat mass and improved glucose metabolism. That’s right, aerobic exercise can actually start to get your blood sugar back down.

Of course, in addition to sticking with your exercise routine, you’ll also want to adopt a diet that helps lower your blood sugar levels, so eventually, your aerobic workouts won’t be so dang hard. There are a lot of diets that can help you do that, including the biological clock diet, the Mediterranean diet, low-carb diets and the super low-cal diet. Take a close look at each eating approach and try the one you think you can stick to, so you can balance your blood sugar and ease the intensity of those oh-so-important aerobic workouts.

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  1. Increased blood sugar levels may decrease benefits of aerobic exercise — MedicalXpress.
  2. Hyperglycaemia is associated with impaired muscle signaling and aerobic adaptation to exercise — Nature Metabolism.
Jenny Smiechowski

By Jenny Smiechowski

Jenny Smiechowski is a Chicago-based freelance writer who specializes in health, nutrition and the environment. Her work has appeared in online and print publications like Chicagoland Gardening magazine, Organic Lifestyle Magazine, BetterLife Magazine,, and