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Researching Whether You Can Get Too Much Exercise

By Andrew Curry , ,

Tracy Baynard, PhD
Photograph courtesy of UIC College of Applied Health Sciences

Tracy Baynard, PhD

Kinesiologist at the University of  Illinois at Chicago

Exercise Physiology

American Diabetes Association Research Funding 
Junior Faculty Development

Everyone knows exercise is good for you, particularly if you have type 2 diabetes. Study after study has shown that the combination of healthy diet and physical activity is one of the most effective treatments for preventing and managing prediabetes and type 2 diabetes.

According to Tracy Baynard, PhD, an exercise researcher at the University of Illinois at Chicago, it might be possible to get too much of a good thing. Her research suggests you may need to back off sometimes to give yourself a chance to recover. And if you’re newly diagnosed with type 2 diabetes and just starting to exercise, going full out at first might even be counterproductive.

There are good reasons doctors prescribe weight loss and exercise for people with type 2. Aerobic fitness is important for your health. “If you have low aerobic fitness, you are at an increased risk for all kinds of chronic diseases,” Baynard says. Weight loss and exercise can help manage high blood glucose, an important factor in slowing the advance of type 2.

Yet for reasons researchers are still trying to understand, people with type 2 diabetes need more work to make the same gains in aerobic fitness as their peers without the disease. As a result, people with diabetes aren’t always well served by one-size-fits-all advice to simply “exercise more.”

That, Baynard says, is because of how the body responds to exercise. Working out should result in fitness gains, making it possible to go harder the next time you walk, run, or cycle. Over time, exercise transforms the body, with lots of positive effects on everything from insulin resistance to mental health.

But pushing too hard can be counterproductive, stalling or even reversing fitness improvements, a phenomenon known as overtraining. It may seem odd to worry about a problem typically faced by  elite athletes pushing the limits of human endurance in the context of an exercise recommendation from your endocrinologist. But people just starting to exercise are pushing the limits of their endurance, too—something exercise recommendations often overlook.

“If you’ve been sedentary for a long time,  it’s possible that you may show signs of overtraining,” Baynard says. In elite athletes, it often shows up as persistent fatigue or sore muscles that don’t go away even after weeks of rest. Depression or a feeling of burnout can also be indicators athletes have pushed too hard for too long.

With the help of a grant from the American Diabetes Association, Baynard is exploring ways to guide workouts to help people get the most out of their exercise. “Can we do something to improve fitness more?” she asks. “Can we find a way to garner the same improvements as in their peers without diabetes?”

Because people with diabetes lag behind in their ability to build aerobic fitness, she says there may be lessons doctors can learn from research into overtraining. Finding ways to push people at the right time—and lay off when overtraining threatens—has the potential to dramatically improve the results people with diabetes get out of exercise.

There’s one problem: It’s hard to know when to go hard, and when to ease off. To tailor exercise recommendations, Baynard is experimenting with a technique called heart rate variability, a measure of the interval between heartbeats and whether these pauses are similar to each other or different. The more the intervals between beats differ, the higher your heart rate variability.

Although it’s outside of our conscious control, these tiny differences in the timing between heartbeats are still dependent on signals from the brain. That makes it an interesting indicator of what’s going on upstairs. Researchers have connected higher heart rate variability to lower stress levels and greater resilience. “If you have a lot of heart rate variability, you can respond very quickly to the stresses of a given day,” Baynard says.

Studies of elite athletes have shown that it is a measure of how ready the body is to meet the challenges of exercise: Less variability is often a sign of overtraining. Baynard wants to see whether it’s possible to use heart rate variability to guide exercise in people with diabetes who are just starting to exercise. “We listen to their physiology to guide them,” she says.

To test her theory, Baynard is working with three groups of people with type 2 diabetes. One group will get typical care over the course of six weeks—diet and exercise recommendations, but no special treatment. The other two groups will get exercise recommendations along with guided coaching.

As part of weekly visits to the gym, Baynard’s team is measuring one group’s heart rate variability and guiding participants’ exercise regimens based on the results. If signs point to overtraining, she prescribes a lighter exercise load for the following week. Improvements in variability, on the other hand, are a green light to push the body harder. “We’re able to determine if it’s a high-exercise week or if they should ease off a little bit,”  she says.

After six months, Baynard will compare the three groups to see how much they’ve improved. If the group that was guided by heart rate variability shows more aerobic fitness than the others, it might be a reason to pursue further research on the technique’s use on people with type 2 diabetes, particularly when they’re just starting to exercise.

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