No time to exercise? Here’s how to get more bang for your buck. Two caveats: A short exercise session doesn’t burn enough calories to help you lose weight. And getting out of your chair throughout the day can help lower your blood sugar.
Martin Gibala is professor and chair of the department of kinesiology at McMaster University in Hamilton, Ontario. He has published numerous studies on the benefits of high-intensity interval training. Gibala spoke to Nutrition Action’s Bonnie Liebman from Hamilton and answered some questions about interval training.
Q: What is high-intensity interval training?
A: Interval training at its heart is just alternating periods of relatively intense exercise with periods of rest or light exercise for recovery. It’s a pattern of peaks and valleys: going hard, backing off, going hard, backing off, and repeating that pattern.
Q: Why do people do it?
A: Interval training is a way to get relatively fit with a relatively lower time commitment. Depending on the survey, 75 percent of people aren’t following the public-health exercise guidelines. And the number-one-cited barrier is lack of time.
Q: How long does interval training take?
A: There’s no accepted definition. In many studies, the time commitment has been around 20 minutes per session, three times per week.
Q: Twenty minutes of working hard?
A: No. That includes recovery periods. One protocol that we’ve used in our lab involves 10 one-minute hard efforts with one minute of recovery between each. The hard efforts are at 85 to 90 percent of your maximum heart rate, so they’re high intensity.
Q: And that’s enough?
A: I don’t want to overstate interval training research. It’s a bit like a new drug on the market. In its early trials it’s showing a lot of promise, but we’re nowhere near the grade A evidence—the large randomized controlled trials—that we need to say that it has all the benefits of traditional endurance exercise.
But we know, for example, that interval training makes the heart a better, stronger pump. It makes the blood vessels more elastic. And it makes your muscles better at using oxygen, because it can rapidly enhance the amount of fuel-burning mitochondria in your muscles.
Q: Does it lower blood sugar?
A: In our study on people with type 2 diabetes, the average blood sugar level over the course of 24 hours was reduced— by a fairly large margin—after only two weeks of interval training. And fasting insulin and glucose scores were reduced after two weeks in a study of sedentary middle-aged individuals without diabetes.
Q: Why would exercise help?
A: Roughly half our body weight is skeletal muscle. That’s where most of our blood sugar goes. When you have prediabetes, your muscles get resistant to taking up blood sugar. Any exercise—not just interval training—dramatically enhances the ability of muscles to take up and store the glucose.
You get more of the transporters that take up the blood sugar and they become more receptive, so it takes less insulin for them to do their job. And you have less sugar floating around in the blood.
Q: Do the people in your studies typically ride stationary bikes?
A: Yes, because it’s easy to quantify their work and power. It’s also safer because you’re not talking about high ground impact. And it’s better tolerated if people have underlying knee or joint issues.
But any exercise that involves large muscle groups, like swimming, stair climbing, or running, should be effective.
Q: Is any exercise better than nothing?
A: Absolutely. And the best exercise is the one that you like and you’re most likely to stick with. If you hate interval training, it’s unlikely that you’ll do it. But if you’re pressed for time—whether it’s an excuse or whether you’re really busy— trying intervals is not a bad strategy.
Q: And you don’t have to sprint?
A: No. Some people think interval training is only sprinting as hard as you can, like you’re saving your child from an oncoming car.
But it can be scaled to any starting level of fitness. Just get out of your comfort zone. If your usual exercise is walking around the block, walk faster between the next two light posts.
You can feel yourself a little more out of breath, maybe it’s harder to talk to your partner, your heart rate’s up a little more. And then you back off. That’s an interval training session for you.
Q: Can interval training be dangerous?
A: The knee-jerk reaction is that interval training is a heart attack waiting to happen. And that’s wrong.
People should be medically cleared before they engage in any type of exercise program. But they don’t need to be afraid of intervals. The potential risks are similar to other forms of exercise. The greater risk is sitting on the couch all day.