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Just Exercise Harder for Less Time, or Not?

by Dr. Sheri Colberg, Ph.D., FACSM

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Everyone is confused about what types and amounts of training people with diabetes should be doing for optimal blood glucose control and health. When I last wrote about this topic, the latest exercise research was older adults with type 2 diabetes enduring six sessions of high-intensity interval training (HIIT) done on a cycle ergometer over two weeks (1). The training sessions, which were typical of some of the latest HIIT, consisted of 60 seconds of cycling done 10 times at ~90% of maximal heart rate, interspersed with 60 seconds of rest—for a total of only 10 minutes of actual exercise and 10 minutes of recovery.

So, that protocol involved almost an all-out sprint for a minute at a time, repeated 10 times with very little rest in between. Some call this low-volume, high-intensity interval training (HIIT); others call it pure torture, even though it did lower overall and after-meal blood glucose levels in these participants.

While interval training is routinely used by sports teams and athletes, is this type of training beneficial for most individuals with diabetes? It certainly saves time—who can’t fit in 10 minutes of exercise three days per week?—but would it benefit weight control in the average person? It simply doesn’t burn that many calories. Actually, it doesn’t save that much time either: when you add in rest intervals and a warm-up and cool-down period, it still takes at least 25 minutes per session and 75 minutes per week.

Interval training does have some benefits. The latest research done in adults with type 1 diabetes involved 90 minutes of moderate cycling on two occasions: one when they interspersed 10 second sprints every 10 minutes without lowering insulin and one time without the sprints (2).  Not surprisingly, their blood glucose levels stayed more stable and dropped less overall when they sprinted occasionally, even though their sprints were significantly shorter than the typical HIIT training involves. Likely, their muscles used more stored carbs (glycogen) to fuel the sprints and less blood glucose—but then you have to worry about preventing later onset hypoglycemia for up to 24 or more hours afterwards.

Another point about HIIT is that it’s painful, and many people will not want to continue doing it over the long haul. Doing it with a coach or a personal trainer is one thing, but most people won’t continue doing this type of training on their own long-term. What’s more, doing really intense exercise can actually cause a short-term elevation in blood glucose instead of a decrease, especially if the intense activity is not repeated enough times (such as the 10 sessions in this study) due to the effects of glucose-raising hormones released by sprinting.

A big drawback of doing low-volume HIIT is simply that not everyone is going to be able to do it, and it may lead to a greater incidence of overuse injuries and other joint problems that will stop you from doing anything after a while. Only the healthiest people who volunteer to participate in those studies are actually able to be included, which gives us no information about how it will work for the rest of us. I personally always use “the grandmother test”: if I can’t imagine my obese grandmother with type 2 diabetes doing it, it’s not likely to work for the majority of people with diabetes who are older and likely overweight.

However, I’m totally in favor of routinely interspersing harder intervals into any regular training session—regardless of how easy or hard it is—both to increase fitness and to use up more blood glucose and stored carbohydrate (glycogen) in muscles. Starting with easier workouts and interspersing slightly harder intervals into them is a lot more realistic for the majority of folks out there just getting started or wanting to be active over a lifetime.  Just do any type of physical activity regularly, and your blood glucose levels and overall health are likely to benefit.


  1. Little JP, Gillen JB, Percival ME, Safdar A, Tarnopolsky MA, Punthakee Z, Jung ME, Gibala MJ. Low-volume high-intensity interval training reduces hyperglycemia and increases muscle mitochondrial capacity in patients with type 2 diabetes. J Appl Physiol. 2011;111(6):1554-60. (
  2. Bally L, Zueger T, Buehler T, Dokumaci AS, Speck C, Pasi N, Ciller C, Paganini D, Feller K, Loher H, Rosset R, Wilhelm M, Tappy L, Boesch C, and Stettler C. Metabolic and hormonal response to intermittent high-intensity and continuous moderate intensity exercise in individuals with type 1 diabetes: a randomised crossover study. Diabetologia 2016 (epub before print). (


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As a leading expert on diabetes and exercise, I recently put my extensive knowledge to use in founding a new information web site called Diabetes Motion (, the mission of which is to provide practical guidance about blood glucose management to anyone who wants or needs to be active with diabetes as an added variable. Please visit that site and my own ( for more useful information about being active with diabetes.