Posted by: shericolberg | February 1, 2012

Should You Just Do Intense Exercise for Less Time?

Just when everyone was already confused about what types and amounts of training people with diabetes should be doing, along comes yet another study to muddy the waters some more. This latest exercise research was undertaken by faculty at McMaster University in Hamilton, Ontario, and appeared in the December 2011 issue of Journal of Applied Physiology (1).

The study involved eight individuals with type 2 diabetes (mean age of 63 years) who agreed to endure six sessions of high-intensity interval training done on a cycle ergometer over a two-week period. The training sessions 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. In other words, it 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 (HIT); others call it pure torture.

Before training and from ∼48 to 72 h after the last training bout, blood glucose responses were monitored using 24-hour continuous glucose monitoring. The exercise definitely had a positive effect on blood glucose levels: both the average levels over 24 hours and the 3-hour postprandial values after all three daily meals were improved significantly even 2-3 days after each training session, suggesting that low-volume HIT can rapidly improve glucose control and induce adaptations in skeletal muscle that improve metabolic health in people with type 2 diabetes.

While interval training is routinely used by sports teams and athletes, I have to question whether doing only this type of training would be 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 with type 2 diabetes? Probably not, as it simply doesn’t burn that many calories. Actually, it doesn’t save that much time either: when you add in the interspersed rest intervals and a warm-up and cool-down period, it still takes at least 25 minutes per session and 75 minutes per week. Current recs from the American Diabetes Association suggest that people with diabetes should try to get at least 150 minutes of moderate to vigorous exercise each week—an average of 30 minutes a day if done five days a week—so you’d only really be saving time on the two extra days you’re not doing the HIT routine.

There is no doubt that doing HIT training does have some benefits. This research suggests that doing thrice-weekly short intensive workouts may help lower blood sugar levels similarly to more frequently performed moderate activities. The sessions themselves dropped blood sugar levels from 137 mg/dL to 119 mg/dL, on average, which isn’t bad for only 10 minutes of exercise. In addition, overall and post-meal blood sugar levels were reduced long after training sessions were completed, which may or may not happen with more moderate workouts.

On the flip side, others who wrote articles about this training regimen also commented that “it requires so much suffering that you’re almost destined to quit.” Unless it’s regularly done with others, a coach, or a personal trainer to ensure motivation and positive feedback, most individuals will not have the drive to 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. (So, you probably couldn’t stop early and gain the same benefits.)

If you can only do five to 10 minutes of exercise, that’s certainly better than nothing, but you really start to see the effects of exercise if you can regularly exercise harder and longer—for 20 to 30 minutes at least a few times a week. Another drawback of doing low-volume HIT is simply that not everyone is going to be able to do it, and it’s certainly not the best routine to start with when you’ve been sedentary for a while. It’s also more likely to result in overuse injuries and other joint problems that will stop you from doing anything after a while.

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 cardiovascular fitness and to use up more blood glucose and stored carbohydrate (glycogen) in muscles, just like was done in one pilot study a few years back (2). 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.

The bottom line: Just get up and off the couch to do any type of physical activity regularly, and your blood glucose levels will thank you.

References Cited:

(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. 2006;111(6):1554-60.

(2) Johnson ST, McCargar LJ, Bell GJ, Tudor-Locke C, Harber VJ, Bell RC. Walking faster:  distilling a complex prescription for type 2 diabetes management through pedometry. Diabetes Care 2006;29:1654-5.

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Responses

  1. I was just writing about interval training last night (link in name) on my fitness blog. No one ever tells you about the added risk of injury doing HIIT due to higher impact when running. Be careful.

    • Absolutely. Injury risk increases more than normal in people with diabetes, too. I don’t see HIT as a long-term exercise for most people, regardless of whether they have diabetes or not. Doing some intervals within normal, moderate training is very beneficial, though, to both blood glucose control and fitness improvements.

  2. Dr Colberg, Have you read “Body By Science” by Dr. Doug McGuff and Tony Little. They claim that you only need 12 minutes of HIIT to get the amazing results everyone is looking for.


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