Interval Training and Varying Intensities

There’s been a lot of talk about the benefits that occur from completing high-intensity exercise intervals as opposed to continuous intensity.  A number of studies show many positive effects occur from this type of training including an increase in fitness and training adaptations.  A recently published study in the International Journal of Sport Nutrition and Exercise Metabolism had male students complete three different tests. Their calorie burning rates were measured at several points after they completed each test (Hazell, Olver et al. 2012).  One test required the student to do nothing out of the ordinary; this group was the control group.  A second test had the participants complete one 30-minute bout of exercise at a moderate intensity.  The final group required the participants to perform two minutes of sprint interval exercise.

High or Low? Which intensity is Better?

As expected, heart rate and other markers of exercise intensity indicated that the two-minute bout of high-intensity exercise caused the greatest response.  Greater numbers of calories were burned to complete the 30 minute bout of exercise when compared to the more intensity, two minute bout of exercise.  This should not be that surprising, after all you are comparing 30 minutes to 2 minutes.  But what is fascinating and reason enough to get you to work a little harder is that when calorie burning was compared through the first 8 hours after completion of each exercise bout, the 30 minute bout of exercise was greater.  But when calorie burning was compared across the next 16 hours or through the first 24 hours after completing the exercise bout, the amount of calories burned was similar between the two exercise groups.

Interval Training: Which Burns More Calories?

In other words, the significantly greater rates of exercise intensity created a situation where the amount of recovery and calorie burning completed was similar to the amount performed by the body after exercising for 28 minutes longer!  To put that in perspective,  these results do NOT mean that continuous intensity exercise is useless or not worth your time.  In fact, hundreds of studies have documented the many positive effects from this type of exercise including improvements in cholesterol, blood pressure, weight loss, etc.

These results DO however, indicate that completing a very brief (2 minutes) period of maximal intensity exercise periodically can have very beneficial effects.  This study was primarily focused upon changes in calorie burning rates over the 24 hour period after completing each exercise bout and they found that over this time period the amount of calories burned were similar.

This makes me think, what would be the impact of finishing each workout with a two minute bout of sprint cycling, rest for 1 minute and complete another two minute bout of sprint cycling?  That’s only five minutes and if over the course of several weeks it led to greater fat loss would it be worth the extra pain?

Reference:

Hazell, T. J., T. D. Olver, et al. (2012). “Two minutes of sprint-interval exercise elicits 24-hr oxygen consumption similar to that of 30 min of continuous endurance exercise.” Int J Sport Nutr Exerc Metab 22(4): 276-283.