Editor's Note:  Amazingly, just 15 minutes of sprint interval training can improve exercise performance by almost 100%! However, Christian Finn explains why sprint interval training isn't necessarily the best option for fat loss. 

You might have seen news reports about a recent study showing that less than 10 minutes of intense exercise a week could be "as effective as an hour of daily moderate activity."

"Short bouts of very intense exercise improved muscle health and performance comparable to several weeks of traditional endurance training," says study co-author Martin Gibala, an associate professor in the department of kinesiology of McMaster.

Here in England, the research was featured on breakfast TV, and I got a lot of questions from people wanting to know "if it was really true." Let's take a closer look at what happened in the study to see what it all means for you.

The research, published in the June 2005 edition of the Journal of Applied Physiology, shows that just 15 minutes of sprint interval training over a two-week period was enough to improve exercise performance by almost 100% [2].

The study was conducted on 16 subjects, all of whom were "recreationally active." In other words, they took part in some form of exercise 2-3 times per week, but none was engaged in a structured training program.

Eight of the subjects (6 men and 2 women) performed the two-week interval training program. The other participants did no exercise. The program consisted of between four and seven 30-second bursts of "all out" cycling followed by four minutes of recovery three times a week (Monday, Wednesday, and Friday) for two weeks.

Subjects were encouraged to pedal as fast as possible during the 30-second sprint. During the four minute recovery period, they remained on the bike and either rested or cycled at a low speed.

Exercise performance was assessed before and after the training program by measuring how long the participants could cycle at an intensity equivalent to 80% of their VO2peak before giving up.

The result?

After training, the individual improvements in performance ranged from 81% to 169%, with the exception of one subject (a 16% decrease) who had injured his ankle before taking the final exercise test. However, even when his results were included, the average time to fatigue in the sprint interval group increased from 26 to 51 minutes, despite no change in VO2peak. The control group showed only a very small improvement.

The muscles of the trained group also showed a significant increase in citrate synthase, an enzyme that is indicative of the tissue's ability to use oxygen.

"The findings really are exciting," says Edward F. Coyle, PhD, director of the human performance laboratory at the University of Texas, Austin. His editorial comments accompany the study. "In today's society, people spend so much time in front of the TV or video screen. It is rare we exercise either intensely or for very long times. Since some people are devoting so little time to exercise, this reminds us how effective or efficient even short amounts of exercise are if performed very intensely."

So, what's the catch?

First, sprint interval training is very hard work.

"The exercise, although only 30 seconds for each of the four bouts, is as hard as you can go," Coyle says. "So the first 15 seconds feel not so bad, and the last 15 seconds are hell."

That's one reason I prefer using shorter intervals lasting around 15 seconds, especially when I'm following a restricted-calorie diet. I think you get many of the same benefits with a lot less pain.

Second, the researchers were measuring changes in exercise performance. They weren't interested in weight loss. Although high-intensity interval training is popular with some people who want to lose fat, it does have some limitations.

No matter how hard you push yourself, there are only so many calories you can burn in such a short period. It's true that an intense workout boosts oxygen consumption (called excess post-exercise consumption, or EPOC for short) and calorie expenditure after exercise to a greater extent than moderate-intensity activity.

However, EPOC is linked with both exercise intensity (how hard you work) and exercise duration (how long you work for) [1]. In my experience, "waves" of intervals interspersed with steady-state cardiovascular exercise works better for fat loss than interval training alone.

In fact, this was the approach I used to get in shape for a recent photo shoot (you can see some of the pictures here). Although the workouts take a little longer (30-40 minutes) than a "pure" bout of interval training (which you can often get done in 20 minutes or less), I was still able to get in and out of the gym—shower included—in less than one hour.

Read other articles by Christian Finn

About the Author

Christian Finn is a Certified Personal Trainer and holds a masters degree with distinction in exercise science. He's lectured at a number of universities and private training organizations around the United Kingdom on fitness training, weight loss and the effective use of nutritional supplements. He writes extensively on the subject and his articles have been published in numerous magazines, leading industry journals and websites worldwide, including Men's Health, Men's Health Muscle, Fit Pro (April/May 2001), CAM magazine (February 2003), Image (January 1997), Zest (March 2004), and Body Life magazine (March/April 1997). He was also featured in the July 2004 issue of Muscle & Fitness (UK edition). His website, TheFactsAboutFitness.com, is dedicated to providing its members up-to-date, unbiased information and research on the world of fitness.

References

1. Borsheim, E., & Bahr, R. (2003). Effect of exercise intensity, duration and mode on post-exercise oxygen consumption. Sports Medicine, 33, 1037-1060
2. Burgomaster, K.A., Hughes, S.C., Heigenhauser, G.J., Bradwell, S.N., & Gibala, M.J. (2005). Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. Journal of Applied Physiology, 98, 1985-1990