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“To our knowledge, this is the first study to demonstrate the effects of a novel interval training program on both traditional and novel CVD risk factors in adolescents.” Duncan S. Buchan et al, University of West Scotland (American Journal of Human Biology, April 5, 2011)

Interval Sprints for Teens

Significant Improvements with 15% of Exercise Time

We’ve been saying for sometime that intervals are for just about everyone. It looks like we’re about to close the loop. A new study by scientists at the University of West Scotland shows that intervals work well for adolescent boys and girls. That’s important because obesity and heart disease often begin in youth. One of the main contributors to both is physical inactivity. (Poor diet is the other main contributor.)

“A high number of youth exhibit…one or more cardiovascular disease risk factor, which they are likely to retain into adulthood,” the Scottish scientists wrote in introducing their study. Kids need to get into the exercise habit as early as possible, and do it in a way they enjoy and will want to continue throughout life. Interval training in its many forms may be just the thing for many young people.

This study appears to be the first to document the positive effects on young people. It examines the effects of brief, intense exercise in comparison to traditional endurance training on cardiovascular disease (CVD) risk factors.

The Study

Forty seven boys and 10 girls, all non-obese volunteers, average age 16.4, were randomly divided into two exercise groups and a control group. Twelve boys and 4 girls were assigned to the moderate exercise group (MOD), and 15 boys and 2 girls were assigned to the high-intensity interval training group (HIT); the remaining 24 (20 boys and 4 girls) served as controls. The two exercise groups performed 3 workouts a week for 7 weeks. The MOD group ran continuously for 20 minutes at approximately 70% of maximum oxygen uptake, while the HIT group sprinted for 30 meters, followed by 20-30 seconds of recovery. Both groups ran shuttle fashion within a 20 meter area marked by cones.

The HIT groups started at the mid-point between the makers, sprinted to one marker (10 meters), turned and sprinted to the other maker (20 meters), and then  recovered while walking back to the mid-point for the next sprint. The MOD group jogged continuously back and forth between the two cones.

Training for both groups was progressive. The HIT group began with four sprints, a total of 2 minutes of maximal effort and 2 minutes of recovery. The number of sprints was increased to five during weeks 3 and 4, and to six during weeks 5 and 6. During week 7 the recovery period was reduced to 20 seconds.

Participants in the MOD group kept pace with a CD that emitted a continuous audio signal for a period of 20 minutes. During week 4 participants were again tested for VO2max to determine training effect; the audio signal was then adjusted to elicit 70% of their new VO2max. 

Extensive measuring and testing was done before and after the exercise intervention, including blood tests, aerobic fitness, and body composition.

The Results

Both protocols were challenging, but the time and energy expenditure was markedly different. By the end of the study the MOD group had completed 420 minutes of exercise, while the HIT group has trained for only 63 minutes, including recovery periods. The estimated energy expenditure for the HIT group was 907 calories compared to 4410 calories for the MOD group.

The HIT group trained for only 15% of the time put in by the MOD group and expended only 20% a many calories.

Both groups substantially improved CVD risk factors. The MOD group, however, exercised six times longer and saw moderately better results.

The HIT group significantly improved systolic blood pressure, aerobic fitness, and body mass index (BMI), while the MOD group saw significant improvements in aerobic fitness, body fat percentage, BMI, and several novel CVD risk factors (fibrinogen, plasminogen activator inhibitor-1, and insulin concentrations). Both programs lowered bad cholesterol (LDL) and raised good cholesterol (HDL).

“These findings demonstrate that brief, intense exercise is a time efficient means for improving CVD risk factors in adolescents,” the study concluded.

“Overall, results of the study indicated that the two exercise programs had distinct cardioprotective effects on adolescent youth,” the researchers added in the “Discussion” portion of the report. “It is not surprising, perhaps, that traditional endurance exercise appears to have had the greatest effect on CVD risk over the 7-week intervention.” In recent investigations, however, “observed changes [following sprint interval training] were similar or to some extent greater than noted with a traditional, continuous exercise protocol.”

In this study, the most striking difference was the effect on aerobic fitness: The MOD group improved aerobic fitness 26.8% compared to an improvement of 8.3% in the HIT group.

“Based on heart rate response (essentially the same for both groups), it is evident that both interventions challenged the heart’s pumping ability throughout the intervention period,” the report observed. “However, the HIT protocol was apparently of insufficient duration to adequately stress the heart’s pumping ability to produce the magnitude of improvements in aerobic fitness observed in the MOD group. Improvements in aerobic capacity were, nevertheless, seen in the HIT group even though their exercise time commitment was only 15% of that of the MOD group. Considering that aerobic fitness appears to be the most important predictor of morbidity and mortality for CVD and for all causes, it is encouraging that both the MOD and the HIT interventions significantly improved aerobic fitness in this study.”

Final Thoughts

In addition to time efficiency, it’s a pretty safe bet that the stop-and-start HIT protocol was more fun and interesting for the teenagers than the monotony of running back and forth at a steady pace for 20 minutes. The HIT protocol was more like basketball, soccer, or other games teenagers play. It’s a lead pipe cinch that they won’t be running at a steady pace in a 20 meter space after they graduate. That’s important, because enjoyment and regularity—few can have one without the other—are the real keys to long-term health and longevity.

There are many ways to do intervals and all of them are more fun and interesting than steady state exercise. That’s my opinion and I’m sticking to it. It's also the conclusion of the Montreal Heart Institute's Centre for Preventive Medicine and Physical Activity (EPIC Centre). "It is proven that, compared to moderate intensity continuous training, interval training is more appreciated by participants," said Valerie Guilbault, an EPIC Centre kinesiologist, in a press release dated April 28, 2011. "This type of training is also more effective, because alternating between short periods of intense effort and rest periods allows for a longer training time," he added. Yes, you can train hard longer.

Most people, kids and adults, are more likely to do short, intense exercise than long, moderate steady-state exercise. (Apologies to Runner’s World readers)

A long run, hike, bike ride, or swim is, of course, a good idea from time to time and might even add to training satisfaction—and results.

Decide what suits you and stick with it. You’ll be well rewarded. Start when you’re young and you’ll be way ahead of the game.

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