Short Is Good

How intervals take you farther

New research shows that just six weeks of interval training—short bursts of high-intensity anaerobic activity—can double muscle endurance and radically boost aerobic capacity. In other words, prep time for your spring marathon or century ride just got considerably shorter.

In a landmark 2005 study, researchers from McMaster University in Ontario measured the performance of amateur cyclists who engaged in 30-second sprint sessions three times a week for two weeks. The results were astonishing: By the end of the trial, riders who once barely lasted 30 minutes at top speed suddenly could blast full throttle for almost an hour. What changed? Experts don't know for certain, but most think the gains had something to do with fast-twitch muscle fibers, which lie dormant "until you're running to save your baby from a speeding car," says McMaster kinesiology professor Martin Gibala. Intervals activate these fast-twitch fibers, tricking them into pinch-hitting when your muscles begin to fatigue.

We enlisted trainer Craig Ballantyne, 30, who has developed interval routines for professional athletes for three years. His six-week program can jump-start your spring training. The key, he says, is to commit yourself fully. "Interval training should be uncomfortable," Ballantyne says. "But in just a few weeks, your fitness level will go through the roof."

The Starting Line
Craig Ballantyne's Turbulence Training system (www.turbulencetraining.com) uses a numeric scale to rank the intensity of intervals: Ten is running for your life; five is a light jog. Since improvements occur within sport-specific muscle groups, Ballantyne recommends tailoring your intervals to your sport: "A swimmer should swim, a cyclist should cycle, and a runner should run."

Weeks 1 & 2: The Ramp-Up
GOAL: To increase muscle endurance and aerobic capacity.
FREQUENCY: Twice a week in place of two of your regular aerobic workouts, with a rest day in between.

1. Warm up for five minutes in your chosen sport at 30 percent of your maximum intensity level.

2. Exercise for two minutes at 70 percent of your maximum intensity level. By the end of the interval, you should be at 95 percent of your maximum heart rate (to determine max heart rate, subtract your age from 220).

3. Follow each interval with an "active rest," exercising for two minutes at 30 percent intensity (e.g., if you run, then walk briskly during the active-rest interval).

4. Repeat for at least four intervals but no more than ten.

5. Finish with a five-minute cool down at 30 percent of your maximum intensity level.

Interval Length: 2:00
Intensity Level: 7

Weeks 3 & 4: The Big Push
GOAL: To improve anaerobic and aerobic endurance and VO₂ max.
FREQUENCY: Three times a week in place of three of your regular aerobic workouts, with a rest day in between.

1. Warm up for five minutes in your chosen sport at 50 percent of your maximum intensity level.

2. Exercise for 60 seconds at 80 percent of your maximum intensity level. By the end of the interval, you should be at 95 percent of your maximum heart rate. Whether you run, bike, or swim, cover the same distance with each subsequent interval.

3. Repeat for at least three but no more than eight intervals.

4. During week three, your active rest should be 90 seconds at 30 percent intensity. During week four, cut active rest to 60 seconds.

5. Finish with a five-minute cool down at 30 percent of your maximum intensity level.

Interval Length: 1:00
Intensity Level: 8

Weeks 5 & 6: The Finish Line
GOAL: To improve muscle endurance and aerobic capacity. Integrate hill sprints (either running or cycling) into your 30-second interval routine to further increase muscle strength and lean muscle mass.
FREQUENCY: Three times a week in place of three of your regular aerobic workouts, with a rest day in between.

1. Warm up for five minutes in your chosen sport at 50 percent of your maximum intensity level.

2. Exercise for 30 seconds at 90 percent of your maximum intensity level. By the end of the interval, you should be at nearly 100 percent of your maximum heart rate.

3. Repeat for at least three but no more than six intervals.

4. During week five, your active rest should be 90 seconds at 30 percent of your maximum intensity level. During week six, cut active rest to 60 seconds.

5. Finish with a five-minute cool down at 30 percent of your maximum intensity level.

Interval Length: 0:30
Intensity Level: 9