Interval Training Can Spice Up a Workout

When it comes to fitness, a lot of people think the only way to improve is to do more, more, more. But one way to enhance your workout makes do with "less": interval training.

Interval training alternates short bursts of intense activity with periods of "active recovery," which means more moderate forms of that same activity. Elite athletes use the technique to improve their speed, endurance and overall fitness. But moderate or beginning exercisers can use the same trick to burn more calories, improve cardiovascular endurance and get a bracing workout in a relatively short time.

"Interval training is not necessarily a hard workout,'' says Richard Cotton, chief exercise physiologist for the American Council on Exercise. "It's very adaptive. It can be a low level, a moderate level or an extremely high level of training. The important point is that it takes you to a level of activity you would not normally reach."

How it works

Interval training draws on the body's two forms of energy production: aerobic and anaerobic. In the aerobic state, the body uses oxygen to convert stored carbohydrates into energy. This is the method you use while walking, jogging, riding a bike or even playing a leisurely game of golf. If you keep working aerobically long enough, or make more strenuous demands, such as sprinting or jumping, the anaerobic process kicks in. The body then makes energy from glycogen stored in the muscles. This is highly inefficient and produces lactic acid, contributing to muscle fatigue. After you stop the high-intensity activity, your body returns to the aerobic state and breaks down lactic acid.

Most people can't keep up anaerobic activity for very long without feeling out of breath and tired, and quite sore later. One step to increasing fitness is to train the body to delay the switch from aerobic to anaerobic for as long as possible. This is where interval training can help. Pushing the body to work hard for short periods can build your aerobic capacity because the body builds new capillaries and does a better job of transporting oxygen to the muscles.

Take running, for instance. Even a trained runner would find it nearly impossible to sprint for two minutes straight. But adding six 20-second sprints to a routine jog is akin to a two-minute sprint without the fatigue and shortness of breath.

"To increase your fitness level, you have to do something to push yourself,'' says Joy DuMay, a Santa Barbara personal trainer. "Most people can't work out hard for 20 minutes. But they can work out hard for a minute or two and then bring it down."

Interval training can also be as easy as slow walking and then resting, or slow walking and then jogging for a few feet. It depends on your fitness level. If your exercise routine is getting stale, interval training can end the doldrums. It's also great for people with limited time.

"When people say they only have 30 minutes and what should they do, I tell them interval training,'' Mr. Cotton says. "It's a highly efficient workout."

Getting started

Interval training can work with any type of aerobic exercise. You should add higher-intensity periods gradually, keep them brief, and always keep the pace comfortable.

"It's very important to get into it gradually,'' Mr. Cotton says. "You can start by very simply varying the pace until you get accustomed to it.'' Tuning into the way your body responds to new demands is crucial to interval training.

Talk to your health care provider before starting or expanding a fitness program. It is important to monitor your heartrate while interval training.

"You don't want to try to do too much all at once. Part of the fun is finding out what you can do comfortably," Ms. DuMay says. "People want results right away, but a big part of interval training is just learning your limitations and responding to how your body feels.''

How hard is "hard"?

Interval training can be complex (a list of durations and distances) or simple (sprinting to the next tree). But in general, you want to make sure your base workout rate is about 65 percent of your maximum heart rate and the bursts of intense activity are about 85 percent of your maximum heart rate.

To calculate your maximum heart rate, subtract your age from 220. A 40-year-old's maximum heart rate is 180. A heart rate of 117 (180 times 0.65) is good for that 40-year-old's moderate workout, while a rate of 153 (180 times 0.85) works for the "harder" periods.

To check your precise heart rate, you can buy a wristwatch-type heart rate monitor for less than $50.