Interval training helps heart get pumped
By the faculty of Harvard Medical School for The Harvard Medical School Adviser

Q: I have high blood pressure, and my doctor wants me to get into better shape. Do you have suggestions?

A: Try interval training. For people with certain types of heart disease, an exercise plan that alternates bursts of moderately intense activity with periods of rest or gentler activity seems to be better than longer stretches of continuous activity. Studies show that interval training can strengthen healthy hearts and help heal damaged ones. It's also a boon for people who are watching their weight and those battling diabetes.

Interval training emerged in the late 1940s when athletic trainers sought an edge for their long-distance runners. Now it's slowly entering the realm of cardiac rehabilitation and fitness centers.

What makes this regimen special? For starters, it lets many exercisers spend more time doing a high-intensity activity. Someone who couldn't run full speed for 5 minutes straight might be able to run full speed for 10 minutes by doing it in 10 oneminute intervals and resting in between (see illustration). Rest breaks give the body time to remove waste products that can make muscles sluggish, tired or painful.

Working the heart and other muscles hard for brief spurts trains them to use oxygen more efficiently. It conditions them to work through brief periods when the demand for oxygen temporarily outstrips the supply. It builds muscles. A handful of studies show that interval training helps cells burn fat more efficiently.

Intense activity, even brief spurts of it, is better than moderate activity at turning on genes that promote the growth of new blood vessels, making blood vessels more flexible, fighting cancercausing agents and easing low-level inflammation.

All these changes add up to being more than just fit. They also quietly guard against invisible forces that damage heart health. These include things like cholesterol build-up in artery walls, the stiffening of arteries or the accumulation of fat.

As you get started, bear in mind that no single program fits all. Interval training is most easily done on a treadmill, where you can tinker with the speed of the machine. But you can do it anywhere you exercise -- around the neighborhood, in a pool, on a bike ride or on a cross-country ski outing. The point is to get the most out of your workouts by changing up the intensity. If you are a jogger, bust out into a sprint now and then. If you swim, alternate fast and slow laps. If you bicycle, sprinkle your ride with a few Tour de France finishes.

While interval training isn't rigorously defined, there are some basic guidelines. Especially for athletes, the high-intensity bursts should get your heart to beat faster than 80 percent of its maximum rate and be strenuous enough to have you breathing hard. Rest periods should be long enough to get you ready to turn it on again but not so long that your heart slows to its resting rate. Just be careful not to overdo it. Don't do interval workouts on consecutive days, never do them while you are injured or ill, and always warm up before exercising and cool down afterward.

Bear in mind that like your heart, your body's other muscles benefit from training. As such, pump up your routine by lifting light weights, doing push-ups or trying other muscle-building exercises. The American Heart Association says resistance training, also called strength training, is a perfect mate for aerobic exercise -- for both healthy folks and those with heart disease. It's taken a while for interval training to catch on with cardiologists. Conventional wisdom once held that damaged hearts required rest, not exercise. Furthermore, intense exercise was thought to be more dangerous and less heart-healthy than continuous exercise.

But several studies have shown that interval training works for people with a range of heart conditions. It's been tested in people with different types of heart problems, including stable coronary artery disease (cholesterol-clogged and narrowed arteries), intermittent claudication (leg pain when walking) and heart failure (weakened heart muscle). In each case, interval training bested traditional continuous exercise.

A very important warning is in order. Revving the heart rate way up could provoke cardiac arrest or other disasters in people at risk for them. So if you have heart disease, high blood pressure or other risk factors, check with your doctor before starting interval training. You may need a stress test or other studies to find out just how hard you can push yourself safely. And even if your doctors give you an exercise prescription that limits your maximum heart rate, you can add variety to your exercise program by throwing in some "mini-intervals " that ramp up your intensity a bit while keeping you within safe limits. And when it comes to exercise for health, every little bit counts.

Copyright 2007 the President and Fellows of Harvard College. Developed by Harvard Health Publications (www.health.harvard.edu). Distributed by UFS. Submit questions to harvard_ adviser@hms.harvard. edu.