Add intervals of intense exercise for a...

My son’s cross country team is utilizing an important training strategy that even non-athletes and people with heart disease may benefit from as well. It’s called interval training and it combines short bursts of intense activity with periods of more moderate exercise or even rest.

When faced with an arduous physical task, most people break up the work with short periods of rest. Piano movers alternate bursts of heavy lifting with rest breaks; people with severe heart failure stop every now and then when climbing stairs. Giving stressed muscles time to recover lets them work harder and longer. The same thing holds true for conditioning the heart. For people with various forms of heart disease, an exercise plan that alternates bursts of intense activity with periods of rest or gentler activity seems to be better than longer stretches of continuous activity.

This pattern, called interval training, has long been the province of sports trainers and competitive athletes. Now it’s slowly entering the realm of cardiac rehabilitation and fitness centers. Done formally or informally, 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.

Bursts of intensity

Interval training alternates bursts of more intense activity, like jogging, with periods of moderate activity or even rest. Adding spurts of vigorous activity burns more calories and benefits the heart and arteries.

German studies in 1997 and 2002, a Canadian study in 2005, one from Texas in 2006, and another from Norway in 2007 all show that interval training works for people with a range of cardiovascular conditions. It’s been tested for stable coronary artery disease (cholesterol-clogged and narrowed arteries), intermittent claudication (leg pain when walking), and heart failure. In each case, interval training bested traditional continuous exercise.

Why interval training is special

Walking is often held up as the gold standard for cardiovascular exercise. Most people can do it, it doesn’t require any special equipment, it’s easy on the knees and other joints, and a host of studies leave little doubt that walking strengthens the heart and lungs and improves the function of blood vessels. That said, there’s also at least as much research showing that more intense activities and exercises yield even bigger benefits. Yet many people shun the idea of taking up jogging or other forms of more intense exercise or don’t think they can sustain it. Interval training may offer the best of both worlds.

What makes this regimen special? For starters, it lets many exercisers spend more time doing a high-intensity activity than they could perform in a single stretch. 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 ten 1-minute intervals and resting in between. 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 helps the body create new muscle fibers. A handful of studies show that interval training also changes mitochondria, the tiny powerhouses that provide energy to cells, so they 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, make blood vessels more flexible, intensify the body’s defenses against harmful antioxidants, and ease low-level inflammation.

All these changes have a tangible product: the ability to be more active. They also quietly guard against invisible forces that erode cardiovascular health — things like the entry of cholesterol into artery walls, the stiffening of arteries, or the accumulation of fat.

Trying interval training

Say you usually walk for 30 minutes at a stretch. To add intervals, walk for five minutes to warm up. Then walk as fast as you can, or jog, for one minute. Go back to your usual pace, or even a bit slower, for three minutes. Repeat the fast walking–slower walking cycle five more times. Here are some other tips:

· The high-intensity bursts should last long enough and be strenuous enough that you are out of breath. If you monitor your heart rate, it should be more than 80% of your maximum heart rate.

· Rest periods should be long enough that you are ready to go again, but not so long that your heart slows to its resting rate.

· Warm up before exercising and cool down afterward.

· Don’t do interval training on consecutive days. Let your muscles recuperate in between. Two or three times a week is plenty.

A warning is in order. Interval training isn’t for everyone. 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.

Julie K. Silver, M.D., is an assistant professor in the Department of Physical Medicine and Rehabilitation at Harvard Medical School. She is also the Chief Editor of Books for Harvard Health Publications.

The Harvard Heart Letter provides eight pages of monthly heart news, directly from the more than 8,000 doctors and researchers at Harvard Medical School. It’s a source of expert advice for people who may already suffer from heart disease (or their family members) and for people concerned about their risk who wish to take steps towards positive change.