Here's another reason to get up off the couch and get moving: Regular exercise can help prevent sudden cardiac arrest, especially if it's kept up over the long term.

Women who did no regular exercise or very low levels of exercise -- less than two hours a week -- faced 6.4 times the risk of having their heart stop suddenly during or soon after a workout than women who regularly engaged in moderate or vigorous exercise for more than two hours a week, according to new research presented Thursday at the Heart Rhythm Society's annual meeting in New Orleans.

Exercise does tax the heart, so the study did find an overall six-fold increase in the risk of sudden cardiac death during exercise or within the hour immediately following a moderate-to-vigorous workout.

But the researchers also found that a program of regular exercise reduced this overall risk of sudden cardiac death: Women who exercised four to seven hours a week cut their odds for such an event in half, compared to women who exercised less.

All things considered, "exercise over the long term is beneficial for the risk of sudden death. There's a transient increased risk during and right after exercise that is improved with more regular exercise," explained one of the study's authors, Dr. William Whang, a cardiac electrophysiology fellow at Massachusetts General Hospital in Boston, Mass.

Whang said it was important to note that the "absolute risk of sudden death during exercise is extremely low -- about one sudden death per 18 million hours of moderate to vigorous exercise."

Dr. Stephen Siegel, a cardiologist at New York University Medical Center, said this is an old and somewhat complicated issue.

"The performance of exercise increases the risk of sudden cardiac death, but if one exercises regularly, that risk is less," Siegel explained.

Sudden cardiac death is not a heart attack. During a heart attack, a blockage forms that stops blood flow to the heart, depriving it of oxygen. In sudden cardiac death, the heart simply stops. While this stoppage is often linked to irregular heartbeat (arrhythmia), in many cases doctors just don't know the underlying cause.

According to the Heart Rhythm Society, risk factors for sudden cardiac death include high blood pressure, diabetes, high cholesterol, sedentary lifestyle, obesity, smoking, poor diet, heart rhythm problems, a racing heart beat that comes and goes even if you're resting, and fainting with no apparent cause.

Whang and his colleagues gathered data for this study from the Nurses' Health Study, a large ongoing research effort. Information on exercise participation was collected in 1986, 1988, 1992, 1996, 1998 and 2000.

The researchers obtained information on almost 70,000 women with no history of heart disease or stroke at the start of the study. In the 18 years between 1986 and 2004, 140 women included in the study died from sudden cardiac death.

Moderate to vigorous exercise included brisk walking, plus activities more intense than that, such as running or playing tennis, according to Whang.

The researchers found that during and within an hour of a moderate-to-vigorous exercise session, the average woman's risk of sudden cardiac death rose 6.2 times higher than when sedentary. However, for "couch potato" types (women who exercised less than two hours per week) that risk was significantly higher -- 20.9 times higher than when sedentary.

Regular exercise brought the odds of sudden death back to more comfortable levels. Women who worked out more than two hours a week saw their risk of sudden cardiac death during exercise fall to a level of just 3.3 times higher than when sedentary.

More importantly, increasing amounts of regular exercise also appeared to reduce a woman's overall risk of dying from sudden cardiac death, regardless of the time it occurred.

The researchers found that women who exercised two to four hours weekly had about a 10 percent decrease in sudden cardiac death risk, while women who spent four to seven hours a week working up a sweat reduced their risk by 56 percent. Women who worked out more than seven hours a week had a 69 percent decrease in risk, according to the study.

After adjusting for other risk factors, such as body mass index, diet, diabetes and more, the researchers found that the threshold for real heart-healthy benefits kicked in when women exercised for more than four hours a week. At that point, risks for sudden cardiac death begin to noticeably decline.

"One of the most critical things to do to improve your cardiac health and well-being is to exercise on a regular basis," advised Siegel. "Although not without risk, the overall benefit of exercising far exceeds the temporary risk."

Both Whang and Siegel said anyone who hasn't been active should start off slowly, and for most people, it's a good idea to check with their doctor first.

According to Siegel, anyone who has been sedentary and has risk factors for heart disease, such as smoking, diabetes, high blood pressure, high cholesterol or a family history of heart disease, should definitely see their doctor before beginning an exercise program.

He also cautioned that individuals who experience any chest discomfort or pain during a workout should immediately stop exercising and seek medical attention.

More information

The Heart Rhythm Society has more information about sudden cardiac death.