Shoveling snow can be hard on the heart.
Especially for the sedentary, doctors say, tackling heavy snow with only a shovel and determination can put a potentially fatal strain on the heart. Every winter, Americans in snowy states drop in their tracks or wind up in emergency rooms - their hearts stopped, damaged or in pain after sudden and unaccustomed exertion in the cold.
There are no national statistics on shoveling deaths. But a 1993 study in The New England Journal of Medicine looked at 1,228 heart-attack victims and found that out-of-shape people increased their risk of a heart attack by a hundredfold when they shoveled snow. Regular exercisers doubled their risk.
But those are relative risks. The risk of suffering a heart attack within an hour of shoveling snow is small, the study found. For example, a 50-year-old nonsmoker in good shape runs a 1-in-500,000 risk of a heart attack within an hour of shoveling snow. One who leads a sedentary existence runs a 1-in-10,000 risk.
But as physical activities go, "snow shoveling is particularly bad," said Dr. McRae Williams, an emergency room doctor at the Greater Baltimore Medical Center. That's because it puts heavy, sudden stress on the heart without simultaneously boosting oxygen supplies to the heart muscle.
A 1995 study in The Journal of the American Medical Association found that the cardiovascular exertion of shoveling snow was equivalent to "maximal" effort on a treadmill for sedentary men.
When we jog or ride a bike, we involve many muscle groups. Heart rates and breathing increase gradually, and the muscle action releases chemicals that cause blood vessels to dilate. As a result, more oxygen can reach the working muscles.
"Blood pressure actually drops," Williams said. "It keeps the vessels open and reduces strain against the heart."
Not with shoveling snow.
"It's not aerobic exercise. It's static lifting," like weightlifting, he said. "It creates stress on the heart at the same time as it raises blood pressure."
Cold temperatures make things worse. The body constricts blood flow to the skin to conserve heat, which also raises blood pressure.
Those who pick up a shovel despite underlying coronary artery disease and high blood pressure are courting disaster.
Massachusetts researchers analyzed data on 260,000 heart attacks and found that risks are more than 50 percent higher in winter than in summer. And they're more likely to be fatal.
Men over 50, women over 60, and those with a sedentary lifestyle or history of heart disease and hypertension probably should not pick up a shovel, experts say. Hire a kid. At the least, consult your doctor first.
"It's important to warm up," Williams said. "Don't go out and try to act like a snowplow."
Lift smaller loads, and don't try to do the job all at once.
"If you're tired, stop and take a break," he said. "Try not to be as much of a tough guy."