Shoveling snow is such an extremely strenuous activity that many people should not do it, warns a team of medical researchers from Detroit. Shoveling a load of medium-weight snow at the rate of 10 shovelsful a minute is equivalent to running at a speed of 5.5 miles an hour, or playing handball or basketball, said Dr. Barry A. Franklin, program director for cardiac rehabilitation and physical fitness at Sinai Hospital in Detroit. Clearing off wet, heavy snow is almost twice as arduous, he reported in the current issue of The Physician and Sportsmedicine. "Besides the hazards of frostbite and low back strains, snow shoveling can be deadly. During the winter months, reports of snow shoveling deaths are common," said Franklin, who also is an assistant professor of physiology at Wayne State University. Unlike other types of exercise, shoveling snow creates a disproportionate strain on the heart, which causes thousands of cases of chest pains, heart attacks and deaths each year, he said. Studies show that at the rate of 10 shovelsful a minute a person has an oxygen consumption of six to 15 times higher than his resting metabolic rate, Franklin said. Anyone over the age of 45 should seriously consider whether they should shovel, especially if they are out of shape, overweight or have a history of heart disease, he said. Elderly persons, people with hypertension or those with a history of heart disease or who run a high risk of heart disease should not shovel snow, he said. Franklin and his colleagues found five factors in shoveling that make it so dangerous for the heart in terms of greatly increased blood pressure and heart rate:

Arm muscles are far less efficient than leg muscles, thereby creating a bigger demand on the heart for the same amount of work done.

Exercising in an upright position can cause pooling of the blood in the legs, making the heart beat faster to circulate blood.

Straining to lift heavy loads can be dangerous because it greatly increases the demand on the heart without significantly increasing the blood flow to the heart muscle.

Temporarily holding the breath while straining produces tremendous sudden fluctuations in heart rate and blood pressure.

Cold air causes blood vessels near the skin to close down, thereby increasing blood pressure. The cold may also constrict coronary arteries.