Healthy people have healthy responses to snow shoveling

November 13, 2001

ANAHEIM, Calif., Nov. 13 - Although manual snow shoveling is a common trigger of heart attack, it doesn't negatively affect blood clotting in healthy males, according to a study presented today at the American Heart Association's Scientific Sessions 2001 conference.

The findings suggest that different types of physical activity have varying effects on blood coagulation or clotting, with moderate exercise protecting young, healthy men.

Since the early 1990s, several studies have suggested that manual snow shoveling increases heart stress and, potentially, the risk of heart attack, especially in individuals who have heart disease or risk factors. These studies are bolstered by evidence of a rise in the heart attack rate after a heavy snowfall.

Many of the studies evaluating snow shoveling and heart attack risk have focused on changes in blood pressure and heart rate, and observed dramatic increases in both. This study focused on factors that affect the blood's ability to clot.

"We know that the majority of heart attacks, including those that occur after physical exertion, result from the formation of a thrombus or clot,"[ says Christopher J. Womack, Ph.D., assistant professor of exercise physiology at Michigan State University in East Lansing. "The clot forms the final blockage in the coronary artery, leading to the heart attack."

The study involved 11 healthy young men (average age 26 years) who performed three types of physical activity: a standard maximal treadmill exercise test, 10 minutes of shoveling snow at their own pace, and 10 minutes of removing snow with a snow blower. Each activity was performed on a separate morning. Blood was drawn before and after each activity and analyzed for changes in the activity of tissue plasminogen activator (tPA, a clot-dissolving enzyme) and plasminogen activator inhibitor 1 (PAI-1, which inhibits clot dissolving) and in levels of tPA antigen (a marker of inactivated tPA and increased clotting potential).

Treadmill exercise increased tPA activity by 33 percent and decreased PAI-1 activity by 34 percent, while tPA antigen levels rose by an average of 274 percent. Following manual snow shoveling, PAI-1 activity decreased by an average of 14 percent, tPA activity remained at normal pre-exercise levels, and tPA antigen levels increased by 63 percent. Use of the snow blower was not associated with changes in any of the clotting factors.

"Different forms of exercise will cause different physiologic responses, especially some of those associated with increased clot dissolving," says Womack. "That finding surprised us because levels of lactic acid, which is a marker of physical strain and exercise tolerance, were higher during manual snow shoveling than during automated snow removal. The heart rate response also was higher during snow shoveling than automated snow removal. "Given the increase in blood lactate, we would have expected to see an increase in the potential for coagulation. The findings could suggest that different factors control blood clotting versus clot dissolving, but we don't know that for sure," says Womack.

The findings may support the idea that young, healthy individuals have protective responses to moderate exercise that prevent heart attacks. In addition, for these young healthy individuals, snow shoveling did not appear to be as physically stressful as maximal treadmill exercise, but was significantly more stressful than automated snow removal.

Whether the findings apply to older individuals, who are at greater risk for heart attack, remains to be determined in a follow-up study the investigators are conducting.

"There is already good data to show that aging reduces the potential for clot dissolving," Womack says. "We want to find out whether aging also affects the response of these parameters during exercise."
-end-
Other investigators in the study are: Chad Michael Paton, B.S.; Adam M. Coughlin, B.S.; Adam T. Dejong, M.S.; Jamie Anderson, B.S.; and Barry A. Franklin, Ph.D.

NR01-1352 (SS2001/Womack)

CONTACT:
For information Nov. 10 - 14, call:
Karen Hunter or Bridgette McNeill
at the Hilton Anaheim Hotel
(714) 251-5801

Abstract 2882

American Heart Association

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