Hey, this explains it while encouraging working out/warming up (do it to A Hard Day's Night!)before shoveling snow in cold weather:
Take Care When the Temp Drops On chilly days, some of us need to take extra precautions before venturing out to exercise. If you have any kind of heart problem, for example, you should consult your doctor before working out in the cold. As the air temperature drops, your body responds by constricting blood vessels, a process that pulls blood toward the trunk to feed your internal organs. When this happens, exercising puts extra strain on your heart as it tries to pump blood to your extremities.
Walking can relieve some of this strain by dilating blood vessels in your legs. The trick is to warm up slowly, to allow your body to adjust to the coldness. If you don't warm up when it's freezing outside, you could set yourself up for angina (severe chest pain) or a heart attack, says Roger Fielding, PhD, assistant professor in the department of health sciences at Boston University. That's why people have heart attacks when shoveling snow.
When you warm up, do it indoors, before exposing your body to the cold air. This reduces the strain on your heart, because your blood vessels become dilated. You'll feel better about going outside, too, because you'll be warm already.
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Take Care When the Temp Drops
On chilly days, some of us need to take extra precautions before venturing out to exercise. If you have any kind of heart problem, for example, you should consult your doctor before working out in the cold. As the air temperature drops, your body responds by constricting blood vessels, a process that pulls blood toward the trunk to feed your internal organs. When this happens, exercising puts extra strain on your heart as it tries to pump blood to your extremities.
Walking can relieve some of this strain by dilating blood vessels in your legs. The trick is to warm up slowly, to allow your body to adjust to the coldness. If you don't warm up when it's freezing outside, you could set yourself up for angina (severe chest pain) or a heart attack, says Roger Fielding, PhD, assistant professor in the department of health sciences at Boston University. That's why people have heart attacks when shoveling snow.
When you warm up, do it indoors, before exposing your body to the cold air. This reduces the strain on your heart, because your blood vessels become dilated. You'll feel better about going outside, too, because you'll be warm already.
More: http://www.prevention.com/cda/feature2002/0,4780,s1-6364,00.html