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The cool-down is another one of those well-established exercise habits, like stretching, that most people swear by without really wondering about the underlying science. And for good reason: it turns out there isn’t really much science there, according to a recent article by Gina Kolata in the New York Times.
Exercise researchers say there is only one agreed-on fact about the possible risk of suddenly stopping intense exercise. When you exercise hard, the blood vessels in your legs are expanded to send more blood to your legs and feet. And your heart is pumping fast. If you suddenly stop, your heart slows down, your blood is pooled in your legs and feet, and you can feel dizzy, even pass out.
So that suggests that, at the very least, you should keep moving, if only at a walk, for a few minutes after vigorous exercise. But there’s no evidence to support the idea that a cool-down will reduce stiffness or muscle soreness the next day, let alone “flush out lactic acid.”
Of course, this may simply be because scientists have yet to do rigorous research into the cool-down. (Kolata does mention a couple of studies that failed to find any benefits.) Based of their personal experiences, many people are firmly convinced that they feel better if they warm down, science or not. And, unlike stretching, there’s no significant evidence that cooling down actually hurts you, so you might as well stick with whatever makes you feel good!