Exercising just 10 minutes every other day may reverse the effects of aging Fitness marketers often use extreme language (“Breakthrough!” “Miraculous!”) to describe the latest hot workout or gear. But scientists and doctors are now using superlatives to discuss what many consider to be one of the most important new fitness approaches in decades: high-intensity interval training, or HIIT, an approach to exercise that people can do in relatively little time, but with oversize benefits. If you ever did wind sprints in high school, then you know what HIIT is — brief bursts of very intense exercise followed by periods...