Your pulse is the best way to gauge exercise intensity, but taking it by hand may cause you to underestimate how hard you're working. "Your heart rate steadily declines once you stop moving [by about fi ve beats every 10 seconds]," says Gary Sforzo, Ph.D., a professor of exercise and sport sciences at Ithaca College. But it takes an average of 17 to 20 seconds for most people to find and take their pulse (for a six-second count), according to a study he co-authored. The lag might lead you to bump up the intensity during the rest of your session when you're already working hard enough. You could pony up for a heart-rate monitor—or use this solution: Add five beats to your count if it takes you only a few seconds to find your pulse. Add 10 if it takes you several seconds to get the right spot or if you stop and catch your breath beforehand.