Declan Connolly, PhD Responds:

Declan Connolly, PhD, associate professor and director of the University of Vermont Human Performance Laboratory, responds: A heart-rate monitor is a great tool. It can help ensure that you're working at a level that's productive but not too hard. For a recreational athlete, a basic monitor ($50 to $60) is fine. A wristwatchlike device will display your heart rate in beats per minute. Bigger faces offer easier readouts. To find your maximum heart rate, subtract your age from 220. Keeping your heart rate in the 65 to 75% max range for 30 to 45 minutes a few times a week is what you're aiming for to help improve cardio fitness or to help with weight-loss efforts. A competitive athlete may prefer a monitor with target rates. If you're shooting for a 70 to 75% max heart rate for 45 to 50 minutes, the programmed monitor gives an audible signal if you fall or rise outside of that range. You also can retrieve a file of your recorded rates after the session.