Heart rate monitors: keeping the beat

Race cars often don't have a speedometer. What they do have is a tachometer that shows how fast the engine is revving.

A heart rate monitor is a tachometer for the human body -- it tells a user how quickly the heart is beating during exercise. Sports- and fitness-related use of the device has mushroomed since its invention in 1977, but many people don't know how to use one effectively. For starters, simple formulas to determine heart rate training zones aren't reliable. A monitor should be used not just to achieve a target, but as a regulator to avoid overtraining. The devices, although generally accurate, can sometimes generate false readings that cause unnecessary worry. And for the easily obsessed, focusing too much on numbers can turn a fun bike ride into a laboratory experiment.

Most monitors have a chest strap sensor that picks up and transmits electrical impulses from the heart to a receiver, worn on the wrist or handlebars of a bike. The receiver converts signals from the strap to a digital display of beats per minute. Strapless models are also available. Basic monitors cost less than $100 and display heart rate and time. Fancier models record heart rates during a workout and can set alarms for high and low heart rate zone limits. Other models integrate bike computer functions, such as speed and distance, or use GPS satellite signals to determine speed, distance, location and altitude in addition to recording heart rate.

The health benefits of exercise aren't gained without enough intensity. The American College of Sports Medicine and the American Heart Assn. suggest that healthy individuals under 65 do moderately intense cardio exercise 30 minutes a day, five days a week or vigorously intense cardio 20 minutes a day, three days a week, in addition to strength training and stretching.

Determining what is "moderately intense" or "vigorously intense" is the rub. That's where heart rate monitors and training zones come in.

Finding a training zone