Last updated: Apr 18, 2008

More people at the gym are wearing odd-looking straps around their chests. That strap's part of a heart rate monitor (HRM), a two-part gizmo that lets you "see" how many times your heart beats per minute.



Here's how they work: The device on your chest sends heart rate info to a wristwatch. By knowing how hard your heart muscle is working—how many times it beats per minute—you can control your workout's intensity.

To use an HRM, you have to know your maximum heart rate, or the fastest your heart can beat in one minute. Here's a rule of thumb: Walk four, even-paced—yet brisk—laps of a quarter-mile running track. During the final lap, take your heart rate. Then, add 40 beats if you're just starting a fitness routine; add 50 if you're in fair shape; add 60 if you're in good shape. That number is your estimated max, says Sally Edwards, author of 10 heart rate books and founder of heartzones.com.

Working different percentages of your max for at least 20 minutes accomplishes different goals. For instance, maintaining 60 to 70 percent of max is the "zone" telling your body to start increasing the rate of fat burned. If you want to get fitter and faster, keep your heart rate between 80 to 90 percent.

Armed with this information, you can vary your workouts to achieve different fitness goals. Thus, HRMs can act as "your coach and your support," Edwards says.

With hundreds of models from dozens of manufacturers, choosing an HRM can be intimidating. (In fact, some fitness experts say that if gadget phobia keeps you from working out, skip the HRMs altogether.) What you need depends on your goals, your budget, and your love—or hatred—of gizmos. Most HRMs fall into three categories:

Push and Play models are simple HRMs; perfect for fitness virgins. Simply strap on the chest and wristband devices, press a button, and the heart-rate readout begins. Cost: $50–$100. Try Sports Instruments Fit 1 HRM, $60. Watch features and calorie counter work in tandem with a percentage of heart-rate display. Programmed workout zones offer easy use.

Zone Monitors allow you to determine your "zone," or range of acceptable heart beats. After you set the high and low ends of your range (often done in increments of 10 percentage points), flashes or beeps announce when you're under or over your target. Good for regular gym-goers. Cost: $100–$150. One model we like is Nike's Imara HMR, $129. This brand-new monitor has a comfortable, slender shape designed just for women. It tracks workout time, average heart rate, and times in various heart zones. Also, consider Timex's Bodylink 59571, $125. Timex uses digital rather than analog technology, claiming that it prevents you from picking up signals from other people's HRMs.

Downloadables collect heart rate information, then allow you to feed the info into to your computer via Windows-compatible software. You can track, store, and analyze your workout output—if you're into that. Over-the-top options include Outlook Express linkups and global positioning systems. Great for the serious athlete and gizmo geek. Cost: $250 and up. Polar S720i targets cyclists; it works well for triathletes and cross-trainers, $319.99–$339.99 (800-227-1314). Enhanced features include altitude and temperature. Good marks for the software and free updates; points lost for inconsistent performance.