Maximize your workout with a HRM
Do you workout religiously without feeling any fitter? Maybe you're training too hard—or not hard enough. Our bodies build endurance and speed at specific exertion levels, which are measured by our heart rate. Strapping on a heart rate monitor can keep you within the correct level of exertion 100 percent of the time so that you don't end up wasting your energy going nowhere on your goal.

"Athletes should train specifically in their aerobic and anaerobic zones," says Jordan D. Metzl, M.D., assistant attending physician in the division of sports medicine at the New York City Hospital for Special Surgery. "Going beyond those ranges fatigues muscles, but doesn't burn fat effectively or build endurance." If you're trying to burn fat, keep your heart rate under 70 percent of your Maximum Heart Rate (MHR). To find your MHR, subtract your age from 220. This will tell you how many beats per minute your heart can pump during hard exercise. If you're 30 years old, for example, your MHR is 190 beats per minute, so for maximum fat burning your heart rate should be under 133 beats per minute.

The aerobic zone—70 to 80 percent of MHR—is just right for building endurance, and you should be able to maintain this effort for long periods of time—even hours. The anaerobic zone—80 to 89 percent of MHR—builds muscle and speed but can only be managed for minutes at a time. Consequently, the bulk of a workout should be in the aerobic zone.

Working out in your anaerobic zone will help raise your "anaerobic threshold"—the point at which the oxygen supply to your muscles starts to dwindle and lactic acid begins to build up. A higher anaerobic threshold allows you to run or bike harder and faster without hitting the wall caused by excess lactic acid buildup. (For more info on raising your anaerobic threshold, read "How to raise your anaerobic threshold and get more mileage from your muscles.")

Staying within a specific zone—be it fat-burning, aerobic, or anaerobic—is a snap with a heart rate monitor. Just plug in your bpms, and the monitor will signal when you've strayed off the mark. It's the perfect training partner so take the pulse of the latest heart rate monitors:

Polar M52 "M" is for motivation. This nifty gray-faced monitor is packed with cardiovascular goodies. It tests fitness, prescribes training zones, and determines calories burned per workout. It even begs you to use it, beeping if it's ignored for three days. The thin band is great for a small wrist and the ergonometrically crafted sensor strap is comfortable enough for everyday wear. Suggested retail price: $170.

Freestyle Circuit Seven is tough enough to withstand being crushed against rocks and other outdoor hazards. Big buttons make setting heart rate zones a snap, even with gloves on. The woven-nylon wristband is bomber, but doesn't have enough eyelets to fit a small wrist. Large numbers are easily seen from a bicycle handlebar, and the rubber mount is included. Suggested retail price: $200.

Schwinn HRM-II Schwinn has wheeled out a bike-friendly heart rate monitor. Big numbers, simple display, and a bright light make heart rate training a breeze. The touch of a button reveals average heart rate and time of day. The Velcro band stays secure. It can be worn on your wrist or bike (handlebar mount included). Suggested retail price: $150.