How to Keep a Beat

by Courtesy Polar Polar's S720i can record 100 hours of data, tell you your altitude, your speed, your heart rate, and which horse is likely to place in the fifth race. Just kidding. Courtesy Polar

If you spend any time watching late-night infomercials, you're well aware the world is awash with gadgets that promise a better workout. But most of the miracle machines are not going to help your average couch potato. So
I was pleased, and a little surprised, to find one fitness gadget that actually makes a difference. The new Polar S720i raises the bar for heart monitors, particularly for athletes who like complicated workouts. Most monitors today allow you to structure your workout according to the desired results: If you want to burn fat, keep your rate on the low side; for strength, get your heart pumping faster. The Polar enhances this feature by letting you program three different target heart rates for five exercises—a feature cross trainers will appreciate. It also tracks speed and mileage, and records altitude gain and loss. You can also graph your workouts on a PC. At $319 the S720i is pricey, and during my 54-mile bike ride it took a while for the monitor to pick up my heartbeat. Getting through the dense manual is a workout in its own right, but anyone who buys this device won't mind the extra sweat.