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.

Client: Health Magazine

Date: April 18, 2008