The monitor straps comfortably to thighs, calves, biceps, or even your lower back. It weighs less than a wristwatch and hides under clothing. Data streams to a phone or sports watch by Bluetooth or ANT+, so you can glance at the figure the same way you might peek at pace. There are no needles, no wires, and no radiation—only light, a strap, and accurate feedback. Understanding this simple science is the first step toward training smarter, recovering faster, and staying ahead of injury.