Heart-Rate Monitor

Garmin's Fenix 3 watch calculates a user's VO2 max number and other stats when paired with a heart-rate monitor. (Garmin)

A device that measures a wearer’s heart rate; particularly useful for monitoring exertion in athletes. Finnish professor and nordic skier Seppo Säynäjäkangas invented the first wearable wireless monitor, the Polar Sport Tester PE2000. It debuted in 1982 and was made up of two pieces: a simplified EKG- and radio-equipped strap worn around the chest, and a wristwatch that received the data and displayed an athlete’s pulse in real time.

The PE2000 is credited with giving rise to high-intensity interval training—and launching decades of R&D to find some alternative to eliminate the dreaded chafing that comes from wearing the strap (a.k.a. the “man bra”). The most promising solution, the optical heart-rate sensors embedded in watches from Apple, Garmin, and others, uses LED lights to illuminate blood vessels and a sensor to detect the volume of blood flow. To date, these devices have proven far less accurate than Säynäjäkangas’s original, though many offer users the ability to unobtrusively gather heart-rate data around the clock.

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