Metronomes help pianists regulate their rhythm and keystrokes, so why not swimmers? The new ear-size Tempo Trainer Pro, which slips under your swim cap and transmits a preset tempo to help you with pacing, does exactly that.

Created by Finis, a California swimming-tools company, the Tempo Trainer Pro is geared toward professionals and serious amateurs — fans include open-water champion Alexander Studzinski and pro triathletes Brendan Sexton and Kristi Johnson — but the device can help anyone who wants to improve in the pool. The concept is simple: Swimmers adjust the waterproof device to beep at preset tempos to 1/100th of a second and work to coordinate their stroke length and count accordingly. 

“The most reliable way to swim faster is not by training limbs, lungs, or muscles with more yards or harder repeats, but by treating speed as a math problem,” says Terry Laughlin, a swim coach who uses the Tempo Trainer Pro in his swim clinics. It helps “build a long, relaxed stroke, and helps ‘hardwire’ your brain to maintain that efficiency as you increase stroke rate or tempo.”   

The Tempo Trainer Pro works to correct the problem that swimmers typically encounter when they try to increase their stroke rate: They tend to lose stroke length. The theory of the Tempo Trainer Pro is that swimmers can find their baseline speed, then work to increase stroke length, training specifically to maintain a lower stroke count at moderate and higher tempos. (It also helps to have coaching and video to improve the process.) 

The device has caught on with Olympic marathon swimmers and pro triathletes, but applications don’t stop at swimming, says Vicki Taylor, Finis’s marketing communications manager. “The Tempo Trainer Pro can also be used for keeping a consistent running and cycling cadence and any sport where you need to work on a timer or beep.” 

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