A human heart beats about 86,000 times per day, accelerating if you drink caffeine or go for a run and slowing down if you lay down or watch TV. You probably don’t notice these fluctuations, but your fitness tracker does, collecting each tiny electrical impulse and storing it carefully on a server.

Hidden among those millions of data points, reveal scientists at the University of California, San Francisco, might be signs of a medical condition that lurks deep in the hearts of some endurance athletes. But you’re not going to find them with your fitness tracker alone.

Gregory Marcus, Ph.D., director of clinical research at the UCSF Division of Cardiology, has found that fitness trackers are a gold mine of potentially life-changing medical data — but only if you use the right tools to dig it out. Parsing through data from thousands of Fit Bit and Apple Watch users with an algorithm called DeepHeart, he has managed to spot signs of atrial fibrillation, a common and often asymptomatic heart condition that can cause the heart to go haywire.

Larry Bird, of Boston Celtics fame, famously suffered from the condition. “We’ve known that atrial fibrillation can be asymptomatic and go clinically undetected,” Marcus tells Inverse.

He is partnered with Cardiogram, a startup that applies machine learning to analyze heart rate data, making sense of the noise. “We saw smart watches as a way to screen for atrial fibrillation, but the first step is to develop algorithms so we can accurately detect it.” Bird, together with tennis legend Billie Jean King, didn’t notice until well into their careers that they had atrial fibrillation. Read more from inverse.com…

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