Nick Watney began Friday, June 19, the same way that he begins almost every day: He checked his phone to see how he’d slept the night before.
The 39-year-old professional golfer had been wearing a fitness tracker on his wrist for almost a year. (He’d chosen a device called the Whoop after he heard about it from PGA Tour mate Rory McIlroy.) Watney used the data to discern patterns about his game: What time did he need to go to bed to play his best? How would his quality of sleep differ if he ate dinner earlier? But on June 19—the day after he’d finished Round 1 of the RBC Heritage tournament in Hilton Head—the device offered him some more alarming information.