For the better part of a decade, Whoop sold itself as a secret weapon for serious athletes. LeBron James was convinced to slap on the company’s fitness band in Whoop’s first year. Michael Phelps came soon after. Other Whoop wearers include Cristiano Ronaldo, Patrick Mahomes, and Rory McIlroy. The message to the public? The world’s best performers track their bodies with this device, and you can, too. It worked. Whoop, the Boston-based health wearable company that Will Ahmed founded in his senior year at Harvard, now operates in more than 200 countries, and, according to Ahmed, grew revenue more than 100% last year, as well as reached cash-flow positive. The hardware — a band worn around the wrist, bicep, or torso — measures sleep, recovery, heart rate variability, and a growing list of biomarkers.…