Marcel Dinkins, CSCS, personal trainer and Peloton fitness instructor in NYC, tells SELF that Whoop has helped her “learn to properly stagger workouts, to take advantage of scheduling naps, and really prioritize proper recovery in between sessions so I can continue to go hard when it’s time to train.” Another cool fitness feature is Whoop Live: You can overlay your Whoop data onto a photo or video, which is a fun way to share your workouts with friends, on social media, or just to keep a visual log of your routines. That number helps her decide how vigorously to exercise each day-or when to rest instead. The tracker calls this metric Strain Coach, which takes into account heart rate variability (HRV), resting heart rate (RHR), and hours of sleep. Strength coach Ava Fagin, CSCS, director of sports performance at Cleveland State University, wears hers 24/7 to keep tabs on her sleep and recovery score. A number of top athletes like Michael Phelps and LeBron James use Whoop, a tracker that focuses on an oft-forgotten part of training: recovery.