Last season, James’ longtime trainer and Cavs staffer Mike Mancias supplied Cavs players with a biometric tracking device called a WHOOP, and many began wearing them. How much sleep were they actually getting? How quickly did they fall asleep? How did LeBron’s heart rate change when he was flying all over the country and losing sleep? What about time zones? The idea is that devices like the WHOOP will, in time, come to function like the sensors that tell Formula One racers when it’s time for a pit stop.