As NBA players land, about two thirds of them “yield” to the floor, in P3’s lingo. That means their ankles, knees, and hips bend in concert to accept the force of the floor. The other third of players bend their ankles and knees, but leave the hips out of the party. Elliott says that in the data, it looks like they are trying to land with their ankles and knees, but that with their hips they are trying to jump. Those “non-yielders,” Elliott reported in video of his talk to Mass General, are 250 percent more likely to have back trouble. “If you have an athlete that has back issues,” he told his audience of doctors, “it might not be that his core is too weak. It might be because the way he lands is creating too much anterior shear in his lumbar spine and he needs to be retrained.”