Any athlete will tell you that training involves a lot of repetition - doing something until it's in the "muscle memory" and doesn't need to be consciously recalled.
For visually impaired athletes, though, it can be harder to train, because they can't see well enough to know what movement they are supposed to imitate. That got Benedict Copping, an engineering student at Imperial College, London, thinking: how to transmit what a coach is feeling when they demonstrate a movement. This is especially true in swimming, where getting motions precisely right can shave an extra fraction of a second from the swimmer's time.
Copping and a group of friends, Jason Cheah, Idrees Rasouli and Shruti Grover, designed the Ghost, a device that tracks the movement of the wearer's arm and allows him or her to repeat the motions precisely. It also has sensors that detect the twisting and flexing in the arm.
For example, a trainer might guide a swimmer through the motions of a stroke. The Ghost notes certain "waypoints" and stores them. When the athlete moves her arm, the Ghost will vibrate to give feedback to show whether the movement is correct. Repeating the motion helps the athlete get it right and also develop the unconscious memory.