The bicep sensor tracks the position and orientation of your upper arm, and infers your shoulder movements. By default, this sensor provides feedback if your shot is too flat. In addition, it shows if you have a hitch in your shot or "catapult" the ball.
Forearm Sensor (2/3)
The forearm sensor, along with the bicep sensor, precisely models your elbow by tracking the position and orientation of your forearm relative to your bicep. By default, this sensor provides feedback if your elbow is too far out. It also shows if your elbow is too flexed or too extended at various phases of your shot.
Hand Sensor (1/3)
The hand sensor works together with the forearm sensor to model your wrist. By default, the hand sensor provides feedback on your wrist snap, and also indicates if you are pushing the ball with your thumb or pinky at release. In addition, it shows if you're too slow at getting shots off.