chapter
Controlling Hand Velocity in Spiking a Ball
Pages 5

Successfully performing a spiking or smashing action, such as found in (table) tennis, badminton, squash, or volleyball, requires that the end-effector (hand, racquet) meets the ball while travelling (a) at a high velocity, and (b) in a particular direction. The latter requirement follows from the necessity to control the direction of ball flight after contact. Scatter in the direction of movement of the effector at the moment of contact can be relatively easily minimized if the rate of change of the direction of movement of the effector is kept to a minimum during the movement. However, such a strategy, which is often seen in novice players who tend to "push" rather than to "hit" a ball, is at odds with the first requirement mentioned, because arriving at the point of contact with a high velocity requires the use of a swinging motion. A large rate of change in the direction of movement of the effector at the moment of ball contact necessarily implies a small time window during which the effector is travelling in the desired direction. For a given rate of change of direction, a better timj,ng accuracy is indicated by a smaller degree of scatter in the direction at the moment of contact. For a given degree of scatter in the direction of movement at the moment of contact, a better timing accuracy is required for a larger rate of change. Hence, the timing accuracy at the moment of contact can be obtained by calculating, over repeated trials, the ratio of the standard deviation of the direction of movement of the effector at the moment of contact over its mean rate of change.