Movement control in springboard diving

Abstract

Many locomotor actions require controlling velocity of approach to a destination, as when a long jumper prepares for take-off, or a gymnast connects with a springboard before a vault. This thesis is about how springboard divers control their approach and take-off.

In a preliminary study, the body kinematics of five springboard divers of varying experience were monitored during diving training. Findings indicated that all but one of the divers displayed a very consistent movement pattern during the forward approach. Significant differences in the accuracy of footfall position at take-off between beginner and advanced divers were noted. As a result, the kinematics of three elite springboard divers were analysed during the forward approach, hurdle, and take-off, to test a theory of how braking and timing of actions might be conjointly controlled.

When an animal approaches a surface the ratio of its distance away at any time to its speed of approach provides a first order estimate of its time-to-contact with the surface. This ratio is termed the tau function. The tau function of x is defined as x divided by its rate of change over time (jr). In symbols: 1(x) = x/z. Controlled braking is possible by simply keeping -c(x), the rate of change of tc(x), constant. Since the visual coupling of the eyes and head to the environment is necessary to establish a perceptual frame of reference for action, the control of body movements relative to head position and the environment was appraised in the main study. In the case of the springboard diver it was hypothesised that the movement of the head would maintain a constant spatio-temporal relationship with the environment at key moments before take-off. It was revealed that all three subjects in the main study regulated their braking when approaching transition and take-off by keeping i(x), constant, thus the data support the hypothesis, and argue further for the tau function in the perceptual regulation of action.

The study of real life non-laboratory skills can provide important insights into movement control systems. In addition, research of this nature can also be of applied value to coaches and athletes alike.