Variability and control in springboard diving

Elite springboard divers typically make very precise and reproducible movements when they perform the same dive many times. However, variability is always present in both technique and outcome. While it is desirable to have low outcome variability this may necessitate real-time adjustments which result in increased technique variability from trial to trial. The aim of the present research was to determine whether feedback control adjustment is used during (a) the hurdle takeoff, (b) the dive takeoff, and (c) the dive flight phase. 15 forward pike dives and 15 forward 2½ somersault pike dives, performed by an international diver, were video recorded at 250 Hz and manually digitised followed by DLT reconstruction of joint centre locations. Orientation angle and joint angles were calculated and fitted with quintic splines to give angular velocities. Foot placements, mass centre location and velocity were determined along with angular momentum about the mass centre. In the hurdle takeoff no adjustment was made to reduce the variability in the foot location at hurdle landing. In the dive takeoff phase an angle-driven simulation model was used to determine the expected variation in mass centre velocity and angular momentum at the instant of takeoff arising from the variation in velocity and angular momentum at touchdown. The simulated variation at the instant of takeoff was greater than the variation in the recorded performances indicating that some adjustment had been made during the takeoff phase. In the flight phase an angle-driven simulation model was used to determine the expected variation in orientation angle at water entry arising from the variation in velocity and angular momentum at takeoff. The variation in the orientation angle at entry obtained from the simulations was greater than the variability in the actual performances, indicating that the diver had used feedback control adjustments in the flight phase to reduce his performance outcome variability. The variation in the angular momentum at takeoff was reflected in the average hip angle in flight, indicating that the hip angle was adjusted to be larger to compensate when the initial angular momentum was greater. The use of feedback control adjustments found in this study demonstrated that variability has a functional role in human movement.