HEAD STABILIZATION IN FORWARD TWISTING SOMERSAULTS

Abstract

In many acrobatic activities the rate of rotation is such that it is not possible to fix the gaze to determine one's orientation throughout the whole period of flight. With increasing head angular velocity the ability to use visual information deteriorates up to 350 degrees/s (Jell et al, 1982; Tomlinson et al, 1980). Stabilisation of the head at particular times during the flight allows visual information to be used during the performance of advanced skills involving rapid rotations. The purpose of this study was to investigate whether elite trampolinists stabilise the head during the performance of forward twisting somersaults. Two cine cameras operating at 100 frames per second recorded four elite trampolinists each performing five forward somersaults with one and one half twists (Rudi). Three dimensional analysis techniques were used to quantify the positions of head and trunk segments. The rate of rotation of the long axes (includes flexion/extension and lateral flexion/extension but not rotation about the long axis) of the head and trunk were compared to assess whether changes in rate of head rotation were associated with a strategy of head stabilisation or with rotation of the upper body. All subjects had two distinct periods of head stabilisation. The first occurred during the first half of flight at times which were consistent within subjects but variable among subjects. Minimum head angular velocity during this first period of stabilisation ranged from approximately 100 degrees/s to 250 degrees/s and was not significantly different from the angular velocity of the trunk. The second period of head stabilisation occurred consistently among subjects between 70% and 90% of the flight phase. Mean head angular velocity during this time ranged from 100 degrees/s to 250 degrees/s and was consistently less than the angular velocity of the trunk (p< .05). It was concluded that elite trampolinists stabilise the head to use visual information when preparing to land.