Minimising peak forces at the shoulders during backward longswings on rings

Abstract

Many elite gymnasts perform the straight arm backward longswing on rings during their competition routines in order to satisfy specific judging requirements. Measured peak combined cable tension during a backward longswing is typically in excess of 9 bodyweights and forces of this magnitude have been associated with an increased risk of injury to gymnasts' shoulders. This study investigated the contribution of longswing technique and the elasticity of the gymnast and rings apparatus to minimising loading at the shoulders. A three-dimensional video and cable tension analysis was conducted on a backward longswing performed by an elite gymnast. This analysis provided information regarding the motion of the rings cables, the gymnast's technique and the elasticity of the rings apparatus. A three-dimensional five-segment computer simulation model of a gymnast swinging on rings was developed. The inertial characteristics for the model were determined from anthropometric measurements of the gymnast and measurements taken directly from the rings apparatus. The simulation model was evaluated by comparing the backward longswing from the data collection with a simulation of the same performance. The root mean squared (rms) differences between the actual performance of the longswing and the simulation for cable tension, orientations of the gymnast and rings cables and the wrist to ankle length of the gymnast were 297 N, 3.3°, 1.1° and 0.06 m, respectively. During the simulated longswing the peak combined force at the shoulders was 8.5 bodyweights. Modifications to the evaluated simulation of the longswing were used to determine the effect of the gymnast's technique, his elasticity and that of the rings apparatus on peak shoulder force. Altering the gymnast's technique, by fixing the gymnast in a straight body configuration throughout the swing, increased the peak shoulder force by 2.56 bodyweights. Removing only the lateral arm movements, which form part of the gymnast's technique, also resulted in an increased peak shoulder force (0.73 bodyweights). Removing only the elasticity of the apparatus or gymnast from the evaluated simulation resulted in smaller increases in peak shoulder force (0.62 bodyweights and 0.53 bodyweights). Although the elasticity of the gymnast and apparatus contribute to minimising peak shoulder force, this study shows that the contribution of a gymnast's technique is considerably greater.