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 (Nissinen, 1983) and forces of this magnitude have been associated with an increased risk of injury to gymnasts' shoulders (Carraffa et al., 1996). 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 differences between the actual performance of the longswing and the evaluated simulation for cable tension and orientations of the gymnast and rings cables were 6.2%, 1.0% and 1.9% respectively. During the evaluated 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 net shoulder forces. 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 lateral arm movements, which form part of the gymnast's technique, also resulted in an increased peak shoulder force (0.73 bodyweights). Removing the elasticity of the apparatus and gymnast in turn resulted in smaller increases in peak shoulder force (0.62 and 0.53 bodyweights). When both aspects of technique were altered the increase in peak shoulder force was 2.5 times greater than when both components of elasticity were removed. Although the elasticity of the gymnast and apparatus contribute to minimising peak shoulder forces, this study shows that the contribution of a gymnast's technique is considerably greater.

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Numerous planar analyses of sports activities have utilized scaling techniques to convert image coordinates into real-space locations. While in certain circumstances, such as competition, the camera must be elevated above the activity and its tilt accounted for, the influence of tilt on reconstruction accuracy using scaling is currently unreported. A modification of the direct linear transformation (2D-DLT) which considers only the vertical plane provides an alternative approach for planar reconstruction. This study compared the reconstruction accuracy between scaling and 2D-DLT over a range of tilt angles throughout a 6-m horizontal field of view. Four calibration and 30 reconstruction markers of known locations in a vertical plane were videotaped from nine positions to provide tilt angles varying between –2° and +6°. Both techniques were used to estimate real-space locations for the reconstruction markers, and accuracy was calculated by comparing known and reconstructed locations. The smallest reconstruction errors were obtained using 2D-DLT and were unaffected by camera tilt. The scaling technique produced significantly larger (p < 0.01) errors than 2D-DLT, with the exception of 0° and +1° of tilt, and there was a detrimental effect on accuracy as the magnitude of tilt increased. The largest variations in reconstruction errors were associated with scaling, with markers at the extremes of the image showing the largest errors. The 2D-DLT approach provided accurate reconstruction data for planar analyses across the field of view and throughout the range of tilt angles, and should be preferred over scaling techniques.

The impact loads experienced in landing may be influenced by the joint kinematic strategy used. This study aimed to enhance the understanding of the sensitivity of impact loading to the timing of joint kinematic strategies in simulated forefoot landings. Coordinate and force data of drop landings were used to initiate, drive, and evaluate a wobbling mass model. Ankle, knee, and hip joint angle profile timings were modified in the simulated motions. Changes to the timing of the ankle and knee joint angle profiles were associated with substantial changes in the peak vertical ground reaction force (GFzmax) of up to 3.9 body-weights (BW) and 1.5 BW, respectively, whereas loading was less sensitive to temporal changes in the hip joint strategy. Accentuated impact loads incurred by a modified knee flexion action may be explained by the need to maintain an ordered and controlled load attenuation strategy. Individual strategies and external and joint reaction forces should be considered for developing insight into loading in impact landings.