Shoulder kinetics of pole vaulters during pole bending:

focus on relationships with isokinetic shoulder strength

Abstract

　The purpose of this study was to investigate the relationships between the shoulder kinetics of pole vaulters during pole bending and the isokinetic strength of the shoulder, and to clarify the characteristics of the shoulder kinetics. Three-dimensional coordinates of vaulters' body landmarks were recorded using a motioncapture system. The box reaction force was measured using a force plate placed under the planting box. The joint force and joint torque acting on a hypothetical shoulder joint were estimated using inverse dynamics calculations for a synthetic upper limb segment, assuming both upper limbs to be a single segment. The pole bending phase was divided into 3 sub-phases, “take-off,” “drive,” and “swing,” in order to determine the unique characteristics of shoulder kinetics during vaulting. Isokinetic tests were conducted to measure shoulder strength.
The main findings were as follows:
1) The impulse of the box reaction force of the Y-component (F_Y) in the pole bending phase showed a significant negative correlation with the elastic energy in the pole at maximum pole bending (r=-0.56, p<0.05).
2) The impulse of F_Y increased during the pole-bending phase, approximately 45% of this increase occurring during the drive phase and 48% during the swing phase.
3) The angular impulse of the torque of the hypothetical shoulder joint in the drive phase showed a significant positive correlation with the impulse of F_Y in the same phase (r=0.67; p<0.01). In contrast, the impulse of F_Y showed a significant positive correlation with the impulse of the joint force of the Y component in all subphases (take-off phase r=0.88, p<0.01; drive phase r=0.99, p<0.01; swing phase r=0.96, p<0.01).
4) The maximum extension torque of the hypothetical shoulder joint in the pole-bending phase was not significantly correlated with the maximum isokinetic concentric extension strength, maximum isokinetic eccentric extension strength, or maximum isokinetic internal and external rotation strength of the shoulder joint.
　These results indicate that exertion of the joint force and joint torque of the shoulder during vaulting contributes to pole bending. However, the magnitude of the shoulder joint extension torque during vaulting was not related to the isokinetic strength of the shoulder joint.