Article Title



Kiara Barrett, Hunter J. Bennett. Old Dominion University, Norfolk, VA.

BACKGROUND: The ideal rotation sequence for the definition of shoulder kinematics has been disputed in the literature. The ISB recommends the ZYZ rotation sequence, while recent literature supports the application of an individualized sequence based on the primary movements within the task. However, only a limited set of movements have been previously analyzed: single-planar/clinical tasks, tennis serves, and baseball pitching. Despite the popularity of volleyball in people of all ages, research regarding shoulder kinematics in the volleyball attack is sparse. Furthermore, an ideal rotation sequence to describe this movement has not been reported. Therefore, the purpose of this study was to assess the efficacy of three rotation sequences in describing the motion of the humerus relative to the thorax when performing an overhead volleyball attack. METHODS: Ten experienced volleyball players (women=6, mean 10.7±3.74 years of experience) performed five overhead attacks aimed straight ahead. A 12-camera motion capture system recorded reflective markers placed on the humerus and upper trunk. Shoulder angles were calculated in Visual3D software using the most implemented rotation sequences: XYZ (Lateral-Anterior-Superior), ZYZ, and YXZ. Angles were assessed beginning at ‘takeoff’ (when the participant left the ground) and ended at the completion of the follow through. Angle coherence (agreement) with known flexion/extension (X: 210 deg), abduction (Y: 230 deg), and rotation (Z: 190 deg) ranges of motion was evaluated for each sequence. In addition, instances of gimbal lock were calculated and recorded. RESULTS: The XYZ rotation sequence was the only method with no instance of GL in any participant. Four participants presented with gimbal lock using the ZYZ rotation sequence. Gimbal lock occurred in all participants using the YXZ sequence. For angle amplitude coherence, each sequence exceeded the limit for one rotation: Z” for one subject using ZYZ, X for two subjects using XYZ, and Z for one subject using YXZ. CONCLUSION: In agreement with previous research, we found that the ISB recommendation was not the best-fit sequence for 3D kinematics. We recommend using the XYZ sequence to characterize shoulder kinematics in volleyball attacks as XYZ is the most relevant (widespread in lower extremity biomechanics), anatomically valid, and least affected with gimbal lock.

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