THE EFFECTS OF HAND WEIGHT AND MOVEMENT VELOCITY ON THE SCAPULAR KINEMATICS DURING ARM ELEVATION

Physical Therapy 1 – Orthopaedics. 11:00, Room 101CD,

Presentation SH01

S387

THE EFFECTS OF HAND WEIGHT AND MOVEMENT VELOCITY ON THE SCAPULAR KINEMATICS DURING ARM ELEVATION 1

Yin-Hsin Hsu, 1,2Yi-Fen Shih, 1,2Wen-Yin Chen, 3Hsiu-Chen Lin Faculty and Institute of Physical Therapy, National Yang-Ming University, Taipei, Taiwan 2 Department of Research and Education, Taipei City Hospital, Taipei, Taiwan 3 School of Physical Therapy, China Medical University, Taichung, Taiwan E-mail: [email protected] (YF. Shih)

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INTRODUCTION The movement of the scapula during upper arm activities has been a major interest in the study of shoulder biomechanics. The loading condition and the velocity of the arm movement might affect the scapular muscle control, and result in the alterations in the scapular movement [1,2]. The aim of this study was to investigate the effects of hand loading and arm elevation speed on the scapular kinematics. METHODS Seven young college students with no known shoulder pathology (21.4±1.7 y/o; BMI=22.1±2.2) were recruited for the study. Three-dimensional scapular kinematic data were measured in 4 conditions: scaption (arm elevation in the scapular plane) with and without 2 kg hand weights (W vs. NW), and 4 or 8 seconds to complete the task (4s vs. 8s).

Different combinations of the arm loading and movement speed have been used previously in studying the scapular kinematics. Some authors found no effect of the arm loading and movement speed on the scapular motion, while McQuade [1] and de Grood [2] observed the changes of the scapulohumeral rhythm in response to the phase of arm elevation, the external load, and the arm motion velocity. Our finding of the significant loading and velocity effect on the scapular motion suggested that these two factors should be carefully controlled when assessing the scapular movement.

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Figure 2: Scapular posterior tilt angles. *: significant loading effect

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RESULTS AND DISCUSSION All components of scapular movement were significantly influenced by the presence of the hand loading, whereas the speed of movement only affected the scapular posterior displacement at 30 ± humeral elevation in the lowering phase (pɦ0.05). The effect of the hand loading on the scapular rotations was more prominent during the arm-lowering phase (Figure 1. to 3.).

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The equipment used in this study was an electromagnetic tracking device (Polhemus 3 Space LIBERTYTM, Colchester, VT). The motion sensors were positioned at the spinous process of the 3rd thoracic vertebra, the distal humerus, and the flat superior bony surface of the acromion. The scapular motion data were averaged and analyzed at 30, 60, 90, and 120 degrees of humeral elevation. Two- way ANOVA with repeated measures was used to examine the effects of the load and speed of arm movement on the scapular kinematics.

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Figure 3: Scapular internal rotation angles. *: significant loading effect

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REFERENCES 1. McQuade KJ and Smidt GL. J Sports Phys Ther, 27, 125-33, 1998. 2. de Groot JH, et al. Clin Biomech, 13, 593-602, 1998.

Figure 1: Scapular upward rotation angles. *: significant loading effect XXI ISB Congress, Podium Sessions, Wednesday 4 July 2007

Journal of Biomechanics 40(S2)