The influence of co-contraction on shoulder muscle duringdynamic tracking tasks

• Main Authors: Chia-YuHsu, 許家毓
• Other Authors: Ming-I Lin
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/33405249292879653963

碩士 === 國立成功大學 === 工業與資訊管理學系碩博士班 === 101 === Musculoskeletal disorders of upper extremity is prevalent in the industrial environment, especially around shoulder regions. It is evidenced that high repetitiveness of manual exertion is one of the risk factors of musculoskeletal disorders. This study aimed to first, discuss the relationship between muscle co-contraction and the task performance during repetitive trajectory drawing task, and second, to compare the effectiveness on fatigue detection between wavelet transform and short time fourier transform. Sixteen health young subjects were recruited to perform a serious of repetitive trajectory drawing, before and after a fatigue task. Electromyography was used to monitor the muscular activity of pectoralis clavicular head (PCH), anterior deltoid (AD), middle deltoid (MD), upper trapezius (UT), serratus anteriors (SA), supraspinatus (SS), and infraspinatus (ISS) throughtout the whole experiment. EMG signals were post processing via wavelet and short time fourier transform throughout the frequency domain analysis. Six pairs of muscles co-contraction index were calculated for PCH/MD, PCH/ AD, PCH/SS, ISS/SS, ISS /AD, and ISS/PCH. To objective quantify the influence of muscle fatigue on task performance, drawing deviation rate, the average drawing time, and the average drawing speed were measured. The results of co-contraction index showed that in both directions the pairs with PCH involved are all increased after muscular fatigue. The drawing deviation rate also decreased in both directions. Result of frequency analysis of EMG data demonstrated that the slope in medial frequency from either wavelet transform or short time fourier transform all decease. The result of this study, however does not find a definite relationship between muscle co-contraction and the drawing deviation rate of repetitive movement in 3D dynamic shoulder movement. The future study should consider using needle EMG with more restricted experiment design in order to discover the unsolved mechanism.