Background Work-related musculoskeletal disorders （WMSDs） have high prevalence in sewing machine operators employed in the garment industry. Long work duration, sustained low level work and precise hand work are the...Background Work-related musculoskeletal disorders （WMSDs） have high prevalence in sewing machine operators employed in the garment industry. Long work duration, sustained low level work and precise hand work are the main risk factors of neck-shoulder disorders for sewing machine operators. Surface electromyogram （sEMG） offers a valuable tool to determine muscle activity （internal exposure） and quantify muscular load （external exposure）. During sustained and/or repetitive muscle contractions, typical changes of muscle fatigue in sEMG, as an increase in amplitude or a decrease as a shift in spectrum towards lower frequencies, can be observed. In this paper, we measured and quantified the muscle load and muscular activity patterns of neck-shoulder muscles in female sewing machine operators during sustained sewing machine operating tasks using sEMG. Methods A total of 18 healthy women sewing machine operators volunteered to participate in this study. Before their daily sewing machine operating task, we measured the maximal voluntary contractions （MVC） and 20%MVC of bilateral cervical erector spinae （CES） and upper trapezius （UT） respectively, then the sEMG signals of bilateral UT and CES were monitored and recorded continuously during 200 minutes of sustained sewing machine operating simultaneously which equals to 20 time windows with 10 minutes as one time window. After 200 minutes＇ work, we retest 20%MVC of four neck-shoulder muscles and recorded the sEMG signals. Linear analysis, including amplitude probability distribution frequency （APDF）, amplitude analysis parameters such as roof mean square （RMS） and spectrum analysis parameter as median frequency （MF）, were used to calculate and indicate muscle load and muscular activity of bilateral CES and UT. Results During 200 minutes of sewing machine operating, the median load for the left cervical erector spinae （LCES）, right cervical erector spinae （RCES）, left upper trapezius （LUT） and right upper trapezius （RU展开更多
A rat model of extra-vertebral foramen cervical nerve entrapment was established according to the following parameters： stimulation intensity 20 V; frequency 50 Hz; pulse width 200 μs; duration 333 ms/s for a total ...A rat model of extra-vertebral foramen cervical nerve entrapment was established according to the following parameters： stimulation intensity 20 V; frequency 50 Hz; pulse width 200 μs; duration 333 ms/s for a total of 8 hours. After the electrical stimulation, rats exhibited mild muscle fiber atrophy, mild inflammatory exudates, connective tissue local fibrosis and chondrocyte metaplasia. Mean muscle fiber cross-sectional area was reduced. The nerve myelin sheath continuity was partially demyelinated. The microstructure of nerve cells was disrupted and these symptoms worsened with prolongation of the stimulation. The shoulder, neck and upper extremity muscles on the tested side demonstrated positive sharp waves and fibrillations. The severity increased with continuation of the stimulation. High amplitude and polyphasic motor unit potentials gradually appeared. Similar findings were seen in the contralateral side, but at a less severe level.展开更多
文摘Background Work-related musculoskeletal disorders （WMSDs） have high prevalence in sewing machine operators employed in the garment industry. Long work duration, sustained low level work and precise hand work are the main risk factors of neck-shoulder disorders for sewing machine operators. Surface electromyogram （sEMG） offers a valuable tool to determine muscle activity （internal exposure） and quantify muscular load （external exposure）. During sustained and/or repetitive muscle contractions, typical changes of muscle fatigue in sEMG, as an increase in amplitude or a decrease as a shift in spectrum towards lower frequencies, can be observed. In this paper, we measured and quantified the muscle load and muscular activity patterns of neck-shoulder muscles in female sewing machine operators during sustained sewing machine operating tasks using sEMG. Methods A total of 18 healthy women sewing machine operators volunteered to participate in this study. Before their daily sewing machine operating task, we measured the maximal voluntary contractions （MVC） and 20%MVC of bilateral cervical erector spinae （CES） and upper trapezius （UT） respectively, then the sEMG signals of bilateral UT and CES were monitored and recorded continuously during 200 minutes of sustained sewing machine operating simultaneously which equals to 20 time windows with 10 minutes as one time window. After 200 minutes＇ work, we retest 20%MVC of four neck-shoulder muscles and recorded the sEMG signals. Linear analysis, including amplitude probability distribution frequency （APDF）, amplitude analysis parameters such as roof mean square （RMS） and spectrum analysis parameter as median frequency （MF）, were used to calculate and indicate muscle load and muscular activity of bilateral CES and UT. Results During 200 minutes of sewing machine operating, the median load for the left cervical erector spinae （LCES）, right cervical erector spinae （RCES）, left upper trapezius （LUT） and right upper trapezius （RU
基金the National Natural Science Foundation of China,No. 81171707the Major State Basic Research Program of China,No.2012CB933600+2 种基金Shanghai Pujiang Program,No.11PJD016China Postdoctoral Science Foundation,No. 20090460629Fund for Key Disciplines of Shanghai Municipal Education Commission,No.J50206
文摘A rat model of extra-vertebral foramen cervical nerve entrapment was established according to the following parameters： stimulation intensity 20 V; frequency 50 Hz; pulse width 200 μs; duration 333 ms/s for a total of 8 hours. After the electrical stimulation, rats exhibited mild muscle fiber atrophy, mild inflammatory exudates, connective tissue local fibrosis and chondrocyte metaplasia. Mean muscle fiber cross-sectional area was reduced. The nerve myelin sheath continuity was partially demyelinated. The microstructure of nerve cells was disrupted and these symptoms worsened with prolongation of the stimulation. The shoulder, neck and upper extremity muscles on the tested side demonstrated positive sharp waves and fibrillations. The severity increased with continuation of the stimulation. High amplitude and polyphasic motor unit potentials gradually appeared. Similar findings were seen in the contralateral side, but at a less severe level.
