Study On Biomechanics Characteristic Of Spine Under Forestry Works Using Chain Saws Based On Ergonomics

The forest work condition is very terrible in China at present.Apart from necessary operation,the operator also needs to bear the impacts of standing or bending for a long time, carrying heavy tools and vibration and noise of machines.All these impacts will decrease the comfort and efficiency of the operator and affect his physical and mental health.Many workers were compelled to quit their jobs because of lumbar back pain,which suffered serious economic expense and loss of labor ability due to lumbar trauma.Consequently,it is necessary to reduce social burdens due to spine trauma.And accurate and credible measurement tools and research of theoretical methodology can make us understand biomechanical characteristic of spine better.Furthermore,we can adopt effectual measures to prevent and decrease the spine trauma related to forestry work,it is one of important studies for the experts in home and abroad.Thus it is most realistic significant to carry out labor burdens and human body biomechanics based on ergonomics.The paper discussed and analyzed the trunk muscles activities and functions from angle of view of surface electromyography and three-dimensional photogrammetry by applying external synchronization technology for the first time,and established the biomechanical models under different forestry work postures using the chain saws by statics theory,the three-dimensional digital model of spine were established based on finite element method.The thesis studied the biomechanical characteristic under different operating postures using chain saws,the lumbar as object.The results were showed as following:The work intensity of trunk muscles activities was different in forestry work conditions; work intensity of Erector spinae were the maximum,approaching over 30%Maximum Voluntary Contraction(MVC),and EMG amplitudes of Rectus abdominis and Oblique external abdominis were 10%MVC.Under different forestry work conditions,the EMG amplitudes of Erector spinae were not at the same level in the process of forestry operating,although the average intensity of Erector spinae was probably identical under different forestry work conditions,the EMG amplitudes of Erector spinae distribute in different ranges of MVE%,and the duration spent in the certain ranges of MVE%is not same in the process of entire operating.The thesis analyzed the influence of terrains and chain saws on the trunk muscles.The results showed that the terrains only influenced the Erector spinae amplitudes(p＜0.05),while it makes no sense to study the the influence of terrains on other muscles amplitudes.The influence of chain saws on the Erector spinae was very significant(p＜0.01),and influence on the right Rectus abdominis and right Oblique external abdominis(p＜0.05).The thesis analyzed limbing,bucking and cutting operation by using chain saw type G621AVS.The results show that difference of the EMG activities among trunk muscles were distinct(p＜0.01),while Oblique external abdominis amplitudes(p＜0.05).These facts indicated that different forestry work postures were the primary influence on EMG activities among trunk muscles.The three-dimensional motion photogrammetry system was used in forestry work for the first time,photography principle of stable location of vidicon is adopted,and the motion ranges of joint angle for the trunk and upper limbs were defined under different forestry work postures, which provided theoretical reference to correct the forestry operating postures.The biomechanical models of lumbar spine under different forestry operating postures were established and calculated the solutions by statics principle,in order to study the biomechanical character of lumbar spine.The results showed that the gravity moment of lumbar spine,power of Erector spinae and compressive stress on the vertebral body and intervertebral disc were as follows in increasing sequence,limbing(G621AVS),cutting(GJ85), cutting(G621AVS),bucking(G621AVS),lifting chain saw(G621AVS and GJ85).The three-dimensional,comprehensive and realistic finite element model of whole spine that incorporated the geometric,material and contact non-linearities was established through using the datum of DICOM based on opinion of "assembled construction".The finite element theory and forestry work postures were combined together,and features of stress of lumbar spine under different forestry work postures were computed by taking advantage of the results of anthropometry,kinematics and statics.The results are as follows:Equivalent stress on the vertebral body and intervertebral disc had a trend of gradual increase from bottom to top under the same forestry work condition.The maximum tress on the same lumbar functional unit under different forestry work conditions were showed from low to high:limbing(G621AVS), cutting(G621AVS),bucking(G621AVS),cutting(GJ85),lifting chain saw of type G621AVS and GJ85.The research can provide theoretical reference to ascertain work intensities of Erector spinae for forestry worker under different forestry work conditions,which has important theoretical value to quantificationally study loads and labor intensities of the lumbar muscles for the forestry workers under different forestry work conditions,to prevent and decrease the lumbar traumas,to provide laboring safety and protection,to diagnose and correct unreasonable operating postures,to train the labor skills,to design and improve forest operating tools,to prevent and treat the occupational diseases.