Trunk Muscle SEMG Activity Pattern Under Different Physical Activity

Introduction:Trunk muscles contain back muscles, abdominal muscles and pelvisacrum muscles which participate in the trunk movement and maintaining the stability of spine. They play an important role in daily life, work, study and labor process. Studies show that trunk muscles are both the power source of turnk movent and the stabilizer which maintain the basic elements of the trunk and spine stability especially the deep back muscles and abdominal muscles. Trunk muscles control disorders, reduction of muscle strength and endurance not only affect the trunk muscles, the body’s overall work capacity and work efficiency, but also have closely relation with spinal diseases ingcluding chronic back pain. Recnet years, with the change of human working patterns, many ergonomics, physiology and labor hygieneresearch studies investigate trunk motor control mechanisms, trunk muscle activity patterns, optimization of human physical operating position.Objective:Using surface electromyography to investigate the characteristics of muscle activity in different turnk movements and provide a theoretical basis for the prevention of injury and improvement of operational performance. Through investigating the muscle activity in voluntary movement, involuntary movement and modeling movement to study the main control mechanism of the trunk, including the subconscious sexual feedforward control, fast feedback control, the mode of motion control and voluntary movement control.Methods:To study the muscle activity characteristics in voluntary movement, asking subjects to do trunk flexion, extension, left flexion, right flexion and axial rotation. Trunk muscle activity characteristic in unbalance situation consists of two parts of study:the influence of exercise-induced fatigue and psychological expectations on trunk muscle action; the influence of psychological expectations and eyes on the activity of the lumbar and leg muscles. Trunk muscle activity during walking is to observe the influence of walking speed and the weight of the extra load on the activity of walking relatied muscles and trunk stability muscle. Comparing the muscle activity under four kinds of lift posture and different load to study the infuleucne of lift posture on muscle activity. Prolonged bed rest study consists of four parts:change of lumbar muscle MVC changes; change of lumbar muscle fatigue resistance; change of lower back muscle reaction time; change of lumbar muscle in flex-relax experiment.Results:(1) Druing flexion multifidus and transversus abdominis activity increase significantly in load while weight is more than20%weight. External oblique muscle activity increases with the load increased significantly during extension. In lateral bending, the multifidus muscle and the erector spinae activity do not exist the unilateral effect. External oblique muscle shows contralateral enhancement effect, suggesting that the muscles play the role of the stabilizing muscles during lateral bending. Multifidus muscle activity and external oblique muscle activity does not exist unilateral effect in the trunk rotation, and the erector spinae muscle activity enhance ipsilateraly with the load increases.(2) Walking speed has significant affect on the waist and legs muscle activity.(3) Psychological expectations do not affect the waist and abdomen muscles in sudden imbalance, the exercise fatigue make the quick response time of ipsilateral multifidus and ipsilateral erector spinae longer, the order of fast response time from short to long is:transversus abdominis<multifidus <erector spinae.(4) Open eyes or close eyes does not affect fast response time and rapid response of the waist and legs muscles during sudden imbalance, fast response time of ipsilateral tibialis anterior muscle is longer when subjects have expection. Tibialis anterior muscle activity has contralateral enhancement effect, the activity of gastrocnemius muscle exists ipsilateral enhancement effect.(5)The activity of rectus abdominis is not affect by lifting position and the weight of lift while multifidus and erector spinae activity increase with the weight of lift. The right side of the multifidus muscle and right erector spinae are affect by lifting posture, knees-bent lifting posture utilize small muscle activity. Prolonged bed rest can cause the disappearance of flex-relax phenomenon. It can significantly induce MVC of multifidus muscle and erector by36%and47%and decline rate of MPF increase by64%and56%.(6) Prolonged bed rest can increase rapid response time of multifidus and erector spinae by21%and25%. Conclusion:(1) In the voluntary movement, lumbar multifidus muscle increase trunk stability through bilateral contraction, and transversus abdominis increase trunk stability through intra-abdominal pressure, but its contribution is less than the multifidus muscle.(2) There are difference between trunk muscle activity and leg muscle activity while walking speed changes, leg muscle activity increase significantly.(3) Trunk stability muscles activity are earlier than turnk movement muscles during sudden imbalance.(4) Expection does not affect the waist and abdominal muscles quick response time and rapid response in sudden imbalance, only affects the fast response time of ipsilateral tibialis anterior muscle.(5)Exercise fatigue makes the rapid response time of ipsilateral multifidus muscle and the ipsilateral erector spinae longer.(6) Knees-bent lifting need less use of the muscle activity, it is recommended while lifting and the weight of lift should not exceed60%of their body weight (7) Prolonged bed rest can cause the disappearance of flex-relax phenomenon. It can significantly induce MVC of multifidus muscle and erector, and increase the decline rate of MPF. Prolonged bed rest can also increase rapid response time of multifidus and erector spinae.