Shin Gwanseob, D'Souza Clive, Liu Yu-Hsun
Department of Industrial and Systems Engineering, University at Buffalo, State University of New York, Buffalo, NY 14260, USA.
Spine (Phila Pa 1976). 2009 Aug 1;34(17):1873-8. doi: 10.1097/BRS.0b013e3181aa6a55.
In vivo measurements of low back flexion posture and muscle activity before, during, and after static flexion.
To identify the occurrence of creep and muscle fatigue development in the low back during static upper body deep flexion that resembled an above ground work posture.
Static lumbar flexion has been related to the development of low back disorders, and its injury mechanism has been focused on the changes in passive spinal tissues. Potential influences of muscle fatigue of extensor muscles have not been explored.
A total of 20 asymptomatic subjects performed submaximal isometric trunk extension exertions and an isokinetic trunk flexion before and immediately after 5-minute static flexion while the trunk sagittal flexion angle and the myoelectric activities (electromyography [EMG]) of back extensor muscles were recorded simultaneously. Changes in the flexion-relaxation onset angle, maximum flexion angle, muscle activity level, and the median power frequency of EMG associated with the static flexion were evaluated.
Flexion-relaxation onset angle in isokinetic flexion and EMG amplitude of isometric extension were significantly greater after static flexion, indicating creep of spinal tissues in static flexion. Median power frequency of lumbar erector spinae EMG during isometric extension was significantly lower after static flexion, suggesting the development of muscle fatigue. Consistent but low level of EMG was observed together with sporadic muscle spasms during the static flexion period.
Fatigue of low back extensor muscles may occur in static flexion due to prolonged passive stretching of the muscles. Low back extensor muscles are required to generate more active forces in weight holding or lifting after static flexion to compensate for the reduced contribution of creep deformed passive tissues in maintaining spinal stability and the posture. The degraded force generating capacity of the fatigued muscles can be a significant risk factor for low back pain.
对静态屈曲前、期间和之后的下腰屈曲姿势和肌肉活动进行体内测量。
确定在类似于地面以上工作姿势的静态上身深度屈曲过程中，下腰是否会出现蠕变和肌肉疲劳。
静态腰椎屈曲与下腰疾病的发展有关，其损伤机制一直聚焦于被动脊柱组织的变化。伸肌肌肉疲劳的潜在影响尚未得到探讨。
20名无症状受试者在5分钟静态屈曲前和之后立即进行次最大等长躯干伸展运动和等速躯干屈曲，同时记录躯干矢状面屈曲角度和背部伸肌的肌电活动（肌电图[EMG]）。评估与静态屈曲相关的屈曲-放松起始角度、最大屈曲角度、肌肉活动水平和肌电图的中位功率频率的变化。
静态屈曲后，等速屈曲中的屈曲-放松起始角度和等长伸展的肌电图幅度显著更大，表明静态屈曲时脊柱组织发生蠕变。静态屈曲后，等长伸展期间腰竖脊肌肌电图的中位功率频率显著降低，提示肌肉疲劳的发生。在静态屈曲期间观察到肌电图水平一致但较低，同时伴有零星的肌肉痉挛。
由于肌肉长时间被动拉伸，静态屈曲时下腰伸肌可能会出现疲劳。静态屈曲后，下腰伸肌在负重或举重时需要产生更多的主动力，以补偿蠕变变形的被动组织在维持脊柱稳定性和姿势方面贡献的减少。疲劳肌肉产生力的能力下降可能是下腰痛的一个重要危险因素。
