Dickey James P, McNorton Sara, Potvin James R
Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ont., Canada N1G 2W1.
Clin Biomech (Bristol). 2003 Nov;18(9):783-9. doi: 10.1016/s0268-0033(03)00166-9.
To determine if repeated spinal flexion and loading modulate the deactivation of lumbar muscles near full flexion (flexion-relaxation).
Repeated measures experimental study of the effect of repetitive trunk flexion and added mass on the flexion-relaxation phenomenon.
Repeated flexion causes muscular fatigue, creep of passive tissues and diminished protective reflexes. However, flexion-relaxation has not been studied in repeated trunk flexion, and could be related to the increased risk of low-back disorders.
Thirty healthy young subjects performed 100 trunk flexion movements between standing and full flexion. Erector spinae electromyography and lumbar spine flexion were measured during cycles 1-10 (no load), 11-20 (performed holding a mass in the hands), 81-90 (mass in the hands) and 91-100 (no load). The spinal flexion angle at myoelectric silence and full flexion were extracted from each movement cycle.
Twenty-three of the 30 subjects showed flexion-relaxation throughout the repeated trunk flexion. The flexion-relaxation and maximum flexion angles increased at the end of the experiment; the flexion-relaxation angle relative to the maximum flexion angle also increased. This effect depended on the load condition; the flexion-relaxation and maximum flexion angles showed a greater increase in the unloaded than loaded condition.
The flexion-relaxation phenomenon was changed due to repeated trunk flexion. The increases in flexion-relaxation angle likely involve changes to the neuromuscular control system.
The deactivation of the erector muscles near full flexion occurs at a greater spinal flexion angle and a greater proportion of maximum spinal flexion following repeated spinal flexion. This may be related to the increased risk of injury associated with repeated flexion.
确定重复的脊柱屈曲和负荷是否会调节接近完全屈曲时（屈曲放松）腰椎肌肉的失活。
重复测量实验研究，探究重复性躯干屈曲和附加质量对屈曲放松现象的影响。
重复屈曲会导致肌肉疲劳、被动组织蠕变以及保护性反射减弱。然而，重复性躯干屈曲中的屈曲放松现象尚未得到研究，且可能与下背部疾病风险增加有关。
30名健康年轻受试者在站立和完全屈曲之间进行100次躯干屈曲动作。在第1 - 10个周期（无负荷）、第11 - 20个周期（手持重物进行）、第81 - 90个周期（手持重物）和第91 - 100个周期（无负荷）期间，测量竖脊肌肌电图和腰椎屈曲情况。从每个运动周期中提取肌电静息时的脊柱屈曲角度和完全屈曲角度。
30名受试者中有23名在整个重复性躯干屈曲过程中表现出屈曲放松。实验结束时，屈曲放松角度和最大屈曲角度增加；相对于最大屈曲角度的屈曲放松角度也增加。这种效应取决于负荷条件；与有负荷状态相比，无负荷状态下屈曲放松角度和最大屈曲角度增加得更多。
重复性躯干屈曲导致屈曲放松现象发生改变。屈曲放松角度的增加可能涉及神经肌肉控制系统的变化。
重复脊柱屈曲后，接近完全屈曲时竖脊肌的失活发生在更大的脊柱屈曲角度以及更大比例的最大脊柱屈曲时。这可能与重复屈曲相关的损伤风险增加有关。
