Williams M, Solomonow M, Zhou B H, Baratta R V, Harris M
Bioengineering Laboratory, Department of Orthopaedic Surgery, Louisiana State University Medical Center, New Orleans, Louisiana 70112, USA.
Spine (Phila Pa 1976). 2000 Nov 15;25(22):2916-24. doi: 10.1097/00007632-200011150-00014.
The electromyogram of the L1-L7 multifidus muscles of the in vivo cat were recorded while applying a prolonged steady displacement to the lumbar spine through the L4-L5 supraspinous ligament, simulating a moderate anterior flexion.
To demonstrate that tension-relaxation and laxity of the viscoelastic structures (ligaments, discs, and capsules) induced by prolonged static flexion of the spine results in loss of reflexive muscular stabilizing activity and in muscular disorders that may lead to or are associated with low back pain.
Epidemiologic data show that prolonged loading of the spine, such as in some occupational activities, can cause low back pain and muscle spasms. Direct experimental evidence linking prolonged loading to a decrease in spinal stability, low back pain, and muscle spasms was not found. It was hypothesized, however, that mechanoreceptors in the viscoelastic structures, when strained, reflexively activate the multifidus muscles to maintain intervertebral stability; that the reflexive muscular activity decreases with stress-relaxation and laxity in the viscoelastic structures; and that when severe strain and possible damage of the viscoelastic structures occurs with time, nociceptive receptors elicit spasms in the musculature and possible pain.
The lumbar spine of seven in vivo cat preparations was displaced through the L4-L5 supraspinous ligament into moderate flexion that was steadily maintained for 50 minutes while intramuscular electromyograms were recorded from each of the multifidus muscles of L1-L2 through L6-L7. Load and electromyogram were continuously monitored and recorded. Five additional preparations were used as controls, in which dissection and recordings were identical, but the lumbar flexion was excluded.
Prolonged flexion of the lumbar spine resulted in initial reflexive electromyogram from the multifidus muscles that decreased to approximately 5% of its initial value as tension-relaxation began in the viscoelastic structures within the first 3 minutes, after which, random and unpredictable electromyogram discharges (i.e., spasms) of high amplitude were recorded from different levels. In some preparations the spasms were present in L1-L4, and in others in all the levels. In other preparations the spasms were recorded only at L5 and L6. The onset of the spasms was also unpredictable, because they were initiated in some cases within 2-3 minutes after the spine was loaded. In other cases, the spasms were observed anytime during the test period and up to 20 minutes after the load was removed. Spasms were also observed in the spinalis and longissimus muscles.
Prolonged flexion of the lumbar spine results in tension-relaxation and laxity of its viscoelastic structures, loss of reflexive muscular activity within 3 minutes and electromyogram spasms in the multifidus and other posterior muscles.
在通过L4 - L5棘上韧带对活体猫的腰椎施加长时间稳定位移以模拟中度前屈时，记录L1 - L7多裂肌的肌电图。
证明脊柱长时间静态前屈引起的粘弹性结构（韧带、椎间盘和关节囊）的张力松弛和松弛会导致反射性肌肉稳定活动丧失以及可能导致或与腰痛相关的肌肉紊乱。
流行病学数据表明，脊柱长时间负荷，如在某些职业活动中，可导致腰痛和肌肉痉挛。未发现将长时间负荷与脊柱稳定性降低、腰痛和肌肉痉挛联系起来的直接实验证据。然而，据推测，粘弹性结构中的机械感受器在受到拉伸时会反射性地激活多裂肌以维持椎间稳定性；反射性肌肉活动会随着粘弹性结构中的应力松弛和松弛而降低；并且随着时间的推移，当粘弹性结构发生严重应变和可能的损伤时，伤害性感受器会引起肌肉组织痉挛和可能的疼痛。
对7只活体猫的腰椎通过L4 - L5棘上韧带进行位移，使其达到中度前屈并稳定维持50分钟，同时记录从L1 - L2到L6 - L7各多裂肌的肌内肌电图。持续监测并记录负荷和肌电图。另外5只猫作为对照，其解剖和记录过程相同，但不进行腰椎前屈。
腰椎长时间前屈导致多裂肌最初出现反射性肌电图，在最初3分钟内，随着粘弹性结构开始出现张力松弛，该反射性肌电图降至其初始值的约5%，此后，从不同水平记录到高幅度的随机且不可预测的肌电图放电（即痉挛）。在一些实验准备中，痉挛出现在L1 - L4，而在其他准备中则出现在所有水平。在其他准备中，痉挛仅在L5和L6记录到。痉挛的发作也不可预测，因为在某些情况下，它们在脊柱加载后2 - 3分钟内开始。在其他情况下，在测试期间的任何时间直至负荷去除后20分钟都观察到了痉挛。在棘肌和最长肌中也观察到了痉挛。
腰椎长时间前屈会导致其粘弹性结构的张力松弛和松弛，在3分钟内反射性肌肉活动丧失，以及多裂肌和其他后部肌肉出现肌电图痉挛。
