Department of Graduate Education and Research Programs, Canadian Memorial Chiropractic College, Toronto, Ontario, Canada.
J Electromyogr Kinesiol. 2013 Aug;23(4):794-800. doi: 10.1016/j.jelekin.2013.04.002. Epub 2013 May 1.
Repetitive trunk flexion elicits passive tissue creep, which has been hypothesized to compromise spine stability. The current investigation determined if increased spine flexion angle at the onset of flexion relaxation (FR) in the lumbar extensor musculature was associated with altered dynamic stability of spine kinematics. Twelve male participants performed 125 consecutive cycles of full forward trunk flexion. Spine kinematics and lumbar erector spinae (LES) electromyographic (EMG) activity were obtained throughout the repetitive trunk flexion trial. Dynamic stability was evaluated with maximum finite-time Lyapunov exponents over five sequential blocks of 25cycles. Spine flexion angle at FR onset, and peak LES EMG activity were determined at baseline and every 25th cycle. Spine flexion angle at FR increased on average by 1.7° after baseline with significant increases of 1.7° and 2.4° at the 50th and 100th cycles. Maximum finite-time Lyapunov exponents demonstrated a transient, non-statistically significant, increase between cycles 26 and 50 followed by a recovery to baseline over the remainder of the repetitive trunk flexion cycles. Recovery of dynamic stability may be the consequence of increased active spine stiffness demonstrated by the non-significant increase in peak LES EMG that occurred as the repetitive trunk flexion progressed.
反复的躯干前屈会引起被动的组织蠕变，这被假设会损害脊柱稳定性。本研究旨在确定在腰椎伸肌的屈伸松弛（FR）开始时增加脊柱前屈角度是否与脊柱运动学的动态稳定性改变有关。12 名男性参与者进行了 125 次连续的全向前躯干前屈。在整个重复的躯干前屈试验中，获得了脊柱运动学和腰椎竖脊肌（LES）肌电图（EMG）活动。使用五个连续的 25 个循环块的最大有限时间李雅普诺夫指数评估动态稳定性。在基线和每 25 个循环时，确定 FR 起始时的脊柱前屈角度和 LES EMG 活动的峰值。与基线相比，FR 起始时的脊柱前屈角度平均增加了 1.7°，在第 50 和 100 个循环时，分别增加了 1.7°和 2.4°。最大有限时间李雅普诺夫指数在第 26 至 50 个循环之间表现出短暂的、无统计学意义的增加，然后在重复的躯干前屈循环的其余部分恢复到基线。动态稳定性的恢复可能是由于主动脊柱刚度的增加所致，这表现为随着重复的躯干前屈的进行，LES EMG 峰值的非显著增加。
