School of Kinesiology and Health Studies, Queen's University, 28 Division Street, Kingston, Ontario, Canada K7L 3N6.
Hum Mov Sci. 2012 Jun;31(3):592-603. doi: 10.1016/j.humov.2011.06.009. Epub 2011 Aug 10.
The local dynamic stability of trunk movements was assessed during repetitive lifting using nonlinear Lyapunov analyses. The goal was to assess how varying the load-in-hands affects the neuromuscular control of lumbar spinal stability. Thirty healthy participants (15M, 15F) performed repetitive lifting at 10 cycles per minute for three minutes under two load conditions: zero load and 10% of each participant's maximum back strength. Short- and long-term maximum finite-time Lyapunov exponents (λ(max-s) and λ(max-l)), describing responses to infinitesimally small perturbations, were calculated from the measured trunk kinematics to estimate the local dynamic stability of the system. Kinematic variability was also assessed using mean standard deviations (MeanSD) across cycles. The results of a mixed-design repeated-measures ANOVA showed that increasing the load lifted significantly reduced λ(max-s) (μ(0%-LOAD)=0.379, μ(10%-LOAD)=0.335, p<.001), but not λ(max-l) (μ(0%-LOAD)=0.46E-03, μ(10%-LOAD)=2.41E-03, p=.055) or MeanSD (μ(0%-LOAD)=2.57, μ(10%-LOAD)=2.89, p=.164). There were no between-subject effects of sex, or significant interactions (α<.05). The present findings indicated improved dynamic spinal stability when lifting the heavier load; meaning that as muscular and moment demands increased, so too did participants' abilities to respond to local perturbations. These results support the notion of greater spinal instability during movement with low loads due to decreased muscular demand and trunk stiffness, and should aid in understanding how lifting various loads contributes to occupational low back pain.
采用非线性 Lyapunov 分析评估了重复提举过程中躯干运动的局部动态稳定性。目的是评估手内负荷的变化如何影响腰椎稳定性的神经肌肉控制。30 名健康参与者（15 名男性，15 名女性）在两种负荷条件下进行了重复提举：零负荷和每个参与者最大背部力量的 10%，每分钟 10 个周期，持续 3 分钟。短时间和长时间最大有限时间 Lyapunov 指数（λ(max-s)和 λ(max-l)），用于描述对无穷小扰动的响应，从测量的躯干运动学中计算出来，以估计系统的局部动态稳定性。还使用跨周期的平均标准偏差（MeanSD）评估运动学可变性。混合设计重复测量方差分析的结果表明，增加举起的负荷显著降低了 λ(max-s)（μ(0%-LOAD)=0.379，μ(10%-LOAD)=0.335，p<.001），但不影响 λ(max-l)（μ(0%-LOAD)=0.46E-03，μ(10%-LOAD)=2.41E-03，p=.055）或 MeanSD（μ(0%-LOAD)=2.57，μ(10%-LOAD)=2.89，p=.164）。性别没有受试者间效应，也没有显著的交互作用（α<.05）。本研究结果表明，在举起较重的负荷时，脊柱的动态稳定性得到了改善；这意味着随着肌肉和力矩需求的增加，参与者对局部扰动的反应能力也随之增强。这些结果支持了在低负荷运动时脊柱不稳定增加的观点，这是由于肌肉需求和躯干刚度降低所致，这有助于理解在不同负荷下的提举如何导致职业性腰痛。
