Biodynamic Parameters During a Step Down Task in Subjects with Chronic or Recurrent Low Back Pain Classified with Lumbar Instability
Background: Low back pain (LBP) affect a majority of the population. Lumbar instability has been identified as a factor in a significant portion of individuals with LBP but movement characteristics of this population has seen limited research regarding functional tasks. Objective: This study examined biodynamic parameters during a step task. Design: Quasi-experimental with 2 factors, group and side (L/R), and 1 repeated measure (stepping). Statistics: Two-way Mixed-Design Repeated Measures ANOVA with Alpha = .05. Movement task: Subjects with LBP and lumbar spine clinical instability classification (N=11) and control subjects (N=11) performed a step down task from a 9.5 inch height on left and right side. Main outcomes: sEMG activation (%MVC), sEMG onset time at first weight acceptance, Ground Reaction Force; rise time GRF(z) and 3D trunk range of motion (ROM) related to three phases of the step: (1) First single leg support, (2) double support and (3) second single leg support. Main results: ROM was reduced in the LBP group in the full step phase in the sagittal plane (p=.003, power= .99), in the final phase in the frontal plane (p=.021, power=.99) and in the transverse plane (p=.018, power=.99) on left steps. GRF(z) was slower in the LBP group at first weight acceptance when leading with the left leg (p=.016, power= .99). EMG onsets: The LBP group had delayed muscle onsets of the right hip abductors (p=.043, power=.99), left abdominals with left stepping (p=.008, power=.91) and right lumbar extensors with right stepping (p=.025, power=.93). The LBP group had delayed onset of right lumbar extensors with right stepping but earlier onset with left stepping (p=.025, power.93). EMG activation levels was higher in the LBP group in both left and right steps of right lumbar extensors (p=.047, power=.93), right hip abductors (p=.017, power= .68) and left hip abductors (p= .035, power= .96). Conclusion: Subjects with LBP demonstrated a high-load movement strategy during this low-load step task with reduced ROM, increased muscle activation, delayed muscle onsets and slow GRF(z) rise time. Left stepping presented more challenge for this group of predominantly right-footed subjects with LBP classified with lumbar instability.
Low, back, pain, instability, classification, step, Medicine and Health Sciences
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