Contribution of Lower Limb Eccentric Control to Balance Recovery From Surface Drop Perturbations

Abstract

<h3>Research Objectives</h3> To investigate age-related differences in eccentric neuromuscular control of the knee and its relationship to postural stability during balance recovery following unexpected surface drop perturbations. <h3>Design</h3> Cross sectional, comparative study. <h3>Setting</h3> General community. <h3>Participants</h3> Healthy, community dwelling, and ambulatory older (n=10, age=75.3±5.6) and younger (n=10, age=25.7±2.0) adults. <h3>Interventions</h3> N/A. <h3>Main Outcome Measures</h3> 1) Eccentric knee extension work (J/kg); 2) EMG burst duration (s) in the perturbed leg during the single limb support phase of compensatory stepping; 3) postural sway (standard deviation of center of mass acceleration, m/s2) in the anterior-posterior (A-P), medio-lateral (M-L), vertical directions; 4) margin of stability (MoS) of first compensatory step touchdown after perturbations. <h3>Results</h3> Following an 8 cm surface drop perturbation at gait initiation, older adults (OA) compared to younger adults (YA), demonstrated reduced eccentric knee extensor work (OA: 0.013±0.005 J/kg, YA: 0.020±0.007 J/kg, p=0.034), rectus femoris EMG burst duration (OA: 0.35±0.07s, YA: 0.47±0.08s, p< 0.01), MoS (OA: 68.41±14.30%, YA: 82.88±13.24%, p=0.04), and increased postural sway in all directions (A-P: OA: 2.29±1.38m/s2, YA: 1.03±0.54 m/s2, p=0.02, M-L: OA: 1.42±0.71 m/s2,YA: 0.72±0.41m/s2, p=0.02, Vertical: OA: 4.17±1.01m/s2, YA: 1.74±0.86m/s2, p< 0.01). There was a negative correlation between eccentric work and postural sway in the M-L direction (r = -0.54, p=0.012) and a positive correlation between eccentric work and MoS (r = +0.55, p=0.009). <h3>Conclusions</h3> This study is the first to demonstrate that age-related differences in eccentric control of the perturbed leg are associated with maintaining postural stability and improving compensatory stepping balance response following unexpected surface drop perturbations. Older adults demonstrated deficits in eccentric knee extensor control and this contributed to greater postural sway and unstable compensatory stepping during balance recovery. This finding provides insight into mechanisms of fall recovery and directions for lower limb strengthening exercises for aging populations. Future investigations of these mechanisms in aging populations with a disability due to neurological or musculoskeletal impairments such as Parkinson's disease, stroke, and osteoarthritis are warranted. <h3>Author(s) Disclosures</h3> The contents of this abstract were developed under a grant from NIDILRR (90AR5028).