Slower speeds in patients with diabetic neuropathy lead to improved local dynamic stability of continuous overground walking

Patients with diabetic peripheral neuropathy are significantly more likely to fall while walking than subjects with intact sensation. While it has bee n suggested that these patients walk slower to improve locomotor stability, slower speeds are also associated with increased locomotor variability, an d increased variability has traditionally been equated with loss of stabili ty. If the latter were true, this would suggest that slowing down, as a loc omotor control strategy, should be completely antithetical to the goal of m aintaining stability. The present study resolves these seemingly paradoxica l findings by using methods from nonlinear time series analysis to directly quantify the sensitivity of the locomotor system to local perturbations th at are manifested as natural kinematic variability. Fourteen patients with severe peripheral neuropathy and 12 gender-, age-, height-, and weight-matc hed non-diabetic controls participated. Sagittal plane angles of the right hip, knee, and ankle joints and tri-axial accelerations of the trunk were m easured during 10 min of continuous overground walking at self-selected spe eds. Maximum finite-time Lyapunov exponents were computed for each time ser ies to quantify the local dynamic stability of these movements. Neuropathic patients exhibited slower walking speeds and better local dynamic stabilit y of upper body movements in the horizontal plane than did control subjects . The differences in local dynamic stability were significantly predicted b y differences in walking speed, but not by differences in sensory status. T hese results support the hypothesis that reductions in walking speed are a compensatory strategy used by neuropathic patients to maintain dynamic stab ility of the upper body during level walking. (C) 2000 Elsevier Science Ltd . All rights reserved.