Walking stability is essential for performing daily living activities with independence, dignity and confidence. Statistics reveal that patients with lower limb impairments are continually increasing with an increase in accidents or sports-related injuries, neurological deficiencies, and elderly population. The recovery from such impairments usually took a significantly long time and affect patient’s health, psychology, social issues, and increased healthcare costs.
A survey of the literature reveals that the pre-assessment of such patients can potentially reduce stability risks, however, the existing assessment techniques are lacked to quantify stabilities with distinct criteria, during gait transitional phases, and varying degrees of lower limb impairments. On the other hand, various wearable orthoses are prescribed clinically or available commercially to assist gait deficiencies, however, their impacts on walking stabilities have remained unclear.
This research introduces new applications of control engineering theory to assess gait dynamic stabilities using mathematical models, distinct analysis criteria, and over varying walking terrains. The ankle-foot deficiencies such as foot drop, Charcot-Marie-Tooth, eversion, and inversion are imitated with a uniform degree of impairments using healthy subjects and adjustable orthoses. The gait dynamic stabilities are assessed using frequency models of neuromechanical signals such as centre-of-pressure and centre-of-mass acceleration as a resultant output and input (O/I) responses generated by the neuromotor. The Nyquist and Bode methods are employed to quantify stability margins from gain and phase plots of the modelled signals. The results illustrated the significant impact of imitated impairments on walking stabilities compared to an unrestricted healthy walk. The stability margins during weight loading gait phases showed stable magnitudes quantified from CoP waveforms and unstable responses from CoM-acceleration using 99±0.5% best fit models. During weight unloading gait phases, both the outputs and inputs showed unstable margins. The results are also compared by applying prior stability assessment approaches.
Evaluation of gait contractile dynamics such as damping ratio, peak gain, and natural frequency using vertical CoM-oscillations provide important information about lower limbs contractile dynamics with/without the effect of the wearable orthosis. This pilot study provided proof of concept for neuromechanical balance control assessment applying control engineering theory and with ankle-foot impairments, nevertheless, these methods could be equally applicable for stability assessments in patients with knee or hip joint impairments and/or by wearing other lower limb prosthetics or exoskeleton devices.
