Evaluation of an adjustable ankle-foot orthosis impact on walking stability during gait transitional phases

Walking stability evaluation during gait transitional phases (loading and unloading) has been remained indistinct mainly due to methodological limitations and multiple biomechanical signals being used. This study introduces Nyquist and Bode methods using resultant neuromechanical output/input (O/I) responses to evaluate gait transitional stabilities. The centre of pressure and ground reaction force data are recorded experimentally as output and somatosensory input responses by the neuromotor. Six different walking conditions are simulated by wearing an adjustable orthosis using eleven healthy subjects. The rate of change in O/Is are modelled in time and frequency domains applying linear regression and stability margins are quantified applying N&B methods. Results from outputs showed loading phase as stable and unloading phase as unstable gait phases whereas the margins quantified from inputs showed unstable response during both phases. Stability margins quantified from outputs are decreased (p < 0.05) and instability margins are increased (p < 0.05) on applying ankle-foot restrictions. Overall, the neuromotor output stability margins are greater than the instabilities quantified from inputs. Furthermore, a strong interlimb negative correlation (p < 0.001) was found between loading and unloading phases computed from outputs. This study introduces new stability assessment methods with applications like evaluating lower limb impairments, varying terrains, and stability impacts of wearable devices.