Modelling and analysis of orthoses generated whole-body vertical vibrations impact on limb stability and compliant dynamics in a ramp gait

Whole-body vibrations provide important proprioceptive feedback for the control of human locomotion. However, these vibrations are also reported to have a detrimental effect on several existing musculoskeletal disorders. Studies have to date reported on the limits of these centre-of-mass (CoM) vibrations mainly for the level walk. However, their impact remains unquantified for other walking situations such as ramp ascent and descent (A/D). Orthotic devices have also been reported as improving limb mobility, but their contribution to whole-body vertical dynamics has not yet been investigated in ramp walking studies. This study presents methods for evaluating normal limits of CoM-vibrations on a ramp, with and without the effect of an ankle–foot orthosis (AFO). Experiments are performed on a force plate and CoM-vibrations data is recorded as a function of impact forces for both normal and AFO walking conditions. These CoM-vibrations are then modelled using a regression technique and analysed in the frequency domain. The normal limits of CoM-vibrations are quantified as limb compliance properties and stability margins for both A/D. A comparison between normal and AFO walking conditions identified significant variations (Friedman-test, p < 0.05) in lower limb compliance dynamics and stability margins. Results also showed the significant impact of AFO adjustments on musculoskeletal dynamics. This preliminary study defines the normal limits of impact forces and their efficiency associated with the wearing of an AFO. Clinically, these outcomes are important in evaluating the deleterious effects of impact forces in patients and on the effectiveness of measures taken to overcome impact forces using assistive devices.