Restoring unassisted natural gait to paraplegics via functional neuromuscular stimulation: a computer simulation study

Abstract

Abstract-Functional neuromuscular stimulation (FNS) of paralyzed muscles has enabled spinal-cord-injured patients to regain a semblance of lower-extremity control, for example to ambulate while relying heavily on the use of walkers. Given the limitations of FNS, specifically low muscle strengths, high rates of fatigue, and a limited ability to modulate muscle excitations, it remains unclear, however, whether FNS can be developed as a practical means to control the lower extremity musculature to restore aesthetic, unsupported gait to paraplegics.A computer simulation of FNS-assisted bipedal gait shows that it is difficult, but possible to attain undisturbed, level gait a t normal speeds provided the electrically-stimulated ankle plantarflexors exhibit either near-normal strengths or are augmented by an orthosis, and at least seven muscle-groups in each leg are stimulated. A combination of dynamic programming and a n open-loop, trial-and-error adjustment process was used to find a suboptimal set of discretely-varying muscle stimulation patterns needed for a 3-D, 8 degree-of-freedom dynamic model to sustain a step. An ankle-foot orthosis was found to be especially useful, as it helped to stabilize the stance leg and simplified the task of controlling the foot during swing. It is believed that the process of simulating natural gait with this model will serve to highlight difficulties to be expected during laboratory and clinical trials.

Muscle force redistributes segmental power for body progression during walking

“…The contribution of the hip abductors (e.g. gluteus medius) to body support can, however, be substantial in single-leg stance, as shown by Anderson and Pandy [6] in a 3D model of walking, and hip abductor activity prevents pelvic listing, as shown by Yamaguchi and Zajac [29] in another 3D modeling study. Thus, the support provided by the plantar flexors in our study, especially the support provided by SOL near mid-stance, may be overestimated because of this unaccounted contribution of the hip abductors.…”

Model-based estimation of muscle forces exerted during movements

“…Many investigators also explored minimization of a physiological variable, e.g. muscle stress (Yamaguchi and Zajac, 1990), in addition to the tracking error. This multi-objective crite rion probably increased the tracking errors in favor of esti mating muscular forces based on task objectives.…”

Reconstructing muscle activation during normal walking: a comparison of symbolic and connectionist machine learning techniques

“…Biomechanical models have been described for normal walking (Crowninshield and Brand 1981;Patriarco et al 1981;Hatze 1984;Davy and Audu 1987), walking of paraplegics assisted by functional electrical stimulation (FES) of paralysed muscles (Yamaguchi and Zajac 1990), and for prosthetic gait (Koopman 1989). These models are based on explicit models of the musculoskeletal system that describe the relationships between the neural activation of muscles and the kinematics of movement, using the theories of multi-body dynamical systems and detailed knowledge of the anatomy and contractile properties of muscles.…”