In the past, it has been shown that functional electrical stimulation (FES), when applied to lower limbs, can facilitate quiet stance in patients with various neurological disorders. Furthermore, the literature suggests that able-bodied individuals regulate balance during quiet stance using a control strategy that is similar to proportional-integral-derivative (PID) control. The purpose of this study was to test if a PID control strategy is capable of effectively regulating an FES system at the ankle joints during quiet stance. Specifically, we tested whether able-bodied individuals with compromised visual, vestibular and proprioceptive senses, would exhibit improved ankle joint control if FES was applied to contract the ankle muscles using a closed-loop, PID control strategy. In what follows we show that the proposed PID control strategy was able to outperform voluntary control of the ankle joint, indicating that the controller could be considered for use in neurological patients, including spinal cord injured individuals.
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