Patient-driven control of FES-supported standing up: a simulation study

To control movements aided by functional electrical stimulation (FES) in paraplegic patients, stimulation of the paralyzed lower limbs might be adjusted in response to voluntary upper body effort. Recently, Donaldson and Yu (ibid., vol. 4, p. 280-4, 1996) proposed a theoretical approach, called "control by handle reactions of leg muscle stimulation" (CHRELMS), in which stimulation of the lower limbs depends on upper body effort, i.e., body posture and recorded hand reactions, and is aimed to minimize arm forces during standing up and standing. An alternative strategy is presented in this paper, which accounts for voluntary upper body effort as well, but does not require estimation of hand reactions. The objective of this study is to test both strategies by applying them to a generic two-dimensional (2-D) neuromusculoskeletal model. The model takes into account the major properties of muscle and segmental dynamics during FES-supported standing up movements of a paraplegic patient. In comparison to standing up without FES-support, both closed-loop strategies yield satisfying standing-up movements although no reference information (e.g., a desired trajectory) is required. Arm forces can be significantly reduced. Using the model to optimize the controller, time-consuming and strenuous trial-and-error experimentation could be avoided. However, final experimental studies are planned to verify the presented strategies.