A motorized trike for prolonged cycling training assisted by Functional Electrical Stimulation*

The beneficial effects of training on people’s well-being and quality of life are well known. Individuals with motor disabilities face challenges in engaging in physical activity. Cycling training can be safely performed even by people with strong motor impairments. When cycling training is performed with the assistance of Functional Electrical Stimulation (FES), the therapeutic benefits are combined with the opportunity to engage in sports activities outdoors. This paper presents a mobile FES and motorized cycling system comprising a commercially available passive recumbent trike equipped with a DC brushed motor, an 8-channel neuro-muscular electrical stimulator, a crank encoder, and a pair of power meter pedals. FES is modulated to maintain a target pedaling cadence. To compensate for pedaling unbalances, a symmetry controller that differentiates the stimulation currents between the two legs is included in the control system. The motor action is controlled to maintain a minimum desired target cadence. To manage all the training phases, a high-level control algorithm was developed. In the initial phase, the legs are stimulated and the motor action is used to assist during the initial adaptation period. During the second phase, the cycling movement is only driven by FES until the onset of muscle fatigue. When FES is not able to keep the desired target cadence, FES is switched off and the motor is activated to perform a period of active rest. After few minutes of rest, FES is activated again. A preliminary feasibility test was conducted with a subject with complete Spinal Cord Injury (SCI). The setup and its control software were found to be functioning correctly. The test results indicated that the control system can effectively manage a prolonged training session by alternating phases of FES-induced cycling with phases of active rest solely supported by the motor. This work is a first step towards the development of a sport-therapy platform which can be used for outdoor training by people with motor disabilities. Such a platform may have a strong impact on well-being, quality of life and social inclusion of target users.