Electrically Stimulated Quadriceps Muscle Model for Wheel-chaired Elliptical Stepping Exercise

This paper presents the development of physiologically based mathematical model of quadriceps muscle and the implementation on Functional Electrical Stimulation (FES) assisted wheel-chaired elliptical stepping exercise. Two muscles that make up quadriceps muscle namely rectus femoris and vasti were developed. The muscle models were integrated with humanoid, elliptical stepping ergometer and wheelchair model to simulate the wheel-chaired elliptical stepping exercise. During contraction, both rectus femoris and vasti muscles produce active and passive joint moments at knee and hip joint and hence drive the movement of the elliptical stepping exercise. At appropriate position and timing, a constant 220 μs of stimulation pulse width and 30 Hz of stimulation frequency is delivered to both left and right quadriceps muscles. The produced active, passive and total joint moments during the stimulation were recorded and analyzed. From the analysis, it was confirmed that the produced joint moments were able to drive the movement of the elliptical stepping exercise. The exercise may be performed smoothly with appropriate pattern of FES delivered to quadriceps muscle through the implementation of more advanced control strategy.