ASYNCHRONOUS NEUROMUSCULAR ELECTRICAL STIMULATION By RYAN JAMES DOWNEY A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA

of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy ASYNCHRONOUS NEUROMUSCULAR ELECTRICAL STIMULATION By Ryan James Downey May 2015 Chair: Warren E. Dixon Major: Mechanical Engineering Neuromuscular electrical stimulation (NMES) has been shown to impart a number of health benefits. NMES can also be used to produce functional outcomes such as grasping, walking, reaching, and cycling where it is termed functional electrical stimulation (FES). However, one limitation to NMES/FES is the rapid onset of NMESinduced fatigue. Fatigue limits the duration that NMES can be applied, and thus, the health benefits of NMES may be enhanced by reducing NMES-induced fatigue and allowing NMES to be applied for extended periods of time. Fatigue is also a limitation to FES as it limits the duration that functional tasks can be performed. Two methods to address fatigue include sequential stimulation and asynchronous stimulation. During both sequential stimulation and asynchronous stimulation, multiple stimulation channels are utilized to either segregate the desired muscle into multiple groups of motor units or to segregate multiple synergistic muscles. The stimulus is then switched between stimulation channels as time progresses, thereby reducing the average stimulation frequency of the recruited motor units. Asynchronous stimulation has been shown to reduce NMES-induced fatigue. However, during asynchronous stimulation in man, the extent that NMES-induced fatigue can be further reduced by reducing the stimulation frequency it is not presently clear. In Chapter 2, the ability of both highand low-frequency asynchronous stimulation to reduce NMES-induced fatigue is compared to highand low-frequency conventional