This thesis is an investigation of the neurophysiologic mechanism, central sensitization, underlying pain and dysfunction in osteoarthritis. Central sensitization is an important mechanism in the pathophysiology of osteoarthritis but, to our knowledge, its influence on motoneurone excitability is unknown. Our primary hypothesis states that increasing central sensitization within a spinal segment will cause a greater increase in the excitability of motoneurones in subjects with osteoarthritis when compared to healthy controls. To test this hypothesis, we experimentally induced central sensitization in individuals and monitored the recruitment threshold force of the motor units in the first dorsal interosseous muscle using indwelling electromyography. Findings from this study suggest that central sensitization lowers the motor unit recruitment threshold in osteoarthritis compared to healthy individuals. Motoneurone excitability might be inhibited in healthy individuals with persistent sensitization as well. Thus, central sensitization is an important consideration in the biomechanical dysfunction seen in osteoarthritis. / Canadian Arthritis Network