OBJECTIVES: To investigate non-thermal therapeutic ultrasound on quadriceps spinal reflex excitability in patients with neuromuscular impairment. DESIGN: Randomized controlled laboratory study, pre-test post-test. SETTING: University laboratory. PARTICIPANTS: Thirty recreationally active volunteers with a self-reported history of diagnosed intra-articular knee joint injury and documented quadriceps dysfunction participated. INTERVENTIONS: A non-thermal ultrasound, or sham, treatment was applied to the anteromedial knee. MAIN OUTCOME MEASURE(S): Hoffmann reflex (H-reflex) measurements were recorded at baseline, immediately post, and 20 minutes post intervention. Peak H-reflex amplitude was normalized to the peak muscle response (H:M ratio) measured from the vastus medialis using surface electromyography as an estimate of quadriceps motorneuron pool excitability. An analysis of variance with repeated measures was used for comparisons. RESULTS: A significant group-by-time interaction was observed for mean (p = 0.016) and change (p = 0.044) in H:M ratio. The ultrasound group demonstrated significantly higher mean (p = 0.015) and change (p = 0.028) in H:M ratio 20 minutes post-intervention compared to sham ultrasound. CONCLUSIONS: Quadriceps motoneuron pool excitability was facilitated 20 minutes following a non-thermal therapeutic ultrasound and not a sham treatment. These data provide supporting evidence of the contribution of peripheral receptors in modulation of the arthrogenic response in patients with persistent quadriceps dysfunction. Future research in this area should attempt to identify optimal treatment parameters, and translate to clinical outcomes.

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