30 patients with persistent muscle weakness following an intra-articular knee injury were randomized to either receive non-thermal ultrasound or sham treatment. The purpose of this study was to determine if ultrasound treatment improved quadricep motoneuron pool excitability as measured by Hoffman reflex (H/M ratio). Results showed no immediate change to H/M ratio following treatment, but significantly greater H/M ratio was observed in the ultrasound group compared to the sham group at 20min post-intervention. Compared to baseline, the ultrasound group showed a low-magnitude improvement in H/M ratio while the sham group showed a low-magnitude decline in H/M ratio at 20 minutes after treatment.