Background In our previous study, we reported the neuro-muscular function after the reconstruction of anterior cruciate ligament was changed compared with healthy subjects by electrophysiological study. In this study, the electrophysiological findings were reported in the patient with ankle sprain.

Objective To clarify that the fluctuation of the excitability of spinal neural function after ankle sprain, we studied the alteration of H-reflex from the soleus muscle in a patient with ankle sprain.

Design and setting This study was the single case research, which belonged to the basketball team in university first division.

Patient Subject was 21-year-old male college basketball player, left ankle inversed sprain (grade II). There were swelling, pain and instability. As for the activity of daily life, walking in pain was appeared, and going up and down stairs was needed too much time.

Main outcome measurements H-reflex from soleus muscle was recorded at before injury (medical check), three days after injury and one month after injury. H-reflex and maximal M wave from the bilateral soleus muscle were evoked at rest and amplitude ratio of H/Mmax (H/Mmax) was calculated and H/Mmax was compared between after and before injury.

Results H/Mmax was increased at three days after ankle sprain on both injured side and non-injured side compared with both before and one month after injury, and long-latency-reflex was appeared on the only injured side after three days. After one month, electrophysiological findings became the same as before injury.

Conclusions It was cleared that the excitability of spinal and supra-spinal neural function related to soleus muscle at three days after was increased due to pain, joint effusion and/or instability. Even if a slight injury like ankle sprain, the neural function has to be paid attention at least one month after injury in the field of physiotherapy.