Purpose: To investigate the effect of single session Extracorporeal Shock Wave Therapy (ESWT) over the ankle plantar flexor muscles on the spasticity, muscle architecture, and gait in chronic stroke patients.
Methods: This quasi-experimental, single group study had a repeated measures design. A total of 17 post-stroke patients were selected by convenience sampling method, and received 2000 shots of ESWT on the ankle plantar flexor muscles of the affected side in one session. Outcome measures consisted of Modified Modified Ashworth Scale (MMAS), bilateral leg circumference, and muscle architecture parameters (pennation angle, fascicle length, and muscle thickness) of the medial head of the gastrocnemius muscle, timed up and go (TUG) test, self-reported visual analog scale (VAS) of spasticity, and ankle passive Range of Motion (pROM). All outcomes were measured at 2 times: before the intervention and 30 minutes after the intervention. The muscle architecture parameters and leg circumference were also measured immediately after the intervention. Statistical analysis was done using SPSS 18.0. Repeated measures analysis of variance (ANOVA) was performed to evaluate the effects of intervention in time. 
Results: Wilcoxon test revealed significant improvement in MMAS. Significant improvement in VAS, pROM, and TUG test results is also noted by means of the paired t test. ANOVA showed significant time×side interaction for the pennation angle and leg circumference. Significant effect of time was also shown by ANOVA for leg circumference. Post hoc analyses showed a significant difference for the leg circumference before the intervention and 30 minutes after it. ANOVA showed no significant change in fascicle length and muscle thickness. Spearman’s rho revealed significant positive correlation between the changes of the ankle pROM and improvement of the fascicle length. 
Conclusion: According to the results single session of ESWT over the spastic plantar flexors muscle can improve clinical measures of muscle spasticity and motor function. More studies are needed to clarify the underlying mechanisms for the antispastic effect of ESWT.