Background and aim: Ankle plantar flexor is one of the most susceptible muscles to plasticity and contracture after acquired brain injury. The application of thermal agents was introduced before muscle stretch or active exercises in spastic patients for their relaxation effects. The main aim of the present study was to compare the short-term effect of the ultrasound (US) and infrared (IR) on patients with plantar flexor muscle spasticity.

Materials and Methods: 21 patients were randomly allocated placed to either US(n=11)or IR(n=10)groups. The main outcome measures were, H _max / M _max  ratio, Original Ashworth Scale(OAS), active and passive range of motion (ROM).These tests  performed before, immediately after and 15 minutes after the intervention.

Results: There were no significant changes in H _max / M _max ratio and OAS after the intervention in both groups. The significant changes of the H _max / M _max were observed 15 minutes after intervention in the US group .The change in OAS was also statistical significant in IR group in this period. The changes in active and passive ankle dorsiflexion ROM after the intervention were statistically significant in US group. These changes show the significant changes for ankle passive ROM after15 minutes of  the intervention in IR group.

Conclusion: Our findings demonstrate that one session application of the ultrasound and infrared are not effective in the treatment of muscle spasticity. The ultrasound improved the ankle active and passive ROM. Further research is needed.