Objectives: This study aimed to compare the immediate effect of different durations of superficial heating on the extensibility of the plantarflexors.

Materials and methods: Seventy-five healthy subjects were randomized into one of 3 groups: no heating (control), 15-minute superficial heating, or 30-minute superficial heating. Ankle dorsiflexion active range of motion (AROM) in the lunge position was used as the indicator of plantarflexor’s extensibility, with the lunge position tests performed before and immediately after the intervention.

Results: Immediately after the 15-minute heating intervention, the ankle dorsiflexion AROM was significantly increased in this group. The control and 30-minute heating groups did not have any increase of ankle dorsiflexion AROM.

Conclusion: Superficial heating in the form of hot pack application proved to have an immediate effect in increasing plantarflexor muscle extensibility. The 15-minute application of heating improved the degree of ankle dorsiflexion. This study proposed that 15 minutes of heating was effective in increasing dorsiflexion AROM in healthy subjects.