Temperature affects the torque-velocity relationship of the ankle plantar flexor muscles.

The temperature dependence of muscle's force-generating capacity has been established for over 50 years. While temperature-based interventions may be a viable method to augment force output during human locomotion, there are currently limited in-vivo investigations of how temperature affects force-generating capacity in major lower extremity muscles (e.g., ankle plantar flexors). Here, we tested the effects of temperature-exchanging sleeve worn around the shank (hot: 45 °C, cold: 3 °C, and room temperature: ~22 °C) on maximal isometric and isokinetic plantar flexion torque production. Intramuscular temperature measurements confirmed that the temperature of the medial gastrocnemius increased by 3.3 ± 1.0 °C during hot application and decreased by 4.1 ± 2.1 °C during cold application. The hot application increased peak isometric torque by 12% compared to room temperature (p = 0.017). There was also a significant interaction between temperature and velocity during the isokinetic contractions (p = 0.019) - specifically, hot application enabled faster angular velocities across various isokinetic conditions, and achieved greater torques at faster velocities. The cold temperature did not significantly affect the peak isometric (p = 0.072) and the torque-velocity relationship during isokinetic contractions (p = 0.950). These findings suggest hot temperature applications affect the ankle's torque-velocity relationships, highlighting the potential for non-invasive heat-based interventions to enhance the force-generating capacity of the ankle plantar flexors.