Enhancing motor performance through brief skin cooling: exploring the role of enhanced sympathetic tone and muscle spindle sensitivity.

Background: Although brief skin cooling (BSC) is widely used in sports medicine and rehabilitation for its positive effects on motor performance, the mechanism underlying this motor facilitation effect remains unclear.

Objectives: To explore the hypothesis that BSC enhances muscle force generation, with cold-induced sympathetic activation leading to heightened muscle spindle sensitivity, thereby contributing to this effect.

Methods: The study involved two experiments. Experiment 1 included 14 healthy volunteers. Participants submerged their hand in ice water for 3 min. Sympathetic activity was measured via heart rate (HR), muscle force generation was assessed through plantar flexor strength during maximum voluntary contraction (MVC), and cortical contribution to force generation via the volitional wave (V-wave) with and without the cold pressor test (CPT). Experiment-2 involved 11 healthy volunteers and focused on muscle spindle sensitivity and Ia synapse efficacy, assessed using soleus T-reflex and H-reflex recordings before, during, and after CPT.

Results: Experiment 1 showed significant increases in HR (7.8%), MVC force (14.1%), and V-wave amplitude (93.4%) during CPT compared to pre-CPT values (p = 0.001, p = 0.03, and p = 0.001, respectively). In Experiment-2, hand skin temperature significantly decreased during CPT and remained lower than pre-CPT after 15 min (p < 0.001). While H-reflex and background EMG amplitudes remained unchanged, T-reflex amplitude (113.7%) increased significantly during CPT and returned to pre-CPT values immediately afterward (p < 0.001). A strong correlation was also observed between HR and T-reflex amplitude (r = 0.916, p = 0.001).

Conclusion: BSC enhances muscle spindle sensitivity via the sympathetic nervous system, promoting more significant muscle force generation. The method used in this study can be safely applied in clinical practice.