Effects of different fabrics on the Hoffmann reflex during local heat exposure

[Purpose] The effects of multifunctional garments on neuromuscular performance have gained significant research attention in the health sciences. However, the spinal responses to different fabrics have not yet been considered. In the present study, we examined the effects of typical fabrics (cotton and polyester) on the Hoffmann reflex during local heat exposure. [Participants and Methods] Sixteen healthy males aged 20-40 years participated in this study. A heating device comprising a thermal mat, fabric, and a data logger was fabricated. The fabric was affixed to the skin as the contact surface. The temperature of the right posterior lower leg was increased to 39°C followed by 10 min for adaptation at 39-40°C. The H- and M-waves were recorded at each point, including those without heating. An identical trial was conducted seven days later using the alternative fabric. [Results] M-wave amplitude and latency were significantly decreased during heat exposure without fabric. The H-wave latency was prolonged by sustained thermal heat during the session with polyester. Interestingly, the H-wave amplitudes normalized by the maximal M-wave amplitudes decreased with prolonged heat exposure during the session with cotton. However, this index remains unchanged during the sessions using polyester. [Conclusion] During prolonged localized thermal exposure, cotton reduced spinal excitability, whereas polyester preserved spinal excitability.