Electromyographic Study on the Inhibitory Effects of Local Cold- and Hot-Water Bathing of the Upper Limb on Finger Flexor α-Motor Neuron Activity

This study evaluated the inhibitory effects of cold and heat stimulation on α-ｍotor neuron activity and the associated pain, exploring their clinical applications. Twenty-four healthy young adults participated, undergoing four conditions: (1) cold-water finger immersion, (2) warm-water finger immersion, (3) warm-water forearm immersion, and (4) a control condition. Assessments included grip strength, integrated electromyography (IEMG) of finger flexor muscles, skin temperature, and pain perception. Cold-water finger immersion involved three sets of 5-second ice water immersion with 2-second breaks. Warm-water immersion (finger and forearm) lasted 10 min at 42°C. Measurements were taken before and at 5-minute intervals up to 20 min post-intervention, with pain assessed via the Numerical Rating Scale (NRS). Cold-water finger immersion significantly reduced grip strength, IEMG, and skin temperature while increasing NRS scores. In contrast, warm-water immersion had no significant effect. The cold-water condition also showed a prolonged skin temperature drop. These findings confirm that cold stimulation inhibits α-motor neuron activity, primarily due to pain, though the effect is temporary. Cold stimulation may improve range-of-motion (ROM) exercise performance, potentially preventing joint contractures. This suggests that cryotherapy could be a valuable approach for managing spasticity in post-stroke patients. Since finger flexor spasticity impairs activities of daily living (ADL) and quality of life (QOL), reducing spasticity is crucial for ROM exercises.