Brief Skin Cooling Induces Muscle Spindle Sensitivity With Heightened Sympathetic Outflow

Cryotherapy is a frequently used treatment method in sports medicine and rehabilitation due to its beneficial neuromuscular effects. Its main beneficial effects are motor facilitation, increase isometric force generation, and reduce spasticity. The motor effects of cryotherapy may differ depending on the duration of application, the coolant used agent (ice, ice water, coolant spray, etc.), and the thickness of the subcutaneous adipose tissue. The short-term cold application increases the force of contraction with motor facilitation. As the cold application period gets longer, the effects of the cold that inhibit motor functions such as gamma motor neuron inhibition, muscle spindle inhibition, and muscle conduction block come to the fore.

It is known that the muscle spindle has sympathetic innervation. It has been reported in recent studies that mental arithmetic, cold application to the skin, isometric contraction of remote muscles, and ischemia increase muscle spindle sensitivity through increased sympathetic activity. However, there are very limited studies showing that cold application increases muscle spindle sensitivity through increased sympathetic activity. On the other hand, in terms of determining treatment and rehabilitation strategies, it is important to know how long the effect of the cold application on muscle spindle sensitivity continues. However, it is not clear how long the effect of the cold application on muscle spindle sensitivity lasts after the cold application ends. There is a widespread belief that the motor facilitation effect of cryotherapy can occur with the stimulation of cutaneous cold receptors. Considering this view, it can be thought that the effect of the short-term cold application on muscle spindle sensitivity continues until the skin temperature returns to normal. This research has three hypotheses: First, short-term cold application to the skin increases sympathetic activity. Second, there is an increase in muscle spindle sensitivity with increased sympathetic activity. Third, the effect of short-term cold on muscle spindle sensitivity continues until the skin temperature returns to normal. The purpose of this research is to test these hypotheses.