Final answer:
Cold application causes vasoconstriction, which is the narrowing of blood vessels, while heat application causes vasodilation, the widening of blood vessels. Heat application reduces muscle tension and increases tissue metabolism due to the increased blood flow.
Step-by-step explanation:
The application of cold and heat to the body can have different effects on blood vessels and muscle tension. Cold application typically causes vasoconstriction, which is the narrowing of blood vessels, helping to reduce inflammation and numb pain. On the other hand, heat application causes vasodilation, the widening of blood vessels, which increases blood flow to the area, reduces blood viscosity, and increases tissue metabolism. This can help to relax muscles and relieve pain. Contrary to heat, cold does not increase tissue metabolism, and while heat induces vasodilation, cold will not have this effect.
It is important to note that vasoconstriction can help conserve body heat by reducing blood flow to the surface of the skin, while vasodilation can lead to increased heat loss through radiation and evaporation. Furthermore, upon tissue injury, inflammatory mediators like histamine cause vasodilation, facilitating increased blood flow to the affected area, aiding the inflammatory response, but also causing redness and warmth.