What is the local effect of heat?

Heat application in massage therapy or any therapeutic context primarily leads to increased vasodilation of the capillaries. This process involves the widening of blood vessels, which enhances blood flow to the tissues in the area where heat is applied. Increased circulation results in improved oxygen delivery and nutrient transport to tissues, as well as enhanced removal of metabolic waste products. This is beneficial for relieving muscle tension, alleviating pain, and promoting overall tissue healing.

Applying heat causes the smooth muscles in the walls of blood vessels to relax, leading to this vasodilation effect. This physiological response also promotes an increase in local tissue temperature, further facilitating the healing processes due to improved circulation.

In contrast, the other options point to effects that are not typical consequences of heat application. For instance, increased muscle tone often results from cold therapy or can occur due to stress or tension, rather than heat. Decreased blood flow contradicts the vasodilation effect of heat, and increased tissue density typically suggests a contraction of muscle fibers rather than relaxation and improved circulation associated with heat. Thus, the correct understanding focuses on the vasodilation effect of heat as a primary therapeutic benefit.