Effects Of Heat Heat, being a form of energy, increases metabolic activity in the cells. This increased activity causes an increase in oxygen demand locally. As a result, capillary dilation occurs to increase the amount of blood that brings oxygen and nutrients to the area. Membrane diffusion and enzymatic activity also increase, enabling oxygen consumption and waste removal. The waste products of injury include prostaglandins, bradykinin, and histamine, all implicated in nerve fiber sensitization and pain.
Arthritic joints respond favorably to applications of external heat.
Joint stiffness is reduced due to a decrease in synovial fluid viscosity and an increase in the distensability of the surrounding connective tissue. The increased temperature of the sensory nerves in the skin overlying the joint will create a reflex pain-inhibiting effect as rapidly sent messages of heat are recognized in the brain, blocking out pain messages. The threshold of sensory nerve endings is elevated, resulting in long-term pain relief. 3 Prior heating will facilitate comfortable exercise when connective tissue contractures or scar tissue exists around a joint, limiting its movement. Heating dense connective tissue affects bonds between collagen molecules, making the tissue more pliant.