Which of the following is a physiological effect of applying heat that is supported by the material?

• A. Sensory nerve endings are sedated
• B. Muscle relaxation is promoted
• C. Edema forms immediately
• D. Heart rate decreases markedly under heat

Answer: (B)

When heat is applied, tissue temperature rises and muscles heat up, which directly increases tissue elasticity and reduces muscle tone. The higher temperature makes collagen fibers more extensible and relaxes the muscle spindle–mediated reflexes, so the muscle can stretch more easily and feels looser. This relaxation also helps improve range of motion and comfort during movement or stretching.

In contrast, sensory nerve endings aren’t simply sedated by heat, so numbness of sensation isn’t the primary physiological effect. Edema forming immediately isn’t a standard immediate effect of heat application; edema is tied to inflammatory processes and often increases with heat in some acute situations rather than occurring as an immediate, expected response. Finally, heat tends to raise heart rate through vasodilation and redistribution of blood, not decrease it markedly.