Which statement about heat-induced changes is true?

• A. Increases muscle contraction velocity
• B. Decreases body temperature
• C. Decreases metabolic rate
• D. Decreases blood flow

Answer: (A)

When heat is applied, tissue temperature rises and speeds up the body's chemical and neural processes. Higher temperatures boost enzyme activity and nerve conduction velocity, so muscle fibers respond more quickly and cross-bridge cycling happens faster. This combination makes muscle contraction velocity faster, up to a safe limit. Heat also causes vasodilation, increasing blood flow to the area, and lowers tissue viscosity, which can further facilitate movement. The other statements don’t fit with how heat affects the body: heat raises, not lowers, body temperature; it increases metabolic rate, not decreases; and it increases, not decreases, blood flow.