What happens to tissue viscosity when heat is applied?

• A. Decreased tissue viscosity
• B. Increased tissue viscosity
• C. No change
• D. Initially increases then decreases

Answer: (A)

This question tests how temperature affects tissue viscosity. When heat is applied, molecular motion increases and the forces holding tissue components together loosen. The tissue matrix and its fluids can flow more readily, so viscosity decreases. In practical terms, heating makes tissue less resistant to shear and more easily deformable, aiding movement and potentially improving perfusion in heat therapies. It wouldn’t be correct to say viscosity increases with heat, since higher temperature generally lowers viscosity in soft tissues. The idea of an initial increase before a decrease isn’t typical within the standard therapeutic heating range.