Frictional forces between subtendons are irrelevant to tendon pathology and aging.

 Increased sliding between subtendons directly causes ossification of the Achilles in late adulthood.

Reduced sliding and increased friction between subtendons lead to non-uniform stress distribution, decreased adaptability to load, and a higher incidence of tendinopathy or acute rupture in older adults.

Greater interfascicular mobility enhances elastic recoil but increases rupture risk in older tendons.