The development of fatigue quality in high- and low-stressed tendons of sheep (Ovis aries)

The time taken to rupture in cyclic fatigue tests, to a stress of 45 MPa, w as used to compare the fatigue quality of tendons from sheep of varying age s. Muscle and tendon cross-sectional areas were used to calculate the stres s-in-life of each tendon. For any given age, high-stressed plantaris tendon s were of a higher fatigue quality than low-stressed extensor tendons. Both fatigue quality and stress-in-life increased with age for each tendon type . High-stressed tendons are subjected to large increases in stress-in-life during growth, and fatigue quality increased significantly with this stress . This relationship was not seen, however, in low-stressed tendons, which a re not subjected to a comparable range of stresses over time. It is possibl e that cells modify tendon fatigue quality in response to tendon loading hi story. Whilst Young's modulus was seen to increase with age, no difference was detected between high- and low-stressed tendons.