Mechanical Properties of the Aging Tendon

Abstract

Among the connective tissues, tendons are probably some of the simplest in terms of structure and function. The function of tendon is basically that of a rope transmitting uniaxial force from muscles across joints to generate movement. Tendons can often experience large loads with many repetitions, which may be part of the reason why they are common sites of injury in relation to sports and overuse. When injured, tendons are not very good at regenerating, and this property may also be involved in the increased prevalence of tendon injury with age that has been observed. This chapter provides an introduction to tendon composition and mechanical properties and proceeds to present our current knowledge of how these are affected by aging. While quite a few studies exist within this area, the variations in tendon types, species, and age range as well as methodology provide a mixed message. In spite of contradictory findings, the overall image appears to be that tendons experience a loss of load-bearing material, mechanical stiffness, and strength with old age. These changes relate well to the increased injury risk but the mechanisms are poorly understood. For example the concentration of glycation cross-links increase with age and would be expected to increase rather than reduce connective tissue stiffness. Further research is therefore warranted, especially at a mechanistic level.