|| Checking for direct PDF access through Ovid
Age-related changes in ligaments and joint capsules decrease their stiffness and strength, thereby increasing the probability of injury, including sprains and ruptures caused by low-energy trauma or joint use. In addition, with increasing age, the rate of ligament and capsule healing generally declines, and some of these structures develop degenerative changes. Factors that may contribute to these age-related changes include decreased tissue nutrition, cell senescence, and alterations of the matrix macromolecular framework including posttranslational modification of the collagens. Ligaments and joint capsules consist of small blood vessels and fibroblasts surrounded by an abundant extracellular matrix consisting of a macromolecular framework (primarily type I collagen) and water. Some ligaments and capsules have nerves and nerve endings sensitive to mechanical stimuli. The macromolecular framework and its interaction with the tissue water give ligaments and joint capsules their specialized nonlinear tensile properties characterized by tensile stiffness and strength, anisotropy, and time-dependent viscoelasticity. Maintenance of normal ligament composition and thus normal ligament mechanical properties requires repetitive loading of the tissue. Marked decreased repetitive loading, such as immobilization of joints, alters ligament and joint capsule composition and decreases their stiffness and strength. Increased physical activity increases ligament strength in young animals, and presumably has the same effect in young humans, but to a lesser degree. Some evidence suggests that with increasing age, the ability of ligaments to respond positively to exercise decreases; however, at any age, maintenance of tissue homeostasis requires repetitive loading. Controlled activity can also facilitate healing of ligament and joint capsule injuries. Thus, regular physical activity that does not subject ligaments and capsules to excessive tension is important for maintaining their structure and function, and controlled physical activity can promote recovery of structure and function after injury, even in elderly people.