Với tuổi tác, thay đổi nội dung collagen tuyệt đối ít, trong khi số lượng tương đối của collagen và khối lượng collagen mật độ của sự gia tăng gân do giảm các nội dung proteoglycan nước. Các loại II collagencontaining khu vực lây lan | 4. Aging and Degeneration of Tendons 27 With age the absolute collagen content changes little while the relative amount of collagen and the collagen volume density of the tendon increase due to decrease in the proteoglycan-water content. The type II collagen-containing region spreads significantly from the attachment zone of the tendon into the tendon substance 1 12 18 19 . The mean collagen fibril diameter shows a marked increase during development while a decrease in the proportion of thick fibrils and in the mean area of the fibrils occurs with senescence 13 . Collagen turnover which is relatively low to begin with declines with age as collagen synthesis diminish 11 18 . Due to the agedependent reduction of tendon cells and enzymes that are essential for collagen synthesis repair of the soft tissues such as tendon is delayed in old age. During senescence the mechanical properties of collagen decrease 20 . This is due to changes in collagen crosslinking profile as there is an increase in the crosslinking of the tropocollagen molecules decreasing the solubility of collagen 9 10 . The conversion to nonreducible crosslinks is a spontaneous age-related process although mechanical stress and hormones may have an additional effect 1 21 . The increase in crosslinks has been observed to have an effect on several laboratory-detected phenomena an increased resistance to degrada-tive enzymes 22 reduced solubility of collagen 2 19 23 increased stability to thermal denaturation 2 23 and increased mechanical stiffness 23 24 . The crosslinking of collagen is considered one of the best biomarkers of aging 25 . Elastin and Contractile Proteins With increasing age a decrease in the number of elastic fibers as well as many morphological changes have been observed 11 12 18 . These could be related to an increase in the synthesis of fibrillar glycoproteins associated with partial degeneration of elastin by tissue elastases 21 . The presence of the contractile proteins actin and .
