Embryonic and neonatal animal tendons have a large potential to form fibrils and tendon structures. In adult humans the tendon collagen fractional synthesis rate is around 1% per day but it is unclear to what extent this ends up in structural fibrillar collagen structures of the tendon. Exercise results in increased synthesis and turnover of matrix proteins, with special emphasis on collagen. The stimulation of collagen synthesis by other growth factors can be shown in both animal and human models where insulin like growth factor 1 (IGF-1) and transforming growth factor beta1 (TGF-b1) expression increases accompanying or preceding a rise in procollagen expression and collagen synthesis. As IGF-I decreases with age, it is likely that collagen synthesis will decrease with ageing. The adaptation time to chronic loading is longer in tendon tissue compared to contractile elements of skeletal muscle or heart, and only with very prolonged loading, significant changes in gross dimensions of the tendon are observed. Interestingly, the tendon dimensions do also enlarge with ageing despite a decrease in physical activity. The exact changes in properties of tendons with ageing are not fully determined, but stiffness increases and recent evaluation of the content of cross links reveal that non-enzymatic advanced glycation end products (AGEs) are accumulated in elderly tendons. Interestingly, already in younger age a correlation between AGE content of tendon and age is found. Increased cross-linking may contribute to age related changes in tendon properties.