There are several structural changes that may occur while we advance in age. A phenomenon known as the process of Creep, Hysteresis, and Set.
Creep: change in length of a ligament or capsule when a continuous force is applied to it over time.
Rearrangement of collagen, proteoglycans and water occur. Any collagenous tissue can undergo creep by activities of daily living (ADL) such as postural syndromes and lifestyle habits, and ADL is probably single most important factor in the creep process. Older people are more susceptible but the effect varies in response to injury and disease.
Hysteresis: change in tissue behaviour after creep has occurred. This reflects loss of energy due to prolonged stress. During hysteresis
there is permanent deformation; collagen & proetoglycan bonds are strained and water is lost. There is also a loss of “Normal Tissue Tone” AKA “Turgor” or “viscoelasticity” (which is ability of tissue to resume its shape and structure after deformation).
Set: The
difference between the original shape or length and the final shape or length. A good example is the post partum abdomen, where some women have regained their figure and others have not. Because collagen fibres are broken, the tissue is more susceptible to injury. This is not irreversible, as some restoration may occur over time and water may be reabsorbed.
Creep, Hysteresis and Set are primarily responsible for "postural" changes that occur with advanced age. Spinal compression fractures, anterior head carriage, nutation of the pelvis, also account for loss of standing height.
Incidentally, creep, hysteresis and set are also responsible for explaining why some people have "bigger" feet (meaning they wear bigger shoes) when they are in their golden years.
Now, for prevention.. . Proper nutrition, regular exercise ( a combination of aerobic, flexibility and resistance training) will help to maintain elasticity and strength of the ligaments and muscles in your body. It may also reduce your risk of osteoporosis, and subsequently your risk of compression fractures. Maintaining proper joint biomechanics (i.e. keeping them moving/functioning properly) will also help maintain the elasticity of the ligaments and muscle that attach to that particular joint.
Hopefully I didn't give you a river when you were only asking for a glass of water, but this is kinda my area of expertise
