Loading factor is one of the major causes of osteoarthritis. Among the loading factors increase body weight or obesity and repeated use of joint are the most important in causation of osteoarthritis.
Obesity and osteoarthritis:
Obesity is a known factor in causation or OA of knee and to a lesser extent, hip. During walking three to six times body weight is exerted on a single leg (joints of single leg). For example is a personâ€™s body weight is 50 kilos, 150-300 kilo pressure is exerted on that personâ€™s single leg during walking, whereas only 50 kilo pressure is exerted on that personâ€™s two leg during standing. It is not difficult to imagine what pressure the joints have to withstand during walking, running or jogging or carrying weight. It is also not difficult to imagine the increase in pressure to joints occur if a person gain weight and become obese. In this example, if the same personâ€™s body weight increases from 50 kilo to 70 kilo, he/she has to withstand 210-420 kilo of pressure during walking and much more during running or jogging. Obese person also have more severe symptoms of OA, than thin persons.
Obesity affects the development as well as progression of OA, mainly due to increase in load of weight bearing joints, mainly knee joints. But obesity may also affect joints by other mechanism, other than increase in load of weight bearing joints, as OA increases in hand joints in obese people.
Increase body weight is a greater risk factor for OA among women than men and lowering of body weight is associated with reduces risk of OA, especially among women in whom the relationship of OA and increased body weight is linear.
Repeated joint use and osteoarthritis:
Repeated joint use, due to occupation or recreation is a risk factor of OA. Repeated joint use in occupation carry high risk of OA of that particular joint e.g. farmers suffer from OA of hip joint, miners from OA of knee and spine. The reason of high risk of OA among workers may be the exhaustion of muscles which usually protect joints due to long hours of work.
The professional athletes are at greater risk of OA in later life than common people. Recreational runners do not have higher risk of OA, but injury to knee joint may increase the risk of OA due to running.
Although exercise is an important part of treatment of OA, certain exercises may harm and increase risk of OA. For healthy life a lifestyle with regular exercise is recommended, but many epidemiologic studies of exercise suggest the need of caution due to risk of OA.