Arthritis is defined as "inflammation of the joints." The most common form of arthritis is osteoarthritis (OA), a disease where several factors cause cartilage to become soft and break down. OA is also termed degenerative joint disease.

As OA develops, cartilage that normally covers bone to reduce friction and absorb shock cracks and wears away. As a result, one bone may touch the surface of another bone at the joint. Changes in soft tissue that occur with age - muscles, tendons, ligaments and joint capsule, are associated with joint stiffness.

The effects of OA can be pain after exercise or upon use of the joint, with stiffness, tenderness and even rubbing noises.

OA can affect virtually any joint but commonly afflicts the knees, hips, spine, distal joints of the feet and first carpometacarpal joints of the hands. Of course, OA at the hip, knee or the spine hinders movement more than OA at other areas.

OA is quite common, occurring in 20 to 30 percent of the population. OA affects about 80 percent of adults over age 65 but less than 5 percent in those under 35 years. Although many older persons have OA, only 15 to 20 percent complain of specific symptoms. Under the age of 50, men and women have similar amounts of OA; above 50, slightly more women are affected.

The causes of OA have not been completely identified, but heredity and multiple environmental factors seem to play a role. At least some aspects of OA may be genetically determined because OA appears in several generations of some families.

Unstable ligaments, abnormal joint motion and prior injury may contribute to premature development of OA. Adults throw their joints out of alignment, damage cartilage through accidents or abuse their joints by placing excessive force on them or overusing them in sports or work activities. When joints are misaligned or damaged, OA can occur.

OA also may result from repeated trauma. A consistent risk factor for OA of the weight-bearing joints is obesity, especially in older women, because the excess weight puts more strain on these joints. Also, a significant increase in knee joint OA was found in football players who had sustained a knee injury. About 90 percent of players (mean age 23 years) competing for a place on a professional team had radiological abnormalities of the foot or ankle, compared with four percent of an age-matched population. All those who had played football for nine years or longer had abnormal findings.

It is not certain whether persons who stress their joints by exercise or in their occupation have more severe OA. It appears that normal joints can tolerate prolonged, vigorous, low-impact exercise, but abnormal joints are more susceptible to develop OA. For all populations, excessive high-impact, high-intensity activity (especially heavy weight-bearing exercise, kneeling or squatting) increases the risk of developing OA of the weight-bearing joints.

When OA occurs in the hip or knee joints, pain and discomfort can reduce a person's desire to move. This predisposes the joint to stiffen and become less flexible, which in turn, causes the person to move even less. Low mobility can decrease muscular strength to approximately 45 percent to 75 percent of normal levels. It becomes a vicious cycle.

When persons with OA of the weight-bearing joints move, they may have to compensate by changing their gait or movement patterns to reduce pain and discomfort. These compensatory movements typically are inefficient, placing a greater load on the cardiorespiratory system and possibly creating additional biomechanical misalignments. Therefore, it becomes more difficult to perform everyday activities such as rising from a chair, walking long distances or climbing stairs.

OA is not necessarily progressive, disabling or crippling and generally can be managed satisfactorily. For serious cases of OA, however, surgery may be necessary to reduce pain and improve a joint's functioning.

Other common treatments include:

• reducing strain on the damaged joint by weight reduction and rest
• relief of pain by analgesics and heat
• active exercises to improve joint range of motion (ROM) and to strengthen surrounding muscles

Exercise can be used to help break the pattern of a painful joint, muscle inhibition, muscle atrophy, impaired joint stability and further injury of the damaged joint surface.

It is not well established in the literature if moderate exercise can prevent, postpone, rehabilitate or provide relief for symptoms of OA. Nevertheless, preliminary evidence suggests that individuals with OA can benefit from regular systematic exercise such as stretching, low-impact aerobic exercise and resistance training (static and dynamic). For this reason, physicians will usually recommend exercise for patients with mild and moderate levels of OA.

Persons with OA should be certain to warm up before starting an exercise program, as this will help to stretch the muscles and reduce the risk of injury. Activities that stretch muscles are beneficial to maintain joint ROM and reduce pain.

Although OA may cause joint symptoms, reduced physical activity and general deconditioning, a recent study suggests that muscle weakness alters the biomechanics of the joint and puts uneven stress across the joint surface, resulting in an acceleration of the degenerative process. Therefore, adequate levels of strength may be protective. Enhanced strength also can decrease pain, so a regular moderate intensity strength training program is recommended.

Consistent cardiovascular exercise can result in weight loss, thereby reducing the forces produced at the weight-bearing joints. Because heavy forces on joints exacerbate arthritic conditions, low-impact exercises such as swimming and cycling are good choices.

Persons with mild OA usually can exercise with few restrictions, but those with moderate pain should emphasize low-intensity cardiovascular and resistance exercises. Persons with severe pain should perform low-impact exercises that do not put excessive stress on the afflicted joints.

Water exercise is beneficial for all sufferers of OA because water reduces the effects of gravity on the joints, permits stretching and provides mild resistance to movement. Warm water also helps soothe sore joints.

For all cases of OA, avoid the following types of activities for the affected joints:

• overstretching
• applying heavy loads
• high-impact exercises
• high-repetition and high-intensity resistance exercises

If an activity causes pain, stop, analyze the movement and attempt to modify it. If pain persists for more than 24 hours, then the amount of exercise should be reduced and/or the activity should be avoided or modified.

Most studies have shown that cardiovascular and resistance exercises have beneficial effects on pain, disability and performance. Thus, the way to measure whether persons with OA are improving is to see if they can do the same amount of exercise (preferably more exercise) with less pain. Although consistent exercise does not replace other forms of treatment, it may add to their effectiveness. It is important that exercise programs are consistent to maintain any positive effects on OA.

Psychological benefits of regular exercise also are important for persons with OA. OA may negatively affect self-assurance and self-image, but exercise can enhance well being by improving physical appearance or mood. Low-impact, moderate-intensity sports also are excellent activities to counter the tendency of individuals with OA to withdraw from social interactions.

It is unlikely that moderate exercise causes the premature development of OA in persons with normal joints. It has been shown repeatedly that persons with mild to moderate OA can exercise safely without exacerbating joint symptoms. For these and other reasons mentioned above, the Arthritis Foundation and many physicians advocate exercise as treatment because persons with OA generally feel better, perform better and have less pain and disability when they are regularly active.