Is your risk for arthritis genetic or activity related?

Both. The cause of autoimmune type arthritis such as rheumatoid arthritis is unknown but may occur when certain factors in the environment trigger the activation of the immune system to inappropriately attack the body's own tissues. There may be some genetic predisposition. Repetitive trauma, instability of joints, and fractures can lead to "wear and tear" osteoarthritis or post-traumatic arthritis.
Both. The emerging evidence suggests both a genetic predisposition as well as environmental influences playing a role in most types of arthritis. Other influences like poor nutrition, diabetes, smoking, obesity and lack of physical fitness certainly play a role.