Strengthening muscles around your joints can help prevent injury, reduce joint pain, and help in recovery from surgery. Many muscles, besides the ones around knees or hips, are involved in balance and gait; and these muscles also influence how much stress joints will experience. Open chain, closed chain, and low impact exercises can help strengthen your knees and hips.
Exercises
Muscles move in pairs. While one muscle contracts, the opposite one relaxes. Muscle relaxation relies on flexibility and so it is important to incorporate flexibility and stretching exercises into your routine.
Open chain exercises
In an open chain exercise your body is stationary while you move your legs or limbs. Open chain exercises, such as sitting in a chair and extending your legs, are helpful when recovering from an ACL (Anterior Cruciate Ligament) injury.
Closed chain exercises
In a closed chain exercise, several body parts move in series, while the leg, foot, or other body part remains stationary. Closed chain exercises are especially helpful in strengthening knees and hips, because they involve more muscles and joints. Squats and lunges are good examples of closed chain exercises. Using closed chain exercises to strengthen your quadriceps (muscles on the front of the thighs), hamstrings (tendons in back of the knee), and abdominal muscles will help support your body weight and put less stress on your hips and knees. A Mayo Clinic-led study also found that strengthening the quadriceps reduced pain and improved function in people with knee-arthritis.
Low impact exercises
Low impact exercises include stationary cycling, tai chi (Chinese exercise system that uses slow, smooth movements), and swimming. Swimming strengthens your muscles without putting strain on your joints. Warm pool water soothes your muscles and prevents muscle injury. Other low impact exercises are floor exercises such as leg lifts, abdominal curls, and crunches.
Physical therapy
Physical therapy focuses on your specific injury or joint problem, as recommended by your doctor. A physical therapist evaluates your pain and knee or hip function, and then establishes a specific program of exercises tailored to your needs. The program will include open chain and closed chain exercises. The exercise program will also include home exercises that you can do on your own. Because some exercises may cause injury when done incorrectly, a physical therapist will teach you the correct way to perform the exercises.
Exercises to avoid
Some exercises or activities may further injure painful joints, because they put sudden pressure or stress on knees or hip joints. Examples are playing tennis and running on hard surfaces.
Sources
http://www.health.harvard.edu/healthbeat/exercise-for-stronger-knees-and-hips?utm
http://www.ihavenet.com/Health-Mayo-Clinic-Hip-Pain-May-be-Relieved-by-Treatments-Other-Than-Surgery.html
http://www.mayoclinic.org/news2011-mchi/6169.html