Arthritis or another medical condition could be the cause of a stiff knee. Overuse of the joints and muscles in your knee can also cause stiffness. Strengthening your hamstrings, quadriceps and other knee-supporting muscles protects your knees from stress and the shock of impact, according to American Academy of Orthopaedic Surgeons. Stretching your muscles improves flexibility, which can prevent stiffness and injury.
Straight Leg Lift
Begin the straight leg lift by lying on your back with your right leg straight and your left leg bent at the knee with your foot flat on the floor. Slowly lift your right leg about a foot off the floor while tightening your thigh muscles. Hold the position for three to five seconds, slowly lower your leg to the floor and repeat the lift. Switch to your left leg while your right leg is bent.
Stand and hold onto the back of a chair or a wall for balance. Lift one foot, grab your ankle and bring the heel toward your buttocks. Hold the position for 30 seconds. You should feel the pull in your quadriceps muscle in the front of your thigh. Keep your knees together. Stop the stretch once your feel the pull in your thigh. Repeat with your other leg.
Stand with your back against the wall and spread your feet about shoulder-width apart. Perform a squat by bending your knees to lower your body slowly; keep your back against the wall. Once your knees are bent at a 30-degree angle, hold the position for a count of five to 10 and slowly raise yourself to starting position. Don't perform squats if they cause knee pain.
Sit on the floor with your back straight and tall. Straighten your legs out in front of you and relax your feet. Place your hands palms-down on the floor and slide them toward your ankles. Hold the position for 30 seconds. You should feel the pull in your hamstring muscles along the back of your thighs and notice the stretch behind your knees. Stop sliding your hands once you feel the stretch in your muscles. Avoid arching your back or locking your knees.
Perform this exercise in the pool to take advantage of the buoyancy of water, which relieves stress on your joints. Hold onto the side of the pool and allow your legs to float. Gently kick your legs to stretch your hamstrings and quadriceps. The kicks work your muscles and flex your knee joints in the same way as leg lifts and squats, but without the added tension of gravity.
Perform a low-impact activity, such as walking, to warm up your muscles for five to 10 minutes before exercising. Consult your doctor about pain or stiffness before performing knee exercises. Pain or stiffness that does not improve could signal a medical condition that needs more aggressive therapy.