Knee pain can be related to overuse where small stresses are repeated a large number of times without allowing adequate recovery, for example running too much too soon, or excessive jumping. Or injuries can be acute where the injury is caused by an impact or twisting such as an anterior cruciate ligament injury. An overuse injury can also be considered to be acute if it is painful or inflammed.
Knee pain is commonly caused by doing too much too soon when you haven't exercised for a long period of time - especially high-impact aerobics; walking, running or jumping on hard surfaces or uneven ground; excessive running up and down stairs (When you walk upstairs you are putting pressure on your knees that is equivalent to four times your body weight, when running up the stairs it can be eight times your body weight).

Prevent knee pain by keeping the muscles that support your knees strong and flexible. Start out slowly. Walk before you run - before you engage in a strenuous high impact activity such as jogging or running, try walking for a week. If walking causes knee pain, you shouldn't be running. Warm up and stretch before working out. Give your body a chance to recover from exercise. If you do high impact activities take every other day off. Avoid running up and down stairs and full squats. Doing knee exercises to strengthen and stretch the muscles that support the knee are vital for knee pain and injury prevention. Proper footwear is also important, especially if walking or running on hard surfaces. Keep your weight under control. Reducing one's weight reduces stress upon the knee.

Reflexology is a valuable tool that helps with not only the pain associated with knee issues, but is also a means for keeping the knees strong and healthy.
These are the main reflex points on which I focus, when attending a client with knee weakness.

Knee Reflex: In order to strengthen the knee joint and to send healing energy to any injured area.
Location: a small, soft triangular section, about 1 inch below the ankle bone.

Spine Reflex: The spine is the main support for the entire body, taking some of the weight off the knees.
Location: inside portion of the feet, running from the neck of the big toes, to the edge of the heel (it follows the natural curve of the instep).

Adrenal Gland Reflex: The adrenal glands increase the body’s natural anti-inflammatory hormones, which seem to soothe problematic knees.
Location: situated directly on the top portion of the kidney reflex points.