When you go upstairs or get up from a chair, you must use the quadriceps that are situated on the front of the thigh. These muscles are very well developed on cyclists and soccer players as they are used in straightening the leg and kicking a ball.

I find these muscles very often test weak or work below par in many knee conditions. The lower fibres of the muscles very often are weak when the knee is tested in the last 10-15º of straightening out. If this postion shows weakness you may feel as if the knee 'gives way' unexpectedly now and then.

The quadriceps are made up of four different muscles:

Rectus Femoris - runs from the front of the pelvis down the middle of the thigh into the kneecap and through to the bump at the top of the shin bone. While sitting put the flat of your hand on the front of the mid thigh area. Now straighten your leg and lift the foot off the floor - you should feel the muscle contracting.

Vastus (2. lateralis; 3. medialis and 4. intermedius). These muscles run from the top of the thigh to either side of the knee cap. If you move your thumb and finger down the thigh to just above the knee cap then straighten the knee fully, then let it bend a little and straighten it again you will feel the muscles working.

As mentioned above weakness in these muscles interferes with the function of stair climbing, walking up an incline as well as getting up and down from a sitting position.