When walking the range of motion needed at the ankle joint is so important. When we place the foot on the ground your body above is required to move forward above that foot. That forward movement takes place at the ankle joint, therefore it should be obvious that there really should be nothing that prevents that forward movement at the ankle. Problems such as arthritis in the ankle joint may affect that forward motion. Another frequent problem that will obstruct that forward motion are tight calf muscles. They stop the leg moving the necessary range of motion above the foot. In the event that motion is halted than a number of things may occur. Firstly, walking is a lot harder. It is more tireing as far more efforts are needed to walk. Secondly, our bodies has to get that movement from somewhere. When it can't get that motion at the ankle, then it might get it in the knee and when that occurs we then walk with a more flexed knee which is actually a hard way to walk. If the body does not compensate at the knee, then it gets the movement at the midfoot. In the event that occurs then the arch of the foot flattens which can bring about a range of clinical problems.
For these reasons, clinicians prefer to measure the range of motion at the ankle joint as part of a biomechanical evaluation. There are several ways of doing this. One way is a non-weightbearing examination with the foot and leg up in the air and the feet are just moved on the leg and the range of motion is assessed. Another, probably better way, is to do what is known as a lunge test. This is a weightbearing way of measuring the ankle joint flexibility and in that position it is usually a better representation of the actuality of the way that we walk.