When walking the range of motion available at the ankle joint is so important. When we place the foot on the ground the body above has to move forward over that foot. This forward movement takes place at the ankle joint, so it must be evident that there ought to be nothing that stops that forward movement at the ankle. Problems such as osteoarthritis within the ankle joint can affect that forward movement. Another common problem which may hinder that forward movement are tight calf muscles. They stop the leg moving the required range of motion over the foot. In the event that movement is halted than a number of things can happen. Firstly, walking is quite a bit more difficult. It is more tireing as far more efforts are needed to walk. Secondly, your body has to obtain that motion from someplace. If it is unable to get that movement at the ankle, then it could possibly get it at the knee and when that occurs we then walk with a more flexed knee that is a hard way to walk. If the body doesn't compensate at the knee, then it gets the movement at the midfoot. If that occurs then the arch of the foot collapses and that can result in a range of clinical problems.
For these reasons, doctors want to assess the range of motion at the ankle joint as part of a biomechanical examination. There are numerous methods for doing this. One way is a non-weightbearing test with the foot and leg up in the air and the foot is just moved on the leg and the range of motion is assessed. Another, possibly better way, is to do what is called a lunge test. This is a weightbearing measure of the ankle joint flexibility and in that position it is probably a better representation of the actuality of the way that we move.