When walking the range of motion available at the ankle joint is so important. When we place the foot on the ground your body above needs to move forward above that foot. That forward motion comes about at the ankle joint, therefore it ought to be obvious that there really should be nothing that prevents that forward movement at that joint. Disorders such as osteoarthritis within the ankle joint can have an effect on that forward movement. Another common problem which can hinder that forward movement are tight calf muscles. They stop the leg moving the desired range of motion over the foot. If that motion is stopped than a number of compensations can happen. Firstly, walking is a lot more difficult. It is more fatiguing as far more efforts are needed to walk. Secondly, the body has got to get that movement from someplace. When it is unable to get that motion at the ankle, then it might get it at the knee and when that happens 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 takes place then the arch of the foot collapses which can result in a variety of clinical disorders.
For these reasons, doctors like to measure the range of motion at the ankle joint as part of a biomechanical examination. There are many ways of 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 tested. Another, possibly better approach, would be to do what is called a lunge test. This is a weightbearing measure of the ankle joint range of flexibility and in that position it is usually a better representation of the actuality of the way that we walk. Research has linked the lunge test to a number of different clinical problems, especially in athletes.