When walking the range of movement available at the ankle joint is really important. Whenever we put the foot on the ground your body above has got to move forward above that foot. This forward motion comes about at the ankle joint, so it must be clear that there really should be nothing which prevents that forward movement at that joint. Disorders such as arthritis within the ankle joint will affect that forward movement. Another common problem that might obstruct that forward movement are tight calf muscles. They stop the leg moving the required range of motion over the foot. In the event that motion is halted than a number of compensations can happen. Firstly, walking will be a lot more difficult. It is more tireing as far more effort is necessary to walk. Secondly, your body has to get that movement from someplace. If it is unable to get that motion at the ankle, then it could possibly get it at the knee and when that happens we then walk with a more flexed knee which is actually a hard way to walk. If the body doesn't compensate at the knee, then it gets the motion at the midfoot. In the event that happens then the arch of the foot collapses and that can cause a variety of clinical conditions.
For these reasons, clinicians like to assess the flexibility at the ankle joint as part of a biomechanical evaluation. 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 feet are just moved on the leg and the range of motion is tested. Another, perhaps better method, would be to do what is called a lunge test. This is a weightbearing way of measuring the ankle joint range of flexibility and in that position it is probably a better representation of the actuality of the way that we walk.