When walking the range of motion needed at the ankle joint is really important. Whenever we put the foot on the floor the body above needs to move forward above that foot. That forward movement comes about at the ankle joint, therefore it ought to be clear that there really should be nothing which stops that forward movement at that joint. Disorders such as arthritis within the ankle joint can have an effect on that forward motion. Another common problem which may obstruct that forward movement are tight calf muscles. They stop the leg moving the desired range of motion over the foot. If that motion is restricted than a number of compensations can occur. Firstly, walking is quite a bit more difficult. It is more fatiguing as far more effort is necessary to walk. Secondly, the body has to obtain that movement from someplace. If it is unable to get that movement at the ankle, then it could get it at the knee and if that occurs we then walk with a more flexed knee which is actually a difficult way to walk. If the body doesn't compensate at the knee, then it gets the movement at the midfoot. In the event that happens then the arch of the foot collapses and that can bring about a variety of clinical problems.
For these reasons, doctors prefer to look at the mobility at the ankle joint as part of a biomechanical evaluation. There are many methods for doing this. One of the ways is a non-weightbearing test with the foot and leg up in the air and the foot is just moved on the lower limb and the range of motion is assessed. Another, possibly better way, is to do what is known as a lunge test. This is a weightbearing way of measuring the ankle joint range of motion and in that position it is usually a better representation of the reality of the way that we move. The lunge test has shown to be both reliable and valid as a clinical assessment technique.