When walking the range of movement needed at the ankle joint is so important. Whenever we put the foot on the floor the body above needs to move forward over that foot. That forward motion occurs at the ankle joint, so it must be clear that there ought to be nothing that prevents that forward movement at the ankle. Problems such as osteoarthritis in the ankle joint can have an effect on that forward movement. Another common problem that may interfere with that forward motion 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 may occur. Firstly, walking will be a lot more difficult. It is more tireing as more effort is needed to walk. Secondly, your body needs to get that motion from somewhere. If it can not get that motion at the ankle, then it can 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 occurs then the arch of the foot collapses which can lead to a variety of clinical disorders.
For these reasons, doctors prefer to measure the flexibility at the ankle joint as part of a biomechanical evaluation. There are many ways of 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 leg and the range of motion is tested. Another, perhaps better approach, is to do what is known as a lunge test. This is a weightbearing measure of the ankle joint range of motion and in that position it is probably a better representation of the reality of the way that we move.