When walking the range of movement needed at the ankle joint is really important. When we are walking and place the foot on the ground, the body above the foot has to move forward over that foot. This forward motion occurs at the ankle joint over a foot that is fixed on the ground, therefore it should be obvious that we do not want anything that limits the motion at this joint and prevents that forward movement of teh body over the ankle. Disorders such as arthritis within the ankle joint can have an effect on that forward movement. Another common problem that could interfere with that forward motion are tight calf muscles. They stop the leg moving the required range of motion above the foot. In the event that movement is halted than a number of compensations can occur. Firstly, walking is a lot more difficult. It is more fatiguing as more efforts are needed to walk. Secondly, our bodies has got to obtain that motion from someplace. When the body is unable to get that motion at the ankle joint, then it may get the motion by moving other joints such as the knee. In that case, we then walk with a more flexed knee that is a difficult and energy consuming way to walk. If the body doesn't compensate for that limited motion at the ankle with a more flexed knee, then it gets the extra movement need at the midfoot. In the event that happens then the arch of the foot collapses which can bring about a range of clinical disorders.
For these reasons, doctors prefer to look at the mobility at the ankle joint as part of a biomechanical examination. There are numerous ways of doing this. One way is a non-weightbearing examination 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, probably better way, 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 probably a better representation of the actuality of the way that we walk.