When walking the range of movement available at the ankle joint is so important. When we put the foot on the ground the body above needs to move ahead above that foot. This forward motion takes place at the ankle joint, so it must be obvious that there really should be nothing which stops that forward movement at the ankle. Problems such as osteoarthritis within the ankle joint will impact that forward movement. Another common problem that may hinder that forward motion are tight calf muscles. They stop the leg moving the required range of motion above the foot. If that movement is restricted than a number of compensations may occur. Firstly, walking is a lot harder. It is more fatiguing as far more efforts are needed to walk. Secondly, your body has to obtain that motion from somewhere. When it can't get that motion at the ankle, then it could get it at the knee and when that takes place 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 motion at the midfoot. In the event that happens then the arch of the foot collapses and that can cause a range of clinical disorders.
For these reasons, clinicians want to measure the range of flexibility at the ankle joint as part of a biomechanical examination. There are many methods for 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 lower limb and the range of motion is measured. Another, probably better method, would be to do what is known as a lunge test. This is a weightbearing way of measuring the ankle joint flexibility and in that position it is usually a better representation of the reality of the way that we move.