When walking the range of movement available at the ankle joint is so important. Whenever we place the foot on the floor your body above has to move ahead above that foot. That forward movement happens at the ankle joint, therefore it must be apparent that there really should be nothing that prevents that forward movement at that joint. Problems such as osteoarthritis within the ankle joint will have an effect on that forward motion. Another frequent problem that will interfere with that forward movement are tight calf muscles. They stop the leg moving the desired range of motion above the foot. If that motion is halted than a number of things may occur. Firstly, walking is a lot more difficult. It is more tireing as more effort is necessary to walk. Secondly, your body has got to get that movement from someplace. If it can't get that movement at the ankle, then it may get it at the knee and when that occurs we then walk with a more flexed knee which is actually a difficult way to walk. If the body does not compensate at the knee, then it gets the movement at the midfoot. If that takes place then the arch of the foot collapses which can cause a range of clinical conditions.
For these reasons, doctors want to assess the flexibility at the ankle joint as part of a biomechanical assessment. There are numerous ways of doing this. One of the ways is a non-weightbearing test with the foot and leg up in the air and the feet are just moved on the lower limb and the range of motion is measured. Another, perhaps better method, would be to do what is called 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 actuality of the way that we move.