When walking the range of movement needed 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 motion happens at the ankle joint, therefore it should be obvious that there really should be nothing which prevents that forward motion at that joint. Problems such as arthritis in the ankle joint will affect that forward movement. Another frequent problem that can hinder that forward movement are tight calf muscles. They stop the leg moving the necessary range of motion over the foot. In the event that motion is halted than a number of things can happen. Firstly, walking is a lot more difficult. It is more fatiguing as much more effort is needed to walk. Secondly, our bodies needs to get that movement from somewhere. If it can not get that motion at the ankle, then it could possibly get it at the knee and when that occurs we then walk with a more flexed knee which is actually a hard way to walk. If the body does not compensate at the knee, then it gets the motion at the midfoot. If that happens then the arch of the foot collapses and that can lead to a variety of clinical problems.
For these reasons, doctors prefer to look at the range of flexibility at the ankle joint as part of a biomechanical evaluation. There are numerous ways of 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 leg and the range of motion is tested. Another, perhaps better way, would be to do what is called 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 actuality of the way that we move.