When walking the range of motion needed at the ankle joint is so important. Once we put the foot on the floor your body above is required to move ahead over that foot. That forward movement comes about at the ankle joint, therefore it must be evident that there really should be nothing which stops that forward movement at that joint. Problems such as arthritis within the ankle joint will affect that forward movement. Another common problem that might interfere with that forward movement are tight calf muscles. They stop the leg moving the desired range of motion above the foot. If that movement is stopped than a number of things may occur. Firstly, walking is a lot harder. It is more fatiguing as much more effort is needed to walk. Secondly, your body needs to get that movement from someplace. If it can't get that movement at the ankle, then it can get it in the knee and if that takes place we then walk with a more flexed knee that is a difficult way to walk. If the body does not compensate at the knee, then it gets the movement at the midfoot. If that happens then the arch of the foot flattens which can lead to a range of clinical problems.
For these reasons, doctors prefer to look at the range of motion at the ankle joint as part of a biomechanical assessment. There are many methods for 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 measured. Another, possibly better way, would be to do what is known as a lunge test. This is a weightbearing way of measuring the ankle joint range of motion and in that position it is probably a better representation of the actuality of the way that we move.