What is “mobility”?
Mobility. It is a term that is thrown around a lot, but what does it really mean. The dictionary defines mobility as ‘the ability to move or be moved freely or easily”. In Physical Therapy we use the term to in reference to the rehabilitation of an affected body part(s) to regain its strength and function to improve a person’s ability to move freely within the environment they move in and interact with. A dancer might require 120 degrees of active ROM of their hip to perform an arabesque. A baseball pitcher might require 100 degrees of shoulder external rotation to throw the ball. A 6 foot gentleman might require 120 degrees of knee flexion to go down the stairs after a knee replacement. They are all examples of mobility necessary to perform freely within the environment they move in.
There are many factors that contribute to a persons mobility. At each specific joint many elements contribute to the movement of the joint in the full range of motion. This could include restricted muscle tissue, joint capsules, and joint space. But our bodies do not operate in single pieces. Our entire nervous system contributes to mobility through motor control dictated by the availability of proprioception, vestibular control, and sensation (touch, visual, auditory). Proprioception is the ability of your central nervous system to know where your limb is in space. Your vestibular system contributes to maintaining balance and special awareness. Mobility comes from the multi sensory integration of all of this information coming together.
That is why a dancer that had the ability to lift her leg above her head before an ankle sprain can no longer do that. Her hip joint hasn’t changed. Her flexibility in her hamstring hasn’t changed. But her body is reacting to a stressful event, by restricting mobility to create a safer environment for the ankle by creating stability at the hip and knee. Until the ankle has regained the strength, ROM, and all sensory functions including proprioception, motor control, and sensation, mobility will be restricted.
So flexibility is a function of mobility, but it is not the sole reason that dancer can perform the arabesque with ease. It is the integration of using the whole nervous system to create an environment of safety to strengthen in the ROM available is the way to gain permanent mobility or the ability to move freely within the environment. As physical therapists we are specialists in evaluating all of these systems and helping them work together in equilibrium after an injury or in pursuit of improving performance. By training the nervous system in connection with strength and flexibility, mobility will be enhanced and maintained.