What systems control our posture?

Question

Answer

There are five dynamic systems for postural control: Musculo-Skeletal, Neuro-Motor, Neuro-Sensory, Gaze Stabilization and the Attentional System.

• Musculo-Skeletal- This system covers joint integrity, muscle strength, and muscle synergies. The musculo-skeletal components are postural alignment, trunk and hip/pelvic control, ankle control as well as our upper body and extremity control.  

• Neuro-Motor- When it comes to our neuromotor system, our nervous system responds in three different ways to control our posture.  It responds reactively, such as when you suddenly lose your balance.  We respond or anticipate proactively, such as when we are about to engage in a task.  For instance, when we pick up a box, our nervous system will send feed-forward signals to our trunk, hip, ankle musculature, and even our upper extremities to anticipate amount of force that needs to be generated in order to lift the box.  We also anticipate how much perturbation is going to be created, so that we do not fall backwards or forward as we make an attempt at lifting the box.  While we are engaged a task, we have this adaptive control or this ongoing adjustment. 

• Neuro-Sensory- The overarching purpose of our sensory system is to know when and how to apply these restoring forces so that we can contain our center of gravity within the limit of stability.  However our central nervous system must have an accurate picture of where the body is in space and whether it is in motion or stationary. 

  There are a variety of sensory inputs coming from our somatosensory, visual, and vestibular subsystems.  All of these sensory inputs must be organized, regulated, and integrated in order to provide us with information of when and how to apply the restoring forces.  It also gives us an accurate picture of where the body is in space, and whether our body needs to be in motion or remain stationary. 

• Gaze Stabilization- Gaze stabilization, in a way, is the motor aspect of our vestibular and our visual sensory systems.  

• Attentional System-  When we are engaged in a task, our postural control and balance are in the background.  They have to operate in a subconscious manner because our attentional system is a conscious event.  We need to free our cortex so that we can motor plan effectively and adapt to changes in the environment.  Our postural control and our balance need to be automatic processes.  A problem happens when our attention overrides our postural control.  If we are constantly thinking about how our body needs to be in the right position or how our balance needs to be maintained, our motions tend to slow down and become inefficient.  For example, when an older adult tries to cross the street they might have to stop and then freeze, because it takes a long time for them to pay attention to what is going on in their environment.  You may also see this in the grocery store.  If you ask your client automatic questions like, “How are you?" or  "Are you having a good day?”, you might not see any change in their gait speed, postural positions or control.  However, when you ask them, “Can you tell me what you did when you were younger?” or “Can you explain to me the theory of relativity?” , you might get a change in their postural control, because it requires a lot more conscious effort.  I put forth cognitive system as an important factor for postural control, because eventually when we train our clients to maintain and improve their postural control and balance, it is in the context of doing something.  We know that the patient is functional and safe when they are able to engage in a novel task that requires a lot of attention or engage in dual tasks while still maintaining their balance and not "freezing".

Editor’s note: This Ask the Expert was adapted from the article "Assessment of Postural Control in the Geriatric Population".  The complete article can be accessed here.