Balance

seesaw

the ability to maintain equilibrium and orientation in a gravitational environment. Horak, F.B. (1987). Clinical measurement of postural control in adults. Physical Therapy, 67, 1881-1885.

The behavior that we call balance results from an interaction of many systems and subsystems. In dynamical systems terms, balance is a collective variable, a measure of the way a system or organism reduces a huge number of potential postural responses to a finite set of possibilities.

interacting subsytems

Interacting subsystems: Fay Horak (1991, p.23) depicts the subsystems that influence balance behavior as interlocking circles.

Horak, F.B. (1991). Assumptions underlying motor control for neurological rehabilitation. in Foundation for Physical Therapy. Contemporary Management of Motor Control Problems, Proceedings of the II-STEP Conference. Alexandria, VA: Author.

Balance rehabilitation versus vestibular rehabilitation

While therapists must often consider the simultaneous interaction of several systems, they occasionally encounter patients whose balance problems result from defects in one specific system. Patients with primary pathology of the vestibular system are treated differently from patients with multi-system "balance disorders."

vestibular rehabilitation
Musculoskeletal system

The musculoskeletal system must possess adequate strength and range of motion to control the gravitational and inertial forces it encounters.

Ground reaction forces help us understand the musculoskeletal system's task.

Motor Coordination
(temporal and spatial sequence of muscle activation)

Horak and Nashner (1986) found that subjects’ balance behavior, while complex, consisted of "a limited repertoire of central motor programs." These stereotyped movement patterns (synergies) were influenced but not dependent on peripheral feedback. They named these the:

  1. ankle strategy
  2. hip strategy
  3. stepping strategy

Horak, F.B., & Nashner, L.M. (1986). Central programming of postural movements: Adaptation to altered support surface configurations. Journal of Neurophysiology, 55, 1369-1381.

Perception of orientation How do we know where we are in space?

How do we know when our postural orientation is changing? What is our frame of reference?

From what sensory systems do we obtain the information necessary to construct a frame of reference?

  1. visual
  2. somatosensory
  3. vestibular
Sensory Organization

We must organize and interpret the raw information we receive from the three sensory systems.

Does a particular system dominate in this process?

What if one system provides information which conflicts with that of a second system?

When might abnormalities in sensory organization lead to balance problems?

How can a therapist assess sensory organization in the clinic?

How can we visualize a simple "flow-through" model of sensory organization and its interaction with other subsystems?

"Predictive central set," also called "central preprogramming"

Fay Horak's (1991, p. 23) term for the CNS' ability to:

Horak, F.B. (1991). Assumptions underlying motor control for neurological rehabilitation. in Foundation for Physical Therapy: Contemporary Management of Motor Control Problems, Proceedings of the II-STEP Conference. Alexandria, VA: Author.
Environmental Adaptation

The motor strategy a person uses depends in part on the type of surface, or on whether they are sitting or standing.

Other resources for the study of balance evaluation and treatment:

Special Series '97 -- New Perspectives on Balance, published in May and June 1997 issues of Physical Therapy

Balance retraining with regard to measures of steadiness, symmetry, and dynamic stability, from Physical Therapy, May 1997

Harada N. Chiu V. Damron-Rodriguez J. Fowler E. Siu A. Reuben DB. (1995). Screening for balance and mobility impairment in elderly individuals living in residential care facilities. Physical Therapy, 75, 462-9.

Functional Reach Test (also described here, although you'll have to search the page).

Last updated 12-20-01 Dave Thompson PT