biodex BioSway Operation Manual page 18

CLINICAL CONSIDERATIONS
proprioception and Kinesthetic Input
The proprioceptive component of balance involves mechanoreceptors located within the skin,
muscle tendons, and ligaments surrounding a joint. These structures play an important role in
providing sensory information relating to touch, body position and rate of movement from
external cues or conscious movement patterns associated with daily living. They also assist with
providing adequate response to perturbations or noxious stimuli via reflex loops within the
spinal cord to protect the body from injury.
Two such mechanoreceptors of importance to postural balance are: Muscle Spindle Fibers (MSF)
and Golgi Tendon Organs (GTO). They consist of afferent nerve fibers and provide the nervous
system with continual impulses regarding the status of a muscle at rest and during movement,
they are crucial to maintaining postural balance.
Muscle Spindle Fibers:
1. Provide information in regards to muscle length, and the rate of change of a muscle's length
2. Myotatic Reflex.
• This is possible due to efferent branches which complete a loop through the spinal cord with
the afferent tracts
• Causes a muscular contraction to protect the muscle during rapid stretching
- Example: during force inversion of the ankle during walking
Golgi Tendon Organs:
1. Located in the tendon near the musculotendinous junction
2. Serve as the protective mechanism to relax an overstretched muscle
3. Senses tension within the prospective muscle and transmits the information to the CNS, and
through polysynaptic reflexes
• Inhibits the motor neurons of the contracting muscle.
• Muscle tension is monitored through out the range of motion by the GTO; this is crucial to pre-
venting muscle strains and tears.
lImItS of StabIlIty
The Limits of Stability (LOS) for standing balance is defined as the maximum angle a person's
body can achieve from vertical without losing balance. Basically, how well can a person control
their Center of Gravity (COG) once it comes outside their Base of Support (BOS). Maintaining
LOS is the result of integration of the sensory and motor control aspects of balance and plays an
important role in activities of daily living. Once the LOS is exceeded a corrective strategy must
take place in order to prevent a fall or stumble. LOS for bilateral stance in normal adults is 8º
anterior, 4º posterior, and 8º laterally to the right and 8º.
the limits of Stability (loS) test
This test challenges patients to move and control their center of gravity within their base of sup-
port. During each test trial, patients must shift their weight to move the cursor from the center
target to a blinking target and back as quickly and with as little deviation as possible. The same
process is repeated for each of nine targets. Targets on the screen blink in random order. Three
skill levels allow the targets to be grouped closer together or spread further apart. If desired, sin-
gle leg LOS test may be performed but no bilateral comparison is provided.
This test is a good indicator of control within a normalized sway envelope. Poor control, incon-
sistencies or increased times suggests further assessment for lower extremity strength, proprio-
ception, vestibular or visual deficiencies may be indicated. The default setting for the LOS test is
75% LOS (moderate skill level).
A static force plate is typically used to record a patient's movement of their COG over their BOS
as an average amount of angular displacement. This is then further defined as a percentage of the
patient's LOS. For example, at 100% LOS, a patient will fall if they do not respond accordingly,
(ankle, knee, hip strategy, or take a step to correct the BOS).
— 4-3 — CLINICAL CONSIDERATIONS