biodex BioSway Operation Manual page 64

CONTENTS
hip Strategy
The hip strategy describes movement about the hip in response to larger losses of balance or
when the support surface does not allow the use of the ankle lever, such as on an icy surface or
when the surface is shorter than the length of the foot. In the hip strategy, activation of muscles
is from the trunk down, or proximal to distal. A loss of balance in the forward direction causes
contraction of the lower-back and hamstring muscles, in that order, to regain balance.
When the hip strategy is used, the muscles of the lower leg (anterior tibialis and gastrocnemius)
are almost silent. Studies have shown that when a walker is used, the body largely abandons the
ankle strategy and relies heavily on the hip strategy for balance. This dependence on the hip
strategy for balance paradoxically may lead to a decrease in ankle sway and contribute to fur-
ther decline in balance arising from loss of ankle strength and flexibility. For this reason the pros
and cons of walker use must be carefully considered before a walker is recommended for fulltime use.
Stepping Strategy
The third strategy employed by the nervous system for balance is the stepping strategy. This
strategy is used when the loss of balance exceeds the area of stability and the person is forced to
step or fall.
SenSory orGanIzatIon for balance
Perhaps the most confusing part of a balance evaluation is the part that examines the sensory
system and its contribution to balance. The sensory system includes the eyes, ears, vestibular
apparatus (inner ear), somatosensory system (touch and proprioception), taste, and smell. The
parts of the sensory system that contribute directly to balance are the visual, vestibular, and
somatosensory (touch and proprioception) systems. The use of multiple systems in balance
allows us to learn new movements quickly and to fine-tune and easily repeat familiar move-
ments.
The sensory system receives input from the environment through specialized receptors located
in the sensory end-organs in the eyes, vestibular apparatus of the inner ear, muscle spindles,
Golgi tendon organs, and touch receptors in the skin. Sensory input is transmitted to the spinal
cord via afferent nerve fibers and then to the brain via spinal nerve tracts such as the spinothala-
mic tract (pain and temperature) and the dorsal column medial lemniscal tract (fine touch, mus-
cle and tendon position sense).
Sensory input provides a continuous flow of information to the CNS, which in turn utilizes this
incoming information to make decisions about movement. The CNS sifts, compares, weighs,
stores, and processes sensory input and uses this information to alter the force, speed, and range
of a movement.
vision
Vision is a critical part of our balance system. It allows us to identify objects and determine their
movement and tells us where we are in relation to other objects (object-to-object orientation).
When we use vision to gather information about the position of our body in the environment or
to determine the position of one body part vis à vis another, then vision is providing proprio-
ceptive information to the CNS as well (visual proprioception).
Vision works in conjunction with the vestibular system, comparing information about velocity
and rotation from the vestibular system with actual visual information. The visual system is a
combination of both central and peripheral vision, although some research has suggested that
peripheral vision is more important for postural control and balance than central vision
(Shumway-Cook & Woollacott, 2001).
APPENDIX C — C-2 —