biodex BioSway Operation Manual page 63

APPENDIX C
movement StrateGIeS for balance, SenSory orGanIzatIon, aGe-related
chanGeS In balance and ctSIb teSt reSult InterpretatIon.
movement StrateGIeS for balance (Robertson)
According to the Systems Approach to motor control, the nervous system uses preprogrammed
strategies or synergies to simplify movement. The central nervous system (CNS) takes advan-
tage of pathways that link together groups of muscles in a flexible and repeatable sequence. This
linking or packaging of muscle groups allows the brain to respond to an infinite variety of cir-
cumstances by drawing on muscle responses that have been successful in the past. This linking
or packaging of muscles in a repeatable sequence is called a movement strategy.
Utilizing a movement strategy simplifies the way the nervous system accesses a motor reaction
in response to sensory input. Strategies are automatic reactions that have evolved over time, tak-
ing into account biomechanical and environmental constraints. Strategies that are successful for
maintaining balance are stored so that the CNS is not forced to start from scratch each time a
loss of balance occurs. Strategies are automatic reactions, slower than reflexes but much faster
than voluntary movements. Three anterior-posterior movement strategies have been identified:
the ankle, hip and stepping strategies.
ankle Strategy
The nervous system employs the ankle strategy in response to small losses of balance and to
adjust balance in quiet standing. The ankle strategy is also called ankle sway and uses the length
of the foot as a lever to correct for minor losses of balance. In the ankle strategy, activation of the
leg muscles is from the floor up or distal to proximal. A small loss of balance in the forward
direction causes contraction of the gastrocnemius, hamstrings, and lower-back muscles, in that
order, to bring the body back into balance.
Figure C.1 Figure C.2
Figures C.1 and C.2: The ankle strategy that is used in response to small perturbations is also called
ankle sway. Illustration © Wild Iris Medical Education.
A small loss of balance in the backward direction causes contraction of the anterior tibialis, quadri-
ceps, and lower abdominal muscles, in that order, to bring the body back into balance. Our bodies
are constantly using this strategy to adjust for minor losses of balance. For example, you would
use the ankle strategy to maintain balance when standing on a bus, to correct for losses of balance
and to prevent yourself from falling as the bus changes speed. You might also use the ankle strate-
gy to maintain your balance on a very soft surface such as thick grass or a piece of foam.
— C-1 — APPENDIX C