[Abstract Title]. - Society for Neuroscience

Abstract: Anticipatory postural adjustments (APA‟s) serve to prepare posture in advance of
perturbations expected from voluntary movement. This study examined whether APA‟s are
adjusted when postural support is increased using familiar (grip) and novel (bite) strategies. 12
healthy subjects (4 male, 8 female) stood on dual force platforms and performed 20 randomised
left and right rapid leg lift tasks in response to a visual cue under 4 conditions: unsupported (US),
bilateral handgrip (HG), bite (BP) and a combined handgrip and bite (H+B) condition. APA
onset and onset of unloading of the lift limb were identified from vertical ground reaction forces
and used to calculate APA duration and amplitude. These were compared between conditions
and repetitions. Lower limb acceleration was recorded by accelerometers placed on the patella.
APA duration was affected by support condition and was shortest with maximum support (H+B),
followed by HG, BP and US. APA amplitude was smallest in the H+B and HG conditions and
significantly larger in BP and US trials. Lower limb acceleration was greater during US trials
compared to HG and H+B, but was not different between HG, BP and H+B conditions. Thus,
changes in APA duration and amplitude between the latter 3 conditions were related to external
support and not due to variations in acceleration.
To determine how long it takes the neuromuscular system to refine postural strategies after
presentation of a new support, an average of the amplitude and duration of the first 2, middle 2
and last 2 repetitions of each leg movement were compared within conditions. The APA had
adapted within the first trial of each task and no further adaptation occurred in APA duration for
any condition. However, amplitude in the most novel condition, BP, was decreased between the
first and middle repetitions. Tasks in which familiar external supports were available required no
further refinement of APA‟s.
The results suggest that with increased external support and sensory cues, less preparation
(decreased APA amplitude and duration) is required and the central nervous system (CNS) can
adapt within the first trial to optimise balance. This supports the hypothesis that postural
preparation and voluntary movement are controlled by parallel processes that allow re-weighting
of postural commands to meet specific demands. In healthy subjects it is evident that the CNS is
able to rapidly adapt to, and integrate multiple sensory and support strategies, from the first
repetition to maintain balance during internal perturbations. This suggests that a healthy nervous
system can predict the effect of changes in postural set and make immediate adjustments to
postural preparation.
Disclosures: L.M. Hall , National Health and Medical Research Council of Australia, B.
Research Grant (principal investigator, collaborator or consultant and pending grants as well as
grants already received); S.G. Brauer, National Health and Medical Research Council of
Australia, B. Research Grant (principal investigator, collaborator or consultant and pending
grants as well as grants already received); P.W. Hodges, National Health and Medical Research
Council of Australia, B. Research Grant (principal investigator, collaborator or consultant and
pending grants as well as grants already received).
Poster
275. Posture: Kinematics and Muscle Activity