[Abstract Title]. - Society for Neuroscience

Poster
275. Posture: Kinematics and Muscle Activity
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 275.14/JJ29
Topic: D.16.d. Kinematics and Muscle Activity
Support: Canadian Institutes for Health Research (MOP- 64414)
Michael Smith Foundation for Health Research Fellowship
Natural Sciences and Engineering Research Council of Canada (RGPIN/239735)
Title: The effect of initial movement dynamics on human responses to postural perturbations
Authors: *C. D. MURNAGHAN, S. N. ROBINOVITCH;
Sch. of Kinesiology, Simon Fraser Univ., Burnaby, BC, Canada
Abstract: Introduction: Falls are a major cause of injury, and often occur while walking,
reaching or bending [1]. Yet, we have little understanding of how the cognitive and
biomechanical demands associated with such tasks influence our ability to recover balance. In
the current study, we used a rocking paradigm to determine how the nature of the baseline task
influences muscle activation patterns and kinematics following an external perturbation to
balance.
Methods: Fourteen women (mean age 23.5±3.5 (SD) yrs) participated in trials where a sudden
backward translation of the support surface was applied as they either stood quietly, or rocked
about the ankles or hips. In all trials, participants were instructed to “recover balance,” and the
perturbation was applied at an instant when the trunk was vertical. Data analysis focused on
comparing static versus dynamic trials in terms of step characteristics, joint angles (acquired with
an 8 camera, 120 Hz motion analysis system), and the time intervals (latencies) between
application of the perturbation and increased activity in various lower extremity muscles
(acquired through surface electromyography at 960 Hz).
Results: We found the nature of the activity at the time of the perturbation influenced both the
pattern of muscle activation in the early-stage balance recovery response, and the subsequent
joint kinematics and tendency to execute a step. When participants rocked forward (in ankle
rocking) or held a static position at the time of the perturbation, we observed early gastrocnemius
(at 94±2.7 (SE) ms) and biceps femoris activity (at 117±3.1 ms), representative of an ankledominant
response [2]. However, when rocking backward, there was early abdominal (at 98±3.7
ms) and rectus femoris activity (at 114±12.0 ms), and later gastrocnemius and biceps femoris
activity (at 124±3.5 ms and 149±3.8 ms), representative of a hip-dominant response. Stepping