Related Experiment Video
Updated: Jul 7, 2026
Experimental Methods to Study Human Postural Control
Published on: September 11, 2019
Effects of trunk exertion force and direction on postural control of the trunk during unstable sitting
HyunWook Lee1, Kevin P Granata, Michael L Madigan
1School of Biomedical Engineering and Sciences, Virginia Polytechnic Institute and State University, Mail Code 0298, Blacksburg, VA 24061, USA. hwlee@vt.edu
Background:
Pushing and pulling exertions have been implicated as risk factors of low-back disorders. In an attempt to investigate the mechanisms by which pushing and pulling influence risk for low-back disorders, the goal of this study was to investigate the effects of trunk exertion force and exertion direction on postural control of the trunk during unstable sitting.
Methods:
Seat movements were recorded while subjects maintained a seated posture on a wobbly chair against different exertion forces (0N, 40N, and 80N) and exertion directions (trunk flexion and extension). Postural control of the trunk was assessed from kinematic variability (root-mean-squared amplitude and 95% ellipse area) and non-linear stability analyses (stability diffusion exponent and maximum finite-time Lyapunov exponent).
Findings:
Kinematic variability and non-linear stability estimates increased as exertion force increased including root-mean-squared amplitude (P<0.001), 95% ellipse area (P<0.001), stability diffusion exponent (P=0.042), and maximum finite-time Lyapunov exponent (P<0.001). A subset of measures indicated postural control of the trunk was poorer during flexion exertions compared to extension exertions including root-mean-squared amplitude (P<0.001), 95% ellipse area (P=0.046), and maximum finite-time Lyapunov exponent (P=0.002).
Interpretation:
Trunk exertion force and exertion direction affect postural control of the trunk. This study may aid in understanding how pushing and pulling exertions can potentially contribute to low-back disorders.
