Trunk-pelvic coordination during unstable sitting with varying task demand: A methodological study

• Published in: Journal of biomechanics 2021-03, Vol.118, p.110299-110299, Article 110299
• Main Authors: Acasio, Julian C., Nussbaum, Maury A., Hendershot, Brad D.
• Format: Article
• Language: English
• Subjects: Biomechanics; Coordination; Correlation analysis; Gravity; Instability; Inter-segmental coordination; Low back pain; Pelvis; Postural control; Stability; Stiffening; System theory; Vector coding; Velocity
• ISSN: 0021-9290; 1873-2380
• DOI: 10.1016/j.jbiomech.2021.110299

Unstable sitting is used commonly to evaluate trunk postural control (TPC), typically via measures based on center-of-pressure (CoP) time series. However, these measures do not directly reflect underlying control/movement strategies. We quantified trunk-pelvis coordination during unstable sitting using vector coding (VC) and correlated such coordination with CoP-based outcomes across varying task demands. Thirteen uninjured individuals (11 male/2 female) sat on an unstable chair at four instability levels, in a random order, defined relative to the individual gravitational gradient (∇G): 100, 75, 60, and 45%∇G. VC assessed trunk-pelvic coordination, and coupling angles classified movements as: 1) anti-phase, 2) in-phase, 3) trunk-phase, or 4) pelvic-phase. With decreasing %∇G (i.e., increasing instability), we found: increased anti-phase movement in the sagittal and frontal planes; decreased in-phase movement in the sagittal and frontal planes; and increased in-phase and pelvic-phase movement in the transverse plane. In the sagittal and frontal planes, we observed significant weak-to-moderate correlations between anti-phase and in-phase movements (0.288