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

Area of Science:

• Biomechanics
• Motor Control
• Human Movement Analysis

Background:

• Unstable sitting is commonly used to assess trunk postural control (TPC).
• Current methods, like center-of-pressure (CoP) analysis, do not fully capture underlying movement strategies.
• There is a need for methods that directly quantify trunk coordination during postural tasks.

Purpose of the Study:

• To quantify trunk-pelvis coordination during unstable sitting using vector coding (VC).
• To correlate VC-derived coordination patterns with traditional CoP-based measures.
• To determine if VC can differentiate between varying levels of postural task demand.

Main Methods:

• Thirteen healthy individuals sat on an unstable chair at four instability levels (100% to 45% ∇G).
• Vector coding (VC) analyzed trunk-pelvis coordination, classifying movements into anti-phase, in-phase, trunk-phase, or pelvic-phase.
• Coordination patterns were correlated with center-of-pressure (CoP) measures.

Main Results:

• Increasing instability led to more anti-phase movements in sagittal/frontal planes and more in-phase/pelvic-phase movements in the transverse plane.
• Correlations between CoP measures and trunk coordination were generally weak.
• VC successfully discriminated between instability levels, identifying stiffening (in-phase) at low instability and anti-phase coordination at high instability.

Conclusions:

• Vector coding provides a more direct measure of trunk postural control strategies during unstable sitting compared to CoP-based methods.
• VC can differentiate between varying postural demands and movement strategies.
• These findings establish a baseline for studying TPC in populations with impairments.