Variability in kinematic coupling assessed by vector coding and continuous relative phase.

Area of Science:

• Biomechanics
• Human Movement Analysis
• Dynamical Systems Theory

Background:

• Spatio-temporal coordination variability in human movement is crucial for understanding motor control.
• Vector coding and continuous relative phase (CRP) are common but distinct methods for assessing movement variability.
• Discrepancies in findings between studies using different variability metrics hinder direct comparisons.

Purpose of the Study:

• To evaluate if vector coding and CRP align with dynamical systems theories of variability and state-space transitions.
• To determine if trends in movement coordination variability are consistent across vector coding and CRP methods.
• To facilitate more accurate comparisons of kinematic variability research.

Main Methods:

• Theoretical analysis using the Lorenz Attractor model.
• Experimental analysis of rearfoot-forefoot coupling during overground walking (22 subjects).
• Experimental analysis of thigh-leg coupling during treadmill locomotion at varying speeds (5 subjects).

Main Results:

• In the theoretical Lorenz Attractor model, CRP variability aligned better with dynamical systems theory than vector coding.
• Experimental results showed method-dependent differences in the magnitude and timing of variability peaks during walking and treadmill locomotion.
• Average variability trends during treadmill locomotion were consistent across both methods as speed increased.

Conclusions:

• Vector coding and continuous relative phase (CRP) exhibit distinct behaviors, particularly concerning state-space transitions in dynamical systems.
• The choice of metric (vector coding vs. CRP) impacts the observed variability, especially peak variability, in human locomotion.
• Direct comparisons between studies using vector coding and CRP for quantifying movement variability require careful consideration due to potential discrepancies.