Coordination dynamics of (a)symmetrically loaded gait

Area of Science:

• Biomechanics
• Human Movement Science
• Dynamical Systems Theory

Background:

• Asymmetries in limb resonant frequencies alter coordination dynamics, affecting relative phase and stability.
• The extended Haken-Kelso-Bunz (HKB) model successfully explains these effects in rhythmic limb movements.
• Previous applications to walking showed phase deviations but not stability changes, possibly due to treadmill constraints or gait complexities.

Purpose of the Study:

• To investigate the effects of asymmetrical and symmetrical leg loads on walking coordination dynamics overground.
• To test the applicability of the HKB model to overground walking stability under load conditions.
• To determine if load-induced stability changes are masked by treadmill use or gait-specific factors.

Main Methods:

• Participants walked overground with asymmetrical (3 or 6 kg ankle weights) and symmetrical loads.
• Walking speed and cadence were controlled using a metronome or self-paced conditions.
• Coordination dynamics were measured by relative phase (ϕ) mean and standard deviation (SDϕ).
• Individual leg local dynamic stability was assessed using the maximum Lyapunov exponent (λMAX).

Main Results:

• Asymmetrical loads induced phase deviations from antiphase, with the loaded leg lagging.
• Both SDϕ and λMAX increased under asymmetrical loading, indicating decreased stability.
• Symmetrical loads did not affect phase but decreased stability.
• The HKB model accurately captured coordination dynamics but showed limitations in modeling load effects on individual limb stability.

Conclusions:

• The HKB model effectively describes coordination dynamics in overground walking.
• Asymmetrical leg loading disrupts gait stability and phase relationships, consistent with theoretical predictions.
• Load-induced stability changes in walking are observable overground, and the HKB model's predictive power for these effects is limited.
• This study highlights the importance of considering overground conditions and specific load impacts when applying oscillator models to human locomotion.