Balance on different unstable supports: a complementary approach based on linear and non-linear analyses

Area of Science:

• Biomechanics
• Motor Control
• Human Movement Science

Background:

• Postural control is vital for daily activities and relies on sensory-motor integration.
• Balance training using unstable surfaces is common, but optimal surface selection remains unclear.
• Non-linear dynamical systems analysis offers novel insights into postural control strategies.

Purpose of the Study:

• To investigate the effects of different unstable supports on center of pressure (CoP) trajectory during single-leg balance.
• To compare linear and non-linear analysis techniques in evaluating postural control strategies on various surfaces.
• To determine if different balance training devices influence CoP dynamics.

Main Methods:

• Seventeen healthy adults performed single-leg balance trials on a force plate and three unstable surfaces (soft disc, foam pad, pillow).
• Center of pressure (CoP) trajectories were analyzed using classical stabilometry (sway path, velocity, RMS) and Recurrent Quantification Analysis (RQA).
• RQA parameters included percent recurrence, determinism, maximum line length, and entropy.

Main Results:

• Both classical and RQA analyses revealed significant differences between stable (force plate) and unstable conditions.
• Classical stabilometric parameters showed significant differences among the unstable surfaces.
• RQA analysis indicated that the dynamic/temporal structure of the CoP trajectory was not significantly influenced by the type of unstable surface.

Conclusions:

• Unstable surfaces significantly alter postural control strategies compared to stable surfaces.
• While different unstable surfaces elicit varied responses in classical stabilometric measures, they do not fundamentally change the underlying dynamic control strategy of the CoP trajectory.
• Non-linear analysis (RQA) provides a deeper understanding of the temporal dynamics of postural control, suggesting robustness across different unstable training devices.