Interpreting common standing postural sway measures.

Area of Science:

• Biomechanics
• Human Motor Control
• Postural Stability

Background:

• Force plates are commonly used to measure standing balance.
• Center of Pressure (CoP) Root-Mean-Square (RMS) and Mean Velocity (MV) are prevalent metrics in balance literature.
• Understanding the specific postural control aspects measured by CoP RMS and MV is crucial.

Purpose of the Study:

• To elucidate the distinct aspects of postural control measured by CoP RMS and MV.
• To clarify the implications of these two common force plate metrics in balance research.

Main Methods:

• Analyzed Center of Pressure (CoP) time series from force plate data during quiet standing.
• Calculated Center of Mass (CoM) from motion capture data.
• Computed RMS and MV for CoP, CoM, and the CoP-CoM difference in anterior-posterior (AP) and medial-lateral (ML) directions.

Main Results:

• CoP RMS strongly correlated with CoM RMS (r > .96), indicating it measures the amount of body sway.
• CoP MV showed a high correlation with the RMS of the CoP-CoM difference (r > .90).
• The CoP-CoM difference relates to torque generation for stability, suggesting CoP MV reflects postural control effort.

Conclusions:

• CoP RMS effectively quantifies the extent of body sway during standing.
• CoP MV effectively quantifies the control effort exerted to maintain stability.
• Reporting both CoP RMS and CoP MV provides a more complete understanding of standing balance.