The choice of reference point for computing sagittal plane angular momentum affects inferences about dynamic balance

Area of Science:

• Biomechanics
• Human locomotion
• Robotics

Background:

• Whole-body angular momentum in the sagittal plane is crucial for assessing dynamic balance during walking.
• Calculating angular momentum requires selecting a reference point, commonly the center of mass (CoM) in biomechanics, but the center of pressure in robotics.

Purpose of the Study:

• To investigate whether the choice of reference point (CoM vs. base of support) affects the interpretation of dynamic balance control during perturbed walking.
• To determine if different reference points influence the understanding of intersegmental coordination patterns during balance recovery.

Main Methods:

• Eleven healthy adults walked on a treadmill with induced balance disturbances (accelerations).
• Sagittal plane angular momentum was calculated using two reference points: center of mass (CoM) and the leading edge of the base of support.
• Principal component analysis was employed to assess the impact of reference point choice on coordination pattern interpretation.

Main Results:

• Peak angular momentum during perturbed walking was consistently correlated with perturbation amplitude, irrespective of the reference point used.
• The relationship between peak angular momentum and perturbation amplitude showed no significant difference between the CoM and base of support reference points.
• Analysis using the CoM facilitates understanding limb momentum contributions, while the base of support may better reveal inverted-pendulum dynamics.

Conclusions:

• The choice of reference point does not fundamentally alter the relationship between whole-body angular momentum and the magnitude of balance disturbances.
• Each reference point offers distinct advantages for interpreting dynamic balance control mechanisms during walking perturbations.
• CoM-based analysis aids in understanding limb coordination for overall momentum regulation, while base of support analysis may highlight gait mechanics.