Force direction pattern stabilizes sagittal plane mechanics of human walking

Area of Science:

• Biomechanics
• Neuroscience
• Human Locomotion

Background:

• Neural control and mechanics of human bipedalism remain incompletely understood.
• Ground reaction force (F) is a key variable linking neural control and body mechanics for upright posture during walking.

Purpose of the Study:

• To develop and validate a model predicting the direction of ground reaction force (F) during human walking.
• To identify the optimal reference frame for describing F direction using a divergent point (DP) model.

Main Methods:

• A divergent point (DP) model was proposed to predict sagittal plane F direction.
• Four different reference frames were tested to evaluate model accuracy and simplicity.
• Model predictions were compared against observed variations in F direction and whole body angular momentum during single leg stance.

Main Results:

• The DP model accurately predicted most of the observed variation in F direction and angular momentum across all tested reference frames.
• A reference frame with vertical orientation and pelvic origin offered the best balance of accuracy and simplicity.
• The DP was located superior to the center of mass (CM), and predicted F generated torque about the CM, inducing pitch oscillations.

Conclusions:

• The DP model provides a robust framework for understanding the mechanics of human bipedalism.
• The observed torque, despite causing oscillations, suggests a critical stability mechanism for upright posture.
• This research offers new insights into the neural control and biomechanical strategies enabling human upright walking.