Ground reaction forces and impulses during a transient turning maneuver

Area of Science:

• Biomechanics
• Human movement analysis
• Gait dynamics

Background:

• Understanding turning kinetics is vital for rehabilitation and assistive technology development.
• Previous research on ground reaction forces (GRFs) during turns was limited to single steps and global reference frames, hindering detailed analysis of body-specific forces.
• A body-referenced frame is needed to accurately interpret forces causing changes in heading and orientation during gait turns.

Purpose of the Study:

• To report ground reaction force (GRF) and ground impulse (GRI) data for three consecutive steps of a turn.
• To express turning kinetics in a body-referenced frame for a clearer understanding of how forces influence motion.
• To investigate differences in medial-lateral and anterior-posterior impulses during straight walking and different phases of a turn.

Main Methods:

• Collected motion and GRF data from 10 subjects walking and performing 90-degree left and right turns at self-selected speeds.
• Focused on turn initiation and apex steps for left turns, and turn termination steps for right turns.
• Rotated GRF data to a body-centered reference frame aligned with the center of mass (COM) trajectory and integrated to calculate GRIs.

Main Results:

• Medial-lateral impulses differed significantly across turning phases: straight steps showed a medial followed by a lateral impulse, initiation/termination steps had sustained medial impulses, and apex steps exhibited a large lateral impulse.
• Anterior-posterior impulses showed initiation steps had greater braking and less propulsion than straight steps.
• Apex steps demonstrated increased propulsion, while termination steps had reduced braking and increased propulsion compared to straight steps.

Conclusions:

• This study provides the first detailed, body-referenced kinetic analysis of multi-step turns.
• Distinct impulse patterns in medial-lateral and anterior-posterior directions characterize different phases of turning.
• Findings offer a foundation for designing targeted interventions to improve turning ability and reduce fall risk in individuals with gait impairments.