Musculoskeletal stiffness changes linearly in response to increasing load during walking gait

Area of Science:

• Biomechanics
• Human-robot interaction
• Exoskeleton technology

Background:

• Biologically inspired exoskeletons are crucial for soldiers carrying heavy loads.
• Understanding human gait modulation under load is key for effective exoskeleton development.

Purpose of the Study:

• To investigate how the human body modulates musculoskeletal stiffness in response to varying backpack loads.
• To inform the design of load-carrying exoskeletons by understanding human adaptation limits.

Main Methods:

• Seventeen subjects walked on a treadmill under nine load conditions (12.5%-40% bodyweight).
• 3D motion analysis (Optotrak) captured kinematics to estimate center of mass (COM).
• Two stiffness estimates were calculated during the stance phase of gait.

Main Results:

• Musculoskeletal stiffness showed a positive, linear relationship with increasing load magnitude.
• The relationship between stiffness and load was steeper when descending loads compared to ascending.
• A potential limit for gait stiffness control was observed around 40% bodyweight.

Conclusions:

• The musculoskeletal system systematically adjusts stiffness to maintain gait stability under increasing loads.
• Current load-carrying capabilities approach a limit, suggesting a need for new gait strategies or assistive devices.
• Findings have direct implications for designing exoskeletons to aid soldiers in load carriage.