Humans prioritize walking efficiency or walking stability based on environmental risk.

Area of Science:

• Biomechanics
• Human locomotion
• Robotics

Background:

• Human gait utilizes passive dynamics for energy efficiency, relying on inverted pendular motion.
• This passive motion inherently reduces anterior-posterior (AP) dynamic stability, increasing fall risk from forward perturbations.

Purpose of the Study:

• To investigate if humans actively regulate step length to modulate passive AP stability.
• To determine if gait stability is adjusted based on task demands, such as walking on obstructed versus clear pathways.

Main Methods:

• Calculated the AP margin of stability, a measure of passive dynamic stability during gait.
• Analyzed gait parameters in 20 healthy adults walking on clear and obstructed walkways.

Main Results:

• Participants increased AP margin of stability when approaching and crossing an obstacle, indicating proactive stability adjustments.
• Step length and center of mass motion were coordinated to maintain specific AP margin of stability levels for each step.
• Passive dynamics were prioritized for energy efficiency, except when stability was compromised by an obstacle.

Conclusions:

• Humans actively control step length to maintain desired levels of passive dynamic stability during both unobstructed and obstructed walking.
• Gait stability is not solely passive but is actively regulated to meet environmental and task-specific demands.
• This active regulation of passive dynamics highlights a sophisticated interplay between efficiency and safety in human locomotion.