Optimism persists when walking in unpredictable environments.

Area of Science:

• Biomechanics
• Motor Control
• Human Movement Science

Background:

• Human walking involves continuous adaptation of control strategies to anticipate and react to environmental disturbances.
• Understanding how motor plans are adapted for stable locomotion in unpredictable conditions is crucial for human movement science.

Purpose of the Study:

• To investigate the adaptation of motor plans during walking in a novel and unpredictable environment.
• To analyze how individuals adjust their whole-body center of mass (COM) trajectory in response to externally applied forces.

Main Methods:

• Participants performed a goal-directed walking task with a randomly applied lateral force field acting on the center of mass (COM).
• The force field magnitude was dependent on forward velocity and randomly directed left or right each trial.
• Center of mass (COM) trajectory deviations were measured to quantify adaptation to the unpredictable force field.

Main Results:

• Practice significantly reduced COM lateral deviations by 28% (left force field) and 44% (right force field).
• Participants developed distinct unilateral strategies, creating bilateral resistance to unpredictable forces, including anticipatory postural adjustments and lateral first steps.
• Catch trials revealed robust impedance control, while short-term predictive adaptations sometimes led to increased deviations when predictions were incorrect.

Conclusions:

• Humans adapt walking by employing a combination of impedance control and short-term predictive strategies to manage unpredictable environmental forces.
• Distinct motor strategies are developed to resist lateral perturbations, demonstrating the nervous system's capacity for adaptive motor planning.
• Competing control strategies may facilitate long-term learning by enabling the nervous system to identify optimal responses in novel environments.