Joint-level kinetic redundancy is exploited to control limb-level forces during human hopping

Area of Science:

• Biomechanics
• Human Locomotion
• Motor Control

Background:

• Compensatory mechanisms leverage neuromechanical redundancy to achieve task goals despite injuries or perturbations.
• The role of joint-level kinetic redundancy in intact, unperturbed human locomotion remains less understood.

Purpose of the Study:

• To investigate if joint-level kinetic redundancy is exploited during human locomotion to meet limb-level force goals.
• To examine how joint torque variance contributes to specific locomotor objectives in hopping.

Main Methods:

• Hopping in place at a constant frequency was analyzed.
• Uncontrolled Manifold (UCM) analysis was used to quantify joint torque variance.
• Limb-level force goals included minimizing vertical ground reaction force (GRF) variance and varying horizontal GRF for positional corrections.

Main Results:

• Hopping subjects utilized joint torque redundancy to minimize vertical GRF variance across landing, mid-stance, and takeoff phases.
• Joint torque variance was also exploited to vary horizontal GRF at landing and takeoff, facilitating positional adjustments.
• Increased timing fluctuations were associated with higher vertical GRF variance.

Conclusions:

• Joint torque variance in human locomotion is not random but exhibits functional relevance.
• This variance is purposefully structured to meet specific locomotor goals, such as force stabilization and positional control.
• Neuromechanical redundancy plays a crucial role in the adaptability and goal achievement of human movement.