Lower extremity control and dynamics during backward angular impulse generation in forward translating tasks

Area of Science:

• Biomechanics
• Neuroscience
• Human Movement Science

Background:

• Complex whole-body movements suggest hierarchical nervous system control.
• Comparing forward jumps with and without backward impulse reveals differences in trunk-leg coordination and reaction forces.

Purpose of the Study:

• To investigate how trunk-leg coordination and reaction force generation influence lower extremity joint control during impulse generation.
• To compare joint kinetics and muscle activation patterns between forward jumps with and without backward rotation.

Main Methods:

• Eight skilled performers executed forward jumps with and without backward rotation (reverse somersault vs. reverse timer).
• Collected sagittal plane kinematics, ground reaction forces, and lower extremity muscle electromyograms during takeoff.
• Calculated lower extremity joint kinetics using inverse dynamics.

Main Results:

• Significant differences observed in inter-segmental coordination, net joint forces, and joint angular velocity profiles between tasks.
• Reverse somersaults showed significantly less knee extensor net joint moment and work, and greater hip extensor net joint moment and work compared to reverse timers.
• Between-task differences in joint kinetics were modulated by selective activation of bi-articular muscles.

Conclusions:

• Altered control of the center of mass relative to the reaction force modifies the dynamics of the lower extremity multi-joint subsystem.
• The nervous system employs distinct strategies for controlling lower extremity joint kinetics based on task demands, particularly involving bi-articular muscle activation.