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

Area of Science:

• Biomechanics
• Motor Control
• Human Movement Science

Background:

• Complex whole-body movements suggest hierarchical control of multiple subsystems by the nervous system.
• Trunk-leg coordination is crucial for regulating the body's center of mass (CoM) relative to the ground reaction force (RF).

Purpose of the Study:

• To investigate if task-specific trunk-leg coordination differences influence lower extremity joint control during the impulse generation phase.
• To compare joint kinetics and muscle activation during backward jumps with and without angular impulse.

Main Methods:

• Eight skilled performers executed backward translating jumps with and without backward rotation (back somersault vs. back timer).
• Sagittal plane kinematics, ground reaction forces (RFs), and lower extremity muscle electromyograms were recorded during takeoff.
• Lower extremity joint kinetics were computed using inverse dynamics.

Main Results:

• Backward somersaults showed reduced knee-extensor moments and increased hip-extensor moments compared to back timers.
• Differences in trunk angular velocity redistributed work done by lower extremity joints.
• Joint kinetics changes were linked to synergistic activation of bi-articular muscles crossing the knee and hip.

Conclusions:

• Task-specific control of the CoM relative to RF modifies knee and hip joint control and dynamics.
• Altered total-body control objectives impact the multi-joint lower extremity subsystem's dynamics.
• Hierarchical control adapts lower extremity joint strategies based on task demands, specifically angular impulse generation.