Muscle force redistributes segmental power for body progression during walking.

Area of Science:

• Biomechanics
• Human locomotion
• Musculoskeletal dynamics

Background:

• Ankle plantar flexors (soleus and gastrocnemius) were previously understood to support the body in single-leg stance for forward progression.
• Their net effect on trunk and leg acceleration is negligible mid-stance but accelerates forward in late stance, suggesting active push-off.

Purpose of the Study:

• To investigate the role of other muscles, beyond ankle plantar flexors, in supporting the body and redistributing segmental power during walking.
• To quantify the contributions of specific muscles to ground reaction forces and segmental accelerations and power.

Main Methods:

• Muscle-actuated forward dynamical simulations were used to emulate walking kinematics and kinetics.
• Simulations analyzed muscle contributions to vertical and horizontal ground reaction forces.
• Quantified muscle contributions to leg and trunk acceleration and mechanical power.

Main Results:

• Eccentric vasti (knee extensors) and concentric gluteus maximus (hip extensors) critically supported the body in early stance before plantar flexor activation.
• Vasti decelerated trunk and leg forward motion and redistributed power to the trunk in mid-stance.
• Rectus femoris and hamstrings showed varied roles in late stance, swing, and early stance, influencing leg and trunk motion and power redistribution.

Conclusions:

• Uniarticular knee and hip extensors are critical for body support at the beginning of stance.
• Redistribution of segmental power by muscles throughout the gait cycle is essential for forward progression of the trunk and legs.