Direct dynamics simulation of the impact phase in heel-toe running

Area of Science:

• Biomechanics
• Human Movement Science
• Sports Engineering

Background:

• Running biomechanics involves complex interactions between muscle activation, body segment dynamics, and surface properties.
• Understanding impact forces is crucial for injury prevention and performance optimization in runners.

Purpose of the Study:

• To investigate the influence of muscle activation, body segment kinematics, and surface characteristics on impact forces during heel-toe running.
• To quantify the contribution of specific factors like plantar flexion, vertical heel velocity, and knee flexion to impact absorption.

Main Methods:

• A 2D, four-segment musculoskeletal model with detailed muscle activation dynamics was used.
• Direct dynamics simulation technique incorporated force-length and force-velocity properties of seven lower extremity muscle groups.
• Non-linear visco-elastic elements modeled the force-deformation characteristics of the heel, shoe, and ground.

Main Results:

• Simulated maximum impact force reached 1.6 times body weight.
• Muscle activation variations showed less than 10% impact force change when resultant joint moments were matched.
• Plantar flexion (85 N/degree) and vertical heel velocity (212 N per 0.1 m/s) were major determinants of impact peak force.
• Initial knee flexion (68 N/degree) contributed to impact absorption.
• Increased surface stiffness led to higher impact forces (60 N per mm decrease in deformation).

Conclusions:

• Plantar flexion, vertical heel velocity at touchdown, and initial knee flexion are key modulators of running impact forces.
• Surface stiffness directly correlates with increased impact forces.
• While muscle activation plays a role, its influence on impact force is highly dependent on the control of initial joint moments.