Dominant role of interface over knee angle for cushioning impact loading and regulating initial leg stiffness

Area of Science:

• Biomechanics
• Human Locomotion
• Impact Injury Prevention

Background:

• Controlled impact loading is crucial for understanding lower limb injury mechanisms.
• Investigating factors like initial knee angle (IKA) and interface properties is essential for mitigating impact forces.

Purpose of the Study:

• To investigate the effects of initial knee angle (IKA) and impacting interface properties on in vivo impact loading and initial leg stiffness.
• To determine whether knee flexion or interface cushioning is more effective in reducing impact severity and protecting the lower limb.

Main Methods:

• A human pendulum system delivered controlled impacts to the foot across three IKAs (0, 20, 40 degrees) and three interfaces (barefoot, soft EVA, hard EVA).
• External impact force and shank shock were measured using a force platform and accelerometer.
• Leg stiffness was calculated from impact velocity and wall reaction force data.

Main Results:

• Larger knee flexion at contact reduced impact force but increased shank shock transmission.
• Softer interfaces significantly reduced initial leg stiffness and impact severity.
• Force rate of loading strongly correlated with limb stiffness (r = 0.95), influenced by heel fat pad and interface deformations.

Conclusions:

• The knee joint does not play a significant role in regulating initial leg stiffness during impact.
• Softer impact interfaces are more effective than knee angle adjustments in reducing impact loading and protecting the lower limb.
• Interface interventions represent a more promising strategy for safeguarding the locomotor system against impact-related injuries.