Optimal shear cushion stiffness at different gait speeds.

Area of Science:

• Biomechanics
• Sports Science
• Orthopedics

Background:

• Impact forces during locomotion can lead to musculoskeletal injuries.
• Shear cushioning systems aim to mitigate these forces.
• Understanding the optimal stiffness is crucial for effective design.

Purpose of the Study:

• To quantify the effects of different shear cushion stiffness levels on impact loading parameters.
• To identify the optimal shear cushion stiffness for various locomotion speeds (walking, jogging, running).

Main Methods:

• A custom sliding platform was used to test five shear cushion stiffness conditions.
• Twelve male collegiate heel-striker participants performed locomotion at 1.5 m/s, 2.5 m/s, and 3.5 m/s.
• Key metrics analyzed included time to peak posterior shear force (TPPSF), peak posterior shear force (PPSF), average posterior loading rate (APLR), and maximum posterior loading rate (MPLR).

Main Results:

• All tested cushion conditions increased sliding displacement and delayed TPPSF compared to a fixed condition.
• For walking, the medium soft condition yielded the lowest APLR and MPLR.
• For jogging and running, the medium stiff condition resulted in the lowest PPSF, APLR, and MPLR, with some exceptions for maximum PLR.

Conclusions:

• Shear cushioning effectively delays impact forces, allowing more time for musculoskeletal absorption.
• Optimal shear cushion stiffness varies with locomotion speed, with medium soft for walking and medium stiff for jogging/running.
• Shear cushion systems show promise for application in future footwear and protective gear designs.