Comparison of Existing Methods for Characterizing Bi-Linear Natural Ankle Quasi-Stiffness

Area of Science:

• Biomechanics
• Human Movement Science
• Orthotics and Prosthetics

Background:

• Natural ankle quasi-stiffness (NAS) is crucial for dynamic motion analysis.
• Traditional NAS models assume linearity, but recent research indicates nonlinearity during the stance phase.
• Existing bi-linear NAS (BL-NAS) models offer improved accuracy over linear models but face adoption challenges.

Purpose of the Study:

• To compare and contrast existing bi-linear NAS (BL-NAS) models.
• To investigate the applicability of BL-NAS models for orthotic device design.
• To provide a basis for developing ankle-foot devices that emulate natural human motion.

Main Methods:

• Comparison of two distinct BL-NAS models against standard single linear NAS (SL-NAS) models.
• Analysis of root-mean-squared error (RMSE) to evaluate model accuracy.
• Examination of early loading (EL) and late loading (LL) NAS across different walking speeds.

Main Results:

• Both BL-NAS models demonstrated lower RMSE compared to SL-NAS models.
• Early loading NAS (EL-NAS) showed no significant difference across walking speeds.
• Late loading NAS (LL-NAS) significantly increased with faster walking speeds.

Conclusions:

• BL-NAS models provide a more accurate representation of natural ankle mechanics than SL-NAS models.
• Findings support the development of ankle-foot orthotics with variable stiffness properties.
• Improved NAS models can facilitate the design of devices that better emulate natural human movement.