Computation methods affect the reported values of in vivo human tendon stiffness

Area of Science:

• Biomechanics
• Human Physiology
• Materials Science

Background:

• Scientific validity of physiological and biomechanical data is compromised by inconsistent measurement techniques.
• In vivo determination of tendon stiffness (K) is particularly affected by varying methodologies.
• Current approaches for calculating tendon stiffness include gradient analysis, point tangents, and linear regressions across the Force-Elongation Relationship (FER).

Purpose of the Study:

• To compare the variability in tendon stiffness (K) estimates derived from different calculation approaches.
• To highlight the discrepancies introduced by various computational methods in determining tendon mechanical properties.
• To assess the impact of different FER models on K estimations.

Main Methods:

• Developed mathematical models for curvilinear Force-Elongation Relationships (FERs) representing low, medium, and high tendon stiffness (K).
• Calculated K values using established literature methods on these models.
• Quantified the differences in K estimates between various computational approaches and reference standards.

Main Results:

• Mathematical modeling revealed substantial variability in K estimates.
• Computational methods, compared to reference standards, showed a wide range of inaccuracies, underestimating K by 26% and overestimating it by 51%.
• The choice of method significantly impacts the recorded value of tendon stiffness.

Conclusions:

• The developed mathematical modeling offers a 'scaling factor' to minimize variability in K estimates across studies.
• This standardization is crucial for researchers and clinicians needing consistent tendon mechanical property values.
• Improved consistency aids in developing accurate models and materials based on human tendon biomechanics.