Error propagation from kinematic data to modeled muscle-tendon lengths during walking

Area of Science:

• Biomechanics
• Human Movement Analysis
• Musculoskeletal Modeling

Background:

• Three-dimensional gait analysis and musculoskeletal modeling derive muscle-tendon lengths during walking.
• Soft tissue artifacts (STA), or skin marker displacement, introduce errors into kinematic data.
• These kinematic errors can propagate to affect calculated muscle-tendon lengths.

Purpose of the Study:

• To develop an analytical method for quantifying error propagation from STA to muscle-tendon lengths.
• To assess the impact of STA on muscle-tendon length calculations in different musculoskeletal models.
• To provide insights into the reliability of gait analysis-derived muscle-tendon lengths.

Main Methods:

• Assigned uncorrelated, isotropic error functions with standard deviations to skin marker coordinates to simulate STA.
• Utilized two musculoskeletal models: one with free joint movement and one with constrained rotational joint movement.
• Quantified STA propagation to muscle-tendon lengths for semimembranosus, gastrocnemius, and soleus using reference kinematic data from two children.

Main Results:

• The standard deviation of muscle-tendon lengths due to STA varied widely, ranging from 6% to 50% of normalized lengths.
• Error propagation was dependent on the specific muscle, STA magnitude, and the type of musculoskeletal model used.
• Demonstrated significant potential impact of STA on the accuracy of modeled muscle-tendon lengths during gait.

Conclusions:

• Soft tissue artifacts significantly influence the accuracy of muscle-tendon length calculations derived from 3D gait analysis.
• The choice of musculoskeletal model affects the magnitude of STA-induced errors.
• Clinical interpretation of muscle-tendon lengths from gait analysis requires careful consideration of potential soft tissue artifact effects.