Agreement between 2D Visual- and 3D Motion Capture-based Assessment of Foot Strike Pattern

Area of Science:

• Biomechanics of running
• Sports science research
• Locomotion analysis

Background:

• Running foot strike patterns are classified as non-rearfoot strike (NRFS) and rearfoot strike (RFS), or as forefoot strike (FFS), midfoot strike (MFS), and RFS.
• Assessment methods include 2D visual analysis and 3D motion capture (e.g., strike index [SI], strike angle [SA]).
• Consistency between these assessment methods is debated.

Purpose of the Study:

• To evaluate the agreement between 2D visual and 3D motion capture methods for classifying foot strike patterns into two (NRFS/RFS) or three (FFS/MFS/RFS) types.
• To test the hypothesis that two-type classification has high inter-method reliability, while three-type classification has lower reliability due to FFS/MFS ambiguity.

Main Methods:

• A controlled laboratory study analyzed 162 foot strikes from four healthy runners.
• Running kinematics and kinetics were captured using 3D motion capture and a force platform.
• Foot strikes were filmed from the sagittal view at 240 fps, and analyzed using visual, SI, and SA methods; kappa values were calculated.

Main Results:

• Classification into two types (NRFS/RFS) showed almost perfect agreement (kappa = 0.89–0.95) across methods.
• Classification into three types (FFS/MFS/RFS) yielded lower agreement (kappa = 0.58–0.71).
• Agreement within the NRFS category (FFS/MFS) was poor (kappa = 0.08–0.33).

Conclusions:

• Two-type categorization of foot strike patterns demonstrates high reliability between 2D and 3D methods.
• Findings suggest that previous laboratory results using two distinct foot strike types are applicable to observational studies, clinical practice, and training contexts.