Simple foot strike angle calculation from three-dimensional kinematics: A methodological comparison

Area of Science:

• Biomechanics
• Sports Science
• Kinesiology

Background:

• Accurate foot strike angle (FSA) determination is crucial for running analysis and wearable sensor validation.
• Simplified methods for collecting 3D kinematic data can enhance efficiency in research and clinical settings.

Purpose of the Study:

• To validate two simplified methods (HEEL-TOE and HEEL-MET5) for estimating running foot strike angle (FSA) using 3D kinematics.
• To compare the accuracy of these simplified methods against a reference foot segment measurement.

Main Methods:

• Three-dimensional kinematic data were collected from runners.
• Markers were placed on the heel and either the second metatarsal (HEEL-TOE) or fifth metatarsal (HEEL-MET5).
• Foot strike angle (FSA) and foot angle throughout ground contact were calculated and compared to a reference method.

Main Results:

• The HEEL-TOE method demonstrated high validity, showing minimal mean difference (0.28°), high correlation (r=0.994), and low bias (-0.20°±1.05°) compared to the reference.
• The HEEL-MET5 method significantly underestimated FSA (mean difference=4.28°), with high correlation (r=0.968) but notable bias (-4.58°±2.61°).
• The HEEL-MET5 method underestimated foot angle in the initial 23-34% of stance across all foot strike patterns.

Conclusions:

• The HEEL-TOE method is a valid and simplified approach for determining running foot strike angle (FSA) from 3D kinematics.
• Caution is advised when using the HEEL-MET5 method due to its tendency to underestimate FSA, likely caused by foot inversion during early stance.