Validity and reproducibility of foot motion analysis using a stretch strain sensor.

Area of Science:

• Biomechanics
• Sports Medicine
• Orthopedics

Background:

• Multi-segment foot analysis is challenging with footwear or orthoses in clinical settings.
• A novel, thin, and flexible stretch strain sensor (STR) offers a portable solution without camera observation.

Purpose of the Study:

• To evaluate the reproducibility and validity of foot motion analysis using the STR.
• To compare STR data with a conventional motion capture system during walking and running.

Main Methods:

• Twenty-one healthy participants underwent simultaneous kinematic data collection using STR and 3D motion capture.
• STR was applied at the spring ligament (SL) and navicular drop (ND) sites.
• Reproducibility assessed via Intra-class correlation (ICC); validity via cross-correlation and Pearson/Spearman correlation.

Main Results:

• The SL method demonstrated high ICCs (0.95-0.96) and strong correlation with forefoot frontal motion (r=-0.64 to -0.67).
• STR measurements significantly correlated with forefoot eversion excursion.
• The ND method showed less association with forefoot and hindfoot kinematics (ICCs 0.93 and 0.71).

Conclusions:

• The STR system exhibits acceptable reproducibility and validity for foot motion analysis.
• This technology facilitates in-shoe foot motion measurement, expanding applications beyond laboratory settings.