Evaluation of DAid® Smart Socks for Foot Plantar Center of Pressure Measurements in Football-Specific Tasks: A Preliminary Validation Study

<b>Background/Objectives:</b> Accurate plantar pressure assessment is essential for injury prevention and rehabilitation monitoring in sports. Wearable sensor technologies, such as DAid^® Smart Socks, offer portable, real-time biomechanical feedback and enable data collection in field conditions. However, there is limited evidence on their level of agreement with a gold standard in measuring the foot plantar center of pressure (CoP) in football-specific tasks. This study aimed to determine the preliminary validity of DAid^® Smart Socks compared with a gold-standard force platform in measuring plantar center of pressure (CoP) during functional football FIFA 11+ Part 2 exercises. <b>Methods:</b> Ten male volunteer youth football players (mean age 12.2 ± 0.42 years; height 158.7 ± 7.72 cm; weight 46.46 ± 8.78 kg; shoe size EU 39.8 ± 2.68) from the Latvian Football Federation Youth League participated. Eight players had right-leg dominance, two had left-leg dominance; three reported past lower-limb injuries. Plantar pressure was measured simultaneously using DAid^® Smart Socks and a 1.5 m entry-level force platform with a calibration factor of 3.2. Center of pressure (CoP) data from the force platform were recorded using Footscan software version 9.10.4. Participants performed two selected FIFA 11+ Part 2 exercises-a single-leg squat (unilateral) and a squat with heel raise, performed bilaterally-under standardized conditions. Each exercise was performed twice, with sock removal and reapplication between trials. Agreement between the DAid^® Smart Socks and the force platform was examined using waveform synchronization, root mean square error (RMSE), Bland-Altman analysis, and Lin's Concordance Correlation Coefficient (CCC) to quantify both relative waveform correspondence and absolute CoP measurement accuracy. <b>Results:</b> Across 160 paired recordings, the DAid^® Smart Socks showed moderate-to-high correlation with the force platform for relative CoP dynamics, with 79% of waveforms demonstrating CCC ≥ 0.60. Absolute agreement was limited, with only 16% of recordings reaching CCC ≥ 0.90, and RMSE values ranging from 2.1 to 18.9 mm (X) and 4.3-34.2 mm (Y). <b>Conclusions:</b> DAid^® Smart Socks showed moderate-to-high correspondence with the force platform in capturing the directional and temporal characteristics of plantar CoP during functional football tasks, with agreement varying across individuals.