Reliability and Repeatability of the Low-Cost G-Force Load Cell System in Isometric Hip Abduction and Adduction Tests: A Pilot Study

Abstract

Background/Objectives: Low-cost portable load cell dynamometers allow for real-time assessment of muscular strength. This study evaluated the reliability and repeatability of the G-Force load cell system during isometric hip abduction and adduction in young physically active Chilean adults. Methods: In total, 24 participants (19 men, 5 women) performed two maximal voluntary contractions per movement, repeated after a 24 h interval. Measured variables included Peak Force, peak rate of force development (Peak RFD), RFD at 50, 100, and 200 ms (RFD50, RFD100, RFD200), and maximum jerk. Reliability was assessed using intraclass correlation coefficients (ICCs), standard error of measurement (SEM), coefficient of variation (CV%) and Bland–Altman plots. Results: Peak Force showed excellent within-day (ICC = 0.94–0.96) and high between-day reliability (ICC = 0.87–0.89; CV = 20–30%). Bland–Altman analysis indicated negligible bias for Peak Force in abduction (−6.54 N; 95% CI −19.55 to 6.47) and adduction (−17.57 N; 95% CI −37.24 to 2.09), confirming the absence of systematic error. Peak RFD, RFD50–200, and maximum Jerk showed moderate repeatability and lower between-day reliability (ICCs = 0.39–0.70; CVs = 34–57%), indicating higher variability in explosive force indices compared with maximal strength. Conclusions: The G-Force load cell reliably measures maximal isometric hip strength, while Peak RFD, RFD50–200, and maximum jerk should be interpreted cautiously. These findings support the device as a practical, low-cost tool for sports and rehabilitation, though future studies should validate dynamic indices in larger and more diverse populations. © 2025 by the authors.