Validation of the G-Force Platform for Isometric Tests in Physically Active Young Adults: A Pilot Study

Objectives: To evaluate the validity, accuracy, and reliability of the G-Force force platform during isometric tests, through comparison with a gold-standard force platform in physically active young adults. Methods: Nine physically active participants (23.67 ± 4.97 years; body mass index: 25.79 ± 3.02 kg/m2) performed isometric posterior lower limb muscle tests per leg, following a standardized warm-up and familiarization protocol. The G-Force platform and compared against a gold-standard device, the Valkyria Trainer Balance (VTB) force platform. The measured variables included Peak Force and peak rate of force development (RFD) at 50, 100 and 150 ms (RFD50, RFD100 and RFD150). Intra- and inter-platform reliability were assessed using intraclass correlation coefficients (ICC), standard error of measurement (SEM), coefficient of variation (CV%), Bland–Altman analysis and Pearson’s correlation coefficients between both platforms. Results: Peak Force showed excellent intra-platform repeatability (ICC = 0.86–0.91) and moderate-to-good inter-platform reliability (ICC = 0.75–0.77), with the G-Force platform generally reporting slightly lower absolute values than VTB. RFD measures demonstrated moderate reproducibility (ICC = 0.75–0.87) and higher variability (CV = 47–57%). Bland–Altman analyses revealed minimal bias for Peak Force, while regression analyses indicated strong, significant associations between G-Force and VTB measurements (R2 = 0.55–0.77; β = 0.74–0.88; p < 0.05). Conclusions: The G-Force force platform is a valid, reliable, and low-cost tool for assessing isometric strength in physically active young adults.