Portable RGB-D Stabilometry for Unsupervised Postural Assessment in Antarctic Field Conditions

Portable quantification of postural sway remains challenging in remote and resource-limited environments where laboratory force platforms and motioncapture systems are impractical. We evaluated an autonomous RGB-D stabilometry workflow during an Antarctic expedition by comparing camera-derived center-of-mass (CoM) sway with a portable center-of-pressure (CoP) reference and testing leave-one-subject-out calibration. Thirteen participants performed modified Romberg trials while an Intel RealSense D455 camera and a Wii Balance Board (WBB) recorded postural data. Full-body CoM trajectories were reconstructed from three-dimensional landmarks; facial-landmark head tracking was evaluated as a secondary fallback modality. In total, 192 quality-controlled WBB-camera pairs were analyzed. Temporal-alignment diagnostics showed strong anteroposterior signal overlap with the CoP reference (median post-lag Pearson r = 0.847-0.929 for full-body tracking; r = 0.825-0.905 for head tracking). Raw full-body metrics underestimated root-mean-square anteroposterior sway (bias = -5.62 mm) and overestimated mean velocity (bias = 8.67 mm/s). Passing-Bablok calibration reduced RMS AP bias relative to the WBB reference to 0.01 mm and narrowed the width of the limits of agreement from 12.15 to 7.15 mm. After empirical mapping, the inter-method reliability of Rambling RMS AP sway relative to the WBB reference was excellent (ICC(2,1) = 0.956), whereas mediolateral outcomes were less reliable and should be interpreted as exploratory in this camera configuration, likely reflecting lower ML amplitude and three-quarter camera geometry. Clock-based fixed windows yielded lower correlations, whereas a single global acquisition-latency correction applied identically to all trials, without per-trial window optimization, recovered correlations close to those of the optimized analysis. All estimates are relative to the portable WBB field reference rather than a laboratory-grade standard, and the calibration is a task- and setup-specific empirical mapping, not a universal biomechanical transformation.