Reference ranges and dimensional structure of upper body posture parameters in adults: a cross-sectional study

Upper body posture assessment using surface topography can support population-level screening, but adult reference data for these parameters remain limited, restricting clinical interpretability. This study aimed to establish reference ranges for upper body posture parameters in adults and characterize their underlying dimensional structure.

This cross-sectional study analyzed DIERS three-dimensional surface topography data from 1,859 adults (mean age 46.9 ± 11.9 years; 52.7% male). Descriptive statistics were generated for 45 DIERS-derived parameters spanning six measurement domains. Participants were classified into three screening categories of scoliotic posture, scoliosis risk, and unclassified, based on pelvic obliquity, vertebral rotation, and apical vertebral deviation. Group differences by age, sex, and screening category were examined using ANOVA and t-tests with false discovery rate correction; effect sizes were quantified with η ² and Cohen's d. Exploratory graph analysis (EGA) with 1,000-iteration bootstrap validation identified the dimensional structure of the retained parameters.

The screening category distribution was scoliotic posture 35.9%, scoliosis risk 5.8%, and unclassified 58.4%, with no significant variation by age or sex. Sex-related differences were pronounced: 13 of 31 significantly different parameters showed large effects (Cohen's d ≥ 0.80), concentrated in distance measurements, postural reference points, spinal curve angles, and shoulder parameters. Age-related between-group differences were observed across multiple parameters, but effect sizes were predominantly trivial to small (η ² < 0.06). EGA identified a stable five-dimension structure (bootstrap support: 98.5%): trunk size and segmental length, coronal deviation and axial rotation, sagittal spinal structure and postural balance, upper-body angular asymmetry, and pelvic asymmetry.

This study established adult population reference ranges for upper body posture parameters derived from surface topography. The analysis revealed pronounced sex-related differences, suggesting that sex-stratified reference values may be more appropriate for clinical interpretation. Five distinct dimensions of upper body posture parameters were identified, indicating that future research should consider coordinated changes across multiple anatomical structures. Together, these findings provide a quantitative basis for interpreting surface topography results in health management and scoliosis screening.