Inter-segmental trunk kinematics differ between wheelchair athletes with high and low trunk function: An exploratory analysis using two inertial measurement units.

PURPOSE: This study examined whether upper and mid trunk kinematics, measured by inertial measurement units at seventh cervical (C7) and eighth thoracic (T8) vertebral levels, distinguishes between clinically defined levels of trunk function to support classifiers' decisions in Paralympic sports. METHODS: Sixty-three wheelchair athletes with neuromusculoskeletal impairment (54 wheelchair basketball players, 7 fencers, and 2 others) were classified into four trunk-hip function groups (Very Low, Low, Moderate, and High) using hierarchical cluster analysis based on the composite score of standardised Manual Muscle Testing of trunk and hip muscles. Participants performed maximum active range of motion (Volume of Action) tasks while sitting in four conditions with progressively reduced external support (Full, Partial, No Support, and Sport Wheelchair). Two Inertial Measurement Units recorded trunk kinematics at 100 Hz. Inter-segmental peak angular differences between sensors were compared across groups using Kruskal-Wallis tests. RESULTS: Active range of motion from individual C7 and T8 sensors differentiated most trunk-hip function group pairs (88% of comparisons). Peak trunk angle differed between sensors in 66% of comparisons, particularly for rotation (8-20°) and lateral tilt (4-14°). These inter-segmental C7-T8 differences separated groups in 23% of comparisons (mean difference: 10°; range: 4-20°). CONCLUSIONS: Active range of motion from a single upper trunk (C7) sensor discriminated between most trunk function group pairs and appears sufficient for classification. Inter-segmental C7-T8 trunk peak angle differences provided limited additional classification value beyond single-sensor measurements, supporting the use of simplified field assessment protocols.