Figure 1
Different levels of external support during trunk VoA (active ROM) assessment. Four testing conditions with progressively reduced external trunk and leg support: (a) full Support with 15° seat inclination, backrest, and footrest, pelvic, thigh, and foot straps; (b) partial Support with flat seat, backrest, and straps; (c) no Support with flat seat without straps; and (d) sport Wheelchair with participant’s personal equipment and adaptive devices.
Figure 2
IMU Sensor orientation processing flow: (a) Sensors were placed at C7 and T8 vertebrae with initial coordinate axes: x-vertical (inferior), y-medio-lateral (right), z-antero-posterior (posterior). (b) Sensor orientations were rotated to align the x-axis with gravity during baseline trials, then transformed using rotational matrices to establish the anatomical reference frame: Z-vertical (upward), Y-medio-lateral (left), and X-antero-posterior (backward). This standardisation defined flexion, left tilt, and left rotation as positive angular values.
Figure 3
Representative examples of the peak matching procedure during lateral tilt in the partial support condition. Panel (a) shows a participant with lower limb impairment but fully preserved trunk function (WB Class 4.5). Panel (b) shows a participant with minimal trunk function (WB Class 1.0) demonstrating a limited volume of action (VoA) with visible compensatory upper trunk movements. Both graphs display lateral tilt cycles with positive peaks indicating left lateral tilt and negative peaks indicating right lateral tilt, interspersed with returns to neutral position (approximately 0°). Yellow circles indicate C7 peaks matched to corresponding T8 peaks (yellow squares). Purple markers indicate negative peaks (right lateral tilt).
Figure 4
Distribution of Trunk–Hip Total Scores (max 28 points) across Trunk Function Clusters. Boxplots show participant distribution across four clusters with cutoff thresholds (red dashed lines) at 7.8, 13.6, and 23.6 points. Dots represent individual participants.
Table 1
Demographics and scores of participants categorised by trunk function clusters
| Trunk Function Cluster | N | Sex (M/F) | Age (years) M ± SD | WB/Other Sports | WB Classification points M ± SD (range) | Trunk–Hip Total Score M ± SD (range) |
|---|---|---|---|---|---|---|
| 1 (Very Low) | 18 | 16/2 | 35.8 ± 11.3 | 15/3 | 1.30 ± 0.37 (1.0–2.0) | 2.20 ± 2.32 (0.0–7.8) |
| 2 (Low) | 10 | 9/1 | 35.4 ± 11.5 | 7/3 | 1.86 ± 0.38 (1.5–2.5) | 11.46 ± 0.9 (7.8–13.6) |
| 3 (Moderate) | 15 | 14/1 | 31.5 ± 10.9 | 12/3 | 2.92 ± 0.51 (2.0–3.5) | 18.62 ± 2.98 (13.6–23.6) |
| 4 (High) | 20 | 15/5 | 32.6 ± 7.2 | 20/0 | 3.92 ± 0.57 (2.5–4.5) | 27.12 ± 1.26 (23.6–28.0) |
| Total | 63 | 54/9 | 33.7 ± 10.2 | 54/9 | 2.7 ± 1.2 (1.0–4.5) | 15.49 ± 10.20 (0.0–28.0) |
WB classification refers to the IWBF functional classification system (1.0-4.5; lower scores indicate more severe impairment); nine participants from other sports lacked this classification. Values are mean ± standard deviation.
Figure 5
The percentage of missing trials (floor effect) grouped by Trunk Function Cluster. Bar colours represent the ergonomic conditions.
Figure 6
Comparison of trunk angle peak values measured by C7 and T8 IMUs across four ergonomic conditions and four Trunk Function Groups. All values are expressed as positive values. Blue and red filled circles (black outlines) represent median values for C7 and T8 measurements, respectively; error bars indicate the interquartile range. Semi-transparent points show individual participant data. Panel rows represent movement directions (A–D); columns represent ergonomic conditions. Wilcoxon Signed-Rank Test (* p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001).
Figure 7
C7–T8 angular difference across trunk function groups and support conditions for (a) flexion, (b) extension, (c) lateral tilt, and (d) rotation. Box plots show median (centre line), interquartile range (box boundaries), and range (whiskers). Brackets indicate significant post-hoc pairwise differences (Wilcoxon test, Bonferroni corrected). Daggers denote the number of ergonomic conditions reaching significance: † = 1, †† = 2, ††† = 3.
Figure 8
Scatterplot of Total ROM of the C7 sensor to the T8 sensor across all directions and conditions. Total ROM represents the cumulative sum of peak angles calculated for each participant across all three planes of motion (flexion/extension, lateral tilt, rotation) and four ergonomic conditions. Data points are coloured according to the Trunk Function groups (Very Low-orange, Low-yellow, Moderate-green, and High-blue). The dashed line represents the linear regression.