Background: Functional assessment in wheelchair basketball (WB) has three evaluation stages: analysis of isolated functions, combined functional measures, and the observation of volume of action (VoA) in a sporting context. Sport class allocation relies on VoA assessed in controlled conditions (VoA-capacity), which corresponds to combined functional measures, and during game observation (VoA-performance). However, the contribution of each assessment phase to sport class allocation remains insufficiently understood. This study examines how trunk and hip muscle strength influences VoA-capacity and evaluates the extent to which VoA-capacity is associated with sport class. Additionally, it compares trunk muscle strength and VoA-capacity across sport classes to characterize functional differences between groups. Methods: A cross-sectional observational study was conducted with 40 officially classified WB players (sport classes 1.0-4.5). Trunk and hip muscle strength were assessed using the Manual Muscle Test (MMT). VoA-capacity was calculated as the sum of maximal trunk reaches in six directions (flexion, extension, rotation for both sides and lateral flexion for both sides) using an Inertial Measurement Unit (IMU) positioned at C7 (seventh cervical vertebra). Multiple linear regression, ordinal regression, Kruskal-Wallis, and Dunn's post-hoc tests were applied. Results: Total Trunk-Hip muscle strength significantly predicted VoA-capacity (p < 0.001), explaining 80% of its variance (R2 = 0.80). When analyzed separately, both trunk strength (p < 0.001) and hip strength (p = 0.006,) were significantly associated of VoA-capacity. VoA-capacity was a significant predictor of sport class (p < 0.001). Significant differences were found between sport classes for VoA-capacity (p < 0.001) and for total Trunk-Hip muscle strength (p < 0.001), with post-hoc comparisons showing the largest contrasts between lower (1.0-2.0) and higher (4.0-4.5) sport classes. Conclusion: Trunk and hip muscle strength showed associations with VoA capacity, suggesting their relevance for understanding players` ability to perform dynamic seated movements. VoA-capacity, was also associated with sport class allocation. Although muscle strength is not a classification criterion in WB, profiling players` muscular strength may offer complementary insights in complex classification scenarios. These findings provide preliminary functional evidence of WB classification and support future investigations integrating VoA-performance to refine assessment models.
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