Isometric trunk strength in seated para-athletes: relationship to manual muscle testing and comparison with non-impaired controls

Introduction Trunk muscle strength is an important performance indicator in para-athletes competing in seated sports and is commonly assessed in classification systems using manual muscle testing (MMT), together with functional and sport-specific tests. Quantitative isometric strength measures may provide complementary information about force-generating capacity. However, the relationship between isometric trunk strength and MMT-assessed trunk and hip strength is not well described in para-athletes with neuromusculoskeletal impairments. This study aimed to examine isometric trunk strength in seated para-athletes and compare it with 1) MMT scores of the trunk and hips and 2) isometric trunk strength in a reference group without physical impairments. Methods Male para-athletes competing in seated sports ( n = 32, 34.7 ± 13.7 years, 8.7 ± 4.1 exercise h/week) and a reference group without physical impairments of similar age and weekly exercise ( n = 10, 35.0 ± 12.5 years, 9.8 ± 6.4 exercise h/week) participated. Isometric strength was measured seated for flexion, extension, rotation, and lateral flexion using a strength rig. MMT of the trunk and hips was summed to obtain an MMT Trunk–Hip score. Associations with isometric strength were examined using Spearman's rank correlation. Para-athletes were categorized into Very Low, Low, Moderate, and High MMT Trunk–Hip groups. Group differences were analyzed using Kruskal–Wallis tests. Results Higher MMT Trunk–Hip scores were associated with greater maximal isometric trunk strength in all movement directions ( p < 0.001), with large effect sizes. The High group did not differ from the reference group, whereas the Very Low and Low groups consistently demonstrated lower strength across directions. The Moderate group showed greater heterogeneity, with strength varying by movement direction. Conclusion MMT Trunk–Hip scores were strongly associated with isometric trunk strength in seated para-athletes, supporting MMT's ability to capture meaningful differences in trunk and hip muscle strength. However, direction-specific variation indicates that MMT does not fully characterize force-generating capacity. Quantitative isometric strength testing may provide complementary information for evaluating and monitoring trunk strength, particularly for performance enhancement. In para-sport classification, these findings support the construct validity of MMT while highlighting the potential value of quantitative strength measures for developing and validating multidimensional assessment methods.