Lateral abdominal muscles of adults with hypermobility may be partially impaired during contraction

Background Muscle function may be impaired in people with generalised hypermobility, yet prior studies have primarily focused on muscles within the extremities. We aimed to examine changes in lateral abdominal muscle (transversus abdominis (TrA) and the external (EO) and internal abdominal obliques (IO)) thickness and length during contraction between participants with and without hypermobility. Methods This cross-sectional study examined 12 participants with hypermobility and 12 age-matched, sex-matched, height-matched and weight-matched participants without hypermobility. The Beighton and Belavy-Owen-Mitchell score assessed systemic hypermobility. Muscle thickness and length were measured via panoramic ultrasound scans at rest and during contraction. Results When compared with rest across all lumbar levels (L1-L5), contraction produced a lesser increase in TrA thickness (β=0.03, p=0.034) for participants with hypermobility compared with control. No group-by-condition interaction was observed for TrA length across all lumbar levels (L1-L5; p=0.269). Contraction produced a greater decrease in EO thickness (β=0.08, p=0.002) at L3 only for participants with hypermobility compared with control. No group-by-condition interactions were observed for IO thickness. Conclusion Participants with hypermobility had partially impaired lateral abdominal muscle function given a lesser ability to increase TrA muscle thickness during contraction compared with controls.