Subgroups of people with low back pain display differences in their lumbar alignment during tests from a clinical examination. However, it is unknown if subgroups display the same patterns during a functional activity test and if gender influences subgroup-related differences.
Test if differences in lumbar alignment between two LBP subgroups are 1) present during a functional activity test of preferred sitting and 2) independent of gender.
Cross-sectional.
154 participants with chronic low back pain were classified based on the Movement System Impairment Classification System by a physical therapist. Participants performed a functional activity test of preferred sitting and clinical tests of maximum flexed and extended sitting. 3D marker co-ordinate data were collected. Sagittal plane lumbar alignment, indexed by lumbar curvature angle, was calculated. A three-way mixed effect analysis of variance was used to examine effects of test, subgroup, gender, subgroup × test, gender × test and subgroup × gender.
The lumbar rotation with extension subgroup [LCA = -8.0° (-9.5,-6.5)] displayed a more extended lumbar alignment than lumbar rotation [LCA = -5.9° (-7.4,-4.4)]. Women [LCA = -10.7° (-12.3,-9.2)] displayed a more extended lumbar alignment than men [LCA = -3.2° (-4.7,-1.7)]. There was a significant gender × test interaction (p = 0.01). The subgroup × test (p = 0.99) and subgroup × gender (p = 0.76) interactions were not significant.
LBP subgroup differences in lumbar alignment are present during preferred sitting. Gender-related differences in lumbar alignment are not driving subgroup differences. These findings highlight the need to use patient-specific clinical characteristics to guide treatment of a functional activity of preferred sitting limited due to low back pain.

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