The lumbar spine displays its greatest mobility in ventral flexion, which is a potential risk factor for low back pain. The relative contribution of each segment to the complete flexion is denoted the spine rhythm, which is required to distinguish between normal and abnormal spinal profiles, and as well to calculate the spinal forces in musculoskeletal models. Nevertheless, different spine rhythms have been reported in literature and the effect of arm position has not been demonstrated. We therefore aimed to investigate the effects of different arm positions on spine rhythm during ventral flexion.
A non-radiological back measurement device was used to determine the real-time back lordosis during ventral flexion while participants (10 males and 10 females without low back pain) held their arms at six different positions.
During flexion with the arms naturally hanging down at both sides, the lumbar range of flexion were 52.6° ± 13.1°. Different arm positions displayed non-significant effect on lumbar range of flexion (P>0.05). The middle and lower levels contributed more to the whole lumbar range of flexion than the upper level (P<0.05), which is independently of arm position.
The lumbar spine displayed greater flexion in the middle and lower levels and its flexion rhythm remained unchanged at different arm positions. These results strike importance to explore for more reasons explaining the different lumbar flexion rhythms reported in literature.

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