A quantitative assessment of the mechanical effects on the lumbar spine and the effects on straight leg raising and lumbar flexion of segmental sustained rotation

[Purpose] This study were to examine the strength and relative direction of the applied force from lumbar segmental sustained rotation (LSSR) on the lumbar spinous process, and to clarify the effects of LSSR on straight leg raising (SLR) and lumbar flexion (LF). [Subjects] 18 pain-free healthy adults volunteered for this study. [Methods] Applied force and direction were measured between the L5–S1 segments using tri-axial pressure sensors. Subjects participated in 3 trials. Subjects underwent localized right rotation, held for 10 seconds, of the L5 in relation to the S1. Sham group subjects followed LSSR group protocols; however L5–S1 rotation was absent. Control subjects rested on a plinth. SLR and LF were measured pre and post-trial. [Results] Outcome data for LSSR forces were as follows; x (0.06N (±0.29)), y (‒5.26N (±0.01)), z (6.16N (±1.33)), and resultant vector magnitude (8.19N (±1.12)). LSSR relative direction results were as follows: x-axis angle, 89. 6 ° (±1.5); y-axis, 130.9 ° (±5.6); and z-axis, 41.6 ° (±4.7). The LSSR group’s LF and SLR were significantly increased compared with those of the sham and control groups. [Conclusion] The identified resultant vector magnitude was 8.19N, less than other techniques. LSSR effectively improves LF and bilateral SLR.