Changes in Regional Activity of the Psoas Major and Quadratus Lumborum With Voluntary Trunk and Hip Tasks and Different Spinal Curvatures in Sitting

Recruitment of Discrete Regions of the Psoas Major and Quadratus Lumborum Muscles Is Changed in Specific Sitting Postures in Individuals With Recurrent Low Back Pain

“…Resolution of this debate has been compromised by a lack of direct EMG recordings and a failure to consider the potential for unique changes in separate LBP subgroups and different regions of these multifascicular muscles. Recent work 34 has reported greater activity of PM fascicles arising from the transverse processes (PM-t) when sitting in a midrange lumbar lordosis compared to a flatback posture, yet similar activity of the anterior fascicles from the vertebral body (PM-v) in these postures. QL EMG signal amplitude did not differ between sitting postures, but the activity level of the posterior QL fascicles (QL-p) was greatest during trunk extension and lateral flexion, whereas the activity of the anterior QL fascicles (QL-a) was greatest during trunk lateral flexion.…”

“…QL EMG signal amplitude did not differ between sitting postures, but the activity level of the posterior QL fascicles (QL-p) was greatest during trunk extension and lateral flexion, whereas the activity of the anterior QL fascicles (QL-a) was greatest during trunk lateral flexion. 34 Different activation levels of distinct regions of the PM and QL, 34 combined with anatomical/biomechanical data of these muscles, 6,36 underpin several hypotheses regarding their activation levels with changes in spinal curvature in sitting in individuals with LBP. We hypothesized that PM and QL activity levels would differ between LBP subgroups that are defined on the basis of trunk ES EMG level when sitting.…”

“…In flat sitting, the LBP ESlow participants, compared to controls, had greater EMG amplitude of the PM-v (which is more active in trunk flexion than extension) 35 and QL-p (which is more active in extension than flexion). 34 This implies a concurrent increase in trunk flexor and extensor torque, respectively, consistent with the objective to maintain the flat lumbar curvature in the sagittal plane. Unlike the QL-p EMG, the QL-a EMG was not different between groups.…”

“…[ research report ] the fact that this muscle has no spine attachment (QL-a runs from the 12th rib to the iliac crest) and has greater function in lateral flexion than in extension. 34 Evidence of increased activation of the PM-v and QL-p in the LBP ESlow group while maintaining specific sitting postures parallels the clinical assumption of muscular overactivity in individuals with LBP. Although activity is not directly related to muscle-length changes, this augmented activity may underpin a tendency for these muscles to be shorter in those with LBP 14,15,38 and is consistent with the observed greater asymmetry of the QL, with marked hypertrophy on the dominanthand side, in cricket fast bowlers with LBP compared to those who were pain free.…”

“…Data from these 10 individuals with recurrent LBP were compared with previously published data from 9 healthy controls (mean  SD age, 23  3 years; height, 169  5 cm; weight, 62  8 kg; 7 male) with no history of LBP. 34 Participants with recurrent LBP were included if they had their initial LBP episode (symptoms between T12 and gluteal fold) more than 12 months prior to the study, with subsequent LBP episodes severe enough to limit activities of daily living and/or cause time off from work and/or sports. Participants were excluded from both groups if they reported any major circulatory, cardiorespiratory, orthopaedic, or neurological conditions, or if they had back surgery or any surgery with an abdominal incision.…”