title: Lumbopelvic muscle activation patterns in three stances under graded loading conditions: Proposing a tensegrity model for load transfer through the sacroiliac joints.
abstract: OBJECTIVE
  According to the conventional arch model of the pelvis, stability of the sacroiliac joints may require a predominance of form and force closure mechanisms: the greater the vertical shear force at the sacroiliac joints, the greater the reliance on self-bracing by horizontally or obliquely oriented muscles (such as the internal oblique). But what happens to the arch model when a person stands on one leg? In such cases, the pelvis no longer has imposts, leaving both the arch, and the arch model theory, without support. Do lumbopelvic muscle activation patterns in one-legged stances under load suggest compatibility with a different model? This study compares lumbopelvic muscle activation patterns in two-legged and one-legged stances in response to four levels of graded trunk loading in order to further our understanding the stabilization of the sacroiliac joints.
  
  
  METHODS
  Thirty male subjects experienced four levels of trunk loading (0%, 5%, 10% and 15% of body weight) by holding a bucket at one side, at three conditions: 1) two-legged standing with the bucket in the dominant hand, 2) ipsilateral loading: one-legged standing with the bucket in the dominant hand while using the same-side leg, and 3) contralateral loading: one-legged standing using the same leg used in condition 2, but with the bucket in the non-dominant hand. During these tasks, EMG signals from eight lumbopelvic muscles were collected. ANOVA with repeated design was performed on normalized EMG's to test the main effect of load and condition, and interaction effects of load by condition.
  
  
  RESULTS
  Latissimus dorsi and erector spinae muscles showed an antagonistic pattern of activity toward the direction of load which may suggest these muscles as lateral trunk stabilizers. Internal oblique muscles showed a co-activation pattern with increasing task demand, which may function to increase lumbopelvic stability (P < 0.05). No unilateral pattern of the internal obliques was observed during all trials.
  
  
  CONCLUSIONS
  Our results suggest that the lumbopelvic region uses a similar strategy for load transfer in both double and single leg support positions which is not compatible with the arch analogy. Our findings are more consistent with a suspensory system (wire-spoke wheel model). If our proposed model holds true, the pelvic ring can only be integrated by adjusting tension in the spokes and by preserving rim integrity or continuity. Thus, we propose that in order to restore tension integrity throughout the pelvic ring, efforts to unlock restrictions, muscular correction of positional faults and lumbopelvic or even respiratory exercises following sacroiliac joint dysfunctions must be taken into consideration. Our hypothetical model may initiate thinking and act as a guide to future work based on a biomechanical approach to the problem of sacroiliac joint dysfunction.
authors.affiliation: Department of Physiotherapy, Faculty of Rehabilitation, P.O. Box15875-4391, Iran University of Medical Sciences, Tehran, Iran. Electronic address: hamed.pardehshenas@hotmail.ca.
authors.forename: Hamed
authors.initials: H
authors.lastname: Pardehshenas
authors.affiliation: Department of Physiotherapy, Faculty of Rehabilitation, P.O. Box15875-4391, Iran University of Medical Sciences, Tehran, Iran. Electronic address: maroufi.n@iums.ac.ir.
authors.forename: Nader
authors.initials: N
authors.lastname: Maroufi
authors.affiliation: Biomechanics Lab. Rehabilitation Research Center, Faculty of Rehabilitation, Department of Rehabilitation Basic Sciences, Iran University of Medical Sciences, Tehran 15459-13187, Iran.
authors.forename: Mohammad Ali
authors.initials: MA
authors.lastname: Sanjari
authors.affiliation: Biomechanics Lab, Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran.
authors.forename: Mohamad
authors.initials: M
authors.lastname: Parnianpour
authors.affiliation: Ezekiel Biomechanics Group, 8608 Dixie Place, McLean, VA 22102, USA.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Levin
mesh_terms: D000009:Abdominal Muscles / Q000502:physiology*; D001696:Biomechanical Phenomena; D004576:Electromyography; D006801:Humans; D008161:Lumbosacral Region / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D010388:Pelvis / Q000502:physiology*; D026741:Physical Therapy Modalities; D011187:Posture / Q000502:physiology; D012446:Sacroiliac Joint / Q000503:physiopathology*; D016474:Weight-Bearing / Q000502:physiology*
keywords: Arch theory; Load transfer; Sacroiliac joint; Self-bracing; Wire-spoke wheel model