Occupational Trunk Flexion and Neuromuscular Disturbance

Details

• Personal Author:
  Granata K ; Madigan ML ; Nussbaum MA
• Description:
  Occupational tasks involving trunk flexion are associated with an increased risk for low back pain (LBP). Previous studies on humans or animal models suggest that prolonged or repetitive trunk flexion alters the viscoelastic behavior of trunk tissues. Recent studies on animal models, however, indicate that prolonged or repetitive stretching of tissues due to flexion also, and perhaps more importantly, alters trunk active neuromuscular behaviors (i.e., muscle reflexes). Considering these changes as disturbances from normal behavior, we aimed to quantify the effects of several distinct exposures to prolonged and repetitive trunk flexion on such disturbances and to measure recovery from them. A biomechanical model was developed to quantify changes in trunk passive and active behaviors, using measures of trunk mechanical impedance (i.e., apparent mass, stiffness, and damping) and reflexive neuromuscular responses. Experimental data were obtained from sudden position-perturbation experiments. Exposures included: 1) prolonged flexed postures with and without added loads, 2) repetitive trunk flexion, and 3) repetitive lifting. Following prolonged trunk flexion, acute changes in trunk stiffness and reflexive responses were found, and which increased with both task duration and an external load. Though the acute disturbance to reflexive responses appeared to compensate for disturbances (decreases) in trunk stiffness, recovery to pre-exposure values occurred quickly. As such, this may leave the spine vulnerable to instability during the relatively slow recovery of trunk stiffness. In contrast, when the effects of trunk weight were excluded during the experiment, by raising participant's legs to induce flexion with the torso upright, the disturbance in reflexive responses continued even after full recovery of trunk stiffness. For this latter experiment, acute changes in trunk stiffness and reflexive response were larger with increasing trunk flexion angle, but similar between trunk flexion durations. Repetitive exposures to trunk flexion that involved longer flexion durations and higher flexion duty cycles were both associated with increased disturbances in trunk stiffness and reflexive responses, and both remained unrecovered following 20 minutes of rest. Disturbances in reflexive trunk responses following repetitive exposures, in contrast with those during prolonged static flexed postures, did not appear as compensatory responses to disturbed (reduced) stiffness. Similar slow recovery patterns in trunk stiffness and reflexive responses were observed following exposures to repetitive lifting. Following repetitive lifting, though, an increasing disturbance was found only with increasing trunk flexion angles. Other measures of trunk mechanical impedance (i.e., apparent mass) and reflexive behavior (i.e., reflex delay) were not substantially affected by any of the exposures. Both trunk stiffness and reflexive responses play important roles in stabilizing the spine. Hence, from a mechanical perspective, these results suggest a higher risk of injury due to spinal instability following exposure to tasks involving prolonged or repetitive flexed postures. In particular, persistent and simultaneous disturbances in trunk stiffness and reflexive responses, along with insufficient recovery time, are likely associated with a higher risk of spinal instability. The current work helps to understand the linkages between occupational trunk flexion and low back pain development, and may contribute to future ergonomic guidelines. [Description provided by NIOSH]
• Subjects:
  Musculoskeletal Diseases Musculoskeletal System Occupational Health Safety
• Keywords:
  Exposure Assessment Lifting Low Back Disorders Low Back Pain MSD Musculoskeletal Disorders Neuromuscular Function Posture Repetitive Work
• Series:
  Grant Final Reports
• Publisher:
  National Institute for Occupational Safety and Health
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Final Grant Report
• Place as Subject:
  OSHA Region 3 ; Virginia
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  OEP - Office of Extramural Programs
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-86
• NIOSHTIC Number:
  nn:20059646
• NTIS Accession Number:
  PB2021-100156
• Citation:
  Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-008504, 2012 Oct; :1-86
• Contact Point Address:
  Maury A. Nussbaum, Department of Industrial and Systems Engineering, Virginia Tech, 250 Durham Hall (0118), Blacksburg, VA 24061
• Email:
  nussbaum@vt.edu
• Federal Fiscal Year:
  2013
• NORA Priority Area:
  Healthcare and Social Assistance ; Services
• Performing Organization:
  Virginia Polytechnic Institute and State University
• Peer Reviewed:
  False
• Start Date:
  20060801
• Source Full Name:
  National Institute for Occupational Safety and Health
• End Date:
  20120731
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:03b5b83ad23741df48023867b041009482888d05d665554bf9f24cea4d1d70c6a6f02582b7a81e7640e9821083b31a7e2006364748e67bb976a732bc0d9ee1eb
• Download URL:
  https://stacks.cdc.gov/view/cdc/218984/cdc_218984_DS1.pdf
• File Type:
  [PDF - 1.75 MB ]