¹Université Laval, Québec, Canada
²Centre interdisciplinaire de recherche en réadaptation et intégration sociale (CIRRIS), Québec, Canada
³INRS (Institut National de Recherche et de Sécurité), Vandœuvre-lès-Nancy, France
⁴Université de Sherbrooke, Sherbrooke, Canada
⁵Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), Montréal, Canada

Text

Introduction: Work-related musculoskeletal disorders, especially low back pain (LBP), are a major cause of occupational disability and are exacerbated by manual material handling (MMH) tasks. Quantitative guidelines based on psychophysical and biomechanical data collected from asymptomatic workers are available for the prevention of LBP during MMH tasks (lifting, lowering, pushing, pulling, carrying). Very few address the issue of workers with LBP returning to work. LBP is associated with several sensorimotor (e.g. proprioceptive changes) and psychosocial (e.g. kinesiophobia) factors that may modify their response to MMH and should be considered to guide their return to work. To our knowledge, one study has proposed lifting guidelines for LBP patients (Fergusson et al., 2005), but none have addressed the tasks of lowering, pushing, pulling or carrying. The aim of this study is to develop a reference tool related to MMH tasks adapted to the return to work of people with LBP.

Methods: Seventy participants with chronic LBP and 70 participants without LBP will be recruited (all participants < 65 years old). Half of the participants will be female. Participants will perform a series of MMH tasks and a submaximal electromyography (EMG) normalization protocol of 12 abdominal and lumbar muscles (longissimus, iliocostalis, multifidus, rectus abdominis, external and internal obliques). MMH tasks include lifting/lowering boxes from various heights and pushing/pulling a sled. Some authentic movement combinations will also be performed to assess if natural coordination patterns are disrupted by the presence of LBP (e.g. lift-pivot-deposit). Each task will be performed with an incremental weight to assess participants’ psychophysical limit. Equipment includes instrumented hand force handles (Kistler), force platforms (AMTI), optoelectronic camera system (Optitrack), and wireless EMG sensors (Delsys). Compression and shear forces at L5-S1 will be estimated by an EMG-driven model supported by optimization. This model uses the results of multisegmental inverse dynamics and normalized EMG to estimate muscle forces, accounting for passive resistance of muscles and spine. The percentage of participants performing each task (acceptability criterion) will be used to assess the level of risk. The total risk for each weight in the different tasks will correspond to the highest level of risk among the biomechanical and acceptability criteria. Participants with LBP will also undergo a series of tests and questionnaires to assess their psychological (kinesiophobia, pain catastrophizing) and physical (flexion-relaxation phenomenon, exercise-induced sensitization) characteristics. These variables could be used to determine multiplier factors that could affect the calculation of recommended handling loads for each task.

Results/Discussion: Thirty participants have been recruited so far. The data collected will be incorporated into an assessment tool designed to facilitate return to work and minimize the risk of LBP flare-ups due to MMH occupational tasks. An advisory committee will be consulted to ensure that the tool developed meets the needs of occupational therapists and ergonomists.