Summary

Loads on the lumbar spinal column are a significant risk factor for backaches. It is important to know the distribution of these internal forces during work activities both for prevention and for worker rehabilitation. Musculoskeletal (MS) modelling of the spinal column is the only non-invasive approach that can estimate loads on the spinal column’s internal structures.

Two models have been developed in Quebec: a finite element model (FEM) guided by movement and another model guided by electromyographic (EMG) measurements of muscle activation (EMGM). These models are therefore sensitive to individual movement and muscle activation strategies. A third model, which allows lumbar stability to be assessed, is also associated with the FEM and makes it possible to better understand stability margins and the risks of hypermobility, among other things.

The general objectives of this study are to (1) amalgamate the MS models (FEM, EMGM, lumbar stability) in a hybrid model with the aim of obtaining the solution that is the most sensitive to individual movement and trunk muscle activation strategies; (2) retain the characteristics related to the personalization of this model by integrating natural spinal column curves; and (3) implement and validate the submaximal EMG normalization technique.

This research report summarizes the contents of three articles that described the results in relation to these objectives. On the basis of two independent data sets concerning static (article 1) and dynamic (article 2) lifting tasks, the results of this project confirmed that the maximal EMG normalization technique can be replaced by the submaximal technique. The success of this validation allows one to use an EMG-based MS model in workers who have backache or are unable to produce the maximal voluntary contractions needed for the maximal normalization technique. In addition, it was shown that personalized spinal column profiles must be taken into account in MS modelling of the spinal column (article 3).

Together, these results show that estimates concerning joint loading (compression and shear) and lumbar stability indices are much less subject to error than estimates of muscle force and should therefore be preferred when documenting exposure during different tasks and the effects of interventions. This hybrid model can therefore be applied in evaluating the risk associated with different work tasks or in measuring results to assess the effects of ergonomic or clinical interventions.