The assessment of muscle activity (MA) via surface electromyography (sEMG) within a workplace setting offers valuable insights into workers' physical strain, but it encounters certain challenges. Particularly, the analysis of sEMG data presents difficulties when it requires normalization using maximal voluntary isometric contractions (MVIC). Given that familiarity with generating maximum forces cannot be assumed in samples from the field of occupational science, it becomes necessary to familiarize participants with the normalization task. This is crucial to ensure consistent and replicable performance of MVICs. This paper aims to investigate how familiarization can improve the capability of reproducing maximal voluntary force (MVF) of a high percentage (85% and 90%) and to assess its impact on the reliability of MA of lower leg (gastrocnemius medialis and tibialis anterior) and trunk muscles (obliquus externus abdominis) in MVICs, for a worker-specific sample. The results demonstrate that one or two familiarization days can enable a high degree of reproduction with a range of 85% of the absolute MVF and a low percentage of standard error of the mean (%SEM) in intra-day reliability of the sEMG amplitude. However, it is important to note that the reliability of sEMG varied among subjects and individual muscles, particularly for the trunk muscles. Still, our findings underscore the significance of familiarization sessions when utilizing MVIC normalization for a worker-specific sample.

The complete article is published in the "International Journal of Industrial Ergonomics" (2023).