Contents lists available at ScienceDirect International Journal of Industrial Ergonomics journal homepage: www.elsevier.com/locate/ergon Associations between low back muscle activity, pelvic movement and low back discomfort development during prolonged standing – An exploratory laboratory study Rudolf Wall a,* , Thomas Läubli a,b , Robert Seibt a , Monika A. Rieger a , Benjamin Steinhilber a a University Hospital Tübingen Institute of Occupational and Social Medicine and Health Services Research, Wilhelmstraße 27, 72074, Tübingen, Germany b Federal Institute of Technology Zürich, Switzerland ARTICLE INFO Keywords: Surface electromyography Kinematics Standing work Musculoskeletal disorders Low back discomfort ABSTRACT Low back discomfort (LBD) is common in long-term standing work. The aim of this study was to investigate whether development of LBD during standing is related to lumbar muscle activity and pelvic movement. In a secondary analysis we investigated whether age, gender, and standing work habituation moderates the above- mentioned relationship. Sixty subjects (15 young females, 15 young males, 15 older males, and 15 young males habituated to standing work) were included and had to stand for 4.5 h over three periods with two seated breaks. Surface electromyography, a gravimetrical position sensor, and a numeric rating scale were used to assess lumbar muscle activity, pelvic movement, and LBD, respectively. 22 of 55 analyzed subjects (40%) reported LBD and were assigned to the discomfort developer (DD) group. The remaining subjects (non-discomfort developer: NoDD) showed a statistically significant increase of medio-lateral pelvic movement in the progression of the three standing periods. Almost no differences occurred in lumbar muscle activity (except for the 5th percentile of surface electromyography, which was higher in NoDD). No influence of age, gender, or standing habituation was found. Increased pelvic movement may protect from LBD development during prolonged standing, although differences are very small and clinical relevance is unclear. 1. Introduction Discomfort in the lower back region includes a broad spectrum of symptoms, of which pain is the most distinct and most investigated. Low back pain (LBP) is a widespread disorder (March et al., 2014). Although LBP seems to be a general epidemic with a one year pre- valence up to 65% (Walker, 2000), it was found to be more common in certain occupations compared to the general working population (Punnett, 2014). Work-related physical factors that may cause LBP are whole body vibrations, repetitive tasks, lifting, pushing, pulling, and constrained trunk postures (Chen et al., 2004; da Costa and Vieira, 2010; Griffith et al., 2012; Lötters et al., 2003). Additionally, work- related psychosocial factors contribute to LBP development, such as high job demands and low social support (da Costa and Vieira, 2010; Lang et al., 2012). Further, the prevalence of LBP seems to increase with age, and is more common in women than in men (Dionne et al., 2006; Wong et al., 2017). More recent studies found that occupational standing for a prolonged period of time was associated with LBP (Coenen et al., 2016; da Costa and Vieira, 2010; McCulloch, 2002). In this respect, it is suggested that transient LBP development during standing predicts fu- ture clinically relevant LBP in previously asymptomatic individuals (Nelson-Wong and Callaghan, 2014). Interestingly, several studies showed that the number of previously asymptomatic people who de- velop LBP during standing seems to be consistently between 32 and 70% (Aghazadeh et al., 2015; Marshall et al., 2011; Nelson-Wong et al., 2008, 2012; Nelson-Wong and Callaghan, 2010). Occupational standing is widespread within industrialized countries and across professions. In Germany and Canada, about 40–50% of the full-time working popula- tion are required to stand for the larger time of their shifts (Tissot et al., 2005; Wittig et al., 2013). Thus, the amount of people at a higher risk of developing musculoskeletal disorders in the lower back region com- pared to the general population is substantial (Andersen et al., 2007; Pensri et al., 2009; Werner et al., 2010). A wide range of mechanisms for causal relationships between LBP/ LBD and prolonged standing are discussed in the literature. Some https://doi.org/10.1016/j.ergon.2019.07.001 Received 16 January 2019; Received in revised form 11 June 2019; Accepted 4 July 2019 * Corresponding author. University Hospital Tübingen Institute of Occupational and Social Medicine and Health Services Research, Wilhelmstraße 27, 72074, Tübingen, Baden-Württemberg, Germany. E-mail address: rudolf.wall@med.uni-tuebingen.de (R. Wall). International Journal of Industrial Ergonomics 72 (2019) 380–389 0169-8141/ © 2019 Elsevier B.V. All rights reserved. T