In studies examining

dose–response relationships between knee-straining work activities and degenerative knee disorders, retrospective exposure assessment has usually been based on self-reports (Felson et al. 1991; Vingard et al. 1991; Coggon et al. 2000; Sandmark et al. 2000; Seidler et al. 2008; Muraki et al. 2009; Klussmann et al. 2010). However, as various studies have shown, the validity of self-reports, specifically in this field, might be questionable (Baty et al. 1986; Burdorf and Laan 1991; Viikari-Juntura et al. 1996; Ditchen et al. 2013). Alternatively, prospective methods of exposure Combretastatin A4 concentration assessment such as workplace observations, video-recordings, or exposure measurements that provide more accurate data are applied in assessing knee-straining postures. Yet, they are only rarely used, potentially as a result of the associated technical and financial Selleck MK0683 efforts and the question of optimal cost efficiency by weighing up precision and costs against each other (e.g. Trask et al. 2014). Consequentially, in studies using these methods, exposure assessment is often conducted for only short sequences and focuses on small participant groups. For example, Kivimäki et al. (1992) investigated knee disorders of floor layers, carpet layers, and painters (N = 35) by videotaping working tasks including kneeling and squatting with a total observation time of 12 h. A similar approach was used

in a Danish study (Jensen et al. 2000a) on kneeling and squatting of carpenters and floor layers. The authors filmed short working sequences and extrapolated the duration of knee-straining postures to an entire work shift. This procedure may have led to overestimation of the daily knee-loading, as critically stated by the authors in a recent publication

(Jensen et al. 2010). To avoid this source of bias, Burdorf et al. (2007) examined the entire work shift to investigate the effects of mechanised equipment on physical load among road workers and floor layers (N = 59) Docetaxel in the Netherlands. A complex method of exposure assessment was applied, with work postures (e.g. kneeling and squatting) being measured by an ambulant-monitoring equipment system using accelerometry combined with a hand-held computer for real-time observations by the researchers. On the one hand, such technical solutions deliver valid exposure data of whole work shifts. On the other hand, this approach must be seen as an exception as it requires enormous effort in terms of time, technical and human resources. Beyond different tools for exposure assessment as described above, there may be different approaches to estimate the exposure in a study population either on an “individual” level, i.e. for each subject separately, or using a “group approach” where all subjects of an exposure group are assigned the group mean (Svendsen et al. 2005).