With regard to the high variability of the exposure within a single task module, we found different reasons that may explain this. In many tasks, different working heights influenced workers’ posture, for example while working on scaffoldings, as do painters and roofers. A similar effect could be observed for roofers on steep roofs; the degree of the roof pitch strongly determined the workers’ postures (standing, “knee-supporting position” (Jensen et al. 2000b), or kneeling/squatting). Other factors that influenced the choice of posture included different structures on construction
sites, different working techniques, and, last but not least, individual preferences. It is difficult to compare our results with those of similar studies as only a few studies have been concerned with the daily exposure to the knee. In a Finnish study (Kivimäki et al. Wortmannin concentration 1992) on knee disorders of carpet and floor BV-6 mouse layers and painters, 35 subjects performing different tasks were videotaped for a total time of 12 h. In this study, only short working sequences of between 33 and 102 min were analysed, without regard to breaks, preparation work, et cetera. By projecting
these results onto a whole work shift, the comparison with our findings yielded agreements (e.g. parquet or floor layer, installing base: approx. 60 % of knee strain per day to approx. 62 % per day in our study) and strong disagreements (e.g. parquet or floor layer, installing mosaic parquet: approx. 90 % per day to approx. 52 % per day in our study). In accordance
to our study, the authors found large task-specific differences in the degree of exposure within a job category; for example, floor layers’ percentage of click here kneeling and squatting ranged from 0 % (grinding) to approximately 90 % (installing mosaic parquet) of the observation time. The importance of including all daily activities in the analysis of kneeling and squatting is made apparent in the studies of Jensen et al. in Denmark. In a first study, the authors videotaped floor layers and carpenters during short time sequences of three to 30 min (Jensen et al. 2000a, b). By extrapolating Niclosamide their findings on the duration of kneeling and squatting to a whole work shift, they stated an average daily percentage of time spent in these postures of approximately 56 % (floor layers) and 25 % (carpenters). In a second study, the authors videotaped each of four floor layers for an entire work shift and analysed the duration of kneeling, squatting, kneeling back on heels, and crawling tasks (Jensen et al. 2010). The average percentage of time spent in these postures was 41.0 % (SD = 7.5), which is consistent with our result of 39.0 % (SD = 16.3) from analysing all floor layers’ tasks measured in our study. As mentioned before, the analysis of only short working sequences may lead to overestimation of the real exposure.