Occupational kneeling and squatting: development and validation of an assessment method combining measurements and diaries

Abstract

Objectives: As knee-straining postures such as kneeling and squatting are known to be risk factors for knee disorders, there is a need for effective exposure assessment at the workplace. Therefore, the aim of this study was to develop a method to capture knee-straining postures for entire work shifts by combining measurement techniques with the information obtained from diaries, and thus avoiding measuring entire work shifts. This approach was applied to various occupational tasks to obtain an overview of typical exposure values in current specific occupations.

Methods: The analyses were carried out in the field using an ambulatory measuring system (CUELA) to assess posture combined with one-day self-reported occupational diaries describing the durations of various work tasks. In total, 242 work shifts were measured, representing 81 typical tasks from 16 professions. Knee-straining postures were analysed as daily time intervals for five different postures. The accuracy of the method was examined by comparing the results to measurements of entire work shifts.

Results: Unsupported kneeling was the most widely used knee posture in our sample (median 11.4 % per work shift), followed by supported kneeling (3.0 %), sitting on heels (1.1 %), squatting (0.7 %), and crawling (0.0 %). The daily time spent in knee-straining postures varied considerably, both between the individual occupations, within an occupation (e.g. parquet layers: 0.0-88.9 %), and to some extent even within a single task (e.g. preparation work of floor layers (22.0 ± 23.0 %). The applied measuring method for obtaining daily exposure to the knee has been proven valid and efficient randomly compared with whole-shift measurements (p = 0.27).

Conclusions: The daily degree of postural exposure to the knee showed a huge variation within the analysed job categories and seemed to be dependent on the particular tasks performed. The results of this study may help to develop an exposure matrix with respect to occupational knee-straining postures. The tested combination of task-based measurement and diary information may be a promising option for providing a cost-effective assessment tool.

Fig. 1

Knee-straining postures: a unsupported kneeling (roofer); b supported kneeling (tiler), c sitting on heels (installer), d squatting (reinforcement ironworker); and e crawling (floor layer). Subjects b–d are equipped with the CUELA measuring system

Fig. 2

Screenshot of the analysis software depicting a measuring-based vector puppet (top left), the synchronised video sequence (top right), angular-time-graphs of the measured knee flexion (for both knees), and automatic identification codes for various postures (colour bars, bottom)

Fig. 3

Pilot study: comparison of measured (white) and “reconstructed” (black) exposure to the knee: time intervals spent in knee-straining postures during an entire work shift (n = 14) in three occupations (subject ID 1–8 service technicians, ID 9–12 ramp agents, ID 13–14 nursery nurses)

Fig. 4

Distribution of daily time intervals spent in five different knee-straining postures over all measurements (box-plots showing percentiles 5, 25, 50, 75, and 95; N = 242 work shifts)