Sample and procedure

A priori we aimed at estimating the prevalence of MSDs with a precision of 5-6%, and expected that the prevalence of MSDs would be around 40% [8]. This leads to an estimated sample size of 257–369 among both occupations. Therefore, we aimed at including 300 participants for each occupation. Based on previous results we expected the response rate to be around 40% [30]. Therefore, we randomly selected 750 bricklayers and 750 construction supervisors from a Dutch registry comprised of all employed Dutch construction workers. The random selection was performed by the independent data manager of the registry, frequently assisting in selecting samples for research purposes.

Among the bricklayers were both those working in the construction of new buildings as in renovation. Among the construction supervisors were those working in ground, road and water construction and in commercial and industrial building. Furthermore, the selection was not restricted based on the type of construction supervisor (main or assisting supervisor).

In the collective labour agreement of the workers is recorded that research is performed under the authority of Arbouw, The Health and Safety Institute for the Dutch Construction Industry. The workers are reminded in writing of this agreement and informed about the aims of the present research. Workers can choose whether or not to participate voluntarily. The workers are aware of the fact that by filling in and returning the questionnaire, they give the researchers written consent to use their information anonymously for research purposes. The survey was conducted from December 2009 to January 2011 and consisted of a baseline questionnaire and a follow-up questionnaire one year later. At baseline, all participants received a sealed envelope at their home address containing a postcard with an invitation to participate, a questionnaire survey and an incentive (lottery ticket for a national lottery) [30]. At follow-up, only those who had responded at baseline were sent a second postcard, a follow-up questionnaire and an incentive (lottery ticket). Completing the questionnaires took approximately 20 min. The participants were asked to fully complete and return the questionnaire within two weeks. One reminder containing a postcard was sent to all participants after one week.

Questionnaire

The questionnaire comprised multiple parts involving health-related topics, but to address the present research questions, only the items regarding musculoskeletal complaints and the associated or aggravating tasks and activities, are reported.

Analysis

The analyses were performed separately for the two occupational groups. Information from the open-ended question on perceived causes or aggravating factors was categorised and described qualitatively. Descriptive statistics were presented as the percent, median and Inter Quartile Range (IQR). To gain insight in the characteristics and representativeness of the respondents, we tested i) for differences in age between responders and the initial sample using a t- test and ii) the relation between age (years) and having MSDs at baseline, and the relation between having or having not MSDs at baseline and response at follow-up using univariate logistic regression analysis. Statistical significance was set to an alpha level of 0.05. The prevalence and 95% confidence interval (CI) of the MSDs was calculated using the baseline data. Confidence intervals were calculated by using the Wald method when the sample consisted of more than 150 persons and the adjusted Wald method when the sample consisted of less than 150 persons [32].

Problems experienced during work was recoded into three categories (0–3 = no/little, 4-6= medium, 7–10 = many problems). Changes in the problems experienced during work were assessed by calculating the difference in the score between baseline and follow-up. We defined a difference over time in problems during work as a decrease or increase of 2 points or more. Furthermore, we assessed for every body region the frequencies and percentages of the reported tasks or activities that caused or aggravated the complaints of the body region under consideration. Next, for every task or activity a top-three of involved body regions was constructed and reported. The IBM SPSS Statistics 19 software was used to analyse the data.

Characteristics of the study population

We found no difference in age between the responding bricklayers and the initial sample of bricklayers. However, we did find a statistically significant difference in age for the construction supervisors. At baseline, the responding construction supervisors were older (5.5 years, p<0.01) than the sample.

Next to this, we found a statistically significant association between age (years) and response at follow-up for both bricklayers (OR 1.04 per year, 95% CI: 1.02-1.06) and construction supervisors (OR 1.03 per year, 95% CI: 1.00-1.05). Furthermore, we found a statistically significant association between age and having MSDs at baseline for the bricklayers (OR 1.02 per year, 95% CI: 1.00-1.04), but not the supervisors (OR 1.02 per year, 95% CI: 1.0-1.05. However, there was no relation between having versus not having MSDs at baseline and response at follow-up for both bricklayers (OR 1.09, 95% CI: 0.61-1.97) or supervisors (OR 0.85, 95% CI: 0.48-1.49).

Prevalence of self-reported musculoskeletal health complaints

Among the supervisors, more than half of the respondents reported one or more regular or long-lasting musculoskeletal complaints (57%, 132/232). The highest prevalence of complaints was found for the back, the shoulder/upper arm, neck and knee (Table 2). Half of the supervisors with complaints, reported one complaint (68/132). Nearly one quarter (30/132) of the supervisors reported two complaints and another quarter of the respondents with complaints (34/132) reported three or more complaints.

Recurrent complaints, work-relatedness and problems during work

Occupational physical tasks and activities

Irrespective of the body region involved, bricklayers with MSDs most often report that they perceived the following tasks either caused or aggravated their symptoms: ‘Working with a bent back’ (72%, 128/179), ‘Carrying and lifting’ (64%, 115/179), ‘Working with arms above shoulder height’ (59%, 106/179) and ‘Kneeling and stooping (55%, 98/179). In general, construction supervisors most often pereceived that the following tasks either caused or aggravated their symptoms ‘Carrying and lifting’ (58%, 76/132), ‘Working with a bent back’ (47%, 62/132), ‘Walking across the construction site (44%, 58/132), and ‘Standing’ (42%, 55/132).

Among the workers in both occupations, several participants reported other causes for their MSD. Most of these other causes were not work-related causes, including sports activity (n=12) or neural symptoms after a disc herniation (n=10). None of the bricklayers reported distress as a cause or aggravator of their MSD, whereas seven of the supervisors did.

Strengths and limitations

Earlier research in the construction field showed that construction workers are at risk for MSDs [21, 33] and that MSDs are a determinant of early retirement or disability [5, 16]. Based on these previous findings and the high prevalence of MSDs found in the present study, the prevention of MSDs among construction workers is of significant importance. However, to target workplace interventions further knowledge on the nature and degree of MSDs is required. Our study provides, based on a random, adequately sized sample of workers an improved understanding of MSDs in the construction industry [30]. We used a sampling strategy based on occupation and verified the participants’ occupation during the previous year. By doing so, we made certain that the results of the present study are not contaminated by other occupations.

However, some limitations regarding the representativeness of the workers participating in the present study must be noted. First, the construction supervisors who responded were older than the Dutch population supervisors. Second, among the bricklayers age might have affected the prevalence of MSDs, possibly leading to a higher prevalence we found. Third, the follow-up data might be contaminated by the finding that the older workers are more likely to participate in the follow-up. On the other hand, we also verified whether the presence or absence of MSDs at baseline might have affected follow-up response, but we did not find an indication for this. Our follow-up data are therefore not likely to be a contaminated by a selection process due to MSDs in itself.

Our response rate at baseline is similar to the response rates in other surveys [9, 16, 30]. Despite our effort to increase the response rate by sending reminders and incentives, our baseline response rate of 37% is rather low. Therefore, the sample considered in the present study reflects a portion of the population. Based on the finding that more older supervisors responded, it must be concluded that we the younger population construction supervisors is underrepresented in our present study. Future research should therefore try to reach this population, perhaps by considering other survey modalities or incentives more attractive to them. Nonetheless, our response at follow-up was relatively high (80%).

Regarding the generalisability of our results regarding the factors that cause or aggravate MSDs for supervisors, it must be noted that within the occupation of ‘construction supervisor’, differences exist in the number of physical tasks and activities performed during a regular working day. Some supervisors participate regularly or often in manual tasks (mainly those supervisors working on smaller building projects), whereas other supervisors never do so and are mainly or only involved in managerial tasks. Based on our data we are not able to discriminate between the two types of supervisors. Our findings regarding the perceived causing and aggravating activities fit in with previous results on demands and health effects for those occupations. In a systematic review we found for example that frequent and deep bending, lifting and carrying and working with the arms more than 60^o elevated are common for bricklayers [7]. In the present study we found that these demands are perceived as causing or aggravating factors for MSDs. On the other hand, the present study showed that a considerable number of bricklayers perceived kneeling and stooping as a cause or aggravator of their MSD, but from the literature this activity did not appear to be that common. For supervisors little was known about physical demands, but the present study illustrates that these demands should not be to easily neglected.

In the present study, we used a self-reporting measure of (work-related) MSDs. Therefore, our six-month prevalence estimate could be higher than the prevalence of diagnosed work-related MSDs [34, 35]. Furthermore, there are likely to be seasonal differences in prevalence. Based on literature, it seems likely that musculoskeletal complaints will more prevalent during the winter than during the summer [36], with probably larger differences for the bricklayers then the supervisors [37]. By asking the workers in December/January about their MSDs during the past six months, we aimed at finding a good estimate of workers who might benefit from preventive actions without too much bias due to including only winter or only summer months.

Furthermore, it could be argued that the interpretation of our results regarding the seriousness of the MSDs is limited because we did not describe a variety of dimensions, such as trouble, pain or disability [38, 39]. Instead, we deliberately chose to assess the dimension that is, in our opinion, of highest relevance for occupational health care professionals targeting workplace adjustments, namely the extent of the problems experienced during work due to MSDs.

Implications

We found that among two distinctly different construction occupations more than half of the workers suffer from MSDs in one or more body region. Among the bricklayers, two-thirds of the population reports two or more complaints. Furthermore, approximately 40% of the workers in both occupations report that that they experience many problems during work due to their MSDs, irrespective of their occupation. This suggests that MSDs should be considered a priority in occupational preventive healthcare, irrespective of the type of occupation.

Based on our results, a job-specific approach should be considered. In the first place, bricklayers report that their MSDs are work-related twice as often (81%) as supervisors. As a consequence, our results indicate that the following activities should be targeted for ergonomic improvement among bricklayers: carrying and lifting, working with a bent back and working above shoulder height. For construction supervisors, the activities ‘standing’ and ‘walking across the construction site’ deserve attention among workers with MSDs.

For workers with MSDs, it should be kept in mind that depending on the type of occupation, a closer look at different occupational activities is warranted. For example, bricklayers with MSDs associated with the knee report that kneeling and stooping are the most important factors causing or aggravating their complaints. In addition, supervisors with knee complaints also report that climbing ladders and scaffolds can cause or aggravate their MSDs. A similar reasoning applies for complaints of the back: in both occupations, preventive actions at the workplace should be primarily directed at reducing the amount of working with a bent back and carrying and lifting. For supervisors, the tasks of ‘standing’ and ‘driving vehicles’ should also be considered as a desired point of action. In summary, workers with MSDs may experience problems or the aggravation of their complaints due to their job-specific occupational activities, depending on the body region involved.

Further research

The present study provides occupational healthcare professionals with knowledge that is applicable for evidence-based decision making regarding the necessity and importance of ergonomic adjustments in construction-related occupations. However, this report represents only one step toward effective prevention of MSDs. It is important to integrate this knowledge into policies related to occupational healthcare for construction workers, such as periodic surveillance of workers’ health [7]. Thereafter, it is necessary to verify whether such workers’ health surveillance leads to behavioural changes and preventive actions at the workplace [40] and ultimately to a reduction of MSDs and improved work functioning.