Main findings
This 3-month randomised controlled trial among female cleaners from 9 workplaces in Denmark significantly improved their individual physical and cognitive behavioural resources. The PCT intervention improved trunk muscle strength and balance, and the CBTr intervention reduced kinesiophobia. In the following, implications and perspectives on the improvements of these resources for the prevention of deterioration among cleaners will be discussed.
Comparison with other studies
Our study is the first RCT among workers with high physical work demands demonstrating a workplace training intervention to improve muscle strength in an ITT-analysis. It is well recognized that the dose of a work task is relative to the capacity of the performing worker [
30,
31]. Therefore, the relative physical work exposure on the musculoskeletal system of the worker can be considered reduced when strength improvements are obtained. Generally, the strength level of the cleaners in the current study was comparable to reports from previous studies with a representative sample of the Danish population [
32] and a sample of Danish cleaners [
8], although trunk strength was below the previous reports. High muscle strength has been shown to characterize senior (> 8 years) cleaners without muscle pain in comparison with cleaners with similar seniority with muscle pain [
8]. Therefore, the increased muscle strength from the PCT may improve the cleaners' tolerance for high work loads and possibly reduce the risk for deterioration, i.e. musculoskeletal disorders.
The PCT was tailored to improve both strength and coordination of the cleaners. Accordingly, the PCT resulted in an improved postural balance. The PCT included training of the
bracing manoeuvre, which produces a global co-activation of the muscles of the abdominal wall [
33]. In our study, the only instruction that was given during the balance test was "stand as still as possible" and the test leader was blinded to the randomisation. Therefore, the improved balance may imply that the cleaners in PCT were able to transfer and use the improved strength and coordination of abdominal wall muscles in tasks not related to the training. Some studies suggest that poor stabilisation may predispose injury and musculoskeletal disorders [
34‐
36]. Thus, the improvements in strength and balance in PCT may prevent deterioration of health among female cleaners in the longer term.
CBTr was shown to decrease kinesiophobia compared to both REF and PCT. Pain-related fear of movement is closely related to measures of disability and catastrophising [
9,
37‐
39]. Furthermore, kinesiophobia is shown to predict long-term recovery from pain-related functional disability among males with chronic non-specific low back pain [
40] and improved kinesiophobia among work-disabled pain patients have shown positive effects on return to work [
41]. Thus, reductions in kinesiophobia may reflect reduced pain-related fear of movements related to work tasks.
Baseline values of kinesiophobia among the working cleaners were on average 32-34. These values are comparable to a sample of the Dutch general population [
25] and less than the average of 38-40 reported from patients seeking care due to musculoskeletal pain [
40,
42,
43]. Although baseline levels were lower in the current study population, significant improvements were still found. This introduces CBTr as a possible valuable prevention strategy to reduce kinesiophobia in workplace interventions as well as in rehabilitation.
No effects on kinesiophobia, strength and balance were seen across the interventions. This finding indicates that contamination was successfully avoided by the cluster randomisation. However, five out of seven measures of strength and balance were numerically impaired in the CBTr-group, and kinesiophobia was numerically increased in the PCT-group. These changes were not significantly different from REF, and conclusions can not be drawn on these aspects. However, for improvements to be fully reflected in the ability to tolerate high physical work demands, interventions to counteract the reduced resources and thus improve both physical and cognitive-behavioural resources would probably be optimal. We therefore suggest that future interventions should integrate both PCT and CBTr in one initiative in the prevention on physical deterioration among workers. Future research is needed to verify this recommendation.
Strengths and limitations
This study tested new approaches to prevention of health deterioration among 294 female cleaners from nine representative workplaces [
14]. The interventions were thoroughly developed and tailored to the specific job group of cleaners. Although adherence rates were rather low, they were not lower than intervention studies in similar job groups [
44]. However, the development of the interventions primarily built on a theoretical rationale derived from efficacy studies. Efficacy studies differ from effectiveness studies by being conducted in a context that gives optimal conditions for implementation [
45]. Efficacy is necessary to, but not sufficient for effectiveness [
45] and implementation is suggested to be thought of as interacting with the efficacy to determine effectiveness [
46]. Thus in an effectiveness study, implementation plays an important role in obtaining results. In the current study, two specific efforts were made to support implementation of the interventions. First, workplaces adopting this intervention study were obliged by contract to provide time for the intervention during working hours. Second, each training session was guided by an instructor to personalise the interventions. Although adaption to the workplace setting was performed and pilot studies conducted, the practical rationale behind the interventions could have gained strength, if they had derived from feasibility studies among cleaners. Both inadequate efficacy as well as implementation is a possible reason for the lack of effect in some of the strength parameters. Thus, further efforts to improve implementation and adherence rates of workplace intervention studies in job groups with low socio-economic resources and among workers with low influence on work schedules should be implemented in future study designs.
By the conservative intention-to-treat analyses (with forward and backward carrying of missing observations), a tendency to underestimate the variances appears. It should be mentioned though, that the analyses reported in the results section of this paper follow the standards of the consort statement [
26] and are conservatively designed to false positive finding due to avoid bias associated with non-random drop-out. Even with the relatively large drop-out, intention-to-treat analyses were able to reveal significant intervention effects, supporting our hypotheses of the interventions. Nevertheless, given the large standard deviations shown in table
2 it is likely that this study suffers from impaired power and some false negative results may be evident.
A non-significant increase in kinesiophobia was seen in the PCT-group. Since the increase was non-significant, it cannot be ruled out, that it happened by chance. However, according to the fear-avoidance theory of pain, one reaction to an expected painful stimulus may be avoidance behaviour [
47]. That is, the individual has certain expectations on the painful consequences of an activity, which lead to avoiding the activity. It is well known, that physical training in itself can introduce an acute pain response [
48]. Thus a confirmation of the fearful expectation to physical training may exacerbate the fear of movement and result in the increased kineisophobia seen in the current study. Graded activity has been suggested as treatment method for pain patients with high kinesiophobia. With graded activity, loads are introduced gradually and thereby producing disconfirmations of expectations of pain and harm and actual consequences of the activity [
47]. In the PCT, exercise intensity was increased gradually and instructors carefully informed the participants that some pain and soreness could be experienced after training. However, no cognitive-behavioural or operant exercises were included. Actually, this was avoided to reduce overlapping interventions. In spite of the insignificance, the numerical increase in kinesiophobia in PCT may encourage that future training interventions corporate such kinesiophobia preventive exercises prior to or concurrent with the training.