Abstract: We included six studies (373 workers), four parallel RCTs, one cross-over RCT, and one combined parallel plus cross-over RCT. At least 295 of the employees were female and at least 39 male; for the remaining 39 employees, the sex was not specified in the study trial. The studies investigated different work-break frequencies (five studies) and different work-break types (two studies). None of the studies investigated different work-break durations. We judged all studies to have a high risk of bias. The quality of the evidence for the primary outcomes of self-reported musculoskeletal pain, discomfort and fatigue was low; the quality of the evidence for the primary outcomes of productivity and work performance was very low. The studies were executed in Europe or Northern America, with none from low- to middle-income countries. One study could not be included in the data analyses, because no detailed results have been reported. Changes in the frequency of work breaks There is low-quality evidence that additional work breaks may not have a considerable effect on musculoskeletal pain, discomfort or fatigue, when compared with no additional work breaks (standardised mean difference (SMD) -0.08; 95% CI -0.35 to 0.18; three studies; 225 participants). Additional breaks may not have a positive effect on productivity or work performance, when compared with no additional work breaks (SMD -0.07; 95% CI -0.33 to 0.19; three studies; 225 participants; very low-quality evidence). We found low-quality evidence that additional work breaks may not have a considerable effect on participant-reported musculoskeletal pain, discomfort or fatigue (MD 1.80 on a 100-mm VAS scale; 95% CI -41.07 to 64.37; one study; 15 participants), when compared to work breaks as needed (i.e. microbreaks taken at own discretion). There is very low-quality evidence that additional work breaks may have a positive effect on productivity or work performance, when compared to work breaks as needed (MD 542.5 number of words typed per 3-hour recording session; 95% CI 177.22 to 907.78; one study; 15 participants). Additional higher frequency work breaks may not have a considerable effect on participant-reported musculoskeletal pain, discomfort or fatigue (MD 11.65 on a 100-mm VAS scale; 95% CI -41.07 to 64.37; one study; 10 participants; low-quality evidence), when compared to additional lower frequency work breaks. We found very low-quality evidence that additional higher frequency work breaks may not have a considerable effect on productivity or work performance (MD -83.00 number of words typed per 3-hour recording session; 95% CI -305.27 to 139.27; one study; 10 participants), when compared to additional lower frequency work breaks. Changes in the duration of work breaks No trials were identified that assessed the effect of different durations of work breaks. Changes in the type of work break We found low-quality evidence that active breaks may not have a considerable positive effect on participant-reported musculoskeletal pain, discomfort and fatigue (MD -0.17 on a 1-7 NRS scale; 95% CI -0.71 to 0.37; one study; 153 participants), when compared to passive work breaks. Relaxation work breaks may not have a considerable effect on participant-reported musculoskeletal pain, discomfort or fatigue, when compared to physical work breaks (MD 0.20 on a 1-7 NRS scale; 95% CI -0.43 to 0.82; one study; 97 participants; low-quality evidence). We found low-quality evidence that different work-break frequencies may have no effect on participant-reported musculoskeletal pain, discomfort and fatigue. For productivity and work performance, evidence was of very low-quality that different work-break frequencies may have a positive effect. For different types of break, there may be no effect on participant-reported musculoskeletal pain, discomfort and fatigue according to low-quality evidence. Further high-quality studies are needed to determine the effectiveness of frequency, duration and type of work-break interventions among workers, if possible, with much higher sample sizes than the studies included in the current review. Furthermore, work-break interventions should be reconsidered, taking into account worker populations other than office workers, and taking into account the possibility of combining work-break intervention with other interventions such as ergonomic training or counselling, which may may possibly have an effect on musculoskeletal outcomes and work performance.

Plain-language summary: We searched the literature until 2 May 2019 to find randomised controlled trials (RCTs), quasi-RCTs, cluster-RCTs and cross-over RCTs of work-break interventions aimed at preventing work-related musculoskeletal disorders at work. We analysed all relevant studies to answer the research question and found six studies involving 373 workers, the majority of whom were female (≥ 78%), with a follow-up period of two to 10 weeks. Key results Effect of different work-break frequencies Five of the six studies evaluated different work-break frequencies. The implementation of additional work breaks (three studies) may not have an effect on musculoskeletal pain, discomfort or fatigue when compared to no additional work breaks or work breaks taken as needed. Additional work breaks (three studies) may have a positive effect on productivity and work performance when compared to a conventional work-break schedule. Additional higher frequency work breaks have been compared with additional lower frequency work breaks in one study, which resulted in no differences in participant-reported musculoskeletal pain, discomfort and fatigue, nor in productivity and work performance. Effect of different work-break durations None of the studies evaluated the effect of duration of work breaks. Effect of different work-break types Two of the six studies evaluated different work-break types. Active work breaks (one study) may not reduce nor increase the incidence of participant-reported musculoskeletal pain, discomfort and fatigue, or productivity and work performance. Similarly, different active work breaks have been compared with one another (one study), i.e. relaxation and physical active work breaks, which revealed no differences in participant-reported musculoskeletal pain, discomfort and fatigue, nor in productivity and work performance. Conclusions At present, we conclude that there is very low- to low-quality evidence that different work-break frequencies and types may not considerably reduce the incidence of musculoskeletal disorders. Although the results suggest that there may be a positive effect of different work-break frequencies on productivity and work performance, there is a need for high-quality studies with large enough sample sizes to assess the effectiveness of different work-break interventions. Furthermore, work-break interventions should be reconsidered, taking into account worker populations other than office workers and the possibility of combining work-break interventions with other interventions such as ergonomic training or counselling, which may possibly prevent musculoskeletal disorders.