Influence of Intraoperative Active and Passive Breaks in Simulated Minimally Invasive Procedures on Surgeons' Perceived Discomfort, Performance, and Workload.

Laparoscopic surgeons are at high risk of experiencing musculoskeletal discomfort, which is considered the result of long-lasting static and awkward body postures. We primarily aimed to evaluate whether passive and active work breaks can reduce ratings of perceived discomfort among laparoscopic surgeons compared with no work breaks. We secondarily aimed to examine potential differences in performance and workload across work break conditions and requested the surgeons evaluate working with passive or active work breaks. Following a balanced, randomized cross-over design, laparoscopic surgeons performed three 90 min laparoscopic simulations without and with 2.5 min passive or active work breaks after 30 min work blocks on separate days. The simulation included the following tasks: a hot wire, peg transfer, pick-and-place, pick-and-tighten, pick-and-thread, and pull-and-stick tasks. Ratings of perceived discomfort (CR10 Borg Scale), performance per subtask, and perceived workload (NASA-TLX) were recorded, and the break interventions were evaluated (self-developed questionnaire). Statistical analyses were performed on the rating of perceived discomfort and a selection of the performance outcomes. Twenty-one participants (9F) were included, with a mean age of 36.6 years (SD 9.7) and an average experience in laparoscopies of 8.5 years (SD 5.6). Ratings of perceived musculoskeletal discomfort slightly increased over time from a mean level of 0.1 to 0.9 but did not statistically significantly differ between conditions (p = 0.439). Performance outcomes of the hot wire and peg transfer tasks did not statistically significantly differ between conditions. The overall evaluation by the participants was slightly in favor regarding the duration and content of active breaks and showed a 65% likelihood of implementing them on their own initiative in ≥90 min-lasting laparoscopic surgeries, compared with passive breaks. Both passive and active breaks did not statistically significantly influence ratings of perceived discomfort or perceived workload in a 90 min simulation of laparoscopic surgery, with an overall low mean level of perceived discomfort of 0.9 (SD 1.4). As work breaks do not lead to performance losses, rest breaks should be tested in real-life situations across a complete working shift, where perceived discomfort may differ from this laboratory situation. However, in this respect, it is crucial to investigate the acceptance and practicality of intraoperative work breaks in feasibility studies in advance of assessing their effectiveness in follow-up longitudinal trials.

Intraoperative active and passive breaks during minimally invasive surgery influence upper extremity physical strain and physical stress response-A controlled, randomized cross-over, laboratory trial.

OBJECTIVE: Investigate the effect of passive, active or no intra-operative work breaks on static, median and peak muscular activity, muscular fatigue, upper body postures, heart rate, and heart rate variability. BACKGROUND: Although laparoscopic surgery is preferred over open surgery for the benefit of the patient, it puts the surgeons at higher risk for developing musculoskeletal disorders especially due to the less dynamic and awkward working posture. The organizational intervention intraoperative work break is a workplace strategy that has previously demonstrated positive effects in small-scale intervention studies. METHODS: Twenty-one surgeons were exposed to three 90-min conditions: no breaks, 2.5-min passive (standing rest) or active (targeted stretching and mobilization exercises) breaks after 30-min work blocks. Muscular activity and fatigue of back, shoulder and forearm muscles were assessed by surface electromyography; upper body posture, i.e., spinal curvature, by inclination sensors; and heart rate and variability (HRV) by electrocardiography. Generalized estimating equations were used for statistical analyses. This study (NCT03715816) was conducted from March 2019 to October 2020. RESULTS: The HRV-metric SDNN tended to be higher, but not statistically significantly, in the intervention conditions compared to the control condition. No statistically significant effects of both interventions were detected for muscular activity, joint angles or heart rate. CONCLUSION: Intraoperative work breaks, whether passive or active, may counteract shoulder muscular fatigue and increase heart rate variability. This tendency may play a role in a reduced risk for developing work-related musculoskeletal disorders and acute physical stress responses.

Using a Back Exoskeleton During Industrial and Functional Tasks-Effects on Muscle Activity, Posture, Performance, Usability, and Wearer Discomfort in a Laboratory Trial.

OBJECTIVE: To investigate the effect of using a passive back-support exoskeleton (Laevo V2.56) on muscle activity, posture, heart rate, performance, usability, and wearer comfort during a course of three industrial tasks (COU; exoskeleton worn, turned-on), stair climbing test (SCT; exoskeleton worn, turned-off), timed-up-and-go test (TUG; exoskeleton worn, turned-off) compared to no exoskeleton. BACKGROUND: Back-support exoskeletons have the potential to reduce work-related physical demands. METHODS: Thirty-six men participated. Activity of erector spinae (ES), biceps femoris (BF), rectus abdominis (RA), vastus lateralis (VL), gastrocnemius medialis (GM), trapezius descendens (TD) was recorded by electromyography; posture by trunk, hip, knee flexion angles; heart rate by electrocardiography; performance by time-to-task accomplishment (s) and perceived task difficulty (100-mm visual analogue scale; VAS); usability by the System Usability Scale (SUS) and all items belonging to domains skepticism and user-friendliness of the Technology Usage Inventory; wearer comfort by the 100-mm VAS. RESULTS: During parts of COU, using the exoskeleton decreased ES and BF activity and trunk flexion, and increased RA, GM, and TD activity, knee and hip flexion. Wearing the exoskeleton increased time-to-task accomplishment of SCT, TUG, and COU and perceived difficulty of SCT and TUG. Average SUS was 75.4, skepticism 11.5/28.0, user-friendliness 18.0/21.0, wearer comfort 31.1 mm. CONCLUSION: Using the exoskeleton modified muscle activity and posture depending on the task applied, slightly impaired performance, and was evaluated mildly uncomfortable. APPLICATION: These outcomes require investigating the effects of this passive back-supporting exoskeleton in longitudinal studies with longer operating times, providing better insights for guiding their application in real work settings.

Motor variability during a repetitive lifting task is impaired by wearing a passive back-support exoskeleton.

PURPOSE: Evaluate whether wearing a passive back-support exoskeleton during repetitive lifting impairs motor variability of erector spinae muscle and spine movement and whether this association is influenced by lifting style. SCOPE: Thirty-six healthy males performed ten lifts in four randomized conditions with exoskeleton (without, with) and lifting style (squat, stoop) as dependent variables. One lifting cycle contained four phases: bending/straighten without/with load. Erector spinae muscular activity, thoracic kyphosis and lumbar lordosis were measured with surface electromyography and gravimetric position sensors, respectively. Absolute and relative cycle-to-cycle variability were calculated. The effects of exoskeleton and exoskeleton × lifting style were assessed on outcomes during the complete lifting cycle and its four phases. RESULTS: For the complete lifting cycle, muscular variability and thoracic kyphosis variability decreased whereas lumbar lordosis variability increased with exoskeleton. For lifting phases, effects of exoskeleton were mixed. Absolute and relative muscular variability showed a significant interaction effect for the phase straighten with load; variability decreased with exoskeleton during squat lifting. CONCLUSION: Using the exoskeleton impaired several motor variability parameters during lifting, supporting previous findings that exoskeletons may limit freedom of movement. The impact of this result on longer-term development of muscular fatigue or musculoskeletal disorders cannot yet be estimated.

Effects of a Passive Back-Support Exoskeleton on Knee Joint Loading during Simulated Static Sorting and Dynamic Lifting Tasks.

Due to the load shifting mechanism of many back-support exoskeletons (BSEs), this study evaluated possible side effects of using a BSE on knee joint loading. Twenty-nine subjects (25.9 (±4.4) years, 179.0 (±6.5) cm; 73.6 (±9.4) kg) performed simulated static sorting and dynamic lifting tasks, including stoop and squat styles and different trunk rotation postures. Ground reaction force, body posture and the force between the chest and the BSE's contact interface were recorded using a force plate, two-dimensional gravimetric position sensors, and a built-in force sensor of the BSE, respectively. Using these parameters and the subject's anthropometry, median and 90th percentile horizontal (HOR50, HOR90) and vertical (VERT50, VERT90) tibiofemoral forces were calculated via a self-developed inverse quasi-static biomechanical model. BSE use had a variable effect on HOR50 dependent on the working task and body posture. Generally, VERT50 increased without significant interaction effects with posture or task. HOR90 and VERT90 were not affected by using the BSE. In conclusion, utilizing the investigated exoskeleton is likely to induce side effects in terms of changed knee joint loading. This may depend on the applied working task and the user's body posture. The role of these changes in the context of a negative contribution to work-related cumulative knee exposures should be addressed by future research.

Using a Passive Back Exoskeleton During a Simulated Sorting Task: Influence on Muscle Activity, Posture, and Heart Rate.

OBJECTIVE: To evaluate using a back exoskeleton in a simulated sorting task in a static forward bent trunk posture on muscle activity, posture, and heart rate (HR). BACKGROUND: Potentials of exoskeletons for reducing musculoskeletal demands in work tasks need to be clarified. METHODS: Thirty-six healthy males performed the sorting task in 40°-forward bent static trunk posture for 90 seconds, in three trunk orientations, with and without exoskeleton. Muscle activity of the erector spinae (ES), biceps femoris (BF), trapezius descendens (TD), rectus abdominis (RA), vastus laterals (VL), and gastrocnemius medialis was recorded using surface electromyography normalized to a submaximal or maximal reference electrical activity (%RVE (reference voluntary electrical activity)/%MVE). Spine and lower limb postures were assessed by gravimetric position sensors, and HR by electrocardiography. RESULTS: Using the exoskeleton resulted in decreased BF muscle activity [-8.12%RVE], and minor changes in ES [-1.29%MVE], RA [-0.28%RVE], VL [-0.49%RVE], and TD [+1.13%RVE] muscle activity. Hip and knee flexion increased [+8.1°; +6.7°]. Heart rate decreased by 2.1 bpm. Trunk orientation had an influence on BF muscle activity. CONCLUSION: Using the back exoskeleton in a short sorting task with static trunk posture mainly reduced hip extensor muscle activity and changed lower limb but not spine posture. Implications of using a back exoskeleton for workers' musculoskeletal health need further clarification. APPLICATION: The detected changes by using the Laevo® illustrate the need for further investigation prior to practical recommendations of using exoskeletons in the field. Investigating various work scenarios in different kind of workers and long-term applications would be important elements.

Postural Control When Using an Industrial Lower Limb Exoskeleton: Impact of Reaching for a Working Tool and External Perturbation.

OBJECTIVE: To investigate postural control related to a lower limb exoskeleton (Chairless Chair) when (a) reaching for a working tool, and (b) an external perturbation occurs. BACKGROUND: Lower limb exoskeletons aiming to reduce physical load associated with prolonged standing may impair workers' postural control and increase the risk of falling. METHOD: Forty-five males were reaching for an object (3-kg dumbbell) at the lateral end of their reaching area without the exoskeleton in upright standing (STAND) and with the exoskeleton at a high (EXOHIGH.SEAT) and low sitting position (EXOLOW.SEAT). The task was performed with the object placed in three different angles (120°, 150°, and 180°) in the transversal plane. The minimum absolute static postural stability (SSABS.MIN) as the shortest distance (mm) of the center of pressure to the base of support border was measured (zero indicates risk of falling). Additionally, eight subjects were standing without the exoskeleton or sitting on it (EXOHIGH.SEAT and EXOLOW.SEAT) while being pulled backward. The tilting moment when subjects lost their balance was assessed. RESULTS: SSABS.MIN was lower when using the exoskeleton (p < .05) but still about 17 mm. The location of the object to be reached had no influence. Tilting moments of less than 30 nm were sufficient to let people fall backward when sitting on the exoskeleton (50 nm for STAND). CONCLUSION: Impairments in postural control by the exoskeleton may not be relevant when reaching laterally for objects up to 3 kg. When an external perturbation occurs, the risk of falling may be much higher; irrespective of factors like uneven or slippery flooring. APPLICATION: The risk of falling using the exoskeleton seems to be low when reaching laterally for an object of up to 3 kg. In situations where, for example, a collision with coworkers is likely, this exoskeleton is not recommended.

A passive back exoskeleton supporting symmetric and asymmetric lifting in stoop and squat posture reduces trunk and hip extensor muscle activity and adjusts body posture - A laboratory study.

The influence of a passive exoskeleton was assessed during repetitive lifting with different lifting styles (squat, stoop) and orientations (frontal/symmetric, lateral/asymmetric) on trunk and hip extensor muscle activity (primary outcomes), abdominal, leg, and shoulder muscle activity, joint kinematics, and heart rate (secondary outcomes). Using the exoskeleton significantly and partially clinically relevant reduced median/peak activity of the erector spinae (≤6%), biceps femoris (≤28%), rectus abdominis (≤6%) and increased median/peak activity of the vastus lateralis (≤69%), trapezius descendens (≤19%), and median knee (≤6%) and hip flexion angles (≤11%). Using the exoskeleton had only limited influence on muscular responses. The findings imply the exoskeleton particularly supports hip extension and requires an adjusted body posture during lifting with different styles and orientations. The potential of using exoskeletons for primary/secondary prevention of musculoskeletal disorders should be investigated in future research including a greater diversity of users in terms of age, gender, health status.

The influence of using exoskeletons during occupational tasks on acute physical stress and strain compared to no exoskeleton - A systematic review and meta-analysis.

OBJECTIVES: This systematic review and meta-analysis determined the effects of using an exoskeleton during occupational tasks on physical stress and strain compared to not using an exoskeleton. METHODS: Systematic electronic database searches were performed and the review was prepared according to the PRISMA guidelines. Treatment effects on the predefined outcomes were calculated using standardized mean differences for continuous outcomes in several meta-analyses using Review Manager 5.3. Registration: PROSPERO (CRD42020168701). RESULTS: 63 articles were included in qualitative syntheses and 52 in quantitative, but most of them did not extensively evaluate musculoskeletal stress and strain and the risk of bias was rated high for all included studies. Statistically significant effects of using back, upper-limb, or lower-limb exoskeletons have been observed in the supported body areas (e.g. reduced muscle activity, joint moments and perceived strain). Studies which did not exclusively focus on the supported body area also showed statistically significant effects in the non-supported areas (e.g. changed muscle activity and perceived strain) and in physiological outcomes (e.g. reduced energy expenditure). CONCLUSIONS: Using an exoskeleton during occupational tasks seems to reduce user's acute physical stress and strain in the exoskeleton's target area. However, impact on workers' health is still unknown, primarily because of missing long-term evaluations under real working conditions. Furthermore, this systematic review highlights a lack of studies (1) following high quality methodological criteria, (2) evaluating various inter-related stress and strain parameters instead of only focusing on one specific, and (3) evaluating non-target body areas instead of only the directly supported body area.

The use of exoskeletons in the occupational context for primary, secondary, and tertiary prevention of work-related musculoskeletal complaints.

OCCUPATIONAL APPLICATIONS This guideline includes 20 recommendations and four key statements that achieved consensus or strong consensus regarding the application of exoskeletons in the workplace for the prevention of musculoskeletal complaints and diseases, the general use and implementation of exoskeletons, and recommendations for risk assessment. The guideline is intended for company physicians, occupational physicians, ergonomists, occupational safety specialists, and employers, and serves as information for all other actors in practical occupational safety. Due to the lack of evidence from the scientific literature, the recommendations and key statements are the result of expert discussions that were conducted at a consensus conference in accordance with the Regulations of the Association of the Scientific Medical Societies in Germany, moderated by an external consultant.

TECHNICAL ABSTRACT Background The prevention of work-related musculoskeletal complaints and diseases has high priority, considering the prevalence of musculoskeletal complaints and diseases and the associated high burden on health care systems, the economy, and the people affected. Purpose: This guideline provided recommendations for potential applications of exoskeletons in the workplace for the primary, secondary, and tertiary prevention of musculoskeletal complaints and diseases, general recommendations on the use and implementation of exoskeletons, and recommendations on risk assessment. Methods: A systematic literature search, a survey among exoskeleton manufacturers and companies using exoskeletons, and expert discussions formed the basis of the formulated recommendations and key statements. For reaching consensus on the recommendations and key statements, we applied the Nominal Group and Delphi Techniques under the supervision of an external, independent moderator. Results: We formulated 20 recommendations and four key statements, all of which reached consensus or strong consensus. Conclusion: No answers could be found in the current scientific literature to the central questions in this guideline about primary, secondary, and tertiary prevention. We outline five main directions for future research on exoskeletons in occupational settings. First, using exoskeletons for prevention should be investigated using randomized controlled trials. Second, the effects of exoskeletons on work-related musculoskeletal stress and strain should be investigated both in the body region intended to be supported by the exoskeleton as well as in other non-supported body regions. Third, the effects of exoskeletons should be investigated in samples varying in age, gender, and health status, as well as during different occupational activities. Fourth, a specific risk assessment tool for exoskeletons in occupational settings should be developed and implemented to meet and evaluate the applicable occupational health and safety standards. Fifth, there is a need to expand upon the very limited social science research on the impacts of exoskeletons on employee professional understanding, social role understanding, or diversity.

Sex differences in muscle activity and motor variability in response to a non-fatiguing repetitive screwing task.

BACKGROUND: Musculoskeletal disorders are more prevalent among women than among men, which may be explained by aspects of motor control, including neuromuscular requirements and motor variability. Using an exploratory approach, this study aimed to evaluate sex differences in neuromuscular responses and motor variability during a repetitive task performed on 3 days. METHODS: Thirty women and 27 men performed the non-fatiguing, repetitive, 1-h screwing task. For neuromuscular responses, the mean and difference values of static, median, and peak percentile muscle activity levels (normalized to a reference voluntary contraction force) and, for motor variability, the mean and difference values of relative and absolute cycle-to-cycle variability across days were compared between both sexes for each muscle. A mixed-design analysis of variance was used to assess differences between both sexes. RESULTS: The non-fatiguing character of the screwing task was confirmed by the absence of decreased force levels in maximal voluntary contractions performed before and after the task and by absence of electromyographic signs of muscle fatigue. The static and median muscle activity levels tended to be higher among women (on average 7.86 and 27.23 %RVE) than men (on average 6.04 and 26.66 %RVE). Relative motor variability of the flexor and biceps muscles and absolute motor variability of both upper arm muscles were lower in women (on average 0.79 and 29.70 %RVE) than in men (on average 0.89 and 37.55 %RVE). The median activity level of both upper arms muscles tended to decrease within days among women (on average - 2.63 %RVE) but increase among men (on average + 1.19 %RVE). Absolute motor variability decreased within days among women (on average - 5.32 to - 0.34%RVE), whereas it tended to decrease less or increase within days among men (on average - 1.21 to + 0.25 %RVE). CONCLUSION: Women showed higher levels of muscle activity and lower initial relative and absolute motor variability than males when performing the same occupational task, implying women may have a higher risk for developing disorders and point to both sexes using different intrinsic motor control strategies in task performance. Clearly, biological aspects alone cannot explain why women would be at higher risk for developing disorders than men. Therefore, a wider range of individual and environmental factors should be taken into account for optimizing work station designs and organizations by taking into account sex differences.

Active and passive work breaks during simulated laparoscopy among laparoscopic surgeons: study protocol for a controlled, randomised cross-over laboratory trial.

INTRODUCTION: Laparoscopy has partially replaced open surgery due to the lower infection rate for the patient and hence better and shorter recovery. However, the surgeon's physical load is higher due to longer duration static and awkward body postures, increasing the risk for developing work-related musculoskeletal disorders. Interventions of an organisational nature are work breaks, being either passive or active. The primary objectives of this study are to determine whether passive and active work breaks lead to less discomfort than no work breaks and whether active work breaks lead to less discomfort than passive work breaks. METHODS AND ANALYSIS: A controlled, randomised cross-over trial will be performed in the laboratory, of which its protocol is described here according to the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) 2013 Statement. Recruitment of 21 laparoscopic surgeons started in April 2019 and the study is ongoing. The participating surgeons will perform three 1.5 hour experimental conditions, one without work breaks, one with 2.5 min passive work breaks including rest, and one with 2.5 min active work breaks including mobility and stretching exercises. The work breaks will be taken after 30 and 60 min of work. During the experiments, outcomes will be recorded. The primary outcome is rating of perceived discomfort measured on an 11-point numeric rating scale. The secondary outcomes are performance, muscle activity of selected muscles, upper body angles, heart rate, workload and subjective evaluation of both interventions. The collected data will be tested using a one-way or two-factorial repeated-measures analysis of variance. ETHICS AND DISSEMINATION: Ethical approval of the study protocol was received by the local medical ethical committee of the University of Tübingen in February 2019 (no 618/2018BO2). The results of this study will be presented at national and international conferences, submitted for publications in peer-reviewed journals and serve as the starting point for a feasibility study. TRIAL REGISTRATION NUMBER: NCT03715816.

Influence of a passive lower-limb exoskeleton during simulated industrial work tasks on physical load, upper body posture, postural control and discomfort.

This study investigated the effect of wearing a passive lower-limb exoskeleton on physical load, kinematics, postural control, and discomfort. 45 healthy males participated and were exposed to three 21-min simulations, including screwing, cable-mounting, and clip-fitting. Each exposure comprised one of three exoskeleton statuses (standing, high and low sitting on exoskeleton) and three working distances (optimal, far, very far). The order of exoskeleton status and working distance were randomized across subjects. A force platform was used to calculate the mean center of pressure (COP) and absolute (SSABS) and relative static postural stability (SSREL) as measures of postural control as well as the weight transferred to the exoskeleton supports as indicator of physical load. Neck and back angles were recorded together with electrical activity of four bilateral muscles (trapezius, erector, vastus, gastrocnemius). Discomfort was recorded before and after each exposure on an 11-point numeric rating scale. Physical load decreased due to the exoskeleton carrying up to 64% of the subject's body mass. The COP remained within the base of support with the lowest values of static postural stability for high sitting (27%). During sitting, vastus activity increased (∼95-135%) while gastrocnemius activity decreased (∼25%) compared to standing. Trapezius and erector activity levels showed only minor differences between exposures. Larger working distances resulted in a more anterior COP and increased erector activity. Standing without exoskeleton was related to less discomfort (0.5) than sitting on the exoskeleton (∼1.3). Working postures and distances changed SSREL and activity levels of the vastus, gastrocnemius, and erector, but not SSABS. However, postural stability did not approach a critical state in our simulations without external perturbations. Therefore, investigating exoskeletons in the field will provide useful information about their effectiveness and usability in dynamic working situations where external forces could occur.

Work-break schedules for preventing musculoskeletal symptoms and disorders in healthy workers.

BACKGROUND: Work-related musculoskeletal disorders are a group of musculoskeletal disorders that comprise one of the most common disorders related to occupational sick leave worldwide. Musculoskeletal disorders accounted for 21% to 28% of work absenteeism days in 2017/2018 in the Netherlands, Germany and the UK. There are several interventions that may be effective in tackling the high prevalence of work-related musculoskeletal disorders among workers, such as physical, cognitive and organisational interventions. In this review, we will focus on work breaks as a measure of primary prevention, which are a type of organisational intervention. OBJECTIVES: To compare the effectiveness of different work-break schedules for preventing work-related musculoskeletal symptoms and disorders in healthy workers, when compared to conventional or alternate work-break schedules. SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, CINAHL, PsycINFO, SCOPUS, Web of Science, ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform, to April/May 2019. In addition, we searched references of the included studies and of relevant literature reviews. SELECTION CRITERIA: We included randomised controlled trials (RCTs) of work-break interventions for preventing work-related musculoskeletal symptoms and disorders among workers. The studies were eligible for inclusion when intervening on work-break frequency, duration and/or type, compared to conventional or an alternate work-break intervention. We included only those studies in which the investigated population included healthy, adult workers, who were free of musculoskeletal complaints during study enrolment, without restrictions to sex or occupation. The primary outcomes were newly diagnosed musculoskeletal disorders, self-reported musculoskeletal pain, discomfort or fatigue, and productivity or work performance. We considered workload changes as secondary outcomes. DATA COLLECTION AND ANALYSIS: Two review authors independently screened titles, abstracts and full texts for study eligibility, extracted data and assessed risk of bias. We contacted authors for additional study data where required. We performed meta-analyses, where possible, and we assessed the overall quality of the evidence for each outcome of each comparison using the five GRADE considerations. MAIN RESULTS: 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 breaksThere 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 breaksNo trials were identified that assessed the effect of different durations of work breaks.Changes in the type of work breakWe 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). AUTHORS' CONCLUSIONS: 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.

The Role of Motor Learning on Measures of Physical Requirements and Motor Variability During Repetitive Screwing.

We investigated whether physical requirements and motor variability decreased over days in novices during a repetitive screwing task. Fifty-seven subjects performed one hour of repetitive screwing and fastening on three days, separated by 2⁻7 days. The average physical requirement and relative cycle-to-cycle variability (coefficient of variation, i.e., CV) were calculated from continuous recordings of electromyography of four arm muscles (biceps brachii, triceps brachii, flexor carpi radialis, extensor digitorum), forearm acceleration, and electrocardiography. Muscle activity levels, heart rate, and forearm acceleration decreased from day 1 to day 2 (range: ~4% to ~20%) and/or 3 (range: ~4% to ~28%). Not all muscles showed a similar pattern. Activity of the extensor digitorum and biceps brachii decreased already between days 1 and 2 (range: ~6% to ~13%), whereas activity of the flexor carpi radialis and triceps brachii decreased between days 1 and 3 (range: ~13% to ~20%). No changes in physical requirement were detected between days 2 and 3. Relative motor variability did not change across days, except that variability of forearm acceleration increased from day 1 to 3 (~5%). This study found consistent changes in physical requirements and indicated that several arm muscles show earlier decreases of muscular activity, like the extensor digitorum, compared to other body parts, like the flexor carpi radialis. Moreover, movement strategies may develop differently than muscle activation strategies, based on the different developments of physical requirements and motor variability. The development of physical requirements in industrial tasks is part of daily living and starts at task onset, highlighting the importance of task familiarization and the randomization of experimental conditions in scientific studies.

Influence of Work Pace on Upper Extremity Kinematics and Muscle Activity in a Short-Cycle Repetitive Pick-and-Place Task.

OBJECTIVES: This study investigated the extent to which controlled changes in work pace in a cyclic pick-and-place task influence upper extremity kinematics and muscle activity, and whether an effect depends on working height. METHODS: Thirteen participants performed the task for 4 min at each of five work paces ranging from 8 to 12 cycles·min-1 in each of two experimental conditions where the hand was moved horizontally with an average upper arm elevation of 30° and 50°, respectively. For each work cycle, we calculated the average and standard deviation of the upper arm elevation angle and the activity of the trapezius and deltoid muscles, as well as the angular peak velocity. We summarized these seven variables by calculating averages across cycles and cycle-to-cycle variabilities. RESULTS: At 30° arm elevation, pace significantly influenced within-cycle angle variation, cycle-to-cycle variability of the average angle, angular peak velocity, and cycle-to-cycle variability of peak velocity. However, only angular peak velocity increased monotonically across all paces from 8 to 12 cycles·min-1). Average activity in the trapezius and the deltoid were the only muscle activity variables to increase consistently with pace. These effects of work pace did not change with working height. CONCLUSION: The present study did not find any consistent work pace effect on upper extremity kinematics and muscle activity, in spite of a comprehensive empirical basis compared to previous literature. While our results suggest that work pace may not be of critical concern in an occupational health context, we encourage further studies verifying or disproving this notion.

Is rotating between static and dynamic work beneficial for our fatigue state?

Shoulder disorders comprise a large part of work-related musculoskeletal disorders. Risk factors, such as repetitiveness and monotony, may cause muscle fatigue and be attenuated by task rotation. We investigated rotation between a dynamic box-lifting task and a relatively static pick-and-place task and aimed to determine whether (1) a high rotation frequency leads to less fatigue development than a low rotation frequency, and (2) a self-selected rotation frequency leads to less fatigue development than imposed rotation frequencies. Ten participants performed four one-hour rotation schedules: two low frequency rotation schedules rotating at 30min, one high frequency rotation schedule rotating every sixth minute, and a self-selected rotation schedule. Borg, SOFI and electromyography of Trapezius and Deltoid subparts served as fatigue indicators. We found significant signs of fatigue for most schedules regarding the Borg and SOFI ratings and the M. Trapezius pars Descendens. Task rotation frequency had no significant effect on any of the outcome parameters, whereas the self-selected rotation schedule clearly resulted in less development of perceived fatigue than imposed schedules. In conclusion, we think that freedom of rotation has the greatest potential to attenuate potential development of musculoskeletal disorders and we require due caution with the use and interpretation of EMG indicators of fatigue.

Task variation during simulated, repetitive, low-intensity work--influence on manifestation of shoulder muscle fatigue, perceived discomfort and upper-body postures.

Work-related musculoskeletal disorders are increasing due to industrialisation of work processes. Task variation has been suggested as potential intervention. The objectives of this study were to investigate, first, the influence of task variation on electromyographic (EMG) manifestations of shoulder muscle fatigue and discomfort; second, noticeable postural shoulder changes over time; third, if the association between task variation and EMG might be biased by postural changes. Outcome parameters were recorded using multichannel EMG, Optotrak and the Borg scale. Fourteen participants performed a one-hour repetitive Pegboard task in one continuous and two interrupted conditions with rest and a pick-and-place task, respectively. Manifestations of shoulder muscle fatigue and discomfort feelings were observed throughout the conditions but these were not significantly influenced by task variation. After correction for joint angles, the relation between task variation and EMG was significantly biased but significant effects of task variation remained absent. PRACTITIONER SUMMARY: Comparing a one-hour continuous, repetitive Pegboard task with two interrupted conditions revealed no significant influences of task variation. We did observe that the relation between task variation and EMG was biased by posture and therefore advise taking account for posture when investigating manifestations of muscle fatigue in assembly tasks.

The influence of task variation on manifestation of fatigue is ambiguous - a literature review.

Task variation has been proposed to reduce shoulder fatigue resulting from repetitive hand-arm tasks. This review analyses the effect of task variation, both 'temporal (i.e. change of work-rest ratio)' and 'activity (i.e. job rotation)' variation, on physiological responses, endurance time (ET) and subjective feelings. Pubmed was searched and complemented with references from selected articles, resulting in 17 articles. Temporal variation had some positive effects on the objective parameters, as blood pressure decreased and ET increased, and on the subjective feelings, as perceived discomfort decreased. The observed findings of activity variation showed both positive and negative effects of increased activity variation, while hardly any effects were found on electromyography manifestations of fatigue. In conclusion, the evidence for positive effects of increasing the level of variation is scarce. The number of studies on variation is limited, while in most studies the findings were not controlled for the amount or intensity of work.

Effects of fatigue on trunk stability in elite gymnasts.

The aim of the present study was to test the hypothesis that fatigue due to exercises performed in training leads to a decrement of trunk stability in elite, female gymnasts. Nine female gymnasts participated in the study. To fatigue trunk muscles, four series of five dump handstands on the uneven bar were performed. Before and after the fatigue protocol, participants performed three trials of a balancing task while sitting on a seat fixed over a hemisphere to create an unstable surface. A force plate tracked the location of the center of pressure (CoP). In addition, nine trials were performed in which the seat was backward inclined over a set angle and suddenly released after which the subject had to regain balance. Sway amplitude and frequency in unperturbed sitting were determined from the CoP time series and averaged over trials. The maximum displacement and rate of recovery of the CoP location after the sudden release were determined and averaged over trials. After the fatigue protocol, sway amplitude in the fore-aft direction was significantly increased (p = 0.03), while sway frequency was decreased (p = 0.005). In addition, the maximum displacement after the sudden release was increased (p = 0.009), while the rate of recovery after the perturbation was decreased (p = 0.05). Fatigue induced by series of exercises representing a realistic training load caused a measurable decrement in dynamic stability of the trunk in elite gymnasts.