Variation of force amplitude and its effects on local fatigue

Muscle fatigue tracking during dynamic elbow flexion-extension movements with a varying hand load

Muscle fatigue monitoring, an important element in a fatigue risk management process, can help optimize work intensity and reduce risks for musculoskeletal injuries. An experiment was conducted to determine whether myoelectric manifestations of muscle fatigue can reflect the pace of fatigue development associated with varying load intensity. Twenty male participants performed elbow flexion-extension movements with alternating hand loads (2 kg vs. 1 kg) for 16 min. The pace of fatigue in the biceps brachii in response to load variation was quantified by electromyographic (EMG) fatigue measures collected during the dynamic elbow flexion-extension movements and periodic submaximal isometric elbow flexion trials. The isometric and dynamic EMG measures, except for the amplitude of dynamic EMG, indicated fatigue development during the 2-kg isotonic movements and partial recovery with the 1 kg load. Study results suggest the potential of EMG measures for fatigue monitoring during dynamic work tasks with varying load intensity.

Is there a u-shaped relationship between load levels and fatigue and recovery? An examination of possible mechanisms

In a previous study, an unexpected u-shaped relationship was observed between load level and fatigue/recovery responses. Moderate load levels resulted in lower perceived discomfort, pain, and fatigue, and shorter recovery times compared to either low or high load levels. This phenomenon has been reported in other studies, but no article has examined the possible mechanisms that might explain this u-shaped relationship. In this paper, we re-examined the previously published data and found that the phenomenon does not appear to be due to the experimental artefact; the u-shape may be due to unexpectedly lower fatigue effects at moderate loads, and higher fatigue effects at lower loads. We then conducted a literature review and identified several possible physiological, perceptual, and biomechanical explanatory mechanisms. No single mechanism explains the entirety of the phenomenon. Further research is needed on the relationship between work exposures, fatigue, and recovery, and the mechanisms related to the u-shaped relationship.Practitioner summary: We examine a previously observed u-shaped relationship between load level and fatigue/recovery, where moderate force resulted in lower perceived fatigue and shorter recovery times. A u-shaped fatigue response suggests that simply minimising load levels might not be an optimal approach to reduce the risk of workplace injuries.

Variability of Time- and Frequency-Domain Surface Electromyographic Measures in Non-Fatigued Shoulder Muscles

OCCUPATIONAL APPLICATIONSLocalized Muscle Fatigue (LMF) can be monitored or predicted based on the relative change in the values of surface electromyography (sEMG) measures with respect to the "fresh" or no-fatigue condition. Quantification of LMF based on relative change, though, relies on the assumption that the sEMG measures recorded in a no-fatigue condition can serve as an appropriate reference. Results of this study indicate that sEMG measures in a no-fatigue condition are affected by various work-related factors and provide further guidance on the variability of commonly used time- and frequency-domain sEMG measures to assist the ergonomist in improving the accuracy of LMF assessment.

A genetic algorithm approach to design job rotation schedules ensuring homogeneity and diversity of exposure in the automotive industry

Job rotation is a work organization strategy with increasing popularity, given its benefits for workers and companies, especially those working with manufacturing. This study proposes a formulation to help the team leader in an assembly line of the automotive industry to achieve job rotation schedules based on three major criteria: improve diversity, ensure homogeneity, and thus reduce exposure level. The formulation relied on a genetic algorithm, that took into consideration the biomechanical risk factors (EAWS), workers’ qualifications, and the organizational aspects of the assembly line. Moreover, the job rotation plan formulated by the genetic algorithm formulation was compared with the solution provided by the team leader in a real life-environment. The formulation proved to be a reliable solution to design job rotation plans for increasing diversity, decreasing exposure, and balancing homogeneity within workers, achieving better results in all of the outcomes when compared with the job rotation schedules created by the team leader. Additionally, this solution was less time-consuming for the team leader than a manual implementation. This study provides a much-needed solution to the job rotation issue in the manufacturing industry, with the genetic algorithm taking less time and showing better results than the job rotations created by the team leaders.

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This is the first formulation to consider diversity, exposure, and homogeneity.

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A GA was used and proven to be a reliable solution to design job rotation.

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The formulation increased diversity, decreased exposure, and balanced homogeneity.

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Better results were achieved in all outcomes when compared with manual solutions.

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The formulation is less time-consuming improving factory resource's management.

Exploring Localized Muscle Fatigue Responses at Current Upper-Extremity Ergonomics Threshold Limit Values

OBJECTIVE

The purpose of this study was to evaluate localized muscle fatigue responses at three upper-extremity ergonomics threshold limit value (TLV) duty cycles.

BACKGROUND

Recently, a TLV equation was published to help mitigate excessive development of localized muscle fatigue in repetitive upper limb tasks. This equation predicts acceptable levels of maximal voluntary contraction (% MVC) for a given duty cycle (DC). Experimental validation of this TLV curve has not yet been reported, which can help guide utilization by practitioners.

METHOD

Eighteen participants performed intermittent isometric elbow flexion efforts, in three separate counter-balanced sessions, at workloads defined by the American Conference of Governmental Industrial Hygenists' (ACGIH) TLV equation: low DC (20% DC, 29.6% MVC), medium DC (40% DC, 19.7% MVC), and high DC (60% DC, 13.9% MVC). Targeted localized muscle fatigue (LMF) of the biceps brachii was tracked across numerous response variables, including decline in strength (MVC), electromyography (EMG) amplitude and mean power frequency (MnPF), and several psychophysical ratings.

RESULTS

At task completion, biceps MnPF and MVC (strength) were significantly different between each TLV workload, with the high DC condition eliciting the largest declines in MnPF and MVC.

CONCLUSION

Findings demonstrate that working at different DCs along the ACGIH TLV curve may not be equivalent in preventing excessive LMF. Higher DC workloads elicited a greater LMF response across several response variables.

APPLICATION

High DC work of the upper extremity should be avoided to mitigate excess LMF development. Current TLVs for repetitive upper-extremity work may overestimate acceptable relative contraction thresholds, particularly at higher duty cycles.

The role of at home workstation ergonomics and gender on musculoskeletal pain

BACKGROUND

The recent mandate for university faculty and staff to work-from-home (WFH) during the COVID-19 pandemic has forced employees to work with sub-optimal ergonomic workstations that may change their musculoskeletal discomfort and pain. As women report more work-related musculoskeletal discomfort (WMSD), this effect may be exacerbated in women.

OBJECTIVE

The purpose of this study was to describe university employee at-home office workstations, and explore if at-home workstation design mediates the effect of gender on musculoskeletal pain.

METHODS

University employees completed a survey that focused on the WFH environment, at home workstation design and musculoskeletal pain. Descriptive statistics and regression analysis were used to analyze the responses.

RESULTS

61% of respondents reported an increase in musculoskeletal pain, with the neck, shoulders and lower back being reported most frequently. Women reported significantly greater musculoskeletal pain, but this relationship was significantly mediated by poor ergonomic design of the home workstation. Improper seat-height and monitor distance were statistically associated with total-body WMSD.

CONCLUSIONS

WFH has worsened employee musculoskeletal health and the ergonomic gap between women and men in the workspace has persisted in the WFH environment, with seat height and monitor distance being identified as significant predictors of discomfort/pain.

An exploratory study comparing three work/rest schedules during simulated repetitive precision work

The pattern of work and rest can influence both physical fatigue and task performance in manual operations. However, there is relatively limited evidence regarding the influences of specific work/rest schedules in tasks requiring high repetitiveness and precision demands, along with relatively low exertion levels. Eighteen participants completed an exploratory study that simulated such tasks, to compare the effects of three distinct work/rest schedules (i.e. short frequent [short] and long infrequent breaks [long], and a self-selected schedule) on muscle fatigue, task performance (in terms of accuracy and speed), and preference. Schedules with long or self-selected breaks generally induced less muscle fatigue, compared with the short break condition. Participants preferred the self-selected condition the most and the long-break condition the least. The different schedules tested did not influence task performance. A self-selected schedule may be beneficial for repetitive precision task, to achieve a balance across muscle fatigue, task performance, and individual preference. Practitioner summary: Influences of three work/rest schedules (i.e. short and long breaks, and a self-selected schedule) on fatigue, performance, and preference were explored during repetitive precision tasks. Schedules with long or self-selected breaks induced less muscle fatigue and none of the three schedules influenced performance. A self-selected schedule was the most preferred.

Interrelated hypoalgesia, creep, and muscle fatigue following a repetitive trunk flexion exposure

Repetitive trunk flexion can damage spinal tissues, however its association with low back pain in the workplace may be confounded by factors related to pain sensitivity. Muscle fatigue, exercise-induced hypoalgesia, and creep-induced neuromuscular changes following repetitive trunk flexion may all affect this assumed exposure-pain relationship. This study's purpose was to determine how mechanical pain sensitivity in the low back is affected by a repetitive trunk flexion exposure and identify factors associated with changes in low back pain sensitivity. Pressure pain thresholds, perceptions of sub-threshold stimuli, and muscle fatigue in the trunk and tibia, as well as lumbar spine creep were tracked in 37 young healthy adults before and up to 40 min after a 10-min repetitive trunk flexion exposure. Pressure pain thresholds (p = 0.033), but not perceptions of sub-threshold stimuli (p > 0.102) were associated with approximately a 12.5% reduction in pain sensitivity 10 min after completing the exposure, while creep and local muscle fatigue effects were only observed immediately following the exposure. Creep and fatigue interactions and the corresponding tibial measure co-varied with individual low back pressure pain thresholds. The net hypoalgesic effects of repetitive trunk flexion have the potential to partially mask possibly injurious loads, which could contribute to the severity or incidence of lower back injuries related to these exposures.

Assessment of muscle activity using electrical stimulation and mechanomyography: a systematic review

This research has proved that mechanomyographic (MMG) signals can be used for evaluating muscle performance. Stimulation of the lost physiological functions of a muscle using an electrical signal has been determined crucial in clinical and experimental settings in which voluntary contraction fails in stimulating specific muscles. Previous studies have already indicated that characterizing contractile properties of muscles using MMG through neuromuscular electrical stimulation (NMES) showed excellent reliability. Thus, this review highlights the use of MMG signals on evaluating skeletal muscles under electrical stimulation. In total, 336 original articles were identified from the Scopus and SpringerLink electronic databases using search keywords for studies published between 2000 and 2020, and their eligibility for inclusion in this review has been screened using various inclusion criteria. After screening, 62 studies remained for analysis, with two additional articles from the bibliography, were categorized into the following: (1) fatigue, (2) torque, (3) force, (4) stiffness, (5) electrode development, (6) reliability of MMG and NMES approaches, and (7) validation of these techniques in clinical monitoring. This review has found that MMG through NMES provides feature factors for muscle activity assessment, highlighting standardized electromyostimulation and MMG parameters from different experimental protocols. Despite the evidence of mathematical computations in quantifying MMG along with NMES, the requirement of the processing speed, and fluctuation of MMG signals influence the technique to be prone to errors. Interestingly, although this review does not focus on machine learning, there are only few studies that have adopted it as an alternative to statistical analysis in the assessment of muscle fatigue, torque, and force. The results confirm the need for further investigation on the use of sophisticated computations of features of MMG signals from electrically stimulated muscles in muscle function assessment and assistive technology such as prosthetics control.

A comparison of work-rest models using a "breakpoint" analysis raises questions

OCCUPATIONAL APPLICATIONSDesigning sustainable cyclic work requires attention to both the workload amplitude as well as the duty cycle, the fraction of the work cycle with active workload, that therefore also defines the recovery phase of the cycle. A number of different approaches and models have been developed to calculate the required recovery time for a given load and duty cycle. We present a comparison of three types of models at the "breakpoint" that defines the boundary of load amplitude and duty cycle where fatigue begins to accumulate faster than recovery allows within the work cycle. This comparison shows considerable variation between models of the "allowable" load or duty cycle depending on the method used. Practitioners should thus be cautious applying these models indiscriminately in job design as their results can vary substantially. In particular, differences between the tasks used for model formulation and application may compromise validity, and model application in a given context should be verified before broad application.

Muscle Fatigue in the Three Heads of Triceps Brachii During Intensity and Speed Variations of Triceps Push-Down Exercise

The objective of this study was to investigate the effects of changes in exercise intensity and speed on the three heads of the triceps brachii (TB) during triceps push-down exercise until task failure. Twenty-five subjects performed triceps push-down exercise at three different intensities (30, 45, and 60% 1RM) and speeds (slow, medium, and fast) until failure, and surface electromyography (sEMG) signals were recorded from the lateral, long and medial heads of the TB. The endurance time (ET), number of repetitions (NR) and rate of fatigue (ROF) were analyzed. Subsequently, the root-mean-square (RMS), mean power frequency (MPF) and median frequency (MDF) under no-fatigue (NF) and fatigue (Fa) conditions were statistically compared. The findings reveal that ROF increases with increase in the intensity and speed, and the opposite were obtained for the ET. The ROF in the three heads were comparable for all intensities and speeds. The ROF showed a significant difference (P < 0.05) among the three intensities and speeds for all heads. The three heads showed significantly different (P < 0.05) MPF and MDF values for all the performed exercises under both conditions, whereas the RMS values were significantly different only under Fa conditions. The current observations suggest that exercise intensity and speed affect the ROF while changes in intensity do not affect the MPF and MDF under Fa conditions. The behavior of the spectral parameters indicate that the three heads do not work in unison under any of the conditions. Changes in the speed of triceps push-down exercise affects the lateral and long heads, but changes in the exercise intensity affected the attributes of all heads to a greater extent.

Cognitive stress changes the attributes of the three heads of the triceps brachii during muscle fatigue

INTRODUCTION

Cognitive stress (CS) changes the peripheral attributes of a muscle, but its effect on multi-head muscles has not been investigated. The objective of the current research was to investigate the impact of CS on the three heads of the triceps brachii (TB) muscle.

METHODS

Twenty-five young and healthy university students performed a triceps push-down exercise at 45% one repetition maximum (1RM) with and without CS until task failure, and the rate of fatigue (ROF), endurance time (ET) and number of repetitions (NR) for both exercises were analyzed. In addition, the first and last six repetitions of each exercise were considered non-fatiguing (NF) and fatiguing (Fa), respectively, and the root mean square (RMS), mean power frequency (MPF) and median frequency (MDF) for each exercise repetition were evaluated.

RESULTS

The lateral and long head showed significant differences (P<0.05) in the ROF between the two exercises, and all the heads showed significant (P<0.05) differences in the RMS between the two exercises under NF conditions. Only the long head showed a significant difference (P<0.05) in the MPF and MDF between the two exercises. CS increases the ET (24.74%) and NR (27%) of the exercise. The three heads showed significant differences (P<0.05) in the RMS, MPF and MDF under all exercise conditions.

CONCLUSION

A lower ROF was obtained with CS. In addition, the RMS was found to be better approximator of CS, whereas MPF and MDF were more resistant to the effect of CS. The results showed that the three heads worked independently under all conditions, and the non-synergist and synergist head pairs showed similar behavior under Fa conditions. The findings from this study provide additional insights regarding the functioning of each TB head.

Predicted endurance times during overhead work: influences of duty cycle and tool mass estimated using perceived discomfort

A need for overhead work remains in several industries and such work is an important risk factor for shoulder musculoskeletal problems. In this study, we evaluated the effects of duty cycle and tool mass on endurance times during overhead work. A psychophysical approach was used, via a new methodology that was implemented to more efficiently estimate endurance times (rather than through direct measurements). Participants performed a simulated overhead task in specified combinations of tool mass and duty cycle. Both duty cycle and tool mass have substantial effects on the development of fatigue and estimated endurance times, though the former was more substantial and an interactive effect was evident. Gender differences were not substantial, except when using the largest tool mass. We recommend that, for two-hour periods of overhead work, tool masses greater than 1.25 kg should be avoided, as should duty cycles greater than 50%. Practitioner Summary: The current results may facilitate enhanced design and evaluation of overhead work tasks. In addition, the new estimation approach that was employed may enhance the efficiency of future studies using a psychophysical approach (ie using extrapolation of patterns of reported discomfort to predict longer term outcomes).

Sensitivity, reliability and the effects of diurnal variation on a test battery of field usable upper limb fatigue measures

Fatigue has been linked to deficits in production quality and productivity and, if of long duration, work-related musculoskeletal disorders. It may thus be a useful risk indicator and design and evaluation tool. However, there is limited information on the test-retest reliability, the sensitivity and the effects of diurnal fluctuation on field usable fatigue measures. This study reports on an evaluation of 11 measurement tools and their 14 parameters. Eight measures were found to have test-retest ICC values greater than 0.8. Four measures were particularly responsive during an intermittent fatiguing condition. However, two responsive measures demonstrated rhythmic behaviour, with significant time effects from 08:00 to mid-afternoon and early evening. Action tremor, muscle mechanomyography and perceived fatigue were found to be most reliable and most responsive; but additional analytical considerations might be required when interpreting daylong responses of MMG and action tremor. Practitioner Summary: This paper presents findings from test-retest and daylong reliability and responsiveness evaluations of 11 fatigue measures. This paper suggests that action tremor, muscle mechanomyography and perceived fatigue were most reliable and most responsive. However, mechanomyography and action tremor may be susceptible to diurnal changes.

Responsive upper limb and cognitive fatigue measures during light precision work: an 8-hour simulated micro-pipetting study

Many contemporary occupations are characterised by long periods of low loads. These lower force levels, which are relevant to the development of work-related musculoskeletal disorders, are usually not the focus of fatigue studies. In studies that did measure fatigue in light manual or precision work, within and between measurement responses were inconsistent. The aim of this study was to identify fatigue measures that were responsive at lower force levels (<10% MVC) over the course of an 8-h period. A complementary set of fatigue measures, reflecting both neuromuscular and cognitive mechanisms, was measured during a light precision micro-pipetting task performed by 11 participants. Nine measures were found to be significantly responsive over the 8-h period, including: ratings of perceived fatigue, postural tremor, blink frequency and critical flicker fusion frequency threshold. Common field measures, specifically electromyography RMS amplitude and maximum voluntary contractions, did not lead to extraordinary time effects. Practitioner summary: The findings provide insight towards the responsiveness of a complementary set of field usable fatigue measures at low work intensities Although commonly used measures did not reveal significant increases in fatigue, nine alternative measures were significantly responsive over the 8-h period.

Fatigue Detection Using Phase-Space Warping

A novel application of phase-space warping (PSW) method to detect fatigue in the musculoskeletal system is presented. Experimental kinematic, force, and physiological signals are used to produce a fatigue metric. The metric is produced using time-delay embedding and PSW methods. The results showed that by using force and kinematic signals, an overall estimate of the muscle group state can be achieved. Further, when using electromyography (EMG) signals the fatigue metric can be used as a tool to evaluate muscles activation and load sharing patterns for individual muscles. The presented method will allow for fatigue evolution measurement outside a laboratory environment, which open doors to applications such as tracking the physical state of players during competition, workers in a plant, and patients undergoing in-home rehabilitation.

Neuromuscular manifestations of work-related myalgia in women specific to extensor carpi radialis brevis

This study assessed neuromuscular function in the extensor carpi radialis brevis (ECRB) of female workers diagnosed with work-related myalgia (WRM, n = 14, age 45.2 ± 1.9 years) and the ECRB of healthy controls (CON, n = 10, age 34.6 ± 2.5 years). Groups were compared on voluntary and electrically evoked functional responses at rest (Pre), immediately following a 5 min repetitive task (Post-0) performed at 60% maximal voluntary contraction (MVC), and after 5 min of recovery (Post-5). Despite near complete motor unit activation (MUA) (CON 98% ± 1% vs. WRM 99% ± 1%), at Pre, WRM produced 26% less (P < 0.05) MVC force than CON. Following an MVC, twitch force was increased (P < 0.05) by 94% ± 13% and 54% ± 11% in CON and WRM, respectively (CON vs. WRM; P < 0.05). The peak force and the maximal rates of force development and decline of electrically evoked contractions (10-100 Hz) were generally depressed (P < 0.05) at Post-0 and Post-5 relative to Pre. The response pattern to increasing frequencies of stimulation was not different (P > 0.05) between groups and MUA was not impaired (CON 97% ± 1% vs. WRM 97% ± 1%; P > 0.05). In conclusion, the peripheral weakness observed in the ECRB in WRM at rest does not result in abnormal fatigue or recovery responses after performing a task controlled for relative demand (60% MVC).

Major League Baseball pace-of-play rules and their influence on predicted muscle fatigue during simulated baseball games

Major League Baseball (MLB) has proposed rule changes to speed up baseball games. Reducing the time between pitches may impair recovery from fatigue. Fatigue is a known precursor to injury and may jeopardise joint stability. This study examined how fatigue accumulated during baseball games and how different pace of play initiatives may influence fatigue. Pitcher data were retrieved from a public database. A predictive model of muscle fatigue estimated muscle fatigue in 8 arm muscles. A self-selected pace (22.7 s), 12 s pace (Rule 8.04 from the MLB) and a 20 s rest (a pitch clock examined in the 2014 Arizona Fall League (AFL)) were examined. Significantly more muscle fatigue existed in both the AFL and Rule 8.04 conditions, when compared to the self-selected pace condition (5.01 ± 1.73%, 3.95 ± 1.20% and 3.70 ± 1.10% MVC force lost, respectively). Elevated levels of muscle fatigue are predicted in the flexor-pronator mass, which is responsible for providing elbow stability. Reduced effectiveness of the flexor-pronator mass may reduce the active contributions to joint rotational stiffness, increasing strain on the ulnar collateral ligament (UCL) and possibly increasing injury risk.

The importance of work organization on workload and musculoskeletal health--Grocery store work as a model

We have evaluated the consequences of work organization on musculoskeletal health. Using a postal questionnaire, answered by 1600 female grocery store workers, their main work tasks were identified and four work groups were defined (cashier, picking, and delicatessen work, and a mixed group, who performed a mix of these tasks). The crude odds ratios (ORs) for neck/shoulder complaints were 1.5 (95% CI 1.0-2.2), 1.1 (0.7-1.5) and 1.6 (1.1-2.3), respectively, compared to mixed work. Adjusting for individual and psychosocial factors had no effect on these ORs. For elbows/hands, no significant differences were found. Technical measurements of the workload showed large differences between the work groups. Picking work was the most strenuous, while cashier work showed low loads. Quantitative measures of variation revealed for mixed work high between minutes variation and the highest between/within minutes variation. Combining work tasks with different physical exposure levels increases the variation and may reduce the risk of musculoskeletal complaints.

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.

Effects of job rotation on musculoskeletal complaints and related work exposures: a systematic literature review

The aim of this systematic review was to summarise evidence on the effects of job rotation on musculoskeletal complaints, exposures related to musculoskeletal complaints and sustainable working life parameters. A total of 16 studies were included. No studies on sustainable working life parameters were found. The quality of the studies was assessed using a checklist; eight field studies and three laboratory studies of sufficient quality were used to summarise the following evidence: one field study showed positive results and one field study showed negative results for musculoskeletal complaints, two field studies showed positive results and two field studies showed inconsistent results for exposures, and two field studies showed inconsistent results for musculoskeletal complaints and exposures. Two laboratory studies showed inconsistent results and one laboratory study showed no changes for exposures. In conclusion, there is currently inconsistent evidence for positive or negative effects of job rotation on musculoskeletal complaints and exposures related to musculoskeletal complaints. Practitioner's Summary: Currently, there is inconsistent evidence for recommending job rotation as a strategy for preventing musculoskeletal complaints. Exposures from all involved work activities and body regions should be identified and assessed first, to determine if job rotation provides increased exposure variation and/or beneficial changes in mean exposures related to musculoskeletal complaints.

Detecting within- and between-day manifestations of neuromuscular fatigue at work: an exploratory study

Cumulative neuromuscular fatigue may result from exposure to physically demanding work, such as repetitive and/or sustained work with insufficient recovery. The aims of this exploratory study were to develop a battery of field usable fatigue measures and to document hand/arm fatigue in physically demanding work over multiple workdays and after a weekend break. Sixteen plumbers were observed for five days and measures of handgrip force, variability, tremor and discomfort were obtained pre-, mid- and post-shift. This exploratory study demonstrated increasing fatigue of the hand/arm over the day and persistent fatigue from Tuesday to Friday, and that a number of the measures did not return to baseline values following a weekend break. The findings provide preliminary evidence of cumulative fatigue in residential plumbing and insight into neuromuscular fatigue measurement. However, further work is needed to develop and refine a set of fatigue measures to detect neuromuscular fatigue at the workplace.

PRACTITIONER SUMMARY

Cumulative fatigue has been linked to long-term health outcomes, including work-related musculoskeletal disorders. This paper presents findings from a physically demanding job (i.e. plumbing) revealing persistent fatigue over the work shift(s) and insufficient recovery after a weekend break, and provides insight into fatigue measurement at the workplace.

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.