The risk of distal upper limb disorder in cleaners: A modified application of the Strain Index method

This paper presents a modified application of the Strain Index (SI) method, in evaluation of effort-related variables in cleaning activities (n=40). EMG data were analyzed in the wrist flexor and extensor muscles. Effort-related variables were calculated to each record in four trigger levels (effort values were considered when the amplitude of the signal is above the trigger level for at least 0.5 s). Differences in effort time, intensity, frequency of efforts and in the resulting SI score were observed in the same activity when these variables are calculated with different trigger levels. Vacuuming, cleaning walls, floor scrapping, dusting offices and dusting horizontal surfaces were the most critical cleaning activities in terms of distal upper extremity (DUE) risk disorders; operating mono-disc and scrubber drier floor machines, dry and wet mopping and floor sweeping are among the cleaning activities with comparatively lower risk to DUE disorders. Global values of the cleaning activities (n=40) were calculated: Mean effort-intensity of 59.5% MVE; mean effort duration of 52.6% effort time; mean effort frequency of 7.8 peaks min⁻¹; mean SI score of 8.7 (for a task duration <1 h). The use of EMG data to evaluate effort related variables was found to be an useful alternative to observational methods, when efforts are not clearly associated to hand/wrist movements and when non-cyclical high-frequency activities makes virtually impossible the evaluation of effort variables (intensity, frequency and duration). However, the application of this method requires the definition of an appropriate trigger level and of an activation time.Relevance to industryJob Strain Index (SI) has been widely applied in industry, but not to cleaning activities. Difficulties may occur when observational or self-report methods are applied to activities where hand/wrist efforts are not associated to clear hand/wrist movements and when non-cyclical high-frequency activities make evaluation of effort variables difficult. This study presents a modified application of the original method to calculate wrist exertion variables and it is based on the analysis of EMG data.     

Risk assessment of cheese processing tasks using the Strain Index and OCRA Checklist

The purpose of this study was to conduct and compare two ergonomic risk assessment methods often used in occupational health research and practice: the Strain Index (SI) and Occupational Repetitive Actions (OCRA) Checklist. Seven raters used the SI and OCRA Checklist to assess task-level physical exposures to the upper extremity of workers performing 21 cheese-manufacturing tasks. Of the total task exposures assessed with both methods, nearly half (49.1%) were classified as hazardous using the OCRA Checklist while 60.2% were classified as hazardous using the SI. Although the underlying injury risk characterization constructs of the SI and OCRA Checklist differ, the results indicated that the SI and OCRA Checklist often classified job tasks into similar risk categories. The differences in risk classifications determined by the SI and OCRA Checklist for job tasks were likely related to the definition of variables measured by these assessment methods as well as the complexity of tasks evaluated. By design, the SI is specific to the distal upper extremity while the OCRA Checklist accounts for the entire upper extremity including the shoulder. When conducting risk assessments of industrial work tasks, the choice of analysis tools should be based on the purpose of the assessment and the complexity of task functions. Both the SI and OCRA Checklist yield risk assessment ratings that are similar for cheese processing tasks.     

Pooling job physical exposure data from multiple independent studies in a consortium study of carpal tunnel syndrome

Pooling data from different epidemiological studies of musculoskeletal disorders (MSDs) is necessary to improve statistical power and to more precisely quantify exposure–response relationships for MSDs. The pooling process is difficult and time-consuming, and small methodological differences could lead to different exposure–response relationships. A sub-committee of a six-study research consortium studying carpal tunnel syndrome: (i) visited each study site, (ii) documented methods used to collect physical exposure data and (iii) determined compatibility of exposure variables across studies. Certain measures of force, frequency of exertion and duty cycle were collected by all studies and were largely compatible. A portion of studies had detailed data to investigate simultaneous combinations of force, frequency and duration of exertions. Limited compatibility was found for hand/wrist posture. Only two studies could calculate compatible Strain Index scores, but Threshold Limit Value for Hand Activity Level could be determined for all studies. Challenges of pooling data, resources required and recommendations for future researchers are discussed.

Practitioner Summary: There is a need for standardised measures and measurement protocols of physical exposure for the upper extremity. This study may provide guidance for those planning to conduct an epidemiological study on quantified job physical exposures, or planning to merge physical exposure data from similar studies with some methodologic differences.     

Relationships between observational estimates and physical measurements of upper limb activity †

This study examined the internal validity of observational-based ergonomic job analysis methods for assessing upper limb force exertion and repetitive motion. Six manual tasks were performed by multiple ‘workers’ while direct measurements were made to quantify force exertion and kinematics of the upper limb. Observational-based analyses of force and upper limb motion/repetition were conducted by 29 professional ergonomists. These analysts overestimated the magnitude of individual force exertions – temporal aspects of force exertion (duty cycle) were estimated more accurately. Estimates of the relative severity of repetitive motions among the jobs were accurate. Absolute counts of repetitive motions were less accurate. Modest correlations (r² = 0.28 to r² = 0.50) were observed between ratings of hand activity level and measured joint velocities. Ergonomic job analyses relying on systematic observation should be applied and interpreted with consideration given to the capabilities and limitations of analysts in estimating the physical risk factors. These findings are relevant to a better understanding of the internal validity of ergonomic job analysis methods based on systematic observation.     

Measuring exertion time,duty cycle and hand activity level for industrial tasks using computer vision

Abstract

Two computer vision algorithms were developed to automatically estimate exertion time, duty cycle (DC) and hand activity level (HAL) from videos of workers performing 50 industrial tasks. The average DC difference between manual frame-by-frame analysis and the computer vision DC was ?5.8% for the Decision Tree (DT) algorithm, and 1.4% for the Feature Vector Training (FVT) algorithm. The average HAL difference was 0.5 for the DT algorithm and 0.3 for the FVT algorithm. A sensitivity analysis, conducted to examine the influence that deviations in DC have on HAL, found it remained unaffected when DC error was less than 5%. Thus, a DC error less than 10% will impact HAL less than 0.5 HAL, which is negligible. Automatic computer vision HAL estimates were therefore comparable to manual frame-by-frame estimates.

Practitioner Summary: Computer vision was used to automatically estimate exertion time, duty cycle and hand activity level from videos of workers performing industrial tasks.     

The effects of force and exertion duration on duty cycle time: Implications for productivity

Ergonomics has positive effects on both physical health and productivity, but estimating productivity benefits is difficult at the task design/redesign stage. Rest‐allowance prediction models are not suitable for repetitive, short‐cycle dynamic tasks, and methods–time measurement (MTM) techniques are limited in their suitability for considering ergonomics risk factors such as posture and force. The purpose of this study was to investigate the relationship between force and exertion duration on self‐selected duty cycle time and discomfort. Twenty‐one participants completed repetitive, upper‐limb exertion treatments, each of a 10‐minute duration. Five levels of force (10, 20, 40, 65, and 80% maximum voluntary contraction [MVC]) and exertion period (1, 2, 4, 6.5, and 8 seconds) were investigated. The psychophysical adjustment method was used whereby participants self‐selected a work pace for the second half of each treatment. Duty cycle, derived from the self‐paced cycle time, was the measure of productivity effects in the experiment. Analysis of variance revealed a significant effect on duty cycle time for force, exertion period, and their interaction (each p < 0.0001). Friedman's test indicated a significant effect of force (p < 0.0001) and exertion period (p < 0.0001) on discomfort. Spearman's correlation analysis showed a strong correlation between discomfort and duty cycle time (p < 0.05). Multiple regression analysis was used to develop a predictive model for duty cycle time based on force and exertion period, and this was a good fit to the data (R² = 0.98, p < 0.05). Profiles were generated presenting zones of acceptable self‐selected duty cycle times based on force and exertion duration. © 2010 Wiley Periodicals, Inc.     

Comparative analysis of three methods of risk assessment for repetitive movements of the upper limbs: OCRA index,ACGIH(TLV), and strain index

PurposeLiterature proposes different methods for risk assessment due to repeated movements of upper limbs. The results are sometimes different even if methods are applied in the same work conditions. This study, based only on hand/wrist work involving ulnar deviation, compares three methods among those most used for distal upper extremity (DUE) work-related musculoskeletal disorders (WMSDs): OCRA Index (O.I.), Strain Index (S.I.) and ACGIH(TLV).Design/methodology/approachThe work analyzes the algorithms of the methods in terms of number of parameters considered in the formulas, range of variability for each one, and their interaction in determining the final results. Starting to calculate maximum frequency that each method allows in no-risk conditions (varying force and duty cycle), specific scenarios were also created varying one parameter at a time among those determining risk (i.e. force, posture, recovery time …) for a better comprehension of the different algorithms proposed and the provided final results.FindingsThe results are generally different: in the 21 scenarios analyzed, all the methods indicate the same level of risk in only 6 cases when using the formula for the calculation of the hand activity level (HAL) in ACGIH(TLV), and in only 3 cases when using the table. Force bears a higher relative weight for ACGIH(TLV) compared to the others methods: the number of exertions per second allowed in the no-risk zone decreases markedly as the applied force increases. The S.I. was noted to generally be the most precautionary among those examined regarding the frequencies of movements allowed in the no-risk range. The use of categorical multiplier instead of linear, made the results mainly different in the intermediate risk conditions.Originality/valueThe differences in results are due not only to the different number of parameters considered by methods but also to the different risk limit values inside each algorithm. A greater amount of epidemiological data would be desirable in order to better define the conditions to be considered harmful for a worker performing repeated movements of the upper limbs.     

A Review.of: “Consumer Behaviour and the Behavioural Sciences”. By S. H. Britt. (John Wiley & Sons, 1966.) [Pp. xxxii+592.] 87s.

Abstract

Data on biomechanical overload of the upper limb in animal facility operators are currently scanty. We decided to study this risk in a university animal facility. Eleven different tasks performed by operators were identified. For each of them, the biomechanical overload of the upper limb was evaluated by applying 4 different methods frequently used, hypothesising a task duration of 4 and 8 h. Then two ‘typical’ real working days of the examined facility were reconstructed, and the risk for operators was calculated using the OCRA Index, Checklist and Mini-Checklist. Considering the specific tasks, the results show some difference among methods, but the overall results show an acceptable/slight risk of biomechanical overload of the upper limb in animal facility operators during typical working days.

Practitioner Summary: Upper limb biomechanical overload (UL-BO) is a neglected risk in animal facilities. In a university facility, 11 different tasks were identified, and 2 typical working days were analysed. Even if some task at increased risk may exist, during typical working days, the overall results show that the risk of UL-BO in operators can be considered usually acceptable or, at worst, slight.     

The impact of work configuration,target angle and hand force direction on upper extremity muscle activity during sub-maximal overhead work

Overhead work has established links to upper extremity discomfort and disorders. As many jobs incorporate working overhead, this study aimed to identify working conditions requiring relatively lower muscular shoulder load. Eleven upper extremity muscles were monitored with electromyography during laboratory simulations of overhead work tasks. Tasks were defined with three criteria: work configuration (fixed, stature-specific); target angle (?15°, 0°, 15°, 30° from vertical); direction of applied hand force (pulling backwards, pushing forwards, downwards, sideways, upwards). Normalised electromyographic activity was greater for fixed configurations, particularly when pulling in a backward direction (total activity = 108.3% maximum voluntary exertion (MVE)) compared to pushing down or forward (total activity ranging from 10.5 to 17.3%MVE). Further, pulling backwards at angles of –15° and 0° showed the highest muscular demand (p < 0.05). These results suggest that, if possible, positioning overhead work in front of the body with exertions directed forwards will result in the lowest upper extremity muscle demand.

Statement of Relevance: Overhead work pervades occupational settings and is associated with risk of upper extremity musculoskeletal disorders. The muscular intensity associated with performing overhead work was assessed in several combinations of work placement and hand force direction. These findings should have utility for designing overhead work tasks that reduce muscular exposure.     

The predictive validity of the RSI QuickScan questionnaire with respect to arm,shoulder and neck symptoms in computer workers

The aim of this study was to determine whether results from the RSI QuickScan questionnaire on risk factors for arm, shoulder and neck symptoms can predict future arm, neck and shoulder symptoms in a population of computer workers. For this prospective cohort study, with a follow-up of 24 months, 3383 workers who regularly worked with a computer were approached. Generalised estimating equations (GEE) with 6, 12, 18 and 24 months time lags were used to determine whether high exposure was related to symptoms at follow-up. The results showed that high scores on 9 out of 13 scales, including previous symptoms, were significantly related to arm, shoulder and neck symptoms at follow-up. These results provide support for the predictive validity of the RSI QuickScan questionnaire.

Practitioner Summary: The results showed that high scores on 9 out of 13 scales, including previous symptoms, were significantly related to arm, shoulder and neck symptoms at follow-up. The RSI QuickScan questionnaire may be recommended as a tool in the identification of computer workers who should be targeted with interventions aimed at prevention of future symptoms.     

Characterizing the spatiotemporal evolution of soil salinization in Hetao Irrigation District (China) using a remote sensing approach

ABSTRACT

Soil salinization is a major problem of land degradation in arid and semiarid irrigation districts. This study aims to characterize the spatiotemporal evolution of soil salinization in Hetao Irrigation District (HID) in Inner Mongolia, China, using Landsat Thematic Mapper/Enhanced Thematic Mapper Plus/Operational Land Imager datasets. Salty barren land and farmland are extracted using supervised classification. Then, we develop four integrated soil salinity models (ISSMs) to quantify the intensity of saline farmland. ISSMs are generated through deriving the parameters (E_VI-SIs), which integrate enhanced vegetation index (EVI) and Salinity Index-1 (SI1), EVI and Salinity Index-3 (SI3), Modified Soil Adjusted Vegetation Index (MSAVI) and SI1, and MSAVI and SI3, respectively, from the scatter plots of farmland soils with different salinity in four spectral feature spaces (SFSs). Exponential regression analyses reveal that the E_VI-SI from MSAVI-SI3 SFS has the best fit with in situ soil electrical conductivity measurements (R² = 0.74, root mean square error = 0.31 dS m^–1). Salty barren land clustered in the central and northeast of HID, while the area of salty barren land decreased during 1986–2016. After employing water-saving irrigation since 2000, saline farmland decreased and then remained relatively stable. This study indicates that the SFS integrating MSAVI and SI3 contains effective information for quantifying the saline farmland. Employing water-saving irrigation had a positive effect on controlling salinization.     

An evaluation of patient lifting techniques

Abstract

In the present laboratory study five two-person manual lifting techniques were evaluated as to the amount of physical exertion required of the nurses. Ten female volunteers served as nurses; two healthy volunteers (weight: 55 kg and 75 kg) served as passive patients. The working postures and motions were recorded on videotape. The data thus obtained were used in a anatomical-biomechanical analysis. The perceived exertion by the nurses was measured as well. In almost all situations the compressive forces on the nurse's spine exceeded their acceptable limit of 3425 N. Differences between the lifting techniques were most obvious when the 55 kg patient was lifted. Ratings of the perceived exertion (RPE scores) were higher in symmetrical handling than in asymmetrical handling. The three techniques using asymmetrical hand positions produced less subjective stress. RPE scores and rotation of the back were negatively correlated. Rotating the back when moving a patient from one side to the other seems to ease the task. On the whole, the results of the biomechanical evaluation are in line with the subjective perception of the nurses. In both instances the barrow lift appeared to be the most strenuous one; the Australian lift resulted in low compressive forces and a moderate level of perceived exertion     

Measuring elemental time and duty cycle using automated video processing

A marker-less 2D video algorithm measured hand kinematics (location, velocity and acceleration) in a paced repetitive laboratory task for varying hand activity levels (HAL). The decision tree (DT) algorithm identified the trajectory of the hand using spatiotemporal relationships during the exertion and rest states. The feature vector training (FVT) method utilised the k-nearest neighbourhood classifier, trained using a set of samples or the first cycle. The average duty cycle (DC) error using the DT algorithm was 2.7%. The FVT algorithm had an average 3.3% error when trained using the first cycle sample of each repetitive task, and had a 2.8% average error when trained using several representative repetitive cycles. Error for HAL was 0.1 for both algorithms, which was considered negligible. Elemental time, stratified by task and subject, were not statistically different from ground truth (p < 0.05). Both algorithms performed well for automatically measuring elapsed time, DC and HAL.

Practitioner Summary: A completely automated approach for measuring elapsed time and DC was developed using marker-less video tracking and the tracked kinematic record. Such an approach is automatic, repeatable, objective and unobtrusive, and is suitable for evaluating repetitive exertions, muscle fatigue and manual tasks.     

Application of the Strain Index in multiple task jobs

Six different methods to calculate the Strain Index (SI) scores for jobs with multiple forces/tasks were developed. Exposure data of 733 subjects from 12 different worksites were used to calculate these SI scores. Results show that using different SI computation methods could result in different SI scores, hence different risk level classifications. However, some simpler methods generated SI scores were comparable to the more complicated composite SI method. Despite differences in the scores between the six different SI computation methods, Spearman rank-order correlation coefficients of 0.61-0.97 were found between the methods. With some confidence, ergonomic practitioners may use simpler methods, depending on their specificity requirement in job evaluations and available resources. Some SI computation methods may tend to over-estimate job risk levels, while others may tend to under-estimate job risk levels, due to different ways used in obtaining the various SI parameters and computations.     

Development of role-related minimum cardiorespiratory fitness standards for firefighters and commanders

A minimum cardiorespiratory fitness standard was derived for firefighters following a metabolic demands analysis. Design and minimal acceptable performance of generic firefighting task simulations (i.e. hose running, casualty evacuation, stair climb, equipment carry, wild-land fire) were endorsed by a panel of operationally experienced experts. Sixty-two UK firefighters completed these tasks wearing a standard protective firefighting ensemble while being monitored for peak steady-state metabolic demand and cardiovascular strain. Four tasks, endorsed as valid operational simulations by ≥90% of participants (excluding wild-land fire; 84%), were deemed to be a sufficiently valid and reliable basis for a fitness standard. These tasks elicited an average peak steady-state metabolic cost of 38.1 ± 7.8 ml kg^?1 min^?1. It is estimated that healthy adults can sustain the total duration of these tasks (~16 min) at ≤90% maximum oxygen uptake and a cardiorespiratory fitness standard of ≥42.3 ml kg^?1 min^?1 would be required to sustain work.

Practitioner Summary: A cardiorespiratory fitness standard for firefighters of ≥42.3 ml kg^?1 min^?1 was derived from monitoring minimum acceptable performance of essential tasks. This study supports the implementation of a routine assessment of this fitness standard for all UK operational firefighters, to ensure safe physical preparedness for occupational performance.     

The effects of joint torque, pace and work:rest ratio on powered hand tool operations

Repetitive use of hand-held power tools is associated with work-related upper extremity musculoskeletal disorders. Using a pneumatic nutrunner, 21 men completed twelve 360 repetitive fastener-driving sessions on three joints (hard, soft and control) at slow and fast pace, and two different work:rest patterns. Handgrip force and perceived exertions were collected throughout each session. For the control joint, the mean grip force exerted was 39.6% of maximum voluntary exertion (MVE) whereas during hard and soft joint sessions it was 48.9% MVE and 56.9% MVE, respectively. Throughout each session, the grip force decreased, more while operating soft and hard joints as compared with the control joint (regression slope: ?0.022 and ?0.023, compared with ?0.007 N/drive, respectively), suggesting considerable upper extremity muscular effort by participants during torque buildup. Fast work pace resulted in higher average grip forces by participants but a greater decrease in the force as the session progressed. Providing rest breaks reduced perceived exertions. The findings gain additional knowledge for assembly task design to possibly reduce the hand/arm injury risks for the operator.

Practitioner Summary: Powered hand tools are widely used in assembly and manufacturing industries. However, the nature of their repetitive use on human operator biomechanical and perceptual responses is not fully understood. This study examined work-related risk factors such as joint torque, pace and work:rest ratios on powered hand tool performance.     

The Postural Stability Diagram (PSD): personal constraints on the static exertion of force

Abstract

A chart called the Postural Stability Diagram (PSD) is used to represent static forces at the hands and feet during exertions. The constraints on exertion due to muscular strength and due to the distribution of body weight relative to the contacts of hands and feet with the workplace are discussed. Methods of collecting relevant anthropometric data are described, on which the personal statements about the capacity to exert forces are based. The PSD is intended for the analysis of tasks requiring static exertion. A following paper considers task-demands (environmental statements), which are superimposed on the personal statements on the chart during PSD analysis.     

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

Abstract

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).     

Multifactor association of job,individual and psychosocial factors in prevalence of distal upper extremity disorders and quantification of job physical exposure

The objective of this study was to develop a multifactor model of job, individual and psychosocial factors in prevalence of distal upper extremity musculoskeletal disorders (DUE MSDs); and quantify job physical exposure to establish safe exposure limits. The study sample comprised of 525 workers who were part of a large prospective cohort study and represented a broad array of industrial practices and a wide range of job physical exposure. Only baseline data was considered for the analysis in the study. Workers underwent laptop administered questionnaires, structured interviews, two standardized physical examinations and nerve conduction studies to ascertain demographic, medical history, psychosocial factors and current DUE MSDs. All workers' jobs were individually measured for job physical exposure factors and videotaped. Binomial logistic regression was used to develop and test the multifactor association and quantification of job physical exposure for safe exposure limits. Results indicated that work-related DUE MSDs are multifactor in nature and are significantly affected by specific factors of (1) job physical exposure - percentage duration of exertion (PDOE), workers' subjective ratings of perceived effort or intensity of exertion (IOE) (using Borg CR-10), hand activity level measured by the American conference of Governmental Industrial Hygienists (ACGIH) threshold limit value for hand activity level (TLV for HAL), and presence of 2-point pinch grasps; (2) individual factors - female gender, diabetes, higher body mass index (BMI), and past and current smokers; (3) psychosocial factors - neither likely/unlikely or very unlikely to take up the current job again, divorced/separated, and presence of family problems. Quantification of job physical exposure indicated that prevalence of work-related DUE MSDs significantly increases with efforts per minute (Eff/min) >8 (OR = 1.69, p = 0.006) and woker's perceived effort based on Borg rating for IOE at the end of the shift >3 (OR = 2.46, p < 0.001). Further studies should be conducted to validate these safe exposure limit criteria.