Feasibility of quantifying the physical exposure of materials handlers in the workplace with magnetic and inertial measurement units.

Handling tasks can expose workers to risk factors. The objective was to describe the feasibility of using magnetic and inertial measurement units (MIMUs) to quantify the physical exposure of materials handlers in the workplace. Full-body kinematics were obtained with MIMUs on 10 handlers gathering products ordered by retailers with a pallet truck. An observer classified the visual difference (VD) of segment orientation between a MIMUs avatar and video recordings in three categories (none, minor and major) for each product transfer. The feet, arms, shoulders and head were considered similar for ≥97% of observations. The trunk segment obtained the most differences with 9% of minor VD and 5% of major VD, which were related to the duration of the magnetic disturbances of the MIMUs. Estimating parameters of the physical exposure of handlers in the workplace is feasible with kinematics and an order list, but visual verification remains important for scientific rigour.Practitioner Summary: The feasibility of measuring physical exposure with magnetic and inertial measurement units was evaluated on materials handlers in the workplace. Visual observation of the postures indicated that most of the data is considered acceptable. Magnetic disturbances can increase the measurement error, so data must be verified to ensure validity.

Influence of musculoskeletal pain on workers' ergonomic risk-factor assessments.

This study compares the ergonomic risk-factor assessments of workers with and without musculoskeletal pain. A questionnaire on the musculoskeletal pain experienced in various body regions during the 12 months and seven days preceding the data collection was administered to 473 workers from three industrial sectors. The Ergonomic Workplace Analysis method, developed by the Finnish Institute of Occupational Health (FIOH), was then used by the workers and an ergonomics expert to assess the workstations. The ergonomic quality of the workstations and the need for change were also assessed by the expert and the workers at the workstation, using visual analog scales (VAS). Results show that the workers in this study were exposed to significant musculoskeletal disorder (MSD) risk factors, according to the FIOH assessment and the high percentages of reported pain. The results also show that those who reported pain in the seven days prior to the assessment evaluated their workstations more negatively than subjects who reported no pain, while the expert found no difference between the two groups' exposure to MSD risk factors.

Relative importance of expertise, lifting height and weight lifted on posture and lumbar external loading during a transfer task in manual material handling.

The objective of this study was to measure the effect size of three important factors in manual material handling, namely expertise, lifting height and weight lifted. The effect of expertise was evaluated by contrasting 15 expert and 15 novice handlers, the effect of the weight lifted with a 15-kg box and a 23-kg box and the effect of lifting height with two different box heights: ground level and a 32 cm height. The task consisted of transferring a series of boxes from a conveyor to a hand trolley. Lifting height and weight lifted had more effect size than expertise on external back loading variables (moments) while expertise had low impact. On the other hand, expertise showed a significant effect of posture variables on the lumbar spine and knees. All three factors are important, but for a reduction of external back loading, the focus should be on the lifting height and weight lifted. PRACTITIONER SUMMARY: The objective was to measure the effect size of three important factors in a transfer of boxes from a conveyor to a hand trolley. Lifting height and weight lifted had more effect size than expertise on external back loading variables but expertise was a major determinant in back posture.

Sudden loading perturbation to determine the reflex response of different back muscles: a reliability study.

In this study we estimate the reliability of reflex response variables to identify the main sources of variability and to estimate appropriate measurement strategies to obtain more reliable measures. Back muscle surface electromyography (EMG) was recorded in healthy males during anteriorly-directed sudden loading perturbations applied to the trunk. Measures of EMG reflex latency and amplitude were obtained. The generalizability theory was used as a framework to estimate the magnitude of the different variance components and the reliability of the measures corresponding to various simulations of different measurement strategies. Reliability of the different variables was poor to moderate (intraclass correlation coefficient range 0-0.62). Averaging scores across homologous muscles and several trials were strategies to achieve more acceptable reliability. The reflex response of back muscles is inherently variable, and a large measurement effort is necessary to obtain reliable and, consequently, valid and responsive estimations of this neuromuscular function.

Biomechanical differences between expert and novice workers in a manual material handling task.

The objective was to verify whether the methods were safer and more efficient when used by expert handlers than by novice handlers. Altogether, 15 expert and 15 novice handlers were recruited. Their task was to transfer four boxes from a conveyor to a hand trolley. Different characteristics of the load and lifting heights were modified to achieve a larger variety of methods by the participants. The results show that the net moments at the L5/S1 joint were not significantly different (p > 0.05) for the two groups. However, compared with the novices, the experts bent their lumbar region less (experts 54° (SD 11°); novices 66° (SD 15°)) but bent their knees more (experts approx. 72° (SD approx. 30°); novices approx. 53° (SD approx. 33°), which brought them closer to the box. The handler's posture therefore seems to be a major aspect that should be paid specific attention, mainly when there is maximum back loading. STATEMENT OF RELEVANCE: The findings of this research will be useful for improving manual material handling training programmes. Most biomechanical research is based on novice workers and adding information about the approach used by expert handlers in performing their tasks will help provide new avenues for reducing the risk of injury caused by this demanding physical task.

Evaluation of forearm support provided by the Workplace Board on perceived tension, comfort and productivity in pregnant and non-pregnant computer users.

The aim of the study was to evaluate the effect of forearm support provided by the Workplace Board on perceived tension, comfort and productivity among pregnant and non-pregnant female computer workers. Ten pregnant and 18 non-pregnant women participated in the study. Participants completed three sets of tension/discomfort questionnaires at two week intervals. The first set was completed prior to any workstation intervention; the second set was completed after two weeks working with an ergonomically adjusted workstation; the third set was completed after two weeks working with the Workplace Board integrated into the office workstation. With the Workplace Board, decreased perceived tension was reported in the left shoulder, wrist and low back in non-pregnant women only. The Board was generally liked by all participants, and increased comfort and productivity in all areas, with the exception of a negative effect on productivity of general office tasks. The board is suitable for integration in most office workstations and for most users, but has no special benefits for pregnant women.

Reliability of different thresholds for defining muscular rest of the trapezius muscles in computer office workers.

This study aimed at documenting the reliability of different thresholds used for defining the muscular rest of the trapezius muscles of 27 computer office workers, using surface electromyography (EMG) signals collected in the field. Measurement strategies for increasing the reliability of the results were also explored. Ten different thresholds to define muscular rest were compared: 1) five normalised (individualised) thresholds; 2) three absolute thresholds (in muV); 3) two absolute but individualised thresholds. The reliability was assessed using both a 15-min standardised computer task and 45 min of regular computer work. The main findings were: 1) overall, in a repeated measures study design, muscular rest variables were more reliable with the use of absolute thresholds when compared to normalised and individualised thresholds; 2) excellent reliability (index of dependability >0.75) can be reached when averaging the scores over 2 days; 3) using a standardised task instead of regular work does not necessarily lead to more reliable results.

Effect of a desk attachment board on posture and muscle activity in women during computer work.

Working at a computer is part of a large number of jobs and has been associated with upper extremity musculoskeletal disorders and back pain. The study evaluated the effects of a board attachment on upper extremity and back. The findings are mixed in that the board may have a positive effect in preventing back pain, but may be detrimental to upper extremities. Effect of a desk attachment board on upper extremity and trunk posture, and muscle activity was assessed in women video display terminal users. Participants completed a standard 20-min computer task under two conditions: 1) using a standard desk; 2) using a desk attachment board designed to support the forearms. Bilateral electromyography of the trapezius, multifidus and longissimus muscles and the right anterior deltoid and forearm extensor muscles was recorded. 3-D trunk and upper extremity posture was monitored. Participants were tested before and after 2 weeks of familiarisation with the board in their workplace. Perceived tension and discomfort were recorded before and after use of the board. Use of the board tended to increase muscle activity in the right trapezius and forearm extensor and to decrease muscle activity in the back. Perceived tension in the low back decreased slightly with the board. The board may be useful in reducing tension in the low back during computer work, but may adversely affect the upper extremities.

Reliability of centre of pressure summary measures of postural steadiness in healthy young adults.

This study aimed to (1) estimate the reliability of 36 centre of pressure (COP) summary measures in healthy participants and (2) identify the main sources of variability in order to estimate the most appropriate measurement strategies to improve reliability. Twelve healthy males performed, on two separate days, eight 1-min trials of quiet standing on a force platform in two conditions [eyes open (EO) and eyes closed (EC)]. The generalizability theory was used as a framework to estimate the magnitude of the different variance components (Subject, Trial, Day and all interactions) and the reliability of the measures corresponding to various simulations of measurement strategies. Reliability of the COP summary measures was poor to moderate. Intra-class correlation coefficients were generally higher with EO (mean: 0.46, range: 0.03-0.76) than with EC (mean: 0.41, range 0.02-0.72) across all summary measures. The majority of the variance was attributed to Subject (2%-76%), Subject x Day (0%-24%) and Subject x Day x Trial (16%-79%) variance components depending on the summary measure and condition. The reliability could be improved more efficiently by averaging measurements between-days than by increasing the number of trials during 1 day. For the majority of the summary measures, acceptable reliability can be achieved when at least seven or more trials are averaged during the same testing day.

Manual materials handling in mining: the effect of rod heights and foot positions when lifting "in-the-hole" drill rods.

There is a paucity of studies focusing on the lifting of rods or long awkward heavy objects. In-the-hole (ITH) drilling is a heavy repetitive mining task, which has been identified as having a relatively high incidence and severity rate of musculoskeletal injuries. The purpose of this study was to examine how the load experienced by ITH drill operators changed when lifting a vertical drilling rod (1.61m, 35kg) using two rod heights and four different foot positions. In addition, a symmetrical lift with a lifting index (LI) of 1.4 also served as a comparison to determine possible risk of low back injury. Eleven experienced ITH drill operators participated in the study. Each subject was required to lift a vertical drilling rod until the upper body was in an erect posture using four different foot positions (0 degrees =subject facing the rod, 45 degrees =subject oblique to the rod, 90 degrees =subject right side to the rod and freestyle). In addition, two rod height conditions were studied where the base of the vertical rod was supported either (1) at ground level (height of rod CG=0.83m) or (2) on a 20cm rack (height of rod CG=1.03m). Finally, each subject lifted a 21.5kg box in the sagittal plane, which corresponded to an LI of 1.4 in the NIOSH lifting equation. Reflective markers were placed on the subjects, and three video cameras and one force plate were used to record the forces and the motion of the subjects' segments. Two surface electrodes were applied on the right and the left erector spinae (ES) at the level of L3. Back loading was defined by the level of the peak moments, the mechanical work and erector spinae muscle activity (EMG). It was found that the vertical height of the rod had the most significant impact on back loading, while the effect of the initial foot positioning relative to the rod was limited by the technique adopted by the drillers. Moreover, it was found that some of the subjects used techniques less strenuous for the back than others. Finally, the asymmetrical lifting component was found to be the most negative aspect of lifting an ITH drill rod compared to a standard symmetrical lift (NIOSH).

Comparison of three computer office workstations offering forearm support: impact on upper limb posture and muscle activation.

The aims of the study were: 1) to determine whether resting the forearms on the work surface, as compared to chair armrests, reduces muscular activation; 2) to compare the sensitivity of different electromyographic (EMG) summary parameters. Eighteen healthy subjects performed computer work (with keyboard and mouse alternately) for 20 min while resting their forearms on a work surface adjustable in height (Workstation A), on the chair's armrests with an adjustable workstation (Workstation B) or on their chair's armrests with a non-adjustable workstation (Workstation C). The EMG amplitude of the trapezius and deltoid muscles was little influenced by the workstations, whereas their EMG variability increased with Workstation A, which was interpreted as a positive effect. However, the EMG amplitude of the mouse-side extensor digitorum muscle was higher with Workstation A. Alternating between resting the forearms on the work surface and on the chairs' armrests could solicit different muscles during computer work, and could be considered as a strategy for preventing musculoskeletal disorders. The new exposure variation analysis summary parameters used were sensitive to small workstation changes, thus supporting their use in future studies.

Physical exposure of sign language interpreters: baseline measures and reliability analysis.

Measurement of physical exposure to musculoskeletal disorder risk factors must generally be performed directly in the field to assess the effectiveness of ergonomic interventions. To perform such an evaluation, the reliability of physical exposure measures under similar field conditions must be known. The objectives of this study were to estimate the reliability of physical exposure measures performed in the field and to establish the baseline values of physical exposure in sign language interpreters (SLI) before the implementation of an intervention. The electromyography (EMG) of the trapezius muscles as well as the wrist motions of the dominant arm were measured using goniometry on nine SLI on four different days. Several exposure parameters, proposed in the literature, were computed and the generalizability theory was used as a framework to assess reliability. Overall, SLI showed a relatively low level of trapezius muscle activity, but with little time at rest, and highly dynamic wrist motions. Electromyography exposure parameters showed poor to moderate reliability, while goniometry parameter reliability was moderate to excellent. For EMG parameters, performing repeated measurements on different days was more effective in increasing reliability than extending the duration of the measurement over one day. For goniometry, repeating measurements on different days was also effective in improving reliability, although good reliability could be obtained with a single sufficiently long measurement period.

The effect of sampling frequency on EMG measures of occupational mechanical exposure.

The purpose of the present study was to determine how much it is possible to downsample EMG without loosing the accuracy of some EMG measures of occupational mechanical exposure frequently used in the literature. The EMG signals of four muscles (two trapezius, right deltoid and right extensor digitorum) were collected (sampling frequency: 1024 Hz) from 20 subjects while performing a 20 min computer work task. The EMG RMS amplitude was computed from 0.125 s successive time-windows for the original (1024 Hz) and four additional digitally resampled (at 512, 256, 128 and 64 Hz) EMG signals. Three of the most frequently used data reduction methods (1. gaps analysis, 2. amplitude probability distribution function and 3. exposure variation analysis) were used to summarise the 20 min EMG activation profiles. The results from the exposure variation analysis were summarized into three variables using a new method detailed here. In general, the ANOVA for repeated measures demonstrated that a decrease of the sampling frequency significantly changed the EMG measures (relative to the 1024 Hz sampling condition) most of the time at 64 and 128 Hz, occasionally at 256 Hz, but practically never at 512 Hz. An analysis of the maximal errors (relative to the 1024 Hz condition) across all subjects supported these findings. Consequently, it was concluded that 512 Hz is quite conservative and should practically never lead to invalid EMG parameters estimations. Conversely, 256 Hz represents the lowest limit tolerable for some EMG parameters (gaps analysis, amplitude probability distribution function) while it is unacceptable for others (modified exposure variation analysis).

Reproducibility and validity of workers' self-reports of physical work demands.

The objective of this paper is to provide a systematic review of the reproducibility and validity of self-report questions concerning physical work demands. After a bibliographic search of Medline and Ergonomic Abstracts for 1980-2003, 15 articles meeting the eligibility criteria were reviewed for methodological quality; 82 formulations of questions on physical work demands were evaluated for reproducibility and 83 for validity. Questions evaluated for both reproducibility and validity that performed well in both sets of studies included those on duration or presence of sitting and standing posture, the presence of walking, kneeling or squatting postures, duration or frequency of hands above shoulders, manual handling of more than or less than 10 kg, general level of physical effort, presence and duration of whole-body vibration, and duration of the use of visual display terminals. Suggestions for improving the design of reproducibility and validity studies and directions for future research in physical workload measurement are proposed.

Left-handed versus right-handed computer mouse use: effect on upper-extremity posture.

Alternatives to reduce postural constraints have to be sought in order to reduce musculoskeletal complaints related to computer work. This study aimed at documenting the impact of using the mouse on the left side of a standard keyboard (with a right numeric keypad) on upper-extremity posture. A simulated computer task was performed by 27 subjects in a laboratory before and 1 month after ergonomics training. Shoulder flexion and abduction, as well as wrist extension were reduced with left-handed mouse use. Sixteen of the 27 subjects truly converted to using the mouse with the left hand. After a month of using the mouse with the left hand, the time required to perform the same task reduced, the perceived difficulty and discomfort improved, though the time to perform the task was still longer than when using the mouse with the right hand. For work involving both keyboard and mouse use, and without the need of the numeric keypad, it would probably be preferable to use a keyboard without the numeric keypad if the mouse is to be used on the right-hand side. If such keyboards are unavailable, an interesting alternative would be to use the mouse on the left side provided sufficient time is allowed to get accustomed to it.

Knee flexion and base of support in asymmetrical handling: effects on the worker's dynamic stability and the moments of the L(5)/S(1) and knee joints.

OBJECTIVE: To investigate the effects of knee flexion and of the variations of feet lateral spacing on dynamic stability and on the net joint moments distribution between the back and knees. BACKGROUND: The width of the base of support and knee flexion effects on joint moments in asymmetric handling and especially on the worker's stability have rarely been studied. METHODS: Fourteen healthy male subjects performed an asymmetrical lifting task, using four different techniques: two imposed lateral feet spacings (41 and 57 cm) and two knee flexion amplitudes (slightly and deeply flexed knees). A tridimensional dynamic rigid body model was used to estimate the triaxial net reaction moments at L(5)/S(1) and at the knees, using two force platforms. New developments have been undertaken to characterize workers' stability while handling: the horizontal force required to destabilize the worker was calculated as a measure of dynamic stability. RESULTS: The width of the base of support had little effect on L(5)/S(1) and knee moments; however, the subjects were less stable with the narrow base of support. Using the slightly flexed knees technique, trunk maximal resultant moments were slightly smaller (202 vs. 216 Nm), and maximal resultant knee moments were larger (96 vs. 62 Nm). Furthermore, asymmetric moments at the trunk and the asymmetric position of the knees were reduced with this technique, but subjects were less stable. CONCLUSIONS: The use of a slightly flexed knees technique in asymmetrical handling of low-lying loads appears advantageous because it reduces L(5)/S(1) moments while increasing the knees' flexing moments, although this may compromise workers' stability. RELEVANCE: Handling methods used by workers in asymmetrical handling have rarely been studied. Optimizing the safety of a handling method can involve many parameters, such as reducing joint moments and maximizing stability. The evaluation of the worker's stability while handling in conjunction with joint moments is an interesting alternative to study the safety of handling methods.