An investigation of children's posture and discomfort during computer use

This study investigated schoolchildren's posture and discomfort while working at computers. Sixty-eight children (mean age 9.5 years) were observed at school during normal computer sessions lasting 15-25 min. Rapid upper limb assessment (RULA) was used to evaluate posture, and a body discomfort chart (BDC) and a modified visual analogue scale (VAS) were used to record site and intensity of discomfort. Computer tasks were noted and in accordance with RULA, postures were classified as Action Level (AL) 1 (acceptable) to 4 (needs immediate change). Most children adopted postures at an unacceptable level while working at computers. None of the postures were in AL 1; 60% were in AL 2; 38% were in AL 3; and 2% were in AL 4. Posture became worse over time. Poor posture was associated with discomfort, but it is not clear if it was related to the sitting posture or to the computer use. Children who reported discomfort had a higher mean RULA grand score (5.0) than those who did not report discomfort (4.4). The type of computer task influenced the children's posture. RULA proved generally to be a suitable method for evaluating children's posture.     

Spinal loading in static and dynamic postures: EMG and intra-abdominal pressure study

Abstract

The difference in physiological stress between static posture loading and dynamic lift is poorly understood. Therefore, the quantitative pattern of gradual increase and decrease of stress as measured by EMG of erectores spinae at T₁₂ and L₃ and intraabdominal pressure (IAP) due to steady progressive loading and unloading in static stooping posture was studied and compared with that of stoop lifting of the same weight. For dynamic loading and unloading a steady flow of 25 kg of water into or out of a plastic tub held in the hand while maintaining a stooping posture was used. The subjects also performed stoop lifting weights of 15 and 25 kg. In static posture loading the mean EMG at T₁₂ was approximately 50% of the L₃ level. During unloading in that posture it was reduced to 33%. The level of electromyographic activity at T₁₂ for loading was not significantly different from unloading. At L₃ however, the magnitude increased significantly for unloading. The EMG and intraabdominal pressure responses of static posture were between 33 and 50% of the corresponding phases during stoop lifting of the same weight. An insignificant difference in IAP and heart rate between static posture loading and stoop lifting indicates a less critical role of IAP and no difference in cardiac stress in less stressful tasks.     

Characterization of posture and comfort in laptop users in non-desk settings

Laptop computers may be used in a variety of postures not coupled to the office workstation. Using passive motion analysis, this study examined mean joint angles during a short typing/editing task in college students (n=20), in up to seven positions. Comfort was assessed after task execution through a body map. For three required postures, joint angles in a prone posture were different than those while seated at a couch with feet either on floor or on ottoman. Specifically, the prone posture was characterized by comparatively non-neutral shoulders, elbows and wrists, and pronounced neck extension. Significantly greater intensity and more regions of discomfort were marked for the prone posture than for the seated postures. It is recommended that the prone posture only be assumed briefly during laptop use. Exposure to laptops outside of the office setting should be assessed in future epidemiologic studies of musculoskeletal complaints and computer use.     

The effects of knee angles on subjective discomfort ratings, heart rates, and muscle fatigue of lower extremities in static-sustaining tasks

The purpose of this study was to investigate the effects of knee-flexion angles on subjective discomfort ratings, heart rates, and muscle fatigue using median frequency (MDF) in a static-sustaining task. Thirty healthy participants maintained 13 postures including standing, squatting, sitting, and kneeling postures and then MDFs from the erector spinae, biceps femoris, vastus medialis, gastrocnemius, and tibialis anterior muscles, subjective discomfort, and heart rates were collected every 3 min during a sustained 15 min task. Results showed that the discomfort, heart rate and muscle fatigue were significantly influenced by the body postures. In general, standing and sitting postures showed less discomfort as well as lower heart rates, whereas squatting postures (KF120, KF90, KF60) had higher discomfort and heart rates. Three MDF change trends were reported associated with postures in this study. First, there were less changes of MDFs for standing and sitting postures; second, all patterns of MDFs for KF 150 and KF120 decreased, and lastly some MDFs had increasing trends and others showed decreasing trends for KF30, KF30T, and kneeling postures.     

The effects of knee angles on subjective discomfort ratings,heart rates,and muscle fatigue of lower extremities in static-sustaining tasks

The purpose of this study was to investigate the effects of knee-flexion angles on subjective discomfort ratings, heart rates, and muscle fatigue using median frequency (MDF) in a static-sustaining task. Thirty healthy participants maintained 13 postures including standing, squatting, sitting, and kneeling postures and then MDFs from the erector spinae, biceps femoris, vastus medialis, gastrocnemius, and tibialis anterior muscles, subjective discomfort, and heart rates were collected every 3 min during a sustained 15 min task. Results showed that the discomfort, heart rate and muscle fatigue were significantly influenced by the body postures. In general, standing and sitting postures showed less discomfort as well as lower heart rates, whereas squatting postures (KF120, KF90, KF60) had higher discomfort and heart rates. Three MDF change trends were reported associated with postures in this study. First, there were less changes of MDFs for standing and sitting postures; second, all patterns of MDFs for KF 150 and KF120 decreased, and lastly some MDFs had increasing trends and others showed decreasing trends for KF30, KF30T, and kneeling postures.     

The effects of working height and manipulated weights on subjective strain, body posture and muscular activity of milking parlor operatives--laboratory study

The incidence of work-related musculoskeletal disorders among milking parlor operatives has increased while milking parlors were getting bigger. At the same time parlor design was improved regarding the physical load as well as body postures. In contrast to former studies on workload in parlor milking this project was designed and performed as an experimental study in a laboratory setting including 6 female subjects. Motion analysis and psycho-physiological analysis (EMG, heart rate, subjective perceived strain index) were carried out. Intra-individual comparisons were made for the different settings using general linear models for repeated measurements. The effects of working height and weight of milking unit during parlor milking were investigated regarding the impact on muscular load and body posture. The results showed that the optimal working height for attaching the cluster is having the teats at shoulder level of the parlor operative. Another important workload reduction was achieved by reducing the weight of the milking cluster. The named discomfort, localized fatigue and the body posture analysis provide evidence that the changes in modern milking parlors due to mechanization still bear the risk of overburden for the worker.     

The effect of shoulder posture on performance,discomfort and muscle fatigue whilst working on a visual display unit

An investigation was conducted to determine the relationship between posture and performance while working on a VDU. Twenty-one female subjects performed a 20 min choice reaction time task in a within-subject design with shoulder flexion (0° versus 30°) and noise (55 dB versus 75 dB) as factors. Discomfort measures, electromyography (EMG) measures and measures of performance including reaction time and percentage of errors were collected. The results suggested poorer performance in the 30° shoulder flexion posture compared to the 0° shoulder flexion posture (performance index F_1,20 = 3.95, p = 0.061). There was also significantly greater discomfort and fatigue, as indicated by EMG, in the 30° shoulder flexion compared to 0° shoulder flexion (discomfort: F_1,20 = 99.30; p = 0.0001 EMG: F_1,20 = 4.25, p = 0.052). The results of this study provide the most direct evidence that the posture of VDU users can affect their performance at a task. A number of possible mechanisms for posture to affect performance are explored using the data. The utility of data showing the effect of posture on performance data is discussed in terms of financial modelling to justify the cost of ergonomic intervention. Relevance to industryPoor posture whilst working at a VDU has been previously linked with the development of poor health but has not been directly linked with poor performance. This paper provides evidence to show posture can effect VDU performance. This enables organisations to use estimates of performance changes to model the costs of investment in ergonomic interventions.     

Rapid Communication Effects of posture,weight and frequency on trunk muscular activity and fatigue during repetitive lifting tasks

Abstract

We examined the effects of posture, weight and frequency on trunk muscular activity and fatigue during repetitive dynamic lifting. Electromyographic (EMG) signals from eight primary trunk muscles were collected during 120 min for four different task conditions. The patterns of muscle recruitment and the levels of relative activation were analysed using the normalized EMG data. Median power frequency (MPF) shift patterns were analysed to examine muscular fatigue. The muscles in the dorsal part of the trunk were activated at the symmetric posture, while the muscles on the contralateral side to the workload were more strongly activated at the asymmetric posture. Decreasing trends of MPFs were found in some active muscles, and they were more pronounced for the asymmetric posture than for the symmetric posture. It was also seen that the muscles became fatigued faster for the light load-high frequency task than for the heavy load-low frequency task.     

Shoulder posture and localized muscle fatigue and discomfort

In many industries workers perform manual assembly tasks with hands postured above the shoulders. Awkward shoulder and arm postures are often viewed as acceptable given costs of workplace modification, postural exertions which are in compliance with current design recommendations, ready availability of strong workers, and numbers of electromyographic studies which fail to detect significant signs of localized muscle fatigue (LMF). An experiment was conducted to: (a) study the onset and severity of (LMF) in the shoulder when performing a stylus-to-hole Fitts reciprocal movement task under a range of postures, hand loads, ratios of work-to-rest, and task durations, and (b) to evaluate the efficacy of three techniques (i.e., changes in EMG behaviour, postural tremor, and cross-modal matching estimates) in detecting and monitoring posturally-based LMF and discomfort in the shoulder complex. Experimental findings showed that posturing hands above shoulder level significantly increased the risk of LMF and postural discomfort even in light-weight manual assembly environs where postural exertions are small, and that cross-modal matching estimates and postural tremor were more sensitive metrics of LMF in the shoulder complex than EMG RMS voltage and mean spectral power frequency metrics. The basis for experimental findings, as well as potential application of LMF metrics in future postural stress investigations, are discussed. Recommendations for workplace posture are provided for job designers facing work height decisions in manual assembly environs.     

Lifting in stooped and kneeling postures: Effects on lifting capacity,metabolic costs,and electromyography of eight trunk muscles

Twelve healthy, experienced underground coal miners performed lifting capacity tests in stooped and kneeling postures using a modified psychophysical, procedure. Subjects adjusted weight in a lifting box to the maximum they could handle without undue fatigue in an asymmetric lifting task. Lifting periods were 20 min in duration and the frequency was 10 lifts/min. Tests were performed under a 48-in. roof that restricted the subject's posture. Psychophysical, physiological, and biomechanical dependent measures included the maximum acceptable weight of lift (MAWL), heart rate (HR), rate of oxygen consumption (V̇O₂), ventilation volume rate (V̇_E), respiratory exchange ratio (R), and integrated electromyography (EMG) of eight trunk muscles. Results indicated that the MAWL was significantly lower when kneeling than when stooped (p < 0.05). Furthermore, metabolic demands were greater in terms of HR (p < 0.005) and VO₂ (p < 0.05) when kneeling. Left and right erectores spinae muscles exhibited increased EMG activity in the kneeling posture (p < 0.001). It was concluded that psychophysical lifting capacity is decreased, while the metabolic stress and internal load on the spine are increased, in the kneeling posture. Results of this Bureau of Mines study indicate that it may be advisable to reduce the weight of materials that are handled repetitively in the kneeling posture.     

A field comparison of neck and shoulder postures in symptomatic and asymptomatic office workers

Poor neck and shoulder postures have been suggested to be a cause of neck and shoulder pain in computer workers. The present study aimed to evaluate and compare the head, neck and shoulder postures of office workers with and without symptoms in these regions, in their actual work environments. The two all female subject groups reported significantly different discomfort scores across five trials repeated in a single working day. The results of repeated video capture and two-dimensional motion analysis showed that there were trends for increased head tilt and neck flexion postures in the symptomatic subjects (n = 8), compared to the asymptomatic subjects (n = 8). Symptomatic subjects also tended to have more protracted acromions compared with asymptomatic subjects and showed greater movement excursions in the head segment and the acromion. All subjects demonstrated an approximately 10% increase in forward head posture from their relaxed sitting postures when working with the computer display, but there were no significant changes in posture as a result of time-at-work.     

Optimal work-rest cycles for an isometric intermittent gripping task as a function of force, posture and grip span

The aim of this study was to investigate the maximum acceptable contraction frequencies (i.e. work-rest cycles) for an isometric-intermittent handgrip task as a function of grip span, applied force and shoulder posture using psychophysical and physiological approaches. Twelve healthy males served as subjects. The three grip spans investigated were the optimal, 2 cm narrower than the optimal, and 2 cm wider than the optimal. The grip force levels studied were 15% and 30% of maximum voluntary grip force and the two shoulder postures were 25 degrees flexion and 30 degrees abduction. The psychophysical results indicate that subjects work faster with the narrower grip span at 15% of maximum voluntary grip force level in comparison to working with the optimal and the wider spans. However, when the task required 30% of maximum grip force level, the subjects worked faster with the optimal grip span. These findings were supported by the results of electromyography, heart rate, blood pressure and perceived discomfort. The study suggests that grip span of a tool is an important factor to be considered in predicting optimal work-rest cycles for hand grip tasks, and the optimum setting of grip span of the hand-tool depends on the required task force level. That is, the optimality is relative rather than absolute. In addition, it appears that weaker subjects can work at a higher rate than stronger ones at the same relative force level.     

Static and dynamic lifting strength at different reach distances in symmetrical and asymmetrical planes.

Postural and therefore biomechanical standardization in strength testing has not been rigorously and consistently applied. To develop a quantitative relationship between strength and posture (body position, symmetry, and reach) 30 normal subjects (18 male and 12 females) were required to stoop and squat lift or exert in the relevant posture against a standardized instrumented handle. The isometric lifting efforts and isokinetic lifts were studied. The isokinetic lifts were done at a linear velocity of 50cm/s of the hand displacement from the floor to the knuckle heights of the respective subjects in stoop and squat postures. The isometric stoop lifting efforts were exerted in two standardized postures: (a) with 60 degrees hip flexion; and (b) with 90 degrees hip flexion. The isometric squat lifting efforts were also exerted in two standardized postures: (a) with 90 degrees knee flexion; and (b) with 135 degrees knee flexion. All isometric lifting efforts and isokinetic lifts were performed at half, three-quarters, and full horizontal reach in sagitally symmetrical, 30 degrees left lateral, and 60 degrees left lateral planes. Isometric stoop and squat lifting efforts were also measured in self-selected optimal postures. These 56 conditions were tested in random order. The analysis of variance revealed that the gender, the mode of lifting, the postural asymmetry and reach of lifting affected the strength significantly (p less than 0.0001). Most two-way and three-way interactions were significant (p less than 0.01). Of 108 prediction regression equations, 103 were significant with up to 90% of the variation explained by anthropometric variables and sagittal plane strength. The reach affected the strength most profoundly followed by postural asymmetry and the mode of lifting.     

Optimal work–rest cycles for an isometric intermittent gripping task as a function of force,posture and grip span

The aim of this study was to investigate the maximum acceptable contraction frequencies (i.e. work–rest cycles) for an isometric-intermittent handgrip task as a function of grip span, applied force and shoulder posture using psychophysical and physiological approaches. Twelve healthy males served as subjects. The three grip spans investigated were the optimal, 2 cm narrower than the optimal, and 2 cm wider than the optimal. The grip force levels studied were 15% and 30% of maximum voluntary grip force and the two shoulder postures were 25° flexion and 30° abduction. The psychophysical results indicate that subjects work faster with the narrower grip span at 15% of maximum voluntary grip force level in comparison to working with the optimal and the wider spans. However, when the task required 30% of maximum grip force level, the subjects worked faster with the optimal grip span. These findings were supported by the results of electromyography, heart rate, blood pressure and perceived discomfort. The study suggests that grip span of a tool is an important factor to be considered in predicting optimal work–rest cycles for hand grip tasks, and the optimum setting of grip span of the hand-tool depends on the required task force level. That is, the optimality is relative rather than absolute. In addition, it appears that weaker subjects can work at a higher rate than stronger ones at the same relative force level.     

Static and dynamic lifting strength at different reach distances in symmetrica] and asymmetrical planes

Postural and therefore biomechanical standardization in strength testing has not been rigorously and consistently applied. To develop a quantitative relationship between strength and posture (body position, symmetry, and reach) 30 normal subjects (18 male and 12 females) were required to stoop and squat lift or exert in the relevant posture against a standardized instrumented handle. The isometric lifting efforts and isokinetic lifts were studied. The isokinetic lifts were done at a linear velocity of 50cm/s of the hand displacement from the floor to the knuckle heights of the respective subjects in stoop and squat postures. The isometric stoop lifting efforts were exerted in two standardized postures: (a) with 60° hip flexion; and (b) with 90° hip flexion. The isometric squat lifting efforts were also exerted in two standardized postures: (a) with 90° knee flexion; and (b) with 135° knee flexion. All isometric lifting efforts and isokinetic lifts were performed at half, three-quarters, and full horizontal reach in sagitally symmetrical, 30° left lateral, and 60° left lateral planes. Isometric stoop and squat lifting efforts were also measured in self-selected optimal postures. These 56 conditions were tested in random order. The analysis of variance revealed that the gender, the mode of lifting, the postural asymmetry and reach of lifting affected the strength significantly (p<0·0001). Most two-way and three-way interactions were significant (p<0·01). Of 108 prediction regression equations, 103 were significant with up to 90% of the variation explained by anthropometric variables and sagittal plane strength. The reach affected the strength most profoundly followed by postural asymmetry and the mode of lifting.     

Lifting in four restricted lifting conditions: psychophysical, physiological and biomechanical effects of lifting in stooped and kneeling postures

Many underground coal mines are less than 1.2 m in height, and require that manual lifting tasks be performed in restricted postures (usually stooped or kneeling). Unfortunately, little is known about how these postures affect the underground coal miner's capabilities to perform such work. A previous Bureau of Mines study indicated that lifting capacity is greater when stooped than kneeling when lifting under a 1.2 m roof height (Gallagher et al, 1988). However, many low-seam coal mines present even more restricted headroom than 1.2 m. Therefore, a study was conducted to: (1) examine the psychophysical lifting capacity of low-seam coal miners under four restricted lifting conditions, (2) investigate the associated metabolic costs, and (3) analyse the electromyography (EMG) of trunk muscles when lifting in these restricted positions. Subjects were 12 coal miners accustomed to handling materials in restricted postures (mean age = 35.9 yrs +/- 6.4 SD). Results of this study indicated that lifting capacity was greater when the subjects could assume a stooped posture than when kneeling (p < 0.01). Furthermore, the metabolic cost was greater in the kneeling posture for heart rate (p < 0.001), oxygen consumption (p < 0.001), minute ventilation (p < 0.05] ), and respiratory exchange ratio (p < 0.05), despite the fact that miners lifted less weight in this posture. Analysis of the EMG data indicated increased activity of the electores spinae when kneeling (p < 0.001), but higher latissimus dorsi activity when stopped (p < 0.001). The findings of this study indicate that the weight of supply items should be reduced approximately 14-18% when the kneeling posture must be used for lifting.     

Influences of task posture on physiological task responses

This paper reviews selected research on how task posture may effect task demands. It was found that task performance in stooped or nonerect task postures can result in higher task heart rates, metabolic costs, and ratings of discomfort and fatigue. However it was also found that the type of task performed and the effective work rate will have the greatest impact on the subjective, biomechanical, and physiological strains experienced by the worker. Areas needing further research were identified and discussed.     

Objective and subjective responses of seated subjects while reading Hindi newspaper under multi axis whole-body vibration

Train passengers often read newspapers while traveling. Vibration is one of the key factors that may occasionally inhibit this activity. An experimental study was, therefore, conducted to investigate the extent of interference perceived in reading task by seated subjects in two postures under random vibration. 30 healthy male subjects were exposed to vibration magnitudes of 0.4, 0.8 and 1.2 m/s² in mono, dual and multi axis in the low frequency range 1–20 Hz. The task required subjects to read a given paragraph of Hindi national newspaper, in two seated postures (lap posture with backrest support and table posture with leaning over the table). The reading performance was evaluated by both degradation in performance in terms of time required to complete the task and subjective rating using Borg CR10 scale. Both the methods of reading performance evaluation exhibit progressive increase with an increase in vibration magnitude for both the subject postures in all the direction of vibration and are found to be higher in lateral and vertical direction among mono axes. The effects of multi axis vibration on perceived difficulty have been found to be similar to dual axes vibration and greater than mono axes vibration; however degradation in reading performance in multi axis vibration was also found to be similar to that for lateral direction. A comparison of the effect of postures by both evaluation methods revealed that the reading performance was adversely affected for table posture in all direction of vibration, however for lap posture, only the X-axis vibration effect was more severe.

Relevance to industry

Available ride comfort standards for vehicles do not include the effects of vibrations on passenger activities. Assessment of activity discomfort would be useful for vehicle design optimization to facilitate activity comfort.     

Efficiency and effectiveness of stoop and squat lifting at different frequencies

The study investigated the effects of frequency (10 and 20 lifts/min) and technique (squat and stoop) of repetitive lifting of a barbell (19 kg) on the relationship between mean power output (Pm) and energy cost in 9 male power-lifters. Oxygen uptake (VO2) was measured directly and continuously and power output was deduced from film analysis using an inverse dynamic analysis. Power output and VO2 were significantly greater for squat than for stoop lifting at the same frequency. The mechanical efficiency (ME), defined as Pm divided by the energy equivalence of VO2, increased from 12% at rate 10 to 18.5% at rate 20, but there was no significant difference between the two techniques. The effectiveness (EF), defined as the productive external power output (only work done on the barbell) divided by the energy equivalence of VO2, was significantly higher for the stoop lift than for the squat lift. EF is judged as a more useful measure than ME for characterizing the relative energy cost of a lifting task.     

Posture,discomfort and performance in a VDT task

Improvements in workplace, working posture, and discomfort need to be justified in terms of improvements in performance. Previously, a visual inspection task has been investigated. The objective of the current study was to demonstrate the interactions between workplace, work duration, discomfort, working posture, as well as performance in a 2-h typing task. Three levels of keyboard heights were used to change working posture (e.g. joint angles and postural shifts), and thus presumably discomfort (e.g. rating of perceived discomfort and body part discomfort), and performance (e.g. typing speed, error rate and error correction rate). The results indicated that the hypothesized posture-comfort-performance interrelationships were partially supported. Keyboard height had effects on working posture adopted. As in previous studies, the rate of postural shift was a good indication of discomfort in a VDT task. Discomfort and postural shift rate had adverse effects on performance (e.g. error rate). However, these effects on error rate may not be strong.