Showing papers in "Ergonomics in 1986"

The effect of carried loads on the walking patterns of men and women

Abstract: In order to determine the effect of loads worn or carried on walking mechanics, 11 men and 11 women were filmed using high speed cinematography as they performed overground walking at 1·78 m/s under five load conditions. The loads included a baseline condition in which subjects carried no added load, and additional loads of approximately 9, 17, 29 and 36 kg consisting of standard military items. The latter two loads were added in the form of a framed rucksack system. Values for several variables frequently used to described temporal and kinematic characteristics of walking were quantified from the film. These included stride length, stride rate, single leg support time, double-support time, swing time and the forward inclination of the trunk. The results of the study demonstrated that the males and females displayed significantly different gait patterns under all load conditions. Not unexpectedly, the females required a higher rate of stepping than the males because of their shorter stride lengths. The re...

Perception of draught in ventilated spaces

Abstract: One hundred subjects were exposed to air velocities fluctuating in the same manner as in typically ventilated spaces. Each subject, dressed to obtain a neutral thermal sensation, participated in three experiments at an air temperature of 20, 23 and 26°C. In each experiment subjects were sedentary and exposed to six mean air velocities ranging from 0·05 to 0·40m/s. They were asked whether and where they could feel air movement and whether it felt uncomfortable. Based on the results a draught chart (figure 18) has been evolved identifying the percentage of subjects dissatisfied due to draught as a function of the mean velocity and the air temperature. The turbulence of the air flow in real spaces makes people more sensitive to draught than was found in previous studies with laminar flow. A reduction of velocity limits specified in existing standards is required to diminish complaints. The head region was the most draught-sensitive part of the body for persons wearing normal indoor clothing. No significant d...

Wheelchair ergonomics and physiological testing of prototypes.

Abstract: Two hand rim propelled wheelchairs, a daily-use (active) wheelchair (R) and a marathon sports wheelchair (S), were compared to a three-wheeled crank (C) and a (synchronic) lever (L) propelled wheelchair. All wheelchairs were analysed with respect to cardio-respiratory parameters ([Vdot] E, [Vdot] O2 , HR, RER), power output and gross mechanical efficiency during a continuous exercise test (speed of the treadmill V = 0·96 ms-1; every third minute a one degree increase of the slope). Non-wheelchair users (NW: N = 10) were compared to wheelchair sportsmen (WS: N = 3). The cardio-respiratory strain of hand rim propulsion increases more swiftly for both R and S wheelchairs than for the C and L systems. Mechanical efficiency is significantly lower for the hand rim wheelchairs with a remarkably low efficiency for the S wheelchair. The S wheelchair however showed the lowest energy losses and a lower [Vdot]O 2 compared to the R wheelchair, these being important modalities for high speed and long distance ...

Measurement of work and power output using friction-loaded cycle ergometers

Abstract: Friction-loaded cycle ergometers are widely used to measure the work done in short-duration high-intensity exercise. This work is calculated from the product of the average values of flywheel speed and resistive load. This method assumes the flywheel to be revolving at a constant speed and does not take into account the work required to accelerate it. This study examines the possible error resulting from such an assumption. Ten subjects (five males and five females) each performed a single bout of 30 s maximal exercise on a cycle ergometer, from a rolling start, against a resistive loading of 75 g/kg bodyweight. High frequency logging of the flywheel speed was performed by a microcomputer. Two sets of instantaneous and average values of power and work were calculated by the computer at the conclusion of the exercise. The first used the standard method of calculation and did not take into account the acceleration of the flywheel, whereas the second corrected for it. Statistical comparisons of the two sets ...

The efficiency and walking speed of visually impaired people.

Abstract: All pedestrians have a walking speed which they prefer. This appears to be the speed which, for them, is the most physically efficient. Blind pedestrians, if allowed to set the pace when accompanied by a sighted guide, will prefer to walk at a speed which is close to that of sighted pedestrians. However, when walking independently they adopt a pace which is slower than their preferred walking speed. By converting adopted walking speed into a proportion of preferred walking speed we are able to show that subject data may be pooled and comparisons made which had hitherto been impossible. Furthermore, statements may be made about the physiological efficiency of a performance. For example, efficiency varies with route difficulty, increases with increased preview, and only users of guide dogs reach their optimum efficiency.

Postural analysis of the trunk and shoulders in simulated real time.

Abstract: A new method for analysing and describing the posture of the trunk and shoulders was developed and used to describe the posture of workers performing automobile assembly operations. The system used a videotape to create a permanent record of the jobs and a personal computer to perform the clerical and time-keeping tasks associated with posture analysis. In experiments using an experienced analyst to evaluate a videotape, highly reproducible results were obtained. Furthermore, the new system required substantially less time than existing posture analysis methods to analyse and reduce postural data.

Effects of changes in sitting work posture on static neck and shoulder muscle activity.

Abstract: In order to analyse the effect of changing the sitting posture on the level of neck and shoulder muscular activity, an electromyographic (EMG) study of ten healthy experienced female workers from an electronics plant was undertaken. A standardized, simulated task was performed in eight different sitting work postures. Using surface electrodes, the level of muscular activity was recorded as normalized, full-wave rectified low-pass filtered EMG. The results showed that the whole spine flexed sitting posture gave higher levels of static activity in several neck and shoulder muscles than the posture with a straight and vertical spine, which in turn gave higher levels than the posture with slightly backward-inclined thoraco-lumbar spine.

Influence of heat-stress induced dehydration on mental functions

Abstract: The effect of primary dehydration of various levels (1, 2 and 3% body-weight deficits) on mental functions of different complexities were studied in eight heat-acclimatized subjects drawn from tropical regions of India. These subjects were also studied after a bout of exercise in heat under two conditions viz., Hot Dry (45°C DB, 30% rh), and Hot Humid (39DC DB, 60% rh) at 34°C WBGT. No significant change in routine mental work was seen either under dehydration per se of any level or after subsequent exercise under heat when compared with the normal state. On the other hand, at 2 and 3% levels of primary dehydration a further reduction was noted in all the functions though it was not significant. Inter-variations in Hot Humid and Hot Dry conditions were not significant except for more pronounced reductions in the concentration component in Hot Humid conditions.

What attracts attention when driving

Abstract: Twenty-five observers were asked to report what attracted their attention while driving along a 21·9 km route through a suburban district. A second group of equal size made similar reports in the laboratory while watching a movie film of the same route. The results obtained from the laboratory trial closely parallelled those obtained in the field and it is concluded that laboratory studies using a movie simulation provide a satisfactory means of studying the distribution of attention using a concurrent verbal report technique. It is noted that the absence of a driving task has no substantial effect on attentive behaviour suggesting that the visual information presented by the movie film is sufficient to generate attentive processes characterstic of driving. It is found that advertising attracts a good proportion of attention but in those sections of the route where there was little advertising attention was directed to an even greater extent to other objects not related to driving. It seems that some 30 t...

Load moments and myoelectric activity when the cervical spine is held in full flexion and extension

Abstract: Sustained joint load in extreme positions (namely maximally flexed or extended positions) has been described as causing pain. The aim of the present study is to analyse eight different sitting work postures with respect to extreme positions, and to assess the mechanical load and the levels of muscular activity arising in defined extreme positions of the cervical spine. Ten healthy female workers from an electronics plant took part in laboratory experiments. For seven of these, levels of neck and shoulder muscular activity in sitting postures with the cervical spine in different manually-adjusted extreme positions were recorded using surface electrodes. Loading moments of force about the bilateral motion axis of the atlanto-occipital joint (Occ-C1) and the spinal cervico-thoractc motion segments (C7-T1) were calculated. Extreme or almost extreme positions occurred in sitting postures with the thoracolumbar back inclined slightly backwards or with the whole spine flexed. Electromyographic (EMG) act...

Discomfort and load on the upper trapezius muscle when operating a wordprocessor.

Abstract: Surface electromyogram recordings from the descending part of the trapezius muscle and discomfort ratings were assessed for six female VDT wordprocessor operators during their work. Each operator was studied during three work periods of 3 to 5 hours on different days. During one of the work periods, short pauses (15 s) were introduced every sixth minute. A static local muscular load of 32 and 30% of the maximal voluntary contraction was found on the right and the left side, respectively. The median and peak muscular loads during work were low. There was a significant negative correlation between pauses and static load on the right upper trapezius muscle. The rating of perceived discomfort was less after the work periods with short pauses than after the work periods without.

The motion of a ship at sea and the consequent motion sickness amongst passengers.

Abstract: Measurements were made of the motion of a ship, and of the consequent seasickness experienced by passengers Data are presented for 17 voyages of up to 6 hours duration, involving 4915 passengers Vertical motion occurred up to 1·0 m s−2 rms and vomiting incidence of up to nearly 40% was encountered Both vomiting incidence and illness rating correlated well with root mean square vertical z-axis acceleration The effect of exposure duration was also investigated, producing suggestions for a combined measure of acceleration and time Multiple regression analysis with all six axes of motion revealed only a small increase in correlation when all directions of motion in addition to the z-axis were taken into account

Maximum acceptable weights and maximum voluntary isometric strengths for asymmetric lifting

Abstract: A laboratory study was conducted to determine the effects of asymmetric lifting on psychophysically determined maximum acceptable weights and maximum voluntary isometric strengths. Thirteen male college students lifted three different boxes in the sagittal plane and at three different angles of asymmetry (30,60 and 90°) from floor to an 81-cm high table using a free-style lifting technique. For each lifting task, the maximum voluntary isometric strength was measured at the origin of lift. The maximum acceptable weights and the static strengths for asymmetric lifting were significantly lower than those for symmetric lifting in the sagittal plane for three box sizes (P<0·01). The decrease in maximum acceptable weight and static strength from the sagittal plane values increased with an increase in the angle of asymmetry (P < 0·01). Box size had no significant effect (P≥ 0·05) on the percentage decrease in maximum acceptable weight or voluntary isometric strength from the sagittal plane values. Correction fac...

Treadmill versus walkway locomotion in humans: an EMG study.

Abstract: A descriptive comparative study was done to validate the use of the treadmill as an experimental device to investigate the electromyographic (EMG) signal during human locomotion. Eight subjects walked on a walkway and on a treadmill and EMG recordings of several consecutive strides were made during each procedure. These recordings were made from the soleus, rectus femoris, biceps femoris, vastus medialis and tibialis anterior muscles. By using the correlation coefficient and the value of the slope of the regression line resulting from correlating the linear envelopes (digitized at 50 Hz) of EMG activity from the two walk modes, it was shown that similar profiles of EMG activity exist between the walkway and treadmill. This was so for most muscles investigated with one exception, the biceps femoris. Furthermore, there was a tendency for the treadmill data to indicate slightly larger EMG amplitudes, but lower variation, than did the walkway data. However, in view of the overall similarity of the profiles ob...

Evaluation of foot swelling and lower-limb temperatures in relation to leg activity during long-term seated office work.

Abstract: Seven healthy females were studied during three experimental days, each comprising 8 hours of seated office work at different well-defined levels of leg activity. The mean foot swelling was 4·8% in the case of no leg activity (‘inactive sitting’), 2·3% when the legs were moved freely (‘ semi-active sitting’) and 0·8% at the highest activity level (‘active sitting’). The activity of the soleus muscle was evaluated by EMG and discussed in relation to the function of the musculovenous pump. The decrease in skin temperature (Tsk ) of the foot and lower leg was completed after half the working day, and on average it was 4·6°C/2·8°C (foot) and 3·3°C/l·6°C (lower leg) during ‘inactive sitting’/‘active sitting’. The mean temperature in the flexor hallucis longus muscle (Tm ) decreased by 3·7°C during the 8 hours of ‘inactive sitting’, but was almost constant during ‘active sitting’. The discomfort of the lower leg and foot was significantly correlated to foot swelling and Tm , but not to Tsk . The mean heart rate...

Relation between time to falling asleep behind the wheel on a closed track and changes in subsidiary reaction time during prolonged driving on a motorway

Abstract: Twelve subjects drove on a closed 5-km track until they fell asleep behind the wheel or quitted for other reasons. The instances of falling asleep occurred after 7 to 12 hours of driving. Falling asleep could be characterized by nodding of the head, closing of the eyes and the car continuing in its previous course. On none of these occasions did the experimenter have to take over the control of the car and all subjects woke by themselves. The average duration between three instances of falling asleep was 24 min. After a break with a brisk walk the subjects fell asleep again after an average of 23 min. Two preceding sessions of 3 hours of driving on a motorway with subsidiary reaction time measurements predicted (r= — 0·72 and —0·17) the endurance on the closed track.

Effect of work intensity on performance in a psychomotor task during exercise.

Abstract: The influence of work intensity on performance in a psychomotor task was examined using 10 male subjects. The experiment involved a 60s pursuit rotor task during both the 4th and 6th min of cycling at zero resistance and at 25,40,55,70 and 85% V˙O2 max. A curve of the inverted-U form was found to fit the performance data significantly (p<0·05). The mean optimal loading was calculated to occur at a moderate work intensity of 38% V˙O2 max. The results have implications for activities where psychomotor tasks are superimposed on a requirement for high muscular power output levels.

Psychophysical and physiological responses to lifting symmetrical and asymmetrical loads symmetrically and asymmetrically.

Abstract: Eighteen adult males (mean age 22·6 years, weight 78·6kg and height 176·6cm) participated in a study designed to investigate the effects of symmetrical and asymmetrical lifting on the maximum acceptable weight of lift and the resulting physiological cost. Each subject performed sixty different lifting tasks involving two lifting heights, three lifting frequencies and five containers. For each lifting task, the load was lifted either symmetrically (sagittal lifting) or asymmetrically (turning 90° while continuing to lift). The heart rate and oxygen uptake of the individuals at the maximum acceptable weight of lift were measured. At the end of the experiment, subjects also verbally indicated their preference for symmetrical and asymmetrical lifting. When lifting asymmetrically, subjects accepted approximately 8·5% less weight. There was, however, no difference in the physiological costs when lifting symmetrically or asymmetrically. Lifting asymmetrical loads also resulted in lower maximum acceptable weights...

Vibration and comfort: vertical and lateral motion in the range 0.5 to 5.0 Hz.

Abstract: Three experiments have been conducted to determine the effects of the frequency of whole-body vibration on comfort in the range 0·5–5·0 Hz. With vertical sinusoidal vibration the responses of 40 subjects (20 males and 20 females) were determined at two vibration magnitudes for each of the 11 preferred third-octave centre frequencies from 0·5ndash;5·0Hz. The responses of a subgroup of 10 male subjects to octave bands of vertical random vibration centred on 0·5,10, 2·0 and 40 Hz were determined in the second experiment. Twenty male subjects participated in the third experiment with lateral sinusoidal vibration in the 0·5–5·0 Hz range. The results have been compared with the findings of earlier experiments and the current International Standard. It is concluded that with vertical motion there were small differences between the responses of male and female subjects. There was little effect of vibration magnitude on the frequency dependence of vibration discomfort. Random vibration produced slightly greater di...

Shiftwork, stress, and psychosomatic complaints: a comparison between workers in different shiftwork schedules, non-shiftworkers, and former shiftworkers

Abstract: In a questionnaire study of 3446 blue-collar male workers in the chemical industry of the Federal Republic of Germany, shift- and non-shiftworkers were compared for reported health and stress at work. There were three groups of non-shiftworkers: former shiftworkers who left shiftwork because of a physician's advice, former shiftworkers who were not so advised, and never-shiftworkers. Both shiftworkers and former shiftworkers who left for health reasons showed a higher degree of reported ill health than never-shiftworkers and former shiftworkers who had left for other reasons than health. The results are consistent when stress at work and other potentially confounding factors are controlled. However, stress at work is an important predictor of ill health independent of shiftwork. Furthermore, a rapidly rotating 12-hour shift system (rotating every 2 to 3 days) as compared with a slower rotating 8-hour shift system (rotating every 5 to 7 days) showed no significant differences in workers' ill health when st...

Evaluation of forces on the lumbo-sacral joint and assessment of work and energy transfers in nursing aides lifting patients.

Abstract: Tasks associated with patient handling may present nursing aides with some risk of injuring the lumbar spine. The purpose of this study was to estimate the forces at L5/S1 and to assess mechanical work and energy transfers in a task consisting of raising a patient (a 72·6thinsp; kg manikin) from a chair using three different methods: (A) with the hands; (B) with the forearms behind the patient's back at shoulder level; and (C) with a belt held at waist level. Six male subjects took part in the experiment. Spinal forces were estimated from a static and planar mathematical model used in conjunction with cinematography techniques, a force platform and EMG recordings. External forces and the internal forces (compression and shear at L5/S1) were determined from free-body diagrams and static equations. The model was analysed for its sensitivity in estimating patterns of EMG forces, intra-discal and musculo-ligamentous forces, intra-abdominal pressure and inertial forces. The model was found to discriminate betw...

Reliability of the psychophysical approach to manual lifting of liquids by females.

Abstract: The psychophysical method for setting lifting standards was evaluated by having seven, female college students lift at four diiferent frequencies (1, 3, 6 and 12 lifts min−1). Only one lifting session was performed in a 24 hour period. During the 4 hour lifting task, subjects were asked to select the amount of water that they believed they could lift comfortably for 8 hours. Subjects were encouraged to make as many weight changes as they needed. Each time the weight was changed the carton was weighed and the time was recorded. At 15 min intervals, subjects were asked about their degree of confidence (DOC) that the current weight was the maximum acceptable one for an 8 hour shift. Oxygen consumption was measured at 30,120 and 240 min of the task. The weights chosen by the subjects at 30 min did not differ significantly from the 4 hour values for frequencies of 1, 3 and 6 lifts min−1. However, at 12 lifts min−1 the weight decreased with time such that the 4 hour value was 23% lower than the weight chosen af...

The effects of lunch on cognitive vigilance tasks.

Abstract: An experiment was carried out to investigate the effects of lunch on cognitive vigilance tasks. Subjects who ate lunch prior to testing detected fewer targets in a paced, successive comparison task, but did not show impaired performance on a proportion perception task. The experiment also demonstrated some differences between morning and afternoon performance in subjects who abstained from eating lunch. This shows that performance changes observed in the early afternoon may be attributed to at least two components. The first of these is meal-dependent, whereas the second is endogenous, and occurs even when lunch is not consumed.

The energy cost of women walking and running in shoes and boots.

Abstract: The purpose of this study was to determine the difference in energy cost for women walking and running in shoes versus heavier boots. Seven subjects wore athletic shoes (mean weight = 514 ± 50g) and leather military boots (mean weight = 1371 ± 104g) at three walking speeds (4·0, 5·6 and 7·3km/hour) and two running speeds (8middot;9 and 10·5 km/hour). During each walking and running trial oxygen uptake ([Vdot]O2 ml kg−1 min−1) was measured. The [Vdot]O2 for women wearing boots were significantly higher (P < 0·05) than for shoes for both walking and running, with the exception of the slowest walking speed. The average increment in energy cost was 1·0% per 100-g increase in weight per pair of footwear. These results are similar to those reported for men from other studies which found increments in energy cost of 0·7 to 0·9% per 100-g increase in weight of footwear.

Energy cost of backpacking in heavy boots.

Abstract: Previous studies have investigated the oxygen cost ([Vdot]02) of increasing boot weight during unloaded walking or running, and have shown that for each 100 g increase in weight of footwear there is a 0·7-1·0% increase in [Vdot]O2 In reality (except in athletic events) the use of heavy footwear is associated with load carriage, usually backpacking. We therefore investigated the effects of increasing boot weight by 5% of body weight on the [Vdot]02 of backpacking a load amounting to 35% of the body-weight in five healthy young males who walked at 4·5 km/hour (0% grade) on a motor-driven treadmill. The results indicated a mean increase of 0·96% in [Vdot]02 whilst backpacking for each 100thinsp;-g increase in boot weight. In contrast the oxygen cost of increasing the backpack load was only 0·15% indicating that it was 6·4 times more expensive to carry weight on the feet as compared to the back. It is concluded that the relation between boot weight and oxygen cost, previously developed for unloaded walking an...

Cognitive abilities and safety on the road: A re-examination of individual differences in dichotic listening and search for embedded figures.

Abstract: Five cognitive ability tests were administered to a sample of 153 bus-driver trainees. The embedded figures test (EFT) of Witkin (1950) and the dichotic listening test (DLT) of Gopher and Kahneman (1971) were chosen on the basis of previously reported correlations with driving accident rate. The remainder were designed to cast light on what cognitive processes the EFT and DLT measure, and hence why they should relate to driving ability. The EFT correlated only marginally with success in driver training and with accident rate in a follow-up period of two years. There was no support for the hypothesis that this test measures a general ability to resist the influence of dominant stimuli. Instead a substantial correlation (0·64) was obtained with a typical ‘intelligence’ test. The DLT showed no correlations with driver performance measures, thus failing to replicate earlier findings. There was no support for the hypothesis that this test measures a general ability to switch from one task or mental set to anot...

Acute impairment of the sensitivity of skin mechanoreceptive units caused by vibration exposure of the hand.

Abstract: The thresholds of single mechanoreceptive afferent units, innervating the glabrous skin of the human hand to sinusoidal skin indentations at 2, 20 or 200 Hz were measured before and after 2 min powerful vibration exposures at the same frequencies. The corresponding psychophysical thresholds were measured in collateral experiments while still monitoring the unit responses. An acute but temporary rise in threshold occurred as a consequence of the vibration exposure in three different unit types (FA I, FA II and SA I). A close correlation was found between the neural and psychophysical thresholds with regard to the magnitudes of the shifts and the time courses of the recovery, provided that the thresholds were measured at the appropriate frequencies (i.e. at 200, 20 and 2 Hz while recording from FA II, FA I and SA I units, respectively). It was concluded that the acute impairment of tactile sensibility caused by vibration exposure, as earlier observed in psychophysical studies, most likely can be explained b...

A study stressing the need for a static postural force model for work analysis.

Abstract: The maximum endurance time (MET) in static force exertions was used as a parameter for the assessment of five working postures. By applying the methodology of Rohmert to the construction of a general model for static muscular work and evaluating the measured MET results, the need for a new static posture model has been shown. The aim of the present pilot study was to test MET in load situations that would indicate when the general model can be used or when a new static postural force model is needed. Subjects exerted static postural forces at different load levels until exhaustion. In the first two postures, the strain was concentrated on the upper limbs, where active forces (muscular) play a key-role and justify the use of the model. In the remaining postures, the strain affected mainly the back/trunk, where the mechanical equilibrium of the body is brought about by active (muscles) and passive (skeleton and ligaments) structures. During the tests electromyographic (EMG) measurements of selected muscles ...

Cognitive networks as a guide to menu organization: An application in the automated cockpit

Abstract: When a menu-driven interface controls information in the domain of expertise of the end users, the difficulty that inexperienced users typically have in accessing the panels they seek can be reduced by making the menu organization consistent with the user's cognitive organization. A general tool for deriving a cognitive network is described and applied to the concepts displayed and controlled on the panels of an interface to a flight management system. The cognitive network was used to select the options that would appear on each panel of three different prototypes. The prototypes differed with respect to the amount of redundancy (extra pathways) between a set of dominating panels that appeared on a primary index page and the remaining panels. A fourth prototype was based on the recommendations of a design team rather than the cognitive network derived from a sample of pilots. Four pilots were assigned to each of the four prototypes, in a training session that required the pilots to find specific...