Filling 'gaps' in strength data for design

Data on the physical strength capabilities of users are fundamental to the safe and usable design of products. It is recognised, however, that there are many 'gaps' in the ergonomics data available to designers. Whilst considerable research on human capabilities and limitations has already been carried out, few data exist which are directly applicable in the design process. This paper describes a two-stage research project which was undertaken to try to address some of these data 'gaps'. Potential needs for design-relevant data were identified in Stage 1 of the research and in Stage 2 new data were collected to meet some of those needs. Data were collected on children through to the older adult on a series of six strength measurements, all of which were intended to be directly applicable to design: (1) finger push strength, (2) pinch-pull strength, (3) hand grip strength, (4) wrist-twisting strength, (5) opening strength, and (6) push and pull strength. The methodology, findings and data from this research are presented and discussed.     

Multibody modeling of human body for the inverse dynamics analysis of sagittal plane movements

A multibody methodology for systematic construction of a two-dimensional biomechanical model of a human body is presented, aimed at effective determination of the muscle forces and joint reaction forces in the lower extremities during sagittal plane movements such as vertical jump, standing long jump or jumping down from a height. While the hip, knee and ankle joints are modeled as enforced directly by the muscle forces applied to the foot, shank, thigh and pelvis at the muscle attachment points, the actuation of the other joints is simplified to the torques representing the respective muscle action. The developed formulation is applicable to both the flying and support phases, enhanced by an effective scheme for the determination of reaction forces exclusively in the lower extremity joints. The determination of reactions from the ground is also provided. The problem of muscle force redundancy in the lower extremities is solved by applying the pseudoinverse method, with post-processing procedures used to assure the muscle being tensile. Results of the inverse dynamics analysis of vertical jump are reported.     

Differences in lifting strength profiles between experienced workers and novices at various exertion heights

This study compared lifting strength patterns between experienced workers and novices at various exertion heights. Twenty-one experienced workers and 21 novices were recruited to determine their static-lifting strength under various heights (10-150 cm in increments of 10 cm) using two exertion methods (vertically upward lifting, VUL, and toward body lifting, TBL). Testing posture was also recorded by a motion analysis system for comparing with the corresponding strength values.Results showed that strength during VUL were much higher than strength during TBL at 15 height positions (p < 0.001). Strength in all 30 task combinations showed no difference between the two groups except for the VUL at heights of 100-120 cm. On the average, strength exerted by novices during VUL was 4.57-7.61 kg lower than that of workers while lifting at 100-120 cm heights (all p < 0.05). The strength during TBL consistently decreased with increased heights of lifting. When workers performed VUL, the strength surprisingly remained nearly unchanged throughout the heights of interest. The postures adopted by workers during VUL were also highly differentiated from novices while performing near-floor positions, but the strength was equivalent to each other. This study demonstrated that the static-lifting strength of novices were significantly lower than those of experienced workers while upward lifting near the participant’s elbow height. It was concluded that workers tend to adopt a safer (i.e., more flexed knees) and more skillful technique than novices to generate forces, resulting in lower spinal loads during both methods of lifting.

Relevance to Industry

Many studies have established the human strength data based on student participants who do not have experience in manual materials handling. The present findings clearly suggest that lifting strength data collected on novices (e.g., on students) should be carefully applied in the task (re)design at the workplace as their strength profiles and the postures adopted during lifting differ from workers.     

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.     

Gender differences in hand stability of normal young people assessed at low force levels

To examine gender differences in hand stability, finger position and force holding tasks at low force levels were conducted with 30 male and 30 female young adults. Total fluctuation was defined as the standard deviation of measured data and fluctuation and the 10-Hz component of the physiological tremor were compared between maleand female subjects. In all tasks, the total fluctuation and the 10-Hz tremor were significantly larger in male subjects than females. On average, the fluctuation was 1.3 times larger and the 10-Hz tremor was 1.6 times larger. The results of this study suggest that women have superior hand stability compared with men at low force levels. Finger length, maximal voluntary contraction and surface electromyography were also measured and factors related to gender differences in hand stability are discussed. STATEMENT OF RELEVANCE: Hand stability is crucial for precise manual operations. This study demonstrated gender differences in hand steadiness at low force levels. Though hand dexterity cannot be explained only by hand stability, the results of this study are useful not only for occupational aptitude tests but also for neuropsychological tests.     

Vector representations of human strength in whole body exertion

This paper summarises a number of studies of human strength in tasks of static whole body exertion. Measurements were made using a transducer bar which allowed the simultaneous recording of the vertical and horizontal components of any force applied to it by the subject. In each experimental condition, each subject exerted his or herself in all directions in the sagittal plane (ie, that plane which bisects an individual in the antero-posterior direction). Thirty conditions were investigated. Five heights of the bar above the ground, ranging from 1.75 m to 0.25 m, were tested. Various constraints were imposed upon the placement of the subjects' feet. In some conditions a 'ceiling' or 'wall' confined the subject. The results are presented in the form of diagrams which show the magnitude and direction of all possible force vectors in the sagittal plane.     

Effects of an electric blanket on sleep stages and body temperature in young men

The aim of this study was to investigate any effects of electric blanket on sleep stages and body temperature. Nine male subjects slept under two conditions: using the electric blanket (HB); and not using the electric blanket (C). The ambient condition was controlled at 3°C relative humidity 50?–?80%. Electroencephalography, electrooculography (EOG) and electromyography, rectal temperature, skin temperature and microclimate temperature and humidity were recorded continuously through the night. Body weight was measured before and after sleep. The amount of stage 1 and number of stage 1 and rapid eye movement sleep decreased in HB compared to C. No significant difference was observed in other sleep stages. Rectal temperature was higher in HB compared to C. The thigh, leg and foot skin temperature was higher in HB than C. The microclimate temperature of the foot area was higher in HB compared to C. No significant difference was observed in whole body sweat loss between the conditions. These results suggest that use of an electric blanket under low ambient temperature may decrease cold stress to support sleep stability and thermoregulation during sleep.     

Estimating the angular velocity of a rigid body moving in the plane from tangential and centripetal acceleration measurements

Two methods are available for the estimation of the angular velocity of a rigid body from point-acceleration measurements: (i) the time-integration of the angular acceleration and (ii) the square-rooting of the centripetal acceleration. The inaccuracy of the first method is due mainly to the accumulation of the error on the angular acceleration throughout the time-integration process, which does not prevent that it be used successfully in crash tests with dummies, since these experiments never last more than one second. On the other hand, the error resulting from the second method is stable through time, but becomes inaccurate whenever the rigid body angular velocity approaches zero, which occurs in many applications. In order to take advantage of the complementarity of these two methods, a fusion of their estimates is proposed. To this end, the accelerometer measurements are modeled as exact signals contaminated with bias errors and Gaussian white noise. The relations between the variables at stake are written in the form of a nonlinear state-space system in which the angular velocity and the angular acceleration are state variables. Consequently, a minimum-variance-error estimate of the state vector is obtained by means of extended Kalman filtering. The performance of the proposed estimation method is assessed by means of simulation. Apparently, the resulting estimation method is more robust than the existing accelerometer-only methods and competitive with gyroscope measurements. Moreover, it allows the identification and the compensation of any bias error in the accelerometer measurements, which is a significant advantage over gyroscopes.     

Biomechanical analysis of materials handling manipulators in short distance transfers of moderate mass objects: joint strength,spine forces and muscular antagonism

Although often suggested as a control measure to alleviate musculoskeletal stresses, the use of mechanical assistance devices (i.e. manipulators) in load transfers has not been extensively studied. Without data describing the biomechanical effects of such devices, justification for decisions regarding implementation of such tools is difficult. An experimental study of two types of mechanical manipulators (articulated arm and overhead hoist) was conducted to determine whether biomechanical stresses, and hence injury risk, would be alleviated. Short distance transfers of loads with moderate mass were performed both manually and with manipulator assistance under a variety of task conditions. Using analysis and output from new dynamic torso models, strength demands at the shoulders and low back, lumbar spine forces, and lumbar muscle antagonism were determined. Strength requirements decreased significantly at both the shoulders and low back when using either manipulator in comparison with similar transfers performed manually. Peak spine compression and anteriorposterior (a-p) shear forces were reduced by about 40% on average, and these reductions were shown to be primarily caused by decreases in hand forces and resultant spinal moments. Two metrics of muscular antagonism were defined, and analysis showed that torso muscle antagonism was largest overall when using the hoist. The results overall suggest that hoist-assisted transfers, although better in reducing spine compression forces, may impose relatively higher demands on coordination and/or stability at extreme heights or with torso twisting motions. The relatively higher strength requirements and spine compression associated with the articulated arm may be a result of the high inertia of the system. Potential benefits of practice and training are discussed, and conclusions regarding implementation of mechanical manipulators are given.     

The influence of moving auditory stimuli on standing balance in healthy young adults and the elderly

The maintenance of postural balance depends on effective and efficient feedback from various sensory inputs. The importance of auditory inputs in this respect is not, as yet, fully understood. The purpose of this study was to analyse how the moving auditory stimuli could affect the standing balance in healthy adults of different ages. The participants of the study were 12 healthy volunteers, who were divided into two age categories: the young group (mean = 21.9 years) and the elderly group (mean = 68.9 years). The instrument used for evaluation of standing balance was a force plate for measuring body sway parameters. The toe pressure was measured using the F-scan Tactile Sensor System. The moving auditory stimulus produced a white-noise sound and binaural cue using the Beachtron Affordable 3D Audio system. The moving auditory stimulus conditions were employed by having the sound come from the right to left or vice versa at the height of the participant's ears. Participants were asked to stand on the force plate in the Romberg position for 20 s with either eyes opened or eyes closed for analysing the effect of visual input. Simultaneously, all participants tried to remain in the standing position with and without auditory stimulation that the participants heard from the headphone. In addition, the variables of body sway were measured under four conditions for analysing the effect of decreased tactile sensation of toes and feet soles: standing on the normal surface (NS) or soft surface (SS) with and without auditory stimulation. The participants were asked to stand in a total of eight conditions. The results showed that the lateral body sway of the elderly group was more influenced than that of the young group by the lateral moving auditory stimulation. The analysis of toe pressure indicated that all participants used their left feet more than their right feet to maintain balance. Moreover, the elderly had the tendency to be stabilized mainly by use of their heels. The young group were mainly stabilized by the toes of their feet. The results suggest that the elderly may need a more appropriate stimulus of tactile and auditory sense as a feedback system than the young for maintaining and control of their standing postures.     

Changes in the body size of UK and US children over the past three decades

The major sources of published anthropometric data on children are now over two decades old. Due to concern being expressed regarding the continued validity of such data, changes in the body sizes of the UK child population over the past three decades have been considered. Comparisons were also made between the size of the current UK child population to the current US child population, and to the most comprehensive source of measured data on US children (but which are now over 20 years old). The growth of children in the UK and US over the past three decades was assessed for an indication of secular growth trends. Stature increases were found to have generally been less than body weight increases (as a percentage) at 5th percentile, mean and 95th percentile levels for UK children, and UK children were found to be closer in size to US children now than they were 30 years ago.     

Comparison of three satellite sensors at three spatial scales to predict larval mosquito presence in Connecticut wetlands

Satellite imagery can be used to identify suitable habitat for mosquitoes in areas inaccessible or lacking sufficient ground-based information about the environment but current applications are limited by the spatial and spectral resolution of the sensors. Here, models used to compare prediction of the presence of Anopheles punctipennis larvae in Connecticut wetlands were built using stepwise logistic regression and compared by Akaike's Information Criterion (AIC). Vegetation indices were extracted from three satellite sensor scenes (Hyperion, ASTER and Landsat-TM) at three scales (pixel, wetland perimeter, and wetland area). The best models were developed using ASTER (ROC = 0.80, p = 0.01, AIC 65.37) and Hyperion (ROC = 0.81, p < 0.01, AIC 66.40) at the wetland area level. The Disease Water Stress Index (DWSI), a measure of leaf water content, and Normalized Difference Vegetation Index (NDVI) were significant in many of the models. This comparison of satellite based models demonstrates higher spatial and spectral resolution of ASTER and Hyperion resulted in more parsimonious models than Landsat-TM models. The need for continued research and development into sensors with increased spatial and spectral resolution and the development of mosquito specific indices is discussed.     

DEXA-assessed regional body composition changes in young female military soldiers following 12-weeks of periodised training

Dual-energy X-ray absorptiometry (DEXA) was used to assess whole body and regional soft tissue mass, fat mass and lean body mass compositional changes in 68 female recruits (age 20.8 ± 1.14 years; body mass 59.5 ± 8.79 kg; stature 159.57 ± 5.53 cm) pre- and post 12-weeks of military basic training. A decrease in total body fat tissue mass (10.2%) and regional percent fat (10.9%) was measured with an increase in total lean body mass (8.7%). Of interest were the differences in the responses in the tissue composition of the arms (16.2% loss in fat mass with an 11.6% gain in lean mass), trunk (17.0% decrease in fat mass with a 10.4% increase in lean mass) and the legs (10.5% increase in lean mass but no change in fat mass). These findings show the importance of considering regional rather than whole body composition changes when assessing the effects of a training programme.

Statement of Relevance: Female soldiers experienced a change in total body fat tissue (?10.2%) and lean body mass (+8.7%) after basic training; however, no significant fat mass decrease was evident in the leg region. Regional rather than whole body composition changes need to be considered when assessing the effects of a training programme.     

高校计算机专业开设“RFID技术与应用”课程的探索与尝试

无线射频识别(简称RFID)技术是目前最具发展前景的自动识别技术之一,已经在社会众多领域呈现出广阔的应用前景。本文首先对计算机专业引入RFID技术与应用课程的目的与意义进行了阐述,然后对我院开设"RFID技术与应用"专业选修课的探索与尝试作了介绍。     

Vibration-reducing gloves: transmissibility at the palm of the hand in three orthogonal directions

Vibration-reducing (VR) gloves are commonly used as a means to help control exposures to hand-transmitted vibrations generated by powered hand tools. The objective of this study was to characterise the vibration transmissibility spectra and frequency-weighted vibration transmissibility of VR gloves at the palm of the hand in three orthogonal directions. Seven adult males participated in the evaluation of seven glove models using a three-dimensional hand–arm vibration test system. Three levels of hand coupling force were applied in the experiment. This study found that, in general, VR gloves are most effective at reducing vibrations transmitted to the palm along the forearm direction. Gloves that are found to be superior at reducing vibrations in the forearm direction may not be more effective in the other directions when compared with other VR gloves. This casts doubts on the validity of the standardised glove screening test.

Practitioner Summary: This study used human subjects to measure three-dimensional vibration transmissibility of vibration-reducing gloves at the palm and identified their vibration attenuation characteristics. This study found the gloves to be most effective at reducing vibrations along the forearm direction. These gloves did not effectively attenuate vibration along the handle axial direction.     

Performance of glucose biosensor based on oxygen electrode in physiological fluids and at body temperature

A potentially implantable glucose biosensor for continuous monitoring of glucose levels in diabetic patients has been developed. The glucose biosensor is based on an amperometric oxygen electrode and glucose oxidase immobilized on carbon powder held in the form of a liquid suspension. The enzyme material can be replaced (the sensor recharged) without sensor disassembly. Diffusion membranes made of silastic coatings over a microporous polycarbonate membrane are used. Calibration curves of the sensors in phosphate buffer solution and in undiluted blood plasma at body temperature have been obtained. The reproducibility of the sensor response in serum at body temperature is demonstrated. The sensors have a stable signal during storage and continuous operation at body temperature for a period of at least one month.     

Effects of social and technology overload on psychological well-being in young South Korean adults: The mediatory role of social network service addiction

This study examined the effects of social and information technology overload on psychological well-being. It also explored the mediating role of social network service (SNS) addiction in the hypothesized relationships between these variables. A sample of 419 college students and employees in their 20s and 30s, who were SNS users in South Korea, participated in the study. The results showed that social and information technology overload did not exert a direct impact on psychological well-being. SNS addiction served as a mediator in the relationships between these variables. The theoretical contributions and useful managerial implications of the study, with respect to reducing SNS users' addiction and improving their psychological well-being, were described.     

Personality and media influences on violence and depression in a cross-national sample of young adults: Data from Mexican-Americans, English and Croatians

The issue of potential media effects on psychological health of youth and young adults has been debated for decades. Research on media effects has not always been consistent. One issue that has been raised regards whether the relatively modest media effects found in some research might be explained through mediating personality variables. This hypothesis was examined in three samples of young adults: Mexican-Americans (n = 232), Croatians (n = 455) and English (n = 150). Results indicated that trait aggression was a consistent predictor of both violent crimes and depression across samples. General personality variables were less consistent predictors of violence, although neuroticism consistently predicted depression across samples. Media violence exposure did not predict negative outcomes except among Croatians for whom exposure to violent video games predicted fewer violent crimes, and exposure to television violence predicted increased violent crimes.     

Physiologic responses during rest on a sleep system at varied degrees of firmness in a normal population

This study explores the hypothesis that a high degree of sustained muscle activity associated with a sub-optimal spinal orientation may compromise an individual's ability to relax or initiate sleep. Data from 22 participants who were considered to be part of a normal, back-pain-free population were used in these studies. Participants laid down on a mattress in a foetal position (i.e. on their sides) at three varying bed pressures while EMG activities, heart rates, blood pressures, subjective comfort levels and spinal alignment data were recorded. Minor e^ffects of mattress inflation pressures were associated with changes in EMG activity, heart rate, blood pressure and/or subjective comfort. In contrast, spinal alignment assessment revealed significant di^fferences between the three di^fferent inflation pressures studied (827.4, 2413.2 and 3999.0 Pa). It was concluded that in a population of normal participants, although mattress inflation pressure induced significant changes in spinal alignment, these changes were of little physiological consequence. Nevertheless, this data provides baseline information needed to assess similar correlations in a symptomatic population (e.g. those with either acute or chronic neck or back pain).