Subjective estimates of one-handed carrying tasks

In this study, ten male and five female subjects, ranging between 21 and 23 years in age and in excellent physical health, voluntarily participated. Four different shapes of containers, 8·5 and 12·3 litres in capacity, were used to carry loads for distances of 100, 200, and 300 ft (30·48, 60·96, and 91·44 m, respectively). Individuals first subjectively estimated how much weight they could carry in a given type of container for the required distance and then verified it by actual carrying. The preferred (stronger) hand was used to hold the containers. In addition to the weight acceptable for comfortable carrying, pulse rate and ratings of perceived exertion (RPE) of the arm and whole body were also used as response measures. Results indicated that subjects could quite accurately estimate the amount of weight they could carry comfortably in one hand. RPE for one-handed carrying tasks was not one-tenth of the pulse rate as is the case for whole body tasks. The average pulse rate was 100 beats/min for the weights selected. Shape of the containers significantly influenced the amount of weight subjects were willing to carry in one hand. The acceptable amount of weight decreased with distance, but was found to increase with volume.     

An experimental evaluation of psychophysical criteria for repetitive lifting work

Two experiments were performed to test the reliability and validity of psychophysically determined maximum acceptable workloads for setting lifting standards. The perceived workload in a repetitive diagonal lifting task was found to be a positively accelerated function of the weight lifted and of the work pace respectively. A twofold increase in objective workload resulted in a four- to fivefold increase in perceived workload. This relation was independent of previous occupational experience of lifting work. The psychophysically assessed maximum acceptable workloads for this type of lifting task appeared to be satisfactorily reproducible when subjects had to adjust work pace or when they were left free to adjust both the weight and the work pace. However, the results raised several questions concerning the applicability of the psychophysical assessment of maximum acceptable lifting work. Slight changes in the instructions given to the subjects had a definite effect on the selection of workloads. Furthermore, the workloads selected by subjects with previous occupational experience of lifting work — i e, warehouse workers — were systematically lower than those selected by subjects without such previous experience — i e, office employees. At the same time, the warehouse workers rated perceived exertion higher than the office employees, indicating that previous occupational experience of lifting work enhanced the subjective assessment of physical effort. There were no consistent relations between the workloads found acceptable by the subjects and their physical characteristics and performance capacity.     

One-handed dynamic pulling strength with special reference to speed, handle height and angles of pulling

A laboratory study was conducted to determine the effects of pulling speed, handle height and angle of pull from the horizontal plane on one-handed dynamic pulling strength. The dynamic strength of nineteen male subjects for a 1 m pull was measured at four different handle heights (40%, 50%, 60% and 70% of shoulder height), at three different angles above the horizontal plane (15°, 25° and 35°), and at three different speeds of pulling (mean speed = 0.7, 1 and 1.1 ms⁻¹). In addition, ratings of perceived exertion were recorded for elbow, shoulder and back. Also, the subjects were required to rate the overall comfort for the pull.

Pulling speed, handle height and angle all had a significant effect on both mean and peak dynamic pulling strengths (p 0.01). Among the three variables, pulling speed was found to be the most critical. The mean dynamic strength was 360, 250 and 180 N and the peak strength was 600, 425 and 320 N at 0.7, 1 and 1.1 ms⁻¹, respectively. The strengths decreased with an increase in handle height from 100% at 40% shoulder height to 83% at 70% of shoulder height and were the highest at an angle of 25° from the horizontal plane.

The ratings of perceived exertion for all three body parts decreased with an increase in speed of pulling (p 0.01). The high speed pulls were perceived as being more comfortable than low speed pulls (p 0.01). The handles at 50% and 60% of shoulder height and at an angle of 25° were perceived as being more comfortable than those at other heights and angles (p 0.01).

It is suggested that biomechanical stresses need to be considered along with physical strength and ratings of perceived exertion and comfort to determine optimum speed, height and angle of pulling for high speed pulling tasks.     

Validation of a task demand measure for predicting mental workloads of physical therapists

The purpose of this study is to validate an analytical method in assessing demanded mental workloads for physical therapists, and to discuss its possible ergonomics implications on the design of healthcare working systems in which physical therapists are considered as the users. A task analysis was first used to understand the operation steps of three identified physical therapies. Then, the McCracken–Aldrich technique was applied to assign ratings of mental workload demanded for performing each step of the therapies. Finally, the assigned ratings were validated by the analysis of correlation with the answers of the NASA-TLX questionnaire collected from seventeen physical therapists in the rehabilitation center of a university-affiliated hospital. Results showed that the proposed McCracken–Aldrich technique was suitable as an analysis tool for predicting metal workloads of physical therapists. Some possible implications about the information provision and user interface design for reducing therapists' mental workloads on current therapy operations were discussed.Relevance to industryResults of this paper are expected to contribute the research and development in healthcare industry on its system design and workflow analysis.     

Psychophysical determination of load carrying capacity for a 1-h work period by Chinese males.

This study used the psychophysical approach to examine the effects of container width, the presence or absence of container handles, and different load-carrying frequencies and distances on the maximum acceptable weight carried and the resulting response (heart rate and rating of perceived exertion) by well-conditioned males for a 1-h work period. After training, 12 male subjects performed a load-carrying task at knuckle height. Each subject performed 30 different carrying combinations. The conditions examined were container width, from 15.2 to 55.9 cm; carrying frequency, from 1 carry to 5 carries/min; and carrying distance from 1 to 6 m. The results were compared with prior studies and led to the following conclusions: (1) the use of container handles leads to the subjects carrying a significantly higher maximum acceptable weight than when containers do not have handles, which differs from the results of a previous study by Morrissey and Liou; (2) there were significant reductions in the maximum acceptable carrying weight with increases in container width, frequency and distance; (3) the presence or absence of container handles, different frequencies and load-carrying distances had significant effects on heart rate, although the effect of container width was not significant. In addition, the various frequencies and distances for load carrying had significant interaction effects on heart rate; (4) the effects of various frequencies and load-carrying distances on the rating of perceived exertion were statistically significant. The most stressed body parts were the wrists and arms.     

Psychophysical determination of load carrying capacity for a 1-h work period by Chinese males

This study used the psychophysical approach to examine the effects of container width, the presence or absence of container handles, and different load-carrying frequencies and distances on the maximum acceptable weight carried and the resulting response (heart rate and rating of perceived exertion) by well-conditioned males for a 1-h work period. After training, 12 male subjects performed a load-carrying task at knuckle height. Each subject performed 30 different carrying combinations. The conditions examined were container width, from 15.2 to 55.9 cm; carrying frequency, from 1 carry to 5 carries/min; and carrying distance from 1 to 6 m. The results were compared with prior studies and led to the following conclusions: (1) the use of container handles leads to the subjects carrying a significantly higher maximum acceptable weight than when containers do not have handles, which differs from the results of a previous study by Morrissey and Liou (1988); (2) there were significant reductions in the maximum acceptable carrying weight with increases in container width, frequency and distance; (3) the presence or absence of container handles, different frequencies and load-carrying distances had significant effects on heart rate, although the effect of container width was not significant. In addition, the various frequencies and distances for load carrying had significant interaction effects on heart rate; (4) the effects of various frequencies and load-carrying distances on the rating of perceived exertion were statistically significant. The most stressed body parts were the wrists and arms.     

Evaluation of earcons for portable digital electronic products considering perceptual user characteristics

Earcons, nonverbal sound feedback, have been used for electronic products to give appropriate feedback information for the selected user functions. This study evaluated earcon usability of a portable digital electronic product based on cognition time, error rate, and subjective feelings using 20 male and female subjects. For subjective evaluation, the study assessed various earcons by subjective impression of sounds using 7‐point rating scales. For earcon usability performance, major user functions were used for the product with currently available earcons and for the product with the new earcons (suggested by this study), which considered perceptual characteristics, such as loudness and melody. Statistical results from the study indicated that the new earcons significantly reduced user error rates and therefore generally improved user performance on major functions, such as “PLAY,” “OFF,” “STOP,” “FF” (fast forward), and “REW” (rewind). Subjective data results also showed that users were more satisfied with the new, melody‐based sound feedback. Practical guidelines for sound feedback design of a small digital product are suggested. © 2011 Wiley Periodicals, Inc.     

Tolerability to prolonged lifting tasks assessed by subjective perception and physiological responses

Prolonged physical exertion is regulated subjectively by the perception of effort. This preliminary study was conducted to validate the use of subjective perceptions of effort in assessing objectively tolerable workloads for prolonged lifting tasks. Eight healthy male subjects underwent incremental and 30-minute endurance lifting tests. Cardiorespiratory parameters were monitored with an oxygen uptake analyser and mechanical parameters were calculated using a lift dynamometer. Ratings of perceived exertion were given on Borg's 10-point scale. Physiological responses to repetitive lifting were matched with subjective perceptions. The relationship between the perception of exertion and the duration of the endurance tests was described by power functions; Y=aXⁿ in which 0 > n >1. A single-variable statistical regression for power functions was performed to obtain the individual ‘iso-perception’ curves as functions of the mechanical work exerted. It was found that the ‘iso-perception’ curve corresponding to a ‘moderate’ perception of effort may represent the individual ‘tolerance threshold’ for prolonged lifting tasks, since physiological responses at this intensity of effort did not change significantly and the respiratory exchange ratio was less than one. The individually tolerable power over lime for lifting tasks has been estimated.     

The effects of a 1-year physical exercise programme on development of fatigue during a simulated ambulance work task

The aim of the study was to evaluate the effects of individually prescribed physical exercise programmes on development of fatigue during the carrying of a loaded stretcher up and down the stairs. Nineteen ambulance personnel performed the training for 1 year. Testing occurred before and after 1 year of the training. Both the training group (n = 19) and the control group (n = 15) were assessed for physical capacity and lactate concentration in blood and ratings of perceived exertion during carrying a stretcher on the stairs. When comparisons were made between those who had been training three times/week for 1 year and the control group, lactate concentration was significantly decreased. In conclusion, markers of fatigue during stretcher carrying can be reduced by the use of individually prescribed physical exercise programmes.     

Does load position affect gait and subjective responses of females during load carriage?

Recreational hikers carry heavy loads while often walking long distances over uneven terrain. Previous studies have suggested that not only the load mass but also the position of the load may influence load carriage. The purpose of this study was to determine the effect of vertical load position on gait and subjective responses of female recreational hikers. Fifteen experienced female hikers walked for 2 km over a simulated hiking trail carrying 30% BW in three vertical load positions (high, medium and low). Lower limb and trunk kinematic, electromyography (EMG) and ground reaction force (GRF) data were collected together with heart rate (HR), ratings of perceived exertion (RPE) and discomfort measures. Although HR, RPE and discomfort measures were not able to discern statistical differences between load positions, the high load position was the most preferred by participants. The high load position also resulted in a more upright posture (p < 0.001), decreased gastrocnemius integrated EMG compared to the medium (p = 0.005) and low load positions (p = 0.02) and a higher first peak deceleration vertical GRF compared to the low load position (p = 0.011). However, the absolute differences were small and unlikely to be functionally relevant in load carriage studies. Based on the findings of this study, a high, medium or low load position cannot be preferentially recommended for healthy, experienced, female hikers carrying 30% BW.     

Maximum frequency acceptable to female workers for one-handed lifts in the horizontal plane

Abstract

A laboratory study was conducted to determine the maximum frequencies acceptable to female workers for one-handed lifts in the horizontal plane. A psychophysical method was used to determine maximum acceptable frequency for an 8-hour workday. Ten female college students were required to lift continuously three different loads to two different reach distances (38 and 63 cm) on a 91 cm high work table. The lifting task was paced by a repeating timer which the subject controlled according to her subjective feelings of fatigue. Heart rate and RPE were measured during the last 5min of the experiment to determine the physiological level of functioning and perceived exertion. Psychophysically determined maximum acceptable frequencies were compared with the standards based on methods-time measurement (MTM) analysis.

Statistical analysis showed that both the weight of the load and reach distance had a significant effect on maximum frequency acceptable to the subjects. No single value for percentage of maximum frequency can be used to establish permissible one-handed lift limits in women; rather, this value depends upon the weight of the object and distance of lift. The average maximum acceptable frequency was 51% of the maximum frequency that the subjects could maintain for a period of 4min. The subjects selected workloads which resulted in a mean heart rate of 101 beats/min. The subjects rated the perceived exertion ranging from ‘fairly light’ to ‘somewhat hard’. Performance based on MTM analysis ranged from 11% below to 32% above the maximum workload acceptable to the subjects. The non-significant heart rate differences found among the six load-distance combinations lend strong support for the use of psychophysical methodology in future studies of fatigue criteria. The study also supports the previous findings that separate physiological fatigue criteria are needed for tasks involving arm work and whole body exertion.     

Extending the TAM for a t-commerce

Broadband communication at home allows television to become an e-commerce medium that merges video, voice, and transactional data. t-commerce is electronically mediated commerce using interactive television. Theoretical and empirical analysis was undertaken and reported here to explain the factors that influence potential users’ adoption of t-commerce by extending the technology acceptance model. The study also compared the factors influencing t-commerce adoption between experienced and inexperienced users. Seven factors were identified: perceived ease of use, perceived usefulness, perceived enjoyment, trust, attitude, normative belief of family and friends, and subjective norm. Although the factors were not the same between the two groups, the differences were not large. Perceived enjoyment is the most important factor affecting attitude and behavioral intention toward t-commerce. From a theoretical point of view, the study extended the TAM for t-commerce adoption by potential users in the home environment. Moreover, this study also provided practical implications for t-commerce providers.     

Haptic Seat Interfaces for Driver Information and Warning Systems

The implementation of haptic interfaces in vehicles has important safety and flexibility implications for lessening visual and auditory overload during driving. The present study aims to design and evaluate haptic interfaces with vehicle seats. Three experiments were conducted by testing a haptic seat in a simulator with a total of 20 participants. The first experiment measured reaction time, subjective satisfaction, and subject workloads of the haptic, visual, and auditory displays for the four signals primarily used by vehicle navigation systems. The second experiment measured reaction time, subjective satisfaction, and subjective workloads of the haptic, auditory, and multimodal (haptic + auditory) displays for the ringing signal used by in-vehicle Bluetooth hands-free systems. The third experiment measured drivers' subjective awareness, urgency, usefulness, and disturbance levels at various vibration intensities and positions for a haptic warning signal used by a driver drowsiness warning system. The results indicated that haptic seat interfaces performed better than visual and auditory interfaces, but the unfamiliarity of the haptic interface caused a lower subjective satisfaction for some criteria. Generally, participants showed high subjective satisfaction levels and low subjective workloads toward haptic seat interfaces. This study provided guidance for implementing haptic seat interfaces and identified the possible benefits of their use. It is expected that haptic seats implemented in vehicles will improve safety and the interaction between driver and vehicle.     

The effects of a 1-year physical exercise programme on development of fatigue during a simulated ambulance work task

The aim of the study was to evaluate the effects of individually prescribed physical exercise programmes on development of fatigue during the carrying of a loaded stretcher up and down the stairs. Nineteen ambulance personnel performed the training for 1 year. Testing occurred before and after 1 year of the training. Both the training group (n = 19) and the control group (n = 15) were assessed for physical capacity and lactate concentration in blood and ratings of perceived exertion during carrying a stretcher on the stairs. When comparisons were made between those who had been training three times/week for 1 year and the control group, lactate concentration was significantly decreased. In conclusion, markers of fatigue during stretcher carrying can be reduced by the use of individually prescribed physical exercise programmes.     

Establishment of overall workload assessment technique for various tasks and workplaces

A model for assessing workloads called overall workload level (OWL) was developed by introducing linguistic variable sets and applying the analytic hierarchy process (AHP) to estimate the external workload imposed on a human operator in man–machine systems. To do this, a five-point linguistic variable set scale was constructed and their hierarchical prioritization procedures were set up. The task and workplace variables (e.g., physical, environmental, postural, and mental job demand workloads) which can obtain the operator's perception of workload are selected as workload factors and the AHP technique is used to collect different weights. Finally, OWL is calculated using a computer-assisted system to determine the level of overall workload impinged on an operator. The OWL was implemented in an actual industrial environment from a physiological and epidemiological viewpoint to determine the validity of the model. Furthermore, the results obtained by applying OWL were compared to the results obtained by applying the overall workload (OW) of the NASA task load index (TLX). The results show that there is a close linear relationship among the physiological measurements, the severity of injury and illness rates, OW, and OWL. Thus, this approach can be used for problem identification and for solving widespread occupational workloads.

Relevance to industry

The determination of workloads imposed on a human operator plays an important role in designing and evaluating an existing man–machine system. Therefore, a model for assessing workloads was developed to estimate the external workload imposed on a human operator in man–machine systems. This model can be used for problem identification and for solving widespread occupational workload.     

Red-colored products enhance the attractiveness of women

This research investigated whether carrying red-colored products enhances female sexual attractiveness. In the first experiment, male participants were instructed to observe women carrying laptops in different colors (black, silver, red, or blue). The results indicated that the women who carried red laptops were perceived to possess a significantly higher level of attractiveness and sex appeal than those who carried laptops in other colors; however, the red laptop did not affect men’s perceptions of the assertiveness and health level of the women. In the second experiment, the initial experiment was repeated but female participants observed the women; laptop color did not influence how the participants perceived the women’s attractiveness, sex appeal, assertiveness, and level of health. In other words, women carrying products in red only affected how men, but not women, perceived them; thus, women using red products are more attractive and sexually appealing to men.     

Applying the Technology Acceptance Model to Social Networking Sites (SNS): Impact of Subjective Norm and Social Capital on the Acceptance of SNS

With their heavy traffic and technological capabilities, social networking sites (SNS) introduced a new means of building and maintaining perceived social capital. This study aims to identify underlying factors and causal relationships that affect behavioral intention to use SNS. For this purpose, this research developed an extended technology acceptance model, incorporating subjective norm and perceived social capital for predicting SNS acceptance and usage. Exploratory correlation and path analyses were conducted to identify the relationships between five constructs: perceived usefulness, perceived ease of use, subjective norm, perceived social capital, and intention to use. The results showed that perceived usefulness and perceived ease of use had robust effects on the user's intention to use SNS. The research findings also demonstrated that subjective norm and perceived social capital were significant predictors of both perceived usefulness and perceived ease of use and therefore should be considered as potential variables for extending the technology acceptance model.     

Experiment to select a suitable visual display and evaluate its washout characteristics

Two separate experiments were carried out on a display for a portable microprocessor. Of three phosphorescent displays available for installation, readability times, error rates and subjective preferences were recorded and compared using fifteen subjects. On these measures recorded, the small dot-matrix display (3.5 mm × 5.0 mm) performed better than the large dot-matrix display (5 mm × 8 mm) and considerably better than the segmented display (5 mm × 8 mm). The second experiment set out to quantify the effects of a range of three ambient illuminance levels on the readability of the small dot-matrix display, using the same criteria. Results suggested that for ambient illuminance levels between 0 lux and 15000 lux, a single display intensity was feasible, this being about 40 cdm^?2.     

Biomechanical model for energy consumption in manual load carrying on Indian farms

This study pertains to manually carrying load in Indian farms. Different modes are adopted for carrying farm inputs and farm produce; head, shoulder and back. A biomechanical model was developed and validated to predict metabolic energy consumption for carrying load manually by varying modes, loads and ground inclinations. The model developed incorporated operator, ground inclination and load parameters. Operator parameters included human efficiency, body weight and height of the worker. Load parameters considered were weight of load and mode of load carrying. Experiments on three modes (head, back and shoulder) and three loads (10, 15, 20 kg load) at three slopes (0, 5, 10%) were conducted in a laboratory set up. Twelve farm workers (six males and six females) working in local farms participated in the study. The model closely predicted energy and rest requirement for load carrying in different modes.