Search

The purpose of this study was to describe and quantify measured hand forces during floor to knuckle lifting of various loads. Hand forces of five subjects were measured with a strain gauge apparatus for normal and fast speeds of lifting at 1, 4, and 8 l/min. The pattern of hand force over time exhibited peaks in force in the shape of a spike for all fast lifts, indicating that subjects did not lift smoothly. For normal speed of lift, only one of the five subjects executed some lifts smoothly, indicating that it may be possible to lift smoothly, but most lifters probably do not. Peaks of horizontal and vertical components of hand force were tabulated by speed of lift, frequency, and load.

Research efforts to establish manual materials handling (MMH) capabilities of individuals and populations have been conducted for many years. Most of the previous efforts have explored 'standard postures', utilizing two-handed, symmetric, sagittal plane MMH using unrestricted postures. Recognizing that many industrial MMH activities do not utilize 'standard postures', recent research projects have explored psychophysically determined MMH capacities in a variety of non-standard postures. Among the non-standard postures examined were: twisting while lifting or lowering, lifting and lowering from lying, sitting, kneeling, and squatting positions, and carrying loads under conditions of constricted ceiling heights. This paper presents the results of a series of previous research efforts at Texas Tech University. The results are presented in the form of population capabilities of both males and females for 99 MMH tasks using 'non-standard postures'. The data tables contain means and standard deviations of the data, as well as percentile distributions for the subject populations. Sample sizes for the experimental populations ranged from 45 to 50 subjects of each sex in the first three experiments to 20 subjects of each sex in the fourth set of experiments.

An experiment was conducted to examine the role that maximal lifting power has in predicting maximum acceptable weight of lift (MAWL) for a frequency of one lift per 8 h. The secondary aim of the study was to compare the ability of power to predict MAWL to previously used measures of capacity including two measures of isometric strength, five measures of isokinetic strength, and isoinertial capacity on an incremental lifting test. Twenty-five male subjects volunteered to participate in the experiment. The isometric tests involved maximum voluntary contractions for composite lifting strength at vertical heights of 15 and 75 cm. Peak isokinetic strength was measured at velocities of 0.1, 0.2, 0.4, 0.6 and 0.8 m s-1 using a modified CYBEX II isokinetic dynamometer. Isoinertial lifting capacity was measured on the X-factor incremental lifting machine and peak power was measured on the incremental lifting machine by having subjects lift a 25 kg load as quickly as possible. The results indicate that peak isoinertial power is significantly correlated with MAWL, and this correlation was higher than any of the correlations between the other predictor variables and MAWL. The relationships between the isokinetic strength measures and MAWL were stronger than the relationships between the isometric measures and MAWL. Overall, the results suggest that tests used to predict MAWL should be dynamic rather than static.

Between 1983 and 1990, 32 consecutive patients had 35 thru-knee amputations for ischemia causing infection or gangrene of the lower leg. Twenty-seven patients were nonambulatory, five had limited mobility, and none were considered to be candidates for rehabilitation with a prosthesis after surgery. The average age was 73 years. Thirty-day hospital mortality was 3 per cent. The incidence of complications was low, and healing was achieved in 97 per cent of survivors. One patients required revision to an above-knee amputation. Average postoperative hospital stay was 8.7 days. It is concluded from this study that thru-knee amputation is the treatment of choice in patients with nonsalvageable ischemic legs and in whom ambulation is not planned after operation.

As science and technology become more sophisticated and with the rapid computation capabilities of the modern computer available, it becomes both possible and economically feasible to scientifically study man and his interaction with his working environment. It is now possible for a person seeking employment to expect and obtain a position which will not be unnecessarily hazardous to his immediate health or have detrimental effects over the long run. Manual materials handling is the contributor of over 400,000 back injuries suffered in the U.S. each year. This research is directed at determining the appropriate operator variables to measure for predicting the permissible weight of lift for three ranges of lift: floor to knuckle height, knuckle height to shoulder height, and shoulder height to reach height. A modified psychophysical procedure was used during which the subjects were instructed to adjust the weight in a tote box to the maximum weight they could lift repetitively without excessive strain or fatique. The task consisted of lifting loads under different conditions of task variables, namely, height of lift, frequency of lift, and load size. Industrial workers as well as students of both sexes were used as subjects. Based on the data obtained, the lifting capacity of the worker was determined for the different ranges of lift. In addition, predictive models were developed based on the operator variables and the task variables investigated.

Back injuries resulting from manual materials handling are one of the major sources of compensation claims and time lost from work. One of the possible means of reducing human susceptibility to musculoskeletal injuries is by increasing the individual's lifting capability by prior training. This paper describes a 6 week training programme that successfully increased the maximal oxygen uptake, isometric strength and lifting capability of 10 male subjects. The programme trained subjects for flexibility, muscle strength (by applying the concept of progressive resistance exercise), muscle endurance (by lifting light loads at high frequency of lift) and cardiovascular endurance (by exercising on a bicycle ergometer). The training programme resulted in significant increase in the maximal oxygen uptake and isometric back, arm, leg and shoulder strengths of the subjects. The maximum acceptable weight lifted, using a compact box for different heights of lift, also increased significantly.

An experiment was designed to study the effect of several task variables on the metabolic energy expenditure and heart rate of individuals performing lifting and lowering tasks. The task variables studied were: load of lift (lower), frequency of lift (lower), height of lift (lower), presence of absence of handles, container height, container width (in the frontal plane) and container length (in the sagittal plane). Four male subjects participated in the experiment. Their oxygen uptake and heart rate were monitored. Various strength measurements were made on the subjects before their participation in the study and after the study was over. The data were analyzed separately for lifting and lowering, using the analysis of variance. Container height did not affect the metabolic energy expenditure or heart rate of the subjects for lifting or lowering activities. Presence or absence of handles did not cause a significant change (alpha greater than or equal to .10) in the physiological responses for lowering tasks. All other task variable effects, however, were significant (alpha less than or equal to .01). A strong first and second order interaction was observed among the task variables. There was a significant increase in the strength (alpha less than or equal to .025) of subjects after performing manual materials handling activities for about seven weeks. A dimensional sensitivity analysis indicated that unit change in box width was more expensive than unit change in box length up to .56 m (22 inches). Beyond this, unit change in box length became critical. The weight/bulk ratio of the object did not affect the physiological responses.

A new approach, based on the theory of fuzzy sets and systems, was proposed to assess the acceptability of stresses involved in manual lifting tasks. Nine male subjects participated in a laboratory lifting experiment. A total of 108 data points (9 subjects × 4 levels of frequency × 3 replications) were collected. The maximum acceptable weights of lift were determined using the psychophysical methodology. Metabolic energy expenditure and heart rates were also measured. A hypothesis, stating that the combined effect of biomechanical and physiological stresses leads to an overall measure of lifting task acceptability as expressed by the psychophysical stress, was suggested and evaluated. Conditions were found for which the acceptability measures of the combined and the psychophysical stresses were close to one another. A concept of safety index for a particular weight of load lifted was also proposed.

Ten trained male students between 18 and 28 years of age participated in a study, designed to determine the relationship between perceived exertion and physiological costs of exertion during various manual lifting and lowering tasks. Perceived exertion was defined as one's subjective rating of the intensity of work being performed. Five subjects performed lifting tasks and another five performed lowering tasks. Weight of load lifted or lowered (6.8, 13.6, 20.5 kg), frequency of lift or lower (3, 6, 9 times/min), height of lift or lower (floor to 76 cm, 76 to 127 cm, floor to 127 cm), box width (38, 66 cm), box length (38, 66 cm) and angle of twist of the body (0 degree, 90 degrees) were the independent variables studied. Heart rate, oxygen consumption, and ratings of perceived exertion (RPE) were the response measures. RPE was found almost linearly related to heart rate and oxygen consumption when lifting or lowering loads. For lifting tasks, the coefficient of correlation between RPE and heart rate was 0.673. In the case of lowering tasks, this coefficient was 0.604. When oxygen consumption was considered, the corresponding coefficients for lifting and lowering were 0.734 and 0.619, respectively. The correlation of RPE with the physiological response variables indicates that the severity of manual materials handling tasks in industry can be evaluated quickly and inexpensively by using perceived exertion ratings (RPE).

Five male subjects were trained to work in non-erect task postures and then shovelled in five task postures: normal erect, under ceilings set at 80 and 60% of normal stature; kneeling without ceiling restraint; and, kneeling under a ceiling set at 80% of kneeling height. The steady-state data for all five task postures were averaged with a resulting heart rate of 131 beats min−1 and an oxygen uptake of 1·41−1 These averaged values compared very well with studies of actual coal miners shovelling in normal working environments

Educable and trainable mentally retarded males (N=37) were examined for physical work capacity. Analysis of results indicated that the physical work capacity of the test population was 20 to 30% below that cited in the literature for nonretarded subjects of similar age and sex. Evidence also suggested that developmental and maintenance programs of physical fitness were required in order for mentally retarded persons to qualify for and maintain employment on most of the manual occupational tasks cited.

Most psychophysical studies in manual materials handling (MMH)are involved only with single MMH activities, i.e. lifting, lowering, carrying, holding, pushing or pulling. Very little research has been reported on the determination of operator capacities for combinations of MMH activities (e.g. lifting a box, then carrying the box, or carrying a box, then lowering the box). These kinds of combined activities are prevalent in industry and in our daily lives. The objective of this study was to utilize the psychophysical approach to examine the effects of combinations of lifting, carrying and lowering activities. Twelve male students served as subjects for the study. The capacities that were determined as the maximum acceptable workloads for a 1-h work period for four individual MMH activities—lifting from floor to knuckle height (LFK), lifting from knuckle to shoulder height (LKS), lowering from knuckle to floor height (LOW) and carrying for 3·4 m (C) —and three combined MMH activities—LFK + C, LFK + C + LKS...

The physiological responses of male low seam coal miners were measured both above and below ground to ascertain the characteristics and task demands of mining low coal in very restricted surroundings (seam height 1.2 m or lower). Aerobic capacity was estimated from measurements of expired air and heart rate taken while subjects rode a stationary bicycle. Total ventilation (as measured by a respirometer) was used to assess underground energy expenditure and oxygen consumption. Results indicate that low seam coal miners do not have higher maximum oxygen consumption values than non mining populations. Individual task analyses for oxygen uptake and kilocalorie expenditure are discussed.

In order to establish a valid criteria on which to establish lifting guidelines, lifting capacity determination must be made. This has been attempted using several approaches mainly psychophysical, physiological, and biomechanical methodologies. Although the data obtained from these approaches yield information about lifting capacity, some conflict in these data can be found. The purpose of this paper is to discuss the three different approaches, the data obtained from these approaches, and some data on the lifting capacity for males and females in the industrial workforce. In addition, the conflicts in these data are also presented.

An experiment was designed and conducted for the development, testing and comparison of models for prediction of weight lifting capacity of individuals incorporating static and dynamic strengths. The dependent variable was the maximum acceptable amount of lift and the independent variables were static strengths, and dynamic strengths of the individual in a simulated lifting position and task variables—height and frequency of lift. Data from nine male subjects were used for analysis. It was concluded that both the dynamic and static models developed in this study can predict the maximum acceptable amount of lift with a reasonable degree of accuracy. However, a comparison of the models revealed that the use of the dynamic model with one operator variable resulted in less absolute error between the actual and predicted load than the static model. This study, which is based on data from a limited number of subjects, indicates that the dynamic approach may be superior to the static approach.

Matching the job demands to a person's physical characteristics is an effective method of reducing the risk involved in a manual materials-handling task. Seventy-three male and 73 female industrial workers served as subjects. Maximum Acceptable Load of Lifting (MAL) was determined psychophysical under each combination of the following task conditions: six ranges of lift (floor to knuckle, floor to shoulder, floor to reach, knuckle to shoulder, knuckle to reach and shoulder to reach); four lifting frequencies (2,4,6 and 81/min); and three box sizes (30·48,45·72 and 60·96cm). A factor-score-based model (R2 = 0-924) is developed in this paper based on 100 subjects for predicting an individual's MAL and for describing his/her physical characteristics in terms of strength and anthropometric scores. The model was validated on the remaining 46 subjects and was shown to be superior to the previously developed models from the same data set.

This research was conducted for the purpose of studying the performance and recovery characteristics of men when subjected to low-level, whole-body vertical sinusoidal vibration for durations of one to two hours. Several male subjects performed a vertical compensatory tracking task using a CKT display according to three work-rest schedules under both normal and vibratory environments. The vibratory environment was that of vertical sinusoidal vibration with a frequency of.5 cps and an amplitude- of 0-08 inches resulting in an acceleration intensity of approximately 0.20 g. The working period was divided into equal intervals during which performance was continuously monitored. Decrement of performance was measured using absolute error score. Results and conclusions are presented regarding performance decrement and recovery under varying work-rest schedules. Optimum work-rest schedules and implications of control tasks under a vibratory environment are discussed.