Maximum Acceptable Weight Of Lift Research Articles

The effect of confined space on the maximum acceptable weight of lift : Karwowski, W and Alasbi, HVisions. Proc Human Factors Society 35th Annual Meeting. San Francisco, California, 2–6 September 1991. The Human Factors Society, Santa Monica, California, Vol 1 (1991) pp 804–808 (9 refs)

The effect of confined space on the maximum acceptable weight of lift : Karwowski, W and Alasbi, HVisions. Proc Human Factors Society 35th Annual Meeting. San Francisco, California, 2–6 September 1991. The Human Factors Society, Santa Monica, California, Vol 1 (1991) pp 804–808 (9 refs)

Maximum Acceptable Weights of Lift for Common Coal Mine Supply Items

A series of psychophysical lifting studies was conducted to establish maximum acceptable weights of lift (MAWL) for three supply items commonly handled in underground coal mines (rock dust bags, ventilation stopping blocks, and crib blocks). Each study utilized 12 subjects, all of whom had considerable experience working in underground coal mines. Effects of lifting in four postures (standing, stooping under a 1.5 m ceiling, stooping under a 1.2 m ceiling, and kneeling) were investigated together with four lifting conditions (combinations of lifting symmetry and lifting height). The frequency of lifting was set at 4 per minute, and the task duration was 15 minutes. Posture significantly affected the MAWL for the rock dust bag (standing MAWL was 7% greater than restricted postures and kneeling MAWL was 6.4% less than stooped); however, posture interacted with lifting conditions for both of the other materials. Physiological costs were found to be significantly greater in the stooped postures compared to kneeling for all materials. Other contrasts (standing versus restricted postures, stooping under 1.5 m ceiling versus stooping under 1.2 m ceiling) did not exhibit significantly different levels of energy expenditure. Energy expenditure was significantly affected by vertical lifting height; however, the plane of lifting had little influence on metabolic cost. Recommended acceptable workloads for the three materials are 20.0 kg for the rock dust bag, 16.5 kg for the ventilation stopping block, and 14.7 kg for the crib block. These results suggest that miners are often required to lift supplies that are substantially heavier than psychophysically acceptable lifting limits.

Predicting the Maximum Acceptable Weight of Lift for an Asymmetrical Combination Task

This paper presents prediction models based on a study of a combination lift and lower manual handling task that was designed to simulate the loading of grocery bags into a car trunk. Twelve male subjects performed an externally-paced task of lifting plastic grocery bags (with handles) loaded with weights from 15 cm above the floor and over a wooden sill. There were two different sill heights of 70 cm and 90 cm, and for each of these heights there were two frequencies of 3 and 6 lifts per cycle. A unique lifting sequence and a modified version of the psychophysical methodology was used to determine the maximum acceptable weight of lift (MAWOL). Prediction models were determined for MAWOL based upon task, physiological and anthropometric variables as well as a combinations of these. The results indicated that MAWOL could be predicted fairly well.

Acceptable workloads for three common mining materials.

A series of psychophysical lifting studies was conducted to establish maximum acceptable weights of lift (MAWL) for three supply items commonly handled in underground coal mines (rock dust bags, ventilation stopping blocks, and crib blocks). Each study utilized 12 subjects, all of whom had considerable experience working in underground coal mines. Effects of lifting in four postures (standing, stooping under a 1.5 m ceiling, stooping under a 1.2 m ceiling, and kneeling) were investigated together with four lifting conditions (combinations of lifting symmetry and lifting height). The frequency of lifting was set at four per min, and the task duration was 15 min. Posture significantly affected the MAWL for the rock dust bag (standing MAWL was 7% greater than restricted postures and kneeling MAWL was 6.4% less than stopped); however, posture interacted with lifting conditions for both of the other materials. Physiological costs were found to be significantly greater in the stooped postures compared with kneeling for all materials. Other contrasts (standing versus restricted postures, stooping under 1.5 m ceiling versus stopping under 1.2 m ceiling) did not exhibit significantly different levels of energy expenditure. Energy expenditure was significantly affected by vertical lifting height; however, the plane of lifting had little influence on metabolic cost. Recommended acceptable workloads for the three materials are 20.0 kg for the rock dust bag, 16.5 kg for the ventilation stopping block, and 14.7 kg for the crib block. These results suggest that miners are often required to lift supplies that are substantially heavier than psychophysically acceptable lifting limits.

Maximum acceptable weight of lift for side and back lifting : Lee, K, Waikar, A and Aghazadeh, FJ Human Ergology, 1990, 19. 1, 3–11, 13 refs

Maximum acceptable weight of lift for side and back lifting : Lee, K, Waikar, A and Aghazadeh, FJ Human Ergology, 1990, 19. 1, 3–11, 13 refs

The effect of rigid container shape on maximum acceptable weight of lift : Ostrom, L. T., Smith, J. L., and Ayoub, M. M. In: Countdown to the 21st century. Proc Human Factors Soc 34th ann meeting, Orlando, Florida, 8–12 Oct 1990. Human Factors Soc, Santa Monica, Cal, Vol 1, 1990, pp 767–770, 4 refs

The effect of rigid container shape on maximum acceptable weight of lift : Ostrom, L. T., Smith, J. L., and Ayoub, M. M. In: Countdown to the 21st century. Proc Human Factors Soc 34th ann meeting, Orlando, Florida, 8–12 Oct 1990. Human Factors Soc, Santa Monica, Cal, Vol 1, 1990, pp 767–770, 4 refs

Discriminability of load heaviness: implications for the psychophysical approach to manual lifting.

The main objective of this study was to investigate human ability to discriminate between different levels of load heaviness in manual lifting. Twelve male college students participated in the laboratory experiment. Twenty-eight sequences of five boxes that weighed from 5 to 64 lbs (2.27-29.1 kg) were used. The subjects were asked to arrange boxes in each sequence in order of the perceived (increasing or decreasing) heaviness, i.e., from lightest to the heaviest box, or from heaviest to the lightest box. The subjects were also asked to assign linguistic descriptors of perceived load heaviness to each box in the sequence, and to indicate the confidence levels regarding correctness of the assigned box order and assignment of linguistic values. The independent variables included magnitude of weight and load differential between the successive weights in a sequence. The number of sequential ordering errors, assignment of linguistic variables, and estimated confidence levels were highly dependent on the load differential and weight range. It was concluded that in order to assure reliable results of the psychophysical approach to determining the values of maximum acceptable weight of lift, the adjustment process for male subjects should require using small weights of at least 4 lbs (1.8 kg) to be added or removed from the lifted box. The results of this study also suggest that the error rate in load discriminability can be controlled below the 10% level, if the relative difference in weight between successive boxes lifted is at least 12%. Given the above findings, it is suggested that usefulness of some of the recommendations for setting safe limits for manual lifting tasks, which were reached based on the psychophysical approach and broadly reported in the past, may need to be carefully re-examined. Finally, this study showed that the Weber fraction for load heaviness over the range of lifted weights from 8.6 to 29.1 kg is between 0.03 and 0.04.

Psychophysical capacity of industrial workers for lifting symmetrical and asymmetrical loads symmetrically and asymmetrically for 8 h work shifts.

This paper presents comprehensive maximum acceptable weight of lift (psychophysical lifting capacity) database for male and female industrial workers for lifting symmetrical and asymmetrical loads symmetrically and asymmetrically for 8 h work shifts. The experimental data collected in previous studies on experienced (industrial) and inexperienced (non-industrial) materials handlers (Mital 1984a, Mital and Fard 1986) and the patterns of responses between the two populations (Mital 1985, 1987) were used to generate this database. Since previous work (Mital 1985, 1987) showed that responses of both experienced and inexperienced materials handlers to task variables are similar and also provided multipliers relating the psychophysical lifting capacities of the two populations, it was possible: (1) to convert psychophysical capacity data for asymmetrical lifting of symmetrical and asymmetrical loads, collected on inexperienced workers to reflect psychophysical lifting capacity of experienced workers for asymmetrical lifting; and (2) to take psychophysical lifting capacity data of experienced industrial workers for symmetrical lifting of symmetrical loads and generate from it their psychophysical lifting capacity for symmetrical and asymmetrical lifting of symmetrical and asymmetrical loads by using the response patterns of inexperienced workers to lifting symmetrical and asymmetrical loads symmetrically and asymmetrically. Both approaches were used and, as expected, provided almost identical values for the psychophysical lifting capacity of industrial workers for symmetrical and asymmetrical lifting of symmetrical and asymmetrical loads. Therefore, the final database tables provided in this paper used combined values generated by the two methods.

A psychophysical study of manual lifting in hot environments

A study was conducted to assess the lifting capabilities of acclimatized individuals in hot environments. Six male subjects were selected for the study. The subjects were heat acclimatized for ten days prior to participation in the experiment. A psychophysical experiment was then carried out using three temperature levels (22, 27, and 32°C Wet Bulb Globe Temperature (WBGT), three frequencies of lift (0.1, 3 and 6 lifts/min), and one height of lift (floor to knuckle height). The results indicated that the maximum acceptable weights of lift selected by the subjects at 27°C WBGT were not significantly different from the weights selected at 22°C WBGT. On the other hand, the maximum acceptable weights selected at 32°C WBGT were reduced by approximately 13 percent.

Psychophysical acceptability and perception of load heaviness by females

The objective of the study was to evaluate subjective perceptions of load heaviness, and relate these perceptions to the maximal acceptable weights of lift. Ten female college students experienced in manual lifting participated in the study. In the first experiment, subjects were asked to select one of the seven linguistic values of load heaviness (very light, light, less-than-medium, medium, more-than-medium, heavy, and very heavy), which would best describe the lifted loads. Seven boxes, ranging in weight between 2.3 kg and 22.7 kg, were used for that purpose. In the second experiment, subjects were asked to fill empty boxes to the level they felt would best reflect a given load heaviness category. In the third experiment, the psychophysical methodology was used to determine the maximal acceptable weight of lift for an 8-hour day. The results showed that 50% of the subjects considered a 20.4 kg box (45 lbs) as very heavy, while another 50% believed that such a load was heavy. The average load selected as maximal acceptable weight of lift (MAWL) for an 8-hour day was 16.4 kg (standard deviation (SD) = 5.3 kg). When asked to determine the weights that would best describe a given category of load heaviness, the subjects selected 22.5 kg (SD = 3.7 kg) and 18.4 kg (SD = 2.7 kg) for very heavy and heavy categories, respectively. Further analysis revealed that only 30% of the subjects selected MAWL values that were larger than the pre-weighted boxes independently judged by them as very heavy or heavy categories. Also, 10% and 30% of the subjects selected MAWL values that were larger than the weights chosen during the self-classification procedure as representative of heavy or very heavy categories of load heaviness, respectively. It was shown that the loads selected as the maximum acceptable weights for an 8 h shift were independently judged by the female subjects as being in the more-than-moderate or heavy weight categories. Comparison of the results for females and males led to a conclusion that female subjects were more realistic, with respect to subjective perception of load heaviness, in selecting the MAWL values than were male subjects.

Psychophysical lifting capacity over extended periods

The effect of time on an individual's lifting capacity over extended periods using a psychophysical approach was studied. Twelve male subjects estimated their lifting capacity in a 25 min period, and then attempted to lift this weight for an 8 h period under varying conditions. For one experimental condition the subjects were allowed to adjust the weight, the final adjusted maximum acceptable weight of lift (MAWOL) averaged 85.4% of the original MAWOL determined in the 25 min session. The subjects also attempted to lift for an 8 h period, without any weight adjustments. All 12 subjects lasted the 8 h at 2 lifts per min, but at a frequency of 8 lifts per min only three subjects completed the eight hour lifting task. This indicates that the psychophysical approach is a valid method to measure lifting capacity across the lower lifting frequency range but overestimates the lifting capacity at the higher frequency range. Slight fluctuations were noted in heart rate and oxygen consumption which were recorded every hour.

Evaluating lifting tasks using subjective and biomechanical estimates of stress at the lower back

The objective of this study was to evaluate five different lifting tasks based on subjective and biomechanical estimates of stress at the lower back. Subjective estimates were obtained immediately after the subjects performed the lifting tasks. Rankings for different tasks were obtained according to the perceived level of stress at the lower back. A biomechanical model was used to predict the compressive force at the L5/S1 disc for the weight lifted considering link angles for the particular posture. The tasks were also ranked according to the compressive force loading at the L5/S1 disc. The weight lifted in these tasks for obtaining the subjective estimate of stress was the maximum acceptable weight of lift (MAWOL). This was determined separately for each subject using a psychophysical approach. Subjective estimates of stress were obtained for infrequent lifting, specifically for a single lift, as well as for lifting at a frequency of four lifts per min. The results showed that a lifting task acceptable from the biomechanical point of view may not be judged as a safe or acceptable task by the worker based on his subjective perception. This may result in a risk of the worker not performing the recommended task or not following the recommended method.

Psychophysical models for manual lifting tasks

This paper provides two models for males and females to assess the psychophysical maximum acceptable weight of lift. The weight guidelines generated by the models are a function of lifting frequency, height of lift, sagittal or asymmetrical lifting, task duration, container size in the sagittal plane, presence or absence of container couplings, and percentage of the working population. The developed models were generated from a knowledge base available in the published literature. A computer program was written in BASIC to assist the user in determining the safe load that could be handled by a specified working population. Model validation showed that the models developed predict the maximum acceptable weight of lift with a reasonable degree of accuracy. A comparison between the National Institute for Occupational Safety and Health recommendations and those made on the basis of the models developed in this paper is also presented.

Maximum acceptable weight of lift for an asymmetrical combination manual handling task : Rodrigues, C.C., Congleton, J.J., Koppa, R.J., and Huchingson, R.D.Int J Industr Ergonomics, 1989, 4(3), 245–253, 27 refs

Maximum acceptable weight of lift for an asymmetrical combination manual handling task : Rodrigues, C.C., Congleton, J.J., Koppa, R.J., and Huchingson, R.D.Int J Industr Ergonomics, 1989, 4(3), 245–253, 27 refs

The Effect of Rigid Container Shape on Maximum Acceptable Weight of Lift

In the chemical, pharmaceutical, and paint manufacturing industries raw and finished materials are frequently shipped in cylindrical rigid containers instead of boxes. Psychophysical manual materials handling lifting capacity studies to date have not considered whether rigid container shape has an effect on maximum acceptable weight of lift. Two psychophysical studies were designed and conducted in order to answer this question. During the first experiment ten subjects lifted boxes with three different heights, at three different frequencies, and through three different lift ranges in order to establish a data base in which to compare the results of the second experiment. During the second experiment the same group of subjects lifted cylinders with three different heights at the same frequencies of lift and through the same lift ranges as the first experiment. The subjects adjusted the weight of the box until they felt they could safely lift that weight for eight hours. This weight was the maximum acceptable weight of lift (MAWL). The experimental design for both experiments was a 3 factor randomized complete block design with blocking on subjects. The dependent variables were oxygen consumption (VO2), MAWL, and Borg's rating of perceived exertion. The results indicated that when one designs a lifting task for a rigid container the shape of the rigid container, whether a cylinder or a box, does not need to be taken into account and that current psychophysical lifting capacity prediction models can be used to design cylinder lifting tasks.

Maximum acceptable weight of lift for side and back lifting.

A series of laboratory experiments were conducted to find maximum acceptable weights in front, side, and back lifting. Fifteen college students participated in the experiment. Experimental trials for each type of lifting were conducted for 10 min for each subject at a rate of 4 lifts/min. Psychophysical methodology was used to find the acceptable weight based upon their perceived feeling of stress in the lower back. It was found that subjects are willing to lift the heaviest load using back lifting (average maximum acceptable weight: 41.5 lbs). Front lifting was the close second with 39.4 lbs. Also, there was a significant difference in maximum acceptable weight of lift between side lifting (average maximum acceptable weight: 25.5 lbs) and the other two types of lifting. It was also found that leg strength was a limiting variable for maximum acceptable weight in front lifting. Composite strength and shoulder strength were found to be limiting variables in side lifting. Composite strength was the limiting variable in the back lifting.

Maximum acceptable weight of lift for an asymmetrical combination manual handling task

This paper presents a study on a combination lift and lower manual handling task and was designed to simulate the loading of grocery bags into car trunks. Eighteen male subjects performed an externally-paced task of lifting grocery bags loaded with steel shots from 15 cm above the floor and over a wooden sill. There were two different sill heights of 70 cm and 90 cm, and for each of these heights there were three different sill depths of 28 cm, 43 cm, and 57 cm. The dependent variables were the maximum acceptable weight of lift. Constant conditions were temperature (23–26°C), humidity (52–62%), horizontal distance of lift (136 cm), and time of day the subjects performed the lifting. A unique lifting sequence and a modified version of the psychophysical methodology were used to determine the maximum acceptable weight that subjects were willing to lift. There were no significant differences in the weights lifted across the two sill heights but weights lifted over the 28 cm sill depth was significantly more than the weights lifted for either the 43 cm depth or the 57 cm depth.

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

Twelve healthy, experienced underground coal miners performed lifting capacity tests in stooped and kneeling postures using a modified psychophysical, procedure. Subjects adjusted weight in a lifting box to the maximum they could handle without undue fatigue in an asymmetric lifting task. Lifting periods were 20 min in duration and the frequency was 10 lifts/min. Tests were performed under a 48-in. roof that restricted the subject's posture. Psychophysical, physiological, and biomechanical dependent measures included the maximum acceptable weight of lift (MAWL), heart rate (HR), rate of oxygen consumption (V̇O 2), ventilation volume rate (V̇ E), respiratory exchange ratio (R), and integrated electromyography (EMG) of eight trunk muscles. Results indicated that the MAWL was significantly lower when kneeling than when stooped (p < 0.05). Furthermore, metabolic demands were greater in terms of HR (p < 0.005) and VO 2 (p < 0.05) when kneeling. Left and right erectores spinae muscles exhibited increased EMG activity in the kneeling posture (p < 0.001). It was concluded that psychophysical lifting capacity is decreased, while the metabolic stress and internal load on the spine are increased, in the kneeling posture. Results of this Bureau of Mines study indicate that it may be advisable to reduce the weight of materials that are handled repetitively in the kneeling posture.

The role of lifting belts in manual lifting

The objectives of this research were to demonstrate the effects of belts on load lifting capabilities of individuals using the psychophysical method, subjective surveys, and the measurement of external pressure on the abdomen. Two types of belts were used in this study: (a) the Air belt, a registered trade mark and product of Pneumedic Corporation, which represented the type of support belt characterized by an inflatable bladder; and (b) the CompVest belt, a product and registered trade mark of the Comp Equipment Corporation, which represented a mechanical, elastic type of support. Twelve male college students were required to lift tote boxes containing steel shot from the floor to metacarpal III height (knuckle height) at a rate of three lifts per minute for a period of 45 min. Each subject performed three sets of lifts, i.e. once with no belt (control) and once with each of the two belts. The maximum acceptable weight of lift was recorded. Changes in the external abdominal belt pressures during the lifting were recorded using the Texas Interface Pressure Evaluator. A subjective survey consisting of eight questions was administered to each subject after each belt was tested to determine the subject's feelings. In addition to the above survey, a post-test question was given asking the subjects to rank the three treatments in order of preference. Statistical tests showed that the belts did increase the perceived maximum acceptable weight of lift with respect to the control (no belt); however, there was no significant difference between the two belts. Also, the external abdominal pressures generated by the two belts were essentially the same. Results of the subjective surveys tended to favor the CompVest belt over the Air belt.

Maximum acceptable lifting loads during seated and standing work positions

The psychophysical method was used to determine the maximal acceptable load that eight males (age 22–30 years) would lift in each of four different positions: (1) seated, two-handed, symmetrical lift from a table, to a position 38 cm forward of the edge, (2) a seated lift from a position at the subject's side, on to a table in front of the subject involving a 90 degree twist of the torso, (3) standing, two-handed, symmetrical lift from the table, to a position 38 cm forward of the edge, and (4) standing, vertical lift from 86 above the floor. Subsequent to a training period, subjects lifted a tray with slotted handles at the rate of 1 or 4 lifts/min. Each subject chose the weight of the tray which was acceptable to him by adding or removing flat pieces of lead over a 45 min period. The weight of the tray, heart rate, and the perceived exertion were measured at 15, 30 and 45 min. Oxygen consumption was measured during the last 5 min of the 45 min experiment. Statistical analysis revealed a significant frequency and position effect. An increase in frequency from 1 to 4 lifts/min resulted in a decrease of 1·6 to 2·1 kg in the maximum acceptable weight for the various tasks. On average, the maximum acceptable weight of lift for standing positions was 16% greater than for sitting positions. Oxygen consumption and heart rate were significantly higher for 4 lifts/min than for 1 lift/min; however, the rating of perceived exertion did not differ for any factor.