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Biomedical subjects

W Karwowski

Publications and source records attributed to W Karwowski.

32 records · Page 2Linked to original sources
PubMed1992

Effects of job-simulated flexibility and strength-flexibility training protocols on maintenance employees engaged in manual handling operations.

This study examined the effects of four flexibility and strength-flexibility training protocols on the dynamic strength, endurance time, and truncal flexibility of 24 maintenance employees engaged in manual material handling operations. The study was conducted over an 8-week period. Significant improvement in physical capacity was obtained through flexibility training either by a progressive increase in the holding time with fixed exercise repetition or a progressive increase repetition with fixed holding time. The flexibility and strength-flexibility training protocols exhibited similar effects on physical capacity. It was suggested that a follow-up flexibility protocol should be performed on a daily basis in order to maintain the gains obtained in flexibility during the intensive/short training programme.

Adult↗
PubMed1992

A comparative study of the myoelectric amplitude characteristics for weight-holding tasks.

This study was conducted to examine the effects of load, time, and gender on five amplitude measures of the myoelectric signal (MES) for 10 male and 10 female subjects engaged in upper extremity weight-holding tasks. The results indicated that: (1) measures of amplitude variability (e.g.: standard deviation) are more sensitive to changes in load and time than the full-wave rectified integral and root-mean square indices; (2) both load and time had a significant effect on MES indices, suggesting that amplitude measures may be used as a tool for evaluating the degree of muscular loading and fatigue; (3) females have higher muscular exertion values than males under the same experimental conditions, indicating that females are subjected to higher levels of stresses than males for the same amount of workload. The implications of the results are discussed.

Adult↗
PubMed1991

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.

Adult↗
PubMed1991

Worker selection of safe speed and idle condition in simulated monitoring of two industrial robots.

Industrial robots often operate at high speed, with unpredictable motion patterns and erratic idle times. Serious injuries and deaths have occurred due to operator misperception of these robot design and performance characteristics. The main objective of the research project was to study human perceptual aspects of hazardous robotics workstations. Two laboratory experiments were designed to investigate workers' perceptions of two industrial robots with different physical configurations and performance capabilities. Twenty-four subjects participated in the study. All subjects were chosen from local industries, and had had considerable exposure to robots and other automated equipment in their working experience. Experiment 1 investigated the maximum speed of robot arm motions that workers, who were experienced with operation of industrial robots, judged to be 'safe' for monitoring tasks. It was found that the selection of safe speed depends on the size of the robot and the speed with which the robot begins its operation. Speeds of less than 51 cm/s and 63 cm/s for large and small robots, respectively, were perceived as safe, i.e., ones that did not result in workers feeling uneasy or endangered when working in close proximity to the robot and monitoring its actions. Experiment 2 investigated the minimum value of robot idle time (inactivity) perceived by industrial workers as system malfunction, and an indication of the 'safe-to-approach' condition. It was found that idle times of 41 s and 28 s or less for the small and large robots, respectively, were perceived by workers to be a result of system malfunction. About 20% of the workers waited only 10 s or less before deciding that the robot had stopped because of system malfunction. The idle times were affected by the subjects' prior exposure to a simulated robot accident. Further interpretations of the results and suggestions for operational limitations of robot systems are discussed.

Accidents, Occupational↗
PubMed1987

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.

Journal Article↗
PubMed1986

Development of a safety index for manual lifting tasks.

The concept of a safety index (SI) for assigning a worker to a particular manual lifting task is developed, and a simple formula for its calculation is presented. The proposed index is based upon the combined measure of acceptability of the biomechanical and physiological stress responses of the worker to a lifting task. Individual capacity norms, as opposed to the norms usually given based on population percentiles, are also defined. Numerical examples are given to illustrate the SI approach.

Journal Article↗
PubMed1986

Prediction of maximum acceptable weight of lift in the horizontal and vertical planes using simulated job dynamic strengths.

An investigation was undertaken to determine the feasibility of predicting maximum weights of lift that are acceptable to individuals by measuring the individuals' simulated job dynamic strengths. Since almost all manual materials handling jobs are dynamic in nature, it was hypothesized that correlations between maximum weights acceptable for lifting and the dynamic strengths measured under similar conditions would be high compared to isometric strengths. If so, then a relatively simple procedure can be developed to estimate what people are willing to lift safely. With the use of a specially designed and constructed three-dimensional dynamic strength simulator, 19 males and 6 females lifted loads in two vertical and two horizontal planes. Their dynamic strengths also were measured under identical conditions. The correlations between simulated job dynamic strengths and acceptable weights of lift were much higher (0.52 to 0.67) compared to correlations between isometric strengths and acceptable weights of lift (0.29 to 0.38). This also confirmed earlier findings that dynamic strengths are more suitable predictors of the maximum weights people are willing to handle. Simple equations are presented between simulated job dynamic strengths and maximum acceptable weights of lift in the horizontal and vertical planes. These equations demonstrate that dynamic strength can be used reliably when matching jobs with individuals.

Adult↗
PubMedDate not supplied

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.

Biomechanical Phenomena↗
PubMedDate not supplied

An electromyographic analysis of seated and standing lifting tasks.

The objective of this project was to compare the muscular effort exerted during manual lifting tasks performed in standing versus seated posture. Six male undergraduate and graduate students performed 12 different static and dynamic lifts in both sitting and standing positions. During each effort electromyographic (EMG) data were collected on four muscles groups (low back, upper back, shoulder, and abdominals). Four contractions were designed to elicit maximum muscular effort in the four groups being monitored. The remaining data were then expressed as a percentage of maximum EMG. Each subject performed the following: maximum static lift when sitting; maximum static lift when standing; sitting, static lift with 15.9 kg; standing, static lift with 15.9 kg; dynamic sit-forward lift with 15.9 kg, dynamic stand-forward lift with 15.9 kg, dynamic sit-twist with 15.9 kg, dynamic stand-vertical lift with 15.9 kg. Each of the lifts was performed with a wooden tray with slotted handles. Root mean square (RMS) values of the EMG data were calculated for three second periods. EMG activity in the low back, upper back, and shoulder was greater during sitting lifting than during standing lifting. The sit-twist lift resulted in the highest EMG in the abdominal muscles. Dynamic lifts resulted in more muscle activity than did static lifts. From these data it was concluded that sitting-lifting results in greater stress in the low back, upper back, and shoulders than does lifting while standing.

Adult↗