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

Psychophysically determined symmetric and asymmetric lifting capacity of Chinese males for one hour's work shifts

Eighteen adult males (mean age 22·6 years, weight 78·6kg and height 176·6cm) participated in a study designed to investigate the effects of symmetrical and asymmetrical lifting on the maximum acceptable weight of lift and the resulting physiological cost. Each subject performed sixty different lifting tasks involving two lifting heights, three lifting frequencies and five containers. For each lifting task, the load was lifted either symmetrically (sagittal lifting) or asymmetrically (turning 90° while continuing to lift). The heart rate and oxygen uptake of the individuals at the maximum acceptable weight of lift were measured. At the end of the experiment, subjects also verbally indicated their preference for symmetrical and asymmetrical lifting. When lifting asymmetrically, subjects accepted approximately 8·5% less weight. There was, however, no difference in the physiological costs when lifting symmetrically or asymmetrically. Lifting asymmetrical loads also resulted in lower maximum acceptable weights. No difference in either oxygen uptake or heart rate was observed when the centre of gravity of the load was offset by 10·16 or 20·32 cm from the mid-sagittal plane in the frontal plane towards the preferred hand. All subjects indicated, verbally, that asymmetrical lifting tasks were physically more difficult to perform.

Predicting maximum acceptable weights of symmetrical and asymmetrical loads for symmetrical and asymmetrical lifting

10 undergraduate men were tested to determine the effects of lifting mode and frequency on psychophysically established maximum acceptable weight of lift for 4 hr. of work. The heart rate and rate of perceived exertion (RPE) of the individuals while lifting the maximum acceptable weight of lift were measured. When performing a 90 degrees asymmetric lifting, subjects lifted approximately 10% less weight than lifted in symmetric lifting. Nonsignificant differences in maximum acceptable weight of lift, heart rate, and RPE values were found between asymmetric lifting with trunk rotation and asymmetric lifting with leg rotation. The lifting frequency significantly affected the maximum acceptable weight of lift, heart rate, and RPE. Heart rate and RPE increased with lifting frequency. The maximum acceptable weight of lift at 2 lifts/min. and 4 lifts/min. were approximately 91.5% and 82.5% of that of 1 lift/ min., respectively.

To explore the maximum acceptable weight of lift (MAWL) in different lifting conditions and the suitable lifting equation for the stipulation of occupational health standard of manual lifting tasks in China. The MAWL was investigated among the thirteen male and ten female students using psychophysical methodology and the recommended weight of limit (RWL) was compared. The MAWL of male and female subjects was decreased gradually with the increase of lifting height. Once the height of lifting was over shoulder, the MAWL was decreased dramatically. The RWL was greater than the MAWL at 25 cm horizontal distance in male subjects, but the RWL was smaller than the MAWL at the distance of 45 cm and 63 cm. The average MAWL of male subjects was 30.8% greater than that of female subjects. The MAWL was decreased gradually with increase of the horizontal distance at the same height of lifting. The result of the male subjects was consistent with that of the female subjects. For the asymmetric lifting tasks of the male subjects, the bigger the angle of rotation was, the less the MAWL became. The angle of rotation had negative correlation with the capability of lifting (r = -0.996 6, P < 0.01). When the subjects performed asymmetric lifting tasks, the RWL was smaller than the MAWL and the difference was significant. The revision is sufficient for the horizontal distance and asymmetric lifting in the NIOSH lifting equation, but it is not suitable for height, especially for the task of lifting over shoulder. The RWL for the task of lifting over shoulder should be lowered. The factor of gender should be taken into account in the lifting equation and the constant of gender S can be added. Then S = 1 for male while S = 0.692 for female.

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

Maximum acceptable weights for asymmetric lifting of Chinese females

An experiment was performed to determine whether maximum acceptable weight of lift (MAWL) estimates were consistent with previously reported values when the MAWL was determined without visual feedback during the weight adjustment period. Twelve healthy male students performed four lifting tasks similar to those often performed in previous psychophysical studies: floor to knuckle at 1 lift per min, floor to knuckle at 4.3 lifts per min, knuckle to shoulder at 1 lift per min, and knuckle to shoulder at 4.3 lifts per min. When compared with the previous studies with similar box dimensions, similar trends between the conditions were present, but a slight reduction in weight was usually chosen by the participant in this study. However, the results of this study agreed with previous psychophysical studies when the distance of the load from the spine (moment arm) was taken into consideration by either comparing the MAWLs with those of a large box or by comparing load moments. Hence this study shows that eliminating visual feedback during the adjustment periods did not significantly alter the MAWLs from previous studies. It also indicates that one must use caution when applying the MAWL in the workplace because the MAWL is very sensitive to moment arm.

This paper presents ‘maximum acceptable weight of lift’ design databases for lifting asymmetrical loads by industrial male and female workers. These databases were developed by first collecting experimental data on experienced and inexperienced workers under identical conditions (Study A) and then applying the trends developed, as a result of data comparison, to the data collected on inexperienced workers in a separate independent study (Study B) dealing with lifting asymmetrical loads. Several different task variables are accounted for in the data. These include the following: 1) lifting height (floor to knuckle, knuckle to shoulder, and shoulder to reach); 2) frequency of lift (2, 4, and 6 lifts/min); 3) box-size (30.48, 45.72, and 60.96 cm long in the sagittal plane); and 4) load asymmetry (indicated by the offset of the center of gravity in the frontal plane: 0, 12.7, and 25.4 cm from the mid-sagittal plane; the 0 cm center of gravity (e.g.,) offset indicates symmetrical load).

This paper presents 'maximum acceptable weight of lift' design databases for lifting asymmetrical loads by industrial male and female workers. These databases were developed by first collecting experimental data on experienced and inexperienced workers under identical conditions (Study A) and then applying the trends developed, as a result of data comparison, to the data collected on inexperienced workers in a separate independent study (Study B) dealing with lifting asymmetrical loads. Several different task variables are accounted for in the data. These include the following: lifting height (floor to knuckle, knuckle to shoulder, and shoulder to reach); frequency of lift (2, 4, and 6 lifts/min; box-size (30.48, 45.72, and 60.96 cm long in the sagittal plane); and load asymmetry (indicated by the offset of the center of gravity in the frontal plane: 0, 12.7, and 25.4 cm from the mid-sagittal plane; the 0 cm center of gravity (c.g.) offset indicates symmetrical load).

Introduction The etiology of spinal deformity in idiopathic scoliosis is unclear to date. One of the suspected influences is the asymmetric loading condition involved in the disorder. The aim of this project is to test the hypothesis that asymmetric dynamic loading influences the morphological and biological characteristics of the intervertebral discs in scoliosis. The study is performed with organ cultured discs by using a custom-designed asymmetrical loading device. Material and Methods Bovine caudal discs (6–10 months) were used in current study. For symmetric dynamic loading (Parallel), discs were placed in custom-designed chambers, and compressed by parallel metal plates in a Bose mechanical testing device. For asymmetric dynamic loading (Wedge), a 10° wedge was placed underneath the discs to mimic the load bearing condition of discs in scoliotic patients. The discs were submitted to 2 different load regimes: (1) 1 hour dynamic loading (0.02–0.4 MPa, 1Hz) and 23 hours free swelling culture for 7 days; (2) 1 hour dynamic loading (0.02–0.4 MPa, 1Hz) and 23 hours static loading (0.2 MPa) for 7 days. Disc heights were measured with caliper before and after each loading. After 7 days of culture, gene expression levels of aggrecan (ACAN), type I and II collagen (COL1 and COL2), IL1, IL6, and MMP1 in the annulus fibrosus was analyzed by real-time PCR. Genes that have been found dysregulated in human scoliotic discs compared with healthy controls were also measured in the organ cultured discs, including MMP13, type X collagen (COL10), CXCR4, BMP3, S100A12, and S100A8 ( n = 8). Results Disc height showed a constant drop in load regime 2, while a temporary decrease after 1h dynamic loading followed by free swelling recovery was noted in load regime 1. After 7th dynamic loading, the change in shape was greater in load regime 2 (disc height ratio wedged to non-wedged side of 0.81), than that in load regime 1 (height ratio of 0.87, p &lt; 0.05). Under load regime 2, MMP13 gene expression level increased 6.1-fold in Wedge disc compared with Parallel disc, while gene expression levels of COL10, CXCR4, BMP3, S100A12, and S100A8 were not affected. Gene expression levels of ACAN, COL1 and COL2 under load regime 1 were significantly higher compared with load regime 2. Moreover, discs under load regime 2 showed a trend in higher IL1, IL6, and MMP1 gene expression compared with regime 1. Conclusion Diurnal dynamic loading and free swelling recovery could maintain the gene expression of organ cultured discs at their physiological level. Diurnal dynamic loading followed by static loading mimicked a degenerative condition, as indicated by lower anabolic and higher catabolic gene expression. These results suggest that recovery of disc height and morphology after dynamic load may help to prevent degeneration of discs under constant loading. Asymmetric dynamic and static loading regime induces an increase in MMP13 gene expression compared with symmetric loading, which was also observed in a human scoliosis sample dataset. These results indicate that short-term asymmetric loading may be used to mimic early changes associated with the onset of scoliosis. Acknowledgment This study is supported by AOSpine International.

The purpose of this study was to investigate the maximum acceptable weight of lift (MAWL) by Indonesian inexperienced female manual material handlers. Twenty-one females who were selected based on their physical activity categories voluntarily participated in this study. The participants were asked to determine their MAWLs using the psychophysical method for the lifting tasks at two different lifting frequencies: one lift/5 min and 4 lifts/min. The participants’ heart rate was also recorded to be utilized for investigating the physiological responses while lifting the obtained MAWLs. The obtained MAWLs were also compared to the MAWLs of other study populations, using published data. As the results, two-way analysis of variance test result revealed no significant effect of physical activity category on MAWL (p = 0.890). On the other hand, a significant effect on MAWL for the lifting frequency was observed at p < .001. The comparison of MAWLs obtained in this study to other studies showed that no significant differences on MAWL were found between Indonesian and Chinese inexperienced manual handlers for the lifting tasks at one lift/5 min. The significant differences on MAWL were observed between Indonesian inexperienced and American experienced female manual handlers. However, no significant differences were observed for the lifting tasks at 4 lifts/min. Furthermore, the physiological data analysis revealed that the energy expenditures required for lifting at one lift/5 min was significantly less than the physiological limit, while those of lifting at 4 lifts/min was significantly higher than the limit. The results of this study might be utilized as consideration for determining the safety lifting limit for Indonesian inexperienced female manual material handlers.

PurposeTo determine the effects of asymmetric loads on muscle activity with the bench press.MethodSeventeen resistance-trained men performed one familiarization session including testing one repetition maximum (1RM) and three 5 repetition maximum (RM) lifts; using symmetric loads, 5% asymmetric loads, and 10% asymmetric loads. The asymmetric loading (i.e., reduced load on one side) was calculated as 5% and 10% of the subject`s 1RM load. In the experimental session, the three conditions of 5RM were conducted with electromyographic activity from the pectoralis major, triceps brachii, biceps brachii, anterior deltoid, posterior deltoid, and external oblique on both sides of the body.ResultsOn the loaded side, asymmetric loads reduced triceps brachii activation compared to symmetric loads, whereas the other muscles demonstrated similar muscle activity between the three conditions. On the de-loaded side, 10% asymmetry in loading resulted in lower pectoralis major, anterior deltoid, and biceps brachii activation compared to 5% asymmetric and symmetric loading. On the de-loaded side, only pectoralis major demonstrated lower muscle activation than symmetric loads. Furthermore, asymmetric loads increased external oblique activation on both sides compared to symmetric loads.ConclusionsAsymmetric bench press loads reduced chest and shoulder muscle activity on the de-loaded side while maintaining the muscle activity for the loaded side. The authors recommend resistance-trained participants struggling with strength imbalances between sides, or activities require asymmetric force generation (i.e., alpine skiing or martial arts), to implement asymmetric training as a supplement to the traditional resistance training.

Maximum acceptable weight of lift by Chinese experienced male manual handlers

It is unclear whether the maximum acceptable weight of lift (MAWL), a common psychophysical method, reflects joint kinetics when different lifting techniques are employed. In a within-participants study (n = 12), participants performed three lifting techniques – free style, stoop and squat lifting from knee to waist level – using the same dynamic functional capacity evaluation lifting test to assess MAWL and to calculate low back and knee kinetics. We assessed which knee and back kinetic parameters increased with the load mass lifted, and whether the magnitudes of the kinetic parameters were consistent across techniques when lifting MAWL. MAWL was significantly different between techniques (p = 0.03). The peak lumbosacral extension moment met both criteria: it had the highest association with the load masses lifted (r > 0.9) and was most consistent between the three techniques when lifting MAWL (ICC = 0.87). In conclusion, MAWL reflects the lumbosacral extension moment across free style, stoop and squat lifting in healthy young males, but the relation between the load mass lifted and lumbosacral extension moment is different between techniques. Practitioner Summary: Tests of maximum acceptable weight of lift (MAWL) from knee to waist height are used to assess work capacity of individuals with low-back disorders. This article shows that the MAWL reflects the lumbosacral extension moment across free style, stoop and squat lifting in healthy young males, but the relation between the load mass lifted and lumbosacral extension moment is different between techniques. This suggests that standardisation of lifting technique used in tests of the MAWL would be indicated if the aim is to assess the capacity of the low back.