Differences in lifting strength profiles between experienced workers and novices at various exertion heights

This study compared lifting strength patterns between experienced workers and novices at various exertion heights. Twenty-one experienced workers and 21 novices were recruited to determine their static-lifting strength under various heights (10-150 cm in increments of 10 cm) using two exertion methods (vertically upward lifting, VUL, and toward body lifting, TBL). Testing posture was also recorded by a motion analysis system for comparing with the corresponding strength values.Results showed that strength during VUL were much higher than strength during TBL at 15 height positions (p < 0.001). Strength in all 30 task combinations showed no difference between the two groups except for the VUL at heights of 100-120 cm. On the average, strength exerted by novices during VUL was 4.57-7.61 kg lower than that of workers while lifting at 100-120 cm heights (all p < 0.05). The strength during TBL consistently decreased with increased heights of lifting. When workers performed VUL, the strength surprisingly remained nearly unchanged throughout the heights of interest. The postures adopted by workers during VUL were also highly differentiated from novices while performing near-floor positions, but the strength was equivalent to each other. This study demonstrated that the static-lifting strength of novices were significantly lower than those of experienced workers while upward lifting near the participant’s elbow height. It was concluded that workers tend to adopt a safer (i.e., more flexed knees) and more skillful technique than novices to generate forces, resulting in lower spinal loads during both methods of lifting.

Relevance to Industry

Many studies have established the human strength data based on student participants who do not have experience in manual materials handling. The present findings clearly suggest that lifting strength data collected on novices (e.g., on students) should be carefully applied in the task (re)design at the workplace as their strength profiles and the postures adopted during lifting differ from workers.     

Biomechanical differences between expert and novice workers in a manual material handling task

The objective was to verify whether the methods were safer and more efficient when used by expert handlers than by novice handlers. Altogether, 15 expert and 15 novice handlers were recruited. Their task was to transfer four boxes from a conveyor to a hand trolley. Different characteristics of the load and lifting heights were modified to achieve a larger variety of methods by the participants. The results show that the net moments at the L5/S1 joint were not significantly different (p > 0.05) for the two groups. However, compared with the novices, the experts bent their lumbar region less (experts 54° (SD 11°); novices 66° (SD 15°)) but bent their knees more (experts approx. 72° (SD approx. 30°); novices approx. 53° (SD approx. 33°), which brought them closer to the box. The handler's posture therefore seems to be a major aspect that should be paid specific attention, mainly when there is maximum back loading.

Statement of Relevance: The findings of this research will be useful for improving manual material handling training programmes. Most biomechanical research is based on novice workers and adding information about the approach used by expert handlers in performing their tasks will help provide new avenues for reducing the risk of injury caused by this demanding physical task.     

Spinal loading in static and dynamic postures: EMG and intra-abdominal pressure study

Abstract

The difference in physiological stress between static posture loading and dynamic lift is poorly understood. Therefore, the quantitative pattern of gradual increase and decrease of stress as measured by EMG of erectores spinae at T₁₂ and L₃ and intraabdominal pressure (IAP) due to steady progressive loading and unloading in static stooping posture was studied and compared with that of stoop lifting of the same weight. For dynamic loading and unloading a steady flow of 25 kg of water into or out of a plastic tub held in the hand while maintaining a stooping posture was used. The subjects also performed stoop lifting weights of 15 and 25 kg. In static posture loading the mean EMG at T₁₂ was approximately 50% of the L₃ level. During unloading in that posture it was reduced to 33%. The level of electromyographic activity at T₁₂ for loading was not significantly different from unloading. At L₃ however, the magnitude increased significantly for unloading. The EMG and intraabdominal pressure responses of static posture were between 33 and 50% of the corresponding phases during stoop lifting of the same weight. An insignificant difference in IAP and heart rate between static posture loading and stoop lifting indicates a less critical role of IAP and no difference in cardiac stress in less stressful tasks.     

Dynamic biomechanical modelling of symmetric and asymmetric lifting tasks in restricted postures

This article describes investigations of dynamic biomechanical stresses associated with lifting in stooping and kneeling postures. Twelve subjects volunteered to participate in two lifting experiments each having two levels of posture (stooped or kneeling), two levels of lifting height (350 or 700 mm), and three levels of weight (15,20, or 25 kg). One study examined sagitally symmetric lifting, the other examined an asymmetric task. In each study, subjects lifted and lowered a box every 10 s for a period of 2 min in each treatment combination. Electromyography (EMG) of eight trunk muscles was collected during a specified lift. The EMG data, normalized to maximum extension and flexion exertions in each posture, was used to predict compression and shear forces at the L3 level of the lumbar spine. A comparison of symmetric and asymmetric lifting indicated that the average lumbar compression was greater in sagittal plane tasks; however, both anterior-posterior and lateral shear forces acting on the lumbar spine were increased with asymmetric lifts. Analysis of muscle recruitment indicated that the demands of lifting asymmetrically are shifted to ancillary muscles possessing smaller cross-sectional areas, which may be at greater risk of injury during manual materials handling (MMH) tasks. Model estimates indicated increased compression when kneeling, but increased shear forces when stooping. Increasing box weight and lifting height both significantly increased compressive and shear loading on the lumbar spine. A multivariate analysis of variance (MANOVA) indicated complex muscle recruitment schemes—each treatment combination elicited a unique pattern of muscle recruitment. The results of this investigation will help to evaluate safe loads for lifting in these restricted postures.     

Differences between experts and novices in the monitoring of automated systems

In the future of aviation, operators will have to work with highly automated systems. This necessitates operators monitoring appropriately (OMA). Psychophysiological studies support the idea that eye movements offer an appropriate means for measuring the acquisition of visual information. A normative model for adequate monitoring behaviour was developed and eye movement parameters were defined to identify OMA. The normative model was validated by eye tracking studies with airline pilots and air traffic controllers. The present eye-tracking study focused on differences in monitoring behaviour between experts and novices. Results from 21 experts (experienced pilots and air traffic controllers) and 33 novices (applicants for jobs in aviation) are reported. Significant differences in monitoring behaviour between experts and novices were found. Experts allocate their attention more efficiently. Learning from experts’ monitoring of automated processes will be helpful in learning how to select successful trainees and provide them with appropriate training.     

Effects of work experience and exertion height on static lifting strengths and lift strategies of experienced and novice female participants

In this study, 46 female experienced workers and inexperienced novices (23 each) were recruited to determine their maximum lifting strength at 15 exertion heights between 10 and 150 cm from the floor. The results revealed that the experienced workers' strengths at all 15 heights exhibited relatively little fluctuation, and were approximately 50–70 N lower than those of novices when heights were ≤50 cm. No differences in strengths were observed at 60–150 cm between the groups. The experienced workers tended to adopt a consistently deep squat at lower heights (≤50 cm) and a more erect posture with stiffened arms at higher heights (≥70 cm), resulting in lower L4/L5 disc compression forces and shoulder moments than in novices, respectively. In contrast to the lifting techniques adopted by experienced workers to effectively avoid overloading, the findings suggest that novice female workers who lack experience should be cautious and trained for performing lifting tasks.     

Rapid Communication Effects of posture,weight and frequency on trunk muscular activity and fatigue during repetitive lifting tasks

Abstract

We examined the effects of posture, weight and frequency on trunk muscular activity and fatigue during repetitive dynamic lifting. Electromyographic (EMG) signals from eight primary trunk muscles were collected during 120 min for four different task conditions. The patterns of muscle recruitment and the levels of relative activation were analysed using the normalized EMG data. Median power frequency (MPF) shift patterns were analysed to examine muscular fatigue. The muscles in the dorsal part of the trunk were activated at the symmetric posture, while the muscles on the contralateral side to the workload were more strongly activated at the asymmetric posture. Decreasing trends of MPFs were found in some active muscles, and they were more pronounced for the asymmetric posture than for the symmetric posture. It was also seen that the muscles became fatigued faster for the light load-high frequency task than for the heavy load-low frequency task.     

Quantitative and qualitative differences between experts and novices in chunking computer software knowledge

This study investigated quantitative and qualitative differences between experts and novices in knowledge structure, specifically in their chunking of computer software knowledge. An experiment was conducted to collect pairwise relatedness ratings of 23 concepts in C computer programming from 10 experts and 10 novices. Correlation analyses of relatedness ratings were performed to examine expert‐novice differences in overall knowledge structure. The intragroup correlation coefficients of experts were greater than the intragroup correlation coefficients of novices and the intergroup correlation coefficients between experts and novices. Hence, there existed structural differences of knowledge between experts and novices. To examine how experts differ from novices quantitatively and qualitatively in their knowledge chunking, the relatedness ratings of experts were averaged within the group to give a single set of relatedness ratings, and the relatedness ratings of novices were also averaged within the group to give a single set of relatedness ratings. Then the hierarchical clustering analyses were performed on the set of relatedness ratings for the experts group and on the set of relatedness ratings for the novices group, respectively. The hierarchical clustering of C concepts made by experts and the hierarchical clustering of C concepts made by novices indicated that novices had more but smaller knowledge chunks than experts for the common set of knowledge, and thatthe rough chunking of knowledge made by novices was qualitatively similar to the rough chunking of knowledge made by experts, although on a more detailed level qualitative differences still existed.     

Learning to tie well with others: bimanual versus intermanual performance of a highly practised skill

Studies indicate that novices are faster in manual tasks when performing with a partner (‘intermanual’) than with their own two hands (‘bimanual’). The generality of this ‘mode effect’ was examined using a highly practised bimanual task, shoe tying, at which participants were experts. Speed–variability correlations confirmed participants were bimanually skilled but not intermanually skilled. Contrary to results using novices, intermanual was slower, such that prior skill reverses the effect. Analyses incorporating the similarity of shoe-tying strategies across dyads implicated a perceptual rather than shared knowledge/representation basis for intermanual performance. Practice effects indicated that intermanual performance built upon prior bimanual skill, such that novel relative timings between dyads' hands must be acquired. Motor transfer effects provided support for this conclusion. During shoe tying, hands were tightly coupled in the intermanual mode due to the perceptual coupling constraints of intermanual performance. Increased coupling was correlated with slower performance. Implications for real-world tasks (e.g. surgical knot tying) are described.     

Expert versus novice use of the executive support systems: an empirical study

Expertise is essential in problem solving, particularly for executives. Much literature indicates that, in solving daily problems, executives may employ both analytical thinking and intuition. To develop skills and apply intuition, company executives require the use of support devices such as executive support systems (ESS), but their value may differ substantially between experts and novices.Previous research has failed to address the effects of expertise on ESS use. Therefore, this study examines how professionals use them to address business-oriented tasks. The professionals studied were divided into two groups, depending on whether they were experts or novices in the business represented by those tasks. The findings of the experiments show that computer self-efficacy strongly influenced the use of ESS. Moreover, experts felt that the ESS was of greater use when more powerful systems were employed, while the difference for novices between more and less powerful systems was insignificant. Finally, experts rated their user information satisfaction score significantly higher when employing more powerful systems. However, novices rated systems significantly higher only when they cognitively fit the performed task. Implications are discussed.     

Acceptable weights and physiological costs of performing combined manual handling tasks in restricted postures

Eight healthy, male underground coal miners (mean age = 36.9 yrs +/- 4.5 SD) participated in a study examining psychophysically acceptable weights and physiological costs of performing combined lifting and lowering tasks in restricted head-room conditions. Independent variables included posture (stooping or kneeling on two knees), task symmetry (symmetric or asymmetric), and vertical lift distance (35 cm or 60 cm). All tasks were 10 min in duration and were performed under a 1.22 m ceiling to restrict the subject's posture. Subjects were required to raise and lower a lifting box every 10s, and asked to adjust the box weight to the maximum amount they could handle without undue strain or fatigue. During the final 5 min of each test, data were collected to determine the energy expenditure requirements of the task. Results of this study demonstrated that psychophysical lifting capacity averaged 11.3% lower when kneeling as compared to stooping. Subjects selected 3.5% more weight in asymmetric tasks, and lifted 5.0% less weight to the 60 cm shelf compared to the 35 cm shelf. Heart rate was not significantly affected by posture, but was increased an average of 4 beats/min in asymmetric conditions, and by 3.5 beats/min while lifting/lowering to/from the high shelf. Oxygen uptake was increased by 9% when stooped, by 10% when lifting/lowering asymmetrically, and by 8.2% when performing the task to the high shelf. Results of this study indicate that, wherever possible, materials that must be lifted manually in low-seam coal mines be designed in accordance with the decreased lifting capacity exhibited in the kneeling posture.     

Hand-hold location and trunk kinematics during box handling

Trunk kinematics variables have been shown to be related to low back injury risk during lifting tasks and it was hypothesised that changes in hand-hold positions could influence trunk kinematics and thereby risk. Fourteen subjects lifted a 5 or 10 kg box using four different hand placement locations (two symmetric and two asymmetric) while their trunk kinematics (position, velocity and acceleration in the sagittal, coronal and transverse planes) were captured using the lumbar motion monitor (LMM). These kinematics data were then used to calculate the probability of high risk group membership (PHRGM) as defined in the LMM risk assessment model. The results showed significant effects of hand placement on trunk kinematics, resulting in significant changes in the PHRGM variable ranging from a low of 20% in a the symmetric low load condition to a high of 38% under the asymmetric, 10 kg condition.

Statement of Relevance: Manual materials handlers use a variety of hand-hold positions on boxes during lifting. Where a lifter grabs the box can influence the trunk kinematics during the lifting task and these kinematics have been shown to provide some insight into risk of low back injury. This study documents the trunk postures and kinematics as a function of hand-hold position.     

Cognitive analysis of experts’ and novices’ concept mapping processes: An eye tracking study

The goal of this study was to explore how designated experts (subject experts with extensive experience in science education and concept mapping) and novices (pre-service teachers) establish concept map (CM) development processes while considering their cognitive processes. Two experiments were conducted in which eye-tracking, written, and verbal data were collected from 29 novices and 6 subject matter experts. The results showed that despite some similar strategies, novices and experts followed different patterns during the CM development process. Both experts and novices embraced deductive reasoning and preferred hierarchical type CMs. Additional points studied during the process include filling out requested information in different orders, branch construction pattern, content richness and progress pattern. Furthermore, eye behavior patterns also differed among experts and novices. Expert participants differed from novices in all eye behavior metrics (fixation count, fixation and visit duration for specific actions). Novices’ fixation count (FC) numbers were higher than the experts’ during the entire process and in specific periods. In conclusion, these pattern differences affect the CM development process directly. Considering the patterns revealed in the study may help instructors guide learners more adequately and effectively.     

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.     

Acceptable weights and physiological costs of performing combined manual handling tasks in restricted postures

Eight healthy, male underground coal miners (mean age=36·9 yrs±4·5 SD) participated in a study examining psychophysical acceptable weights and physiological costs of performing combined lifting and lowering tasks in restricted headroom conditions. Independent variables included posture (stooping or kneeling on two knees), task symmetry (symmetric or asymmetric), and vertical lift distance (35 cm or 60cm). All tasks were 10min in duration and were performed under a 1·22 m ceiling to restrict the subject's posture. Subjects were required to raise and lower a lifting box every 10 s, and asked to adjust the box weight to the maximum amount they could handle without undue strain or fatigue. During the final 5 min of each test, data were collected to determine the energy expenditure requirements of the task. Results of this study demonstrated that psychophysical lifting capacity averaged 11·3% lower when kneeling as compared to stooping. Subjects selected 3·5% more weight in asymmetric tasks, and lifted 5·0% less weight to the 60 cm shelf compared to the 35 cm shelf. Heart rate was not significantly affected by posture, but was increased an average of 4 beats/min in asymmetric conditions, and by 3·5 beats/min while lifting/lowering to/from the high shelf. Oxygen uptake was increased by 9% when stooped, by 10% when lifting/lowering asymmetrically, and by 8·2% when performing the task to the high shelf. Results of this study indicate that, wherever possible, materials that must be lifted manually in low-seam coal mines be designed in accordance with the decreased lifting capacity exhibited in the kneeling posture.     

Experienced workers exhibit distinct torso kinematics/kinetics and patterns of task dependency during repetitive lifts and lowers

Individual differences in work methods may be related to the risk of injury during manual material handling tasks, yet existing evidence comparing experienced workers and novices is mixed. This study assessed torso kinematics and kinetics among six experienced workers and six novices during repetitive lifts/lowers under different task configurations (symmetric vs. asymmetric and lift vs. lower). Several important potential confounding effects were controlled. Peak kinematic and kinetic measures were typically higher among experienced workers and suggestive of exposure to higher levels of low back injury risk, though overall exposure levels were moderate. Work methods used by experienced workers were modified between task conditions, whereas novice behaviours were more consistent. Control of torso kinematics/kinetics may thus not be a primary factor in determining experienced worker's work methods, and future investigation is needed to establish if, or under what conditions, these methods are protective and/or should be the basis for interventions including training.

Practitioner Summary: Whether lifting experience reduces low back injury risk is unclear from earlier findings. Results from a controlled experiment suggest that lifting experience may not be associated consistently with reduced physical demands or injury risk. Further investigation is needed to assess the utility of training based on the methods of experienced workers.     

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.     

Relationship between posture and lifting capacity

This study investigates the effect of changes in posture caused by wearing high-heeled shoes on the maximum lifting capacity. Nine female college students, ages 20 to 25 years, participated in this study. Three heel heights (flat, 5 cm and 7.6 cm), two lifting heights (floor to knuckle and knuckle to shoulder), and lifting frequency of 4 per minute were examined. The results indicate that a significant difference exists between MAWOL with flats and that with 7.6 cm heels for both lifting heights. Subjects lifted 21.5% less weight using 7.6 cm heels than wearing flats. No significant difference was found between MAWOL with flats and 5 cm high heels. In addition, in evaluating the tasks subjectively, the subjects reported that they experienced a stress ontheir legs when lifting with 5 cm and 7.6 cm high-heeled shoes. The conclusion of this study indicates that a change in posture affects lifting capacity, and individuals should adjust their predetermined MAWOL while wearing high-heeled shoes.     

Muscular and centre of pressure response to sudden release of load in symmetric and asymmetric stoop lifting tasks

Sudden changes in load during asymmetric lifting may be associated with a particularly high risk of loss of balance and spinal injury. Centre of pressure (COP) motions and electromyographic responses of trunk and lower limb muscles were studied in 10 normal male volunteers during sudden release of 20, 40, 60 and 80N stoop lifting loads in symmetric and asymmetric postures. Similar overall COP responses and muscular response strategies to sudden release of load were seen in both postures, although the asymmetric posture showed a larger medio-lateral COP displacements and greater co-contraction asymmetries. While sudden release of load in asymmetric stoop lifting does not seem to involve a greater risk of fall than symmetric lifting, the muscular response results in more complex and asymmetric loading of the trunk, indicating greater localised segmental loading and therefore increased risk of tissue injury.