Modeling and Validation of Fatigue and Recovery of Muscles for Manual Demolition Tasks

Manual demolition tasks are heavy, physically demanding tasks that could cause muscle fatigue accumulation and lead to work-related musculoskeletal disorders (WMSDs). Fatigue and recovery models of muscles are essential in understanding the accumulation and the reduction in muscle fatigue for forceful exertion tasks. This study aims to explore the onset of muscle fatigue under different work/rest arrangements during manual demolition tasks and the offset of fatigue over time after the tasks were performed. An experiment, including a muscle fatigue test and a muscle fatigue recovery test, was performed. Seventeen male adults without experience in demolition hammer operation were recruited as human participants. Two demolition hammers (large and small) were adopted. The push force was either 20 or 40 N. The posture mimicked that of a demolition task on a wall. In the muscle fatigue test, the muscle strength (MS) before and after the demolition task, maximum endurance time (MET), and the Borg category-ratio-10 (CR-10) ratings of perceived exertion after the demolition task were measured. In the muscle fatigue recovery test, MS and CR-10 at times 1, 2, 3, 4, 5, and 6 min were recorded. Statistical analyses were performed to explore the influence of push force and the weight of the tool on MS, MET, and CR-10. Both muscle fatigue models and muscle fatigue recovery models were established and validated. The results showed that push force affected MET significantly (p < 0.05). The weight of the tool was significant (p < 0.05) only on the CR-10 rating after the first pull. During the muscle fatigue recovery test, the MS increase and the CR-10 decrease were both significant (p < 0.05) after one or more breaks. Models of MET and MS prediction were established to assess muscle fatigue recovery, respectively. The absolute (AD) and relative (RD) deviations of the MET model were 1.83 (±1.94) min and 34.80 (±31.48)%, respectively. The AD and RD of the MS model were 1.39 (±0.81) N and 1.9 (±1.2)%, respectively. These models are capable of predicting the progress and recovery of muscle fatigue, respectively, and may be adopted in work/rest arrangements for novice workers performing demolition tasks.

An Ergonomic Analysis on Working Postures of Construction Site Workers

Risk factors related to work activity and ergonomics can enhance the probability that some persons may develop a MSD (musculoskeletal disorder). Usually the MSD develops due to high task repetition, forceful exertion, and repetitive/sustained awkward postures. MSD is also found in some cases where workers are engaged with working in awkward postures, cold temperatures, contact stress, heavy load, static postures, and vibration, etc. Many studies explain the problems for MSD, but in this chapter an effort is taken to rank the maximum body movement and body parts as per the different types of work flow system such that ergonomics design can be planned. Physical disorders can be avoided by finding and ranking the difficult task and the affected body part due to that kind of work. The prioritization of task will help the organization to think of sustainable designs of working procedure or instruments or machines to provide maximum comfort to humankind. It may also help to frame policies for occupational safety and hazards in workplace.

Exerting control: the grammatical meaning of facial displays in signed languages

Signed languages employ finely articulated facial and head displays to express grammatical meanings such as mood and modality, complex propositions (conditionals, causal relations, complementation), information structure (topic, focus), assertions, content and yes/no questions, imperatives, and miratives. In this paper we examine two facial displays: an upper face display in which the eyebrows are pulled together called brow furrow, and a lower face display in which the corners of the mouth are turned down into a distinctive configuration that resembles a frown or upside-down U-shape. Our analysis employs Cognitive Grammar, specifically the control cycle and its manifestation in effective control and epistemic control. Our claim is that effective and epistemic control are associated with embodied actions. Prototypical physical effective control requires effortful activity and the forceful exertion of energy and is commonly correlated with upper face activity, often called the “face of effort.” The lower face display has been shown to be associated with epistemic indetermination, uncertainty, doubt, obviousness, and skepticism. We demonstrate that the control cycle unifies the diverse grammatical functions expressed by each facial display within a language, and that they express similar functions across a wide range of signed languages.

Effects of handle height and load on the endurance time for simulated demolition tasks

BACKGROUND: Manual demolition tasks are heavy physical demanding tasks which involve forceful exertion of sustained pushing. They result in muscle fatigue which could lead to musculoskeletal disorders. Assessments of maximum endurance time (MET) are essential in understanding the developing of muscle fatigue for these tasks. OBJECTIVE: The objectives of this study were to determine the effects of handle height and load conditions on the MET, and to establish MET models for the simulated demolition tasks. METHODS: Twenty three male participants performed simulated demolition tasks under three loads and three handle heights conditions until they could not do so any longer. Their METs and ratings of perceived exertion were recorded and analyzed. RESULTS: The results showed that both load and handle height were significant (p < 0.0001) factors affecting the MET. Regression models to predict the MET under handle height and load conditions were established. The mean absolute deviations of these models were between 1.91 and 4.84 min. CONCLUSION: The MET models established may be used to estimate the MET which may be adopted in work/rest arrangement for demolition tasks using a handheld demolition hammer.

THE EFFECT OF TRANSFER DISTANCE TO LOWER BACK TWISTING AND BENDING PATTERNS IN MANUAL TRANSFER TASK

Manual material handling (MMH) activities utilize human’s effort with minimal aid from mechanical devices. MMH is typically associated with poor lower back posture which can lead to lower back injury. The likelihood to develop musculoskeletal disorders (MSDs) increases when poor working posture exist in combination with repetition and/or forceful exertion. In manual transfer activity, the distance between lifting origin and destination could affect workers’ exposure on poor lower back working posture. An experimental study was conducted to investigate the effect of transfer distance to lower back twisting and bending pattern in manual transfer activity. Positional body joints data of 26 male subjects were captured using the combination of motion capture (MOCAP) system with MVN studio software. Calculated data were plotted against time to track subjects’ lower back twisting and bending behavior. In general, longer the transfer distance would result in smaller twisting angle but higher bending angle. Statistical analysis in this study suggests 0.75m to 1.00m as the optimum transfer distance to balance lower back twisting and bending exposure on workers. This study is envisioned to provide insights for practitioners to consider space requirements for MMH activity to minimize lower back twisting and bending, and consequently the development of MSDs.

Simulate and sense force exertions during virtual patient transfer tasks

Virtual reality (VR) is commonplace for training, yet simulated physical activities in VR do not require trainees to engage and contract the muscle groups normally engaged in physical lifting. This paper presents a muscle activity-driven interface to elicit the sensation of forceful, physical exertions when lifting virtual objects. Users contracted and attained predefined muscle activity levels that were calibrated to user-specific muscle activity when lifting the physical counterpart. The overarching goal is to engage the appropriate muscles, and thereby encourage and elicit behaviors normally seen in the physical environment. Activities of 12 key muscles were monitored using electromyography (EMG) sensors while they performed a three-part patient lifting task in a Cave Automatic Virtual Environment. Participants reported higher task mental loads and less physical loads for the virtual lift than the physical lift. Findings suggest the potential to elicit sensation of forceful exertion via EMG feedback but needed fine-tuning to offset perceived workload.

Ergonomics Study Among Operators in Water-Jet Production Area in Aircraft Industry

This paper is to conduct the ergonomics risks assessment (ERA) among the operators in water-jet production workstation area in aircraft industry, working with aircraft panels’ liners named Oriented Strand Board (OSB) and the aircraft panels which require forceful exertion, lifting and carrying task in order to complete the operation activity. The possibility of Work Musculoskeletal Disorders (WMSDs) among operators could occur due to their daily working activities. The objectives of this study are to conduct the initial ERA and advance ERA among the waterjet production operators. Twelve male operators had been participated in this study with range age 20 to 40 years old. Nordic checklist, operational interviews, observations, Rapid Entire Body Assessment (REBA) tool and Manual Handling Assessment Chart (MAC) tool as part of advance ERA evaluation were applied in this study. The initial ERA results recommend for further investigation on awkward posture and forceful exertion among the operators in waterjet production. The results from REBA shows that all operators obtain high risk ergonomics score i.e. 10 scores for load weight and high repetitive in lifting and carrying task. The results from MAC validate that gripping mechanism during lifting and carrying activity requires ergonomics intervention for reducing the forceful exertion and high repetitive risk. The results from ERA, REBA and MAC assessment in this study are novel contribution in the aircraft production since the similar data is not exist yet. The results will be translated into measurable design parameters for waterjet workstation improvement in future design workstation.

Integrated ergonomic and productivity analysis for process improvement of panelised floor manufacturing

Workers in the construction manufacturing industry are often exposed to labour-intensive tasks with ergonomic risks such as awkward body posture, forceful exertion, and repetition motion. Due to the increased productivity and increased repetitive motions resulting from improvement initiatives implemented in offsite construction, the investigation of ergonomic risks associated with these changes is needed. In this context, this paper explores an existing panelised floor production line aiming to minimize its ergonomic risks while improving its current productivity rate. Information on human body motion and productivity are extracted from video recordings. The ergonomic risks associated with specific tasks are identified using an existing ergonomic risk assessment tool (i.e., Rapid Entire Body Assessment (REBA)). The information extracted from the simulation model pertaining to ergonomic risks and productivity supports the decisionmaking process and aids in the prioritization of changes to improve the working environment.

An Ergonomic Analysis on Working Postures of Construction Site Workers

Risk factors related to work activity and ergonomics can enhance the probability that some persons may develop a MSD (musculoskeletal disorder). Usually the MSD develops due to high task repetition, forceful exertion, and repetitive/sustained awkward postures. MSD is also found in some cases where workers are engaged with working in awkward postures, cold temperatures, contact stress, heavy load, static postures, and vibration, etc. Many studies explain the problems for MSD, but in this chapter an effort is taken to rank the maximum body movement and body parts as per the different types of work flow system such that ergonomics design can be planned. Physical disorders can be avoided by finding and ranking the difficult task and the affected body part due to that kind of work. The prioritization of task will help the organization to think of sustainable designs of working procedure or instruments or machines to provide maximum comfort to humankind. It may also help to frame policies for occupational safety and hazards in workplace.

Alcohol Consumption Reduces Effortful Fatigue After Sleep: Testing A Theory of Metabolite Depletion and Subsequent Supercompensation

The current work examined whether greater alcohol consumption at night would predict less effortful fatigue the next morning. The theory is that effortful thought and behavior benefit from additional stored metabolites, and that drinking alcohol temporarily reduces metabolites but later increases them. Participants attended a drinking, social event at night. The next morning, they completed an effortful task (a breath-blowing task requiring forceful exertion and persistence) before and after a mentally fatiguing task (controlling attention). Consuming more alcohol during the event predicted less fatigue on the effortful breath-blowing task, computed as the difference between performance on the task before and after the attention control task. Alcohol consumption might be one strategy for reducing later fatigue on effortful tasks.