No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Measurement and evaluation of local muscular strain in the shoulder during constrained work
Abstract
The exposure to local muscular strain during work may be evaluated by vocational electromyography. The aim of the presentation is to briefly describe how electromyography may be used to analyse the muscular strain during work. Different methods for quantifying the myoelectric results are discussed. A brief description of the use of amplitude probability distribution analysis of the myoelectric signals obtained during work is given. A few examples of results obtained from the upper portion of the right and left trapezius muscle in different work situations are presented.
... A common noise correction procedure was applied to the pooled dataset, following the methodology used in prior studies. Specifically, the noise level was determined as the minimum of the moving average over 19 samples (equivalent to 2.375 s) and subtracted from the corresponding samples [14,55,56]. Any data that contained MVE measurements at the beginning or end of the measurement period was excluded from the analysis. ...
... For each participant, the following variables were calculated bilaterally: Relative resting time (RRT), as the total duration of muscle activity < 0.5% MVE related to the total measurement duration [57]; The number of gaps per minute with muscle activity < 0.5% MVE, was defined as the frequency of episodes of muscular rest with a minimal duration of 0.125 s [14] The 10 th percentile of muscle activity (static muscle activity level) [56]; the 50 th percentile of muscle activity (center or median of muscle activity) [56]; 90 th percentile (peak level of muscle activity during the total working shift) [56]; Various lengths of periods with SUMA > 0.5% MVE (interval range: 1.5-5 s to > 20 min) was also analyzed [31]. A SUMA was defined as a period with continuous muscle activity > 0.5% MVE with a duration > 1.5 seconds or more (interval range: 1.5-5 s to > 20 min), and numbers of these periods were analyzed per hour. ...
... For each participant, the following variables were calculated bilaterally: Relative resting time (RRT), as the total duration of muscle activity < 0.5% MVE related to the total measurement duration [57]; The number of gaps per minute with muscle activity < 0.5% MVE, was defined as the frequency of episodes of muscular rest with a minimal duration of 0.125 s [14] The 10 th percentile of muscle activity (static muscle activity level) [56]; the 50 th percentile of muscle activity (center or median of muscle activity) [56]; 90 th percentile (peak level of muscle activity during the total working shift) [56]; Various lengths of periods with SUMA > 0.5% MVE (interval range: 1.5-5 s to > 20 min) was also analyzed [31]. A SUMA was defined as a period with continuous muscle activity > 0.5% MVE with a duration > 1.5 seconds or more (interval range: 1.5-5 s to > 20 min), and numbers of these periods were analyzed per hour. ...
Background
Neck pain remains a persistent challenge in modern society and is frequently encountered across a wide range of occupations, particularly those involving repetitive and monotonous tasks. It might be expected that patterns of trapezius muscle activity at work, characterized by few breaks and prolonged periods of sustained muscle activity, are linked to neck pain. However, previous cross-sectional studies have generally failed to establish a definitive association. While some longitudinal studies have suggested that extended periods of heightened muscle activity could be a risk factor for neck pain, these findings often relied on limited participant numbers or specific professional groups. This study aimed to investigate the relationship between trapezius muscle activity and neck pain by pooling data from seven Scandinavian research institutes encompassing a diverse range of occupational backgrounds.
Methods
Electromyographic (EMG) data for the upper trapezius muscle, collected during working hours, were coupled with questionnaire responses pertaining to neck pain, individual characteristics, and potential confounding variables for a total of 731 subjects. Additionally, longitudinal data from 258 subjects were available. The various EMG datasets were consolidated into a standardized format, and efforts were made to harmonize inquiries about neck pain. Regression analyses, adjusting for sex and height, were conducted to explore the associations between muscle activity variables and neck pain. An exposure index was devised to quantify the cumulative neck load experienced during working hours and to differentiate between various occupational categories.
Results
The cross-sectional data displayed a distinct pattern characterized by positive associations for brief periods of sustained muscle activity (SUMA) and negative associations for prolonged SUMA-periods and neck pain. The longitudinal data exhibited a contrasting trend, although it was not as pronounced as the cross-sectional findings. When employing the exposure index, notable differences in cumulative muscle load emerged among occupational groups, and positive associations with longitudinal neck pain were identified.
Discussion
The results suggest that individuals with neck pain experience higher cumulative workloads and extended periods of muscle activity over the long term. In the short term, they appear to compensate by taking frequent short breaks, resulting in a lower cumulative workload. Regardless of their occupation, it is crucial to distribute work breaks throughout the workday to ensure that the cumulative load remains manageable.
... All data were noise-corrected by subtracting the noise level from all samples. The noise level was determined as the minimum of a moving average over 19 samples, from the corresponding recording (17,44,45). ...
... The following variables were calculated bilaterally: the relative resting time (RRT), which represents the percentage of the total work duration with very low muscle activity <0.5% MVIC (46); the number of gap periods per minute with very low muscle activity <0.5% MVIC, representing the short episodes of "muscle rest" with a minimal duration of 0.125 second (17); and the median of muscle activity during the working day (45). In addition, the number of periods per hour of SUMA >0.5% MVIC with different lengths of continuous activity ranging from 1.5->20 minutes was analyzed (22). ...
... Work related musculoskeletal disorders (WRMSD) are the sort of disorders which may include, muscles, tendons nerves and other soft tissues as well. Mainly they may appear in the form of muscular strain, tendon strain, tendentious and ligament sprain (1,2). They may appear in the different conditions like, carpal tunnel syndrome, epicondylitis, thoracic outlet syndrome, tension neck syndrome, rotator cuff tendentious, tenosynovitis and Bursitis and many other disorders (2)(3)(4). ...
... The WRMSD are more common among the physiotherapist, paramedics, machine operators, original article office workers, carpenters, grocery store workers and truck drivers (7,8) . During an activity when a person, over uses the muscle, improper uses of their muscle feeling of fatigue for longer time can cause a muscle pain that may called as a muscle strain (1,2) .The over stretching of muscle fibers that usually connects the bone to muscle is called as tendon strain and the inflammation of that fibers is known as tendentious (2,3) . The tear of ligament is known as ligament sprain. ...
Background: Work related musculoskeletal disorders (WRMSD) are the sort of disorders which involvessoft tissues. The involvement of soft tissues can be due to the over use, restlessness and improper use. Themain target of WRMSD are working indicuduals.it may cause muscle strain, ligament strain, tendon strain,tendentious and bursitis.Methods: The cross section survey was conducted and data was collected from July to October 2018 fromcivil hospital Quetta, Pakistan. A self-constructed proforma was used among the 97 patients who meet theinclusion and exclusion criteria and Spss version 23 was used.Results: The majority (n=49, 50.5%) were belongs to age group of 21 to 35 and were (n=51, 52.6%) weremale. In marital status majority (n=64, 66%) were married. In involvement of part majority (n=28, 28.9%)were suffering from lower back problem. After checking the type of injury (n=48, 49.5%) were sufferingfrom muscular strain. In the context of onset of injury majority (N=41, 42.3%) were experienced theirproblem suddenly.Conclusion: The study finalized that WRMSD is most common in working individuals especially in olderand females. The WRMDS puts heavy burden on the society, annually. As the participants who belongs tolow socio economic status are more vulnerable for WRMDS.
... The ADPFs increase more slowly when subjects perform the task without BAZAR with the initial muscle activities always higher with respect to the condition with BAZAR. Furthermore, when BAZAR helps the subjects, the mean values of 10th percentile never exceeded the limits (5% MVC) of acceptable muscular load for the static load level (10th) that were found in studies of muscular endurance during dynamic work (Jonsson 1982). Additionally, with the exception of the AD and ECR muscles, the mean values of the median (50th percentile) load level are lower when BAZAR is used ( Figure 6 and Table 4), and they never go over the limit for static load levels (14%, Jonsson 1982). ...
... Furthermore, when BAZAR helps the subjects, the mean values of 10th percentile never exceeded the limits (5% MVC) of acceptable muscular load for the static load level (10th) that were found in studies of muscular endurance during dynamic work (Jonsson 1982). Additionally, with the exception of the AD and ECR muscles, the mean values of the median (50th percentile) load level are lower when BAZAR is used ( Figure 6 and Table 4), and they never go over the limit for static load levels (14%, Jonsson 1982). Furthermore, the peak loads (90th percentile) do not exceed the limit (70%) in both conditions with and without BAZAR. ...
This study aims at evaluating upper limb muscle coordination and activation in workers performing an actual use-case manual material handling (MMH). The study relies on the comparison of the workers’ muscular activity while they perform the task, with and without the help of a dual-arm cobot (BAZAR). Eleven participants performed the task and the flexors and extensors muscles of the shoulder, elbow, wrist, and trunk joints were recorded using bipolar electromyography. The results showed that, when the particular MMH was carried out with BAZAR, both upper limb and trunk muscular co-activation and activation were decreased. Therefore, technologies that enable human-robot collaboration (HRC), which share a workspace with employees, relieve employees of external loads and enhance the effectiveness and calibre of task completion. Additionally, these technologies improve the worker’s coordination, lessen the physical effort required to interact with the robot, and have a favourable impact on his or her physiological motor strategy.
Practitioner summary: Upper limb and trunk muscle co-activation and activation is reduced when a specific manual material handling was performed with a cobot than without it. By improving coordination, reducing physical effort, and changing motor strategy, cobots could be proposed as an ergonomic intervention to lower workers’ biomechanical risk in industry.
... Additionally, the mean values are presented as bar graphs in Fig. 17. The representative value in the APDF analysis is the average work intensity (muscle fatigue) of the task, which is obtained as the value of %MVC at P = 0.5 in the APDF analysis defined by Jonsson (1982). The smaller this value is, the smaller the load on the muscles. ...
In this paper, we proposed a concept of supporting human reaching motion using a branching robot arm system. The proposed robot system comprises a long-reach arm robot with a small arm attached. We primarily focus on the mechanism and control method of the small arm. The small arm incorporates proximity and force sensors and can follow a person’s arm in real time or continue to generate a constant support force. Through participant experiments involving tasks related to fetching an object at a certain height, we confirmed that the proposed system can achieve these tasks. In addition, by varying the degree of assistance, we significantly reduced muscle load. Furthermore, we obtained insights into appropriate tasks and support conditions from the perspective of other muscles and muscle fatigue reduction. We also confirmed the applicability of the proposed system to the subject of object manipulation against a vertical wall as an applied task of reaching.
... The RMS time series values of each task were then normalized by dividing them by the respective peak MVC value for each muscle (%MVC) [37]. The peak (90th percentile) and median (50th percentile) normalized muscle activity values of each task were obtained [40]. ...
This study assessed the impact of a passive back-support exoskeleton (Laevo V2.5; Laevo, Netherlands) on trunk and hip postures, lower back muscle activity and heart rate during four common patient handling tasks: task 1, lying to sitting; task 2, sitting to standing; task 3, standing to sitting; task 4, bed-to-wheelchair transfer. Eight participants performed these tasks with and without the exoskeleton. Significant reductions (19%; p < 0.05) in erector spinae muscle activity were observed during tasks 2 and 4. Moreover, peak bilateral hip flexion angles decreased by up to 29° across tasks, with a notable decrease in median hip flexion angles in three tasks, except for task 3. These findings suggest that the exoskeleton may offer benefits in reducing lower back muscular strain during certain patient transfer tasks, indicating its potential utility in healthcare settings. Further research is needed to fully assess its effectiveness and practicality in improving patient-handling techniques.
... For instance, when considering the joint posture risk factor evaluation, the attributes are the specific joint possible movements (e.g., abduction/adduction, flexion/extension, internal/external rotation for hip joint; flexion, internal/external rotation for knee joint; or plantar/dorsiflexion, inversion/eversion for ankle joint), which are based on the data obtained from inertial sensors. Muscle effort is assessed by estimating the static, maximum, and minimum contraction levels, derived from the amplitude probability distribution function, which is calculated using EMG data from the biceps femoris, rectus femoris, and gastrocnemius lateralis [ 35 ]. For the static standing duration, the attribute is the time spent in continuous static standing work, which can be obtained from CAPTIV software. ...
During orthopedic surgeries, surgeons are generally exposed to prolonged periods of standing, awkward and sustained body postures, and forceful movements, which can increase the likelihood of developing work-related musculoskeletal disorders (WRMSD). Therefore, this study proposes a protocol to measure parameters related to physical risk factors contributing to lower limb WRMSD, during orthopedic surgery procedures. The protocol development was preceded by an initial phase of understanding and specifying the context of use, followed by pre-tests in laboratory environment. It integrates a motion capture system, using inertial measurement units (IMU) to collect posture data from hip, knee, and ankle, and electromyography system (EMG) to measure and record data from muscle activity of biceps femoris, rectus femoris, and gastrocnemius lateralis. Pre-tests provided insights for protocol optimization, estimating a 3-hour data collection session per surgery due to sensor battery limitations, streamlining the process by placing EMG sensors before IMU and refining thigh sensor placement strategies. The protocol presents an opportunity for a real-time and quantitative approach to monitor surgeon's exposure to risk factors contributing to lower limb WRMSD while performing surgical procedures. Two months after pre-tests, the protocol implementation began in a real work context. The study's final outcomes fall outside the paper's scope.
... the processed eMG data collected during the VR tasks were normalised relative to the corresponding MVc (%MVc). then, the normalised muscle activity (%MVc) was summarised as the 10th (static muscle activity), 50th (Median muscle activity), and 90th (peak muscle activity) percentile values (Jonsson 1982). ...
This study evaluated the effects of target sizes on biomechanical and cognitive load and the performance of virtual reality (VR) interactions. In a repeated-measures laboratory study, each of the twenty participants performed standardised VR tasks with three different target sizes: small, medium, and large. During the VR tasks, biomechanical load in the neck and shoulders (joint angles, joint moments, and muscle activity), cognitive load (perceived workload and cognitive stress), and task performance (completion time) were collected. The neck and shoulder joint angles, joint moments, and muscle activities were greater with the large targets compared to the medium and small targets. Moreover, the larger VR targets caused greater temporal demand and longer task completion time compared to the other target sizes. These findings indicate that target sizes in VR interfaces play important roles in biomechanical and cognitive load as well as task performance.
... The 95th percentile values of MVCs of individual muscles were used to normalize the muscle activities of each task (%MVC). The peak (90th percentile) and median (50th percentile) values were summarized for statistical analysis [34]. ...
This study evaluated the effects of a back-support exoskeleton on the trunk and hip joint angles, lower back muscle activity and heart rate during four patient handling tasks: assisting a patient from sitting to lying, laterally repositioning the patient and turning the patient in two directions. Eight participants performed these tasks with and without the exoskeleton. Results demonstrated a significant reduction in the lower back muscle activity, but less pronounced effects for other tasks involving minimal trunk flexion. Hip flexion angles were reduced for all tasks when the exoskeleton was worn. The amount of reduction in the muscle activity and changes in the trunk and hip angles varied by task. The exoskeleton did not affect the heart rate across all tasks. The exoskeleton appeared to be more effective in tasks requiring substantial trunk flexion, indicating its potential benefits for reducing lower back muscle strain during such activities.
... Noraxon's surface electromyography (EMG) IMUs was used to collect muscle activity bilaterally from the participant's upper trapezius, anterior deltoids, lumbar erector spinae, and biceps femoris. The data was collected at a sampling rate of 2000 Hz and filtered using a sixth-order Butterworth filter with levels of 20 Hz and 450 Hz [28]. Next, this filtered data, was used to calculate the median (50th percentile) and peak (90th percentile) amplitude probability density function (APDF) [29]. ...
... Time in demanding postures was also obtained, and such postures were defined when angles were outside the range of recommended limits of the Rapid Upper Limb Assessment (RULA): >10 • neck flexion, >20 • trunk flexion, and > 45 • shoulder elevation (McAtamney & Corlett, 1993). EMG data were analyzed using MATLAB to derive percentile (%ile) values as percent MVC, with 10th%ile representing static demands, 50th%ile representing dynamic demands, and 90th%ile representing peak load (Jonsson, 1982;Veiersted et al., 2013). To detect localized muscle fatigue, power spectrum analyses were performed using Fast Fourier Transforms, from which median power frequency (MdPF) was calculated using 125 msec windows with 62.5 msec overlaps (McDonald et al., 2019). ...
... Thus, although the workers had to perform a carrying task during the gross cable duct positioning, this is not considered in the following analysis. We extracted the average Erector Spinae median activation (ES median) for each worker, as this can be linked to the cumulative fatigue that a worker experiences [31], along with the peak values (ES peak). Higher values correlate with increased risk of developing MSD injuries. ...
This study on occupational back-support exoskeletons performs a laboratory evaluation of realistic tasks with expert workers from the railway sector. Workers performed both a static task and a dynamic task, each involving manual material handling (MMH) and manipulating loads of 20 kg, in three conditions: without an exoskeleton, with a commercially available passive exoskeleton (Laevo v2.56), and with the StreamEXO, an active back-support exoskeleton developed by our institute. Two control strategies were defined, one for dynamic tasks and one for static tasks, with the latter determining the upper body’s gravity compensation through the Model-based Gravity Compensation (MB-Grav) approach. This work presents a comparative assessment of the performance of active back support exoskeletons versus passive exoskeletons when trialled in relevant and realistic tasks. After a lab characterization of the MB-Grav strategy, the experimental assessment compared two back-support exoskeletons, one active and one passive. The results showed that while both devices were able to reduce back muscle activation, the benefits of the active device were triple those of the passive system regarding back muscle activation (26% and 33% against 9% and 11%, respectively), while the passive exoskeleton hindered trunk mobility more than the active mechanism.
... There were no significant differences between the P-AB and NP-AB groups with or without standardization of the cut-off amplitude. When expressing EMG amplitude as %MVC, there was an idea that the baseline amplitude should be subtracted from the maximum peak amplitude among the MVC waveforms for each subject [39]. However, in the present study, subtraction of the baseline amplitude was not conducted according to the definition of %MVC in recent major masseteric EMG studies on the SB and AB [14,16,21,23,[25][26][27][28]33]. ...
Purpose: This study aimed to elucidate the relationship between diurnal masseter muscle activity and awareness of diurnal awake bruxism (d-AB) by conducting a comparative analysis of electromyographic (EMG) data from individuals with and without awareness of diurnal awake bruxism (d-AB), utilizing EMG data gathered from multiple subjects.
Methods: Unilateral masseter electromyography (EMG) recordings were performed during the daytime using an ultraminiature wearable EMG device. A total of 119 participants (59 with awareness of diurnal tooth clenching [d-TC] and 60 without awareness of d-TC) were included. Waveforms longer than 0.25 s with the two amplitude conditions, exceeding twice the baseline and >5% of maximum voluntary clenching, were extracted. In addition, the number of bursts and episodes (groups of bursts), burst duration, and burst peak amplitude were calculated for each participant.
Results: There were no significant differences in the EMG parameters between the groups with and without awareness of d-TC. Additionally, the frequency distribution of the number of EMG waveforms exhibited wide ranges and substantial overlap between the two groups.
Conclusions: The variability in the number of bursts and episodes, burst peak amplitude, and burst duration among subjects suggests the need for an objective classification of d-AB severity based on EMG values. The absence of significant differences and large overlap in frequency distributions between the groups with and without awareness of d-TC indicate difficulty in predicting muscle activity solely based on awareness of d-AB.
... Regarding shoulder muscles load, there are no general criteria for acceptable load level, however, a study provides references on several limit values on the load [18]. The study suggests that the mean load level should not be more than 10% MVE, while the peak loads should not be more than 50% MVE. ...
The application of surface electromyography (sEMG) among oil palm fruit harvesters is still very few, despite subjective assessments that have identified the risk of musculoskeletal disorders (MSD), with the shoulder among the body parts with the risk. Thus, in this study, sEMG was used to measure deltoid and trapezius muscle activation while cutting fruit bunches. Because a prototype of the exoskeleton was also tested in this study, the muscle activation was compared without and with exoskeleton conditions. The field experiment was performed in a State-Owned Enterprise (SoE) plantation in West Java province, involving six experienced harvesters. A statistical analysis was performed to analyze the cutting cycle when harvesting. The results show that sEMG is capable of quantifying muscle activation when the subjects cut the fruit bunches. This may indicate that sEMG could become a very important instrument for investigating the risk of MSDs in the oil palm industry. Furthermore, the exoskeleton was found to be able to reduce muscle activation, especially toward the end of the experiment session. Future studies should consider the longer experiment session in a more controllable experimental setting to solidify the benefit of wearing an exoskeleton in oil palm fruit harvesting.
... EMG signals are acquired at 1000 Hz and two types of filters are applied (EMGWorks, Delsys): firstly, the band-pass filter (10∼350 Hz, 2 nd order butterworth) and secondly, root mean square with a moving average of 125 ms. RVC/MVC results are used as denominators for the processed EMG values and the peak normalized EMG values are calculated at the 90 th percentile [23]. ...
A significant part of the parcel delivery service occurs outside the warehouse, relying entirely on human resources to deliver parcels to the customer's doorstep. The parcel delivery officers carry and hold parcels of about 25 kg of weight during the delivery process through diverse terrains such as elevated ground and staircases especially in many crowded cities. As a result of holding and carrying heavy parcels repeatedly, the officers report upper body musculoskeletal disorders in the arms, and lower back. Robotic exosuits are actively being developed but are primarily oriented toward lifting assistance only and do not cater to the entire upper body assistance. In this paper, we propose a load-redistribution strategy in the form of a fully soft passive wearable robot, that provides load-dependent compression around the lower back for back support and arm assistance. This is achieved through the coupling of the load and the human body, which ensures the wearer receives appropriate assistance only when in need. The suit design parameters are as follows: the elastic component that inherently enhances comfort in breathing even in its tightened state while transmitting compression force onto the human abdominal muscles; and the number of pulleys on the belt to control the amount of belt compression in users of different size; and the length of the corset tendon. The mannequin mock-up experiment and analytical modeling demonstrate the relationship between the design parameters and pressure on the human body. Human experiment also verifies the upper body assistance performance of the suit in significantly reducing the arms' muscle efforts (p < 0.05) in parcel delivery.
... The number and duration of these rest pauses will also be calculated. The 10 th percentile of the amplitude distribution is recommended as measure of a "static muscle activity level", while the 90 th percentile describes the level of peak loads and median level (50 th percentile) of the center of activity of the muscle during an EMG recording (Jonsson, 1982). Gaps are short episodes of muscular rest. ...
Repetitive and monotonous work is often associated with neck pain, potentially resulting in sick leave and reduced productivity. Establishing appropriate muscle activity patterns, including duration and frequency of breaks that can prevent development of neck pain is important for providing workplace guidance. While several smaller studies of monotonous neck-loading work have indicated that such breaks can reduce the risk of neck pain, studies with a higher number of participants are necessary to confirm an association, and if so, to improve the precision of a possible association. The purpose of this protocol is to describe and discuss the background, methods and challenges of a study pooling several datasets with measurements of upper trapezius muscle activity during work and associated measurements of neck pain. Methods: Seven Scandinavian research institutes provided surface electromyographic (EMG) data of upper trapezius muscle activity recorded during working hours along with questionnaire data with information about neck pain and other health-related factors, from a total of 750 participants. The different data sets of the EMG data will be merged into a common format. Various questions on neck pain will be harmonized. Associations between EMG variables and neck pain will be examined with linear mixed model regressions controlled for various confounders. Discussion: Aiming to provide further insight into the possible association between trapezius muscle activity pattern and neck pain, this study protocol highlights the challenges that arise when creating a pooled data set. Solving these challenges may help to increase the knowledge about appropriate muscle activity patterns during work.
... The filtered EMG data were normalized relative to the corresponding MVCs (%MVC). Normalized EMG data were summarized with amplitude probability density function: 10th (representing static muscle activity), 50th (representing median muscle activity), and 90th (representing peak muscle activity) percentile (Jonsson, 1982). ...
This study determined whether a passive shoulder-support exoskeleton would reduce biomechanical load in the shoulders during augmented reality (AR) interactions. Twenty participants were recruited to a repeated-measures laboratory study to perform AR tasks with and without a shoulder-support exoskeleton. The AR tasks consisted of two standardized tasks (omni-directional pointing and cube placing task). Shoulder muscle activity, postures, discomfort, and task performance (i.e., completion time) were measured during the experimental sessions. The result showed that the shoulder muscle activity (trapezius and deltoid muscles) and subjective shoulder discomfort were significantly lower with the exoskeleton compared to the no-exoskeleton condition (p < 0.05). The shoulder posture data showed that the exoskeleton use increased the 50th percentile of the shoulder flexion (p = 0.02). In contrast, the exoskeleton had limited effects on task performance (p > 0.83). These results suggested that a shoulder-support exoskeleton may have potential to reduce shoulder strain during AR interactions.
... Through the person-and musclespecific normalisation of the amplitude parameter RMS (root mean square) calculated from the SEMG signal during physical work in relation to the RMS during maximum voluntary activation (%MVE), work-related muscular stress can be characterised and attributed to a wide range of work activities [21]. An often used characterisation method in ergonomic research is the amplitude probability distribution function with the 10th percentile, the median and the 90th percentile as MSC risk indicators [22]. In cyclic assembly work, SEMG assessment therefore indicates muscle-specific peaks or prolonged episodes of muscle stress that would be of interest for a redesign [23]. ...
Takt work represents a significant risk factor for the development of musculoskeletal complaints and diseases, especially in short-cycle processes. The increased risk results primarily from a permanent uniform load on the musculoskeletal system. Studies on motor variability suggest that an increase in load variation can have positive effects on reducing the risk.
The research project “Integration of activity-specific load changes to reduce physical stress during takt work” aims to demonstrate the increase in load variation by introducing specific load changes during takt work as a possible means of preventing musculoskeletal disorders without causing negative effects on productivity. For this purpose, a pilot study was already carried out with ten subjects, which is presented in more detail in this paper.
As foundation for the description of this study, the given paper first provides background on the applied theoretical concepts as well as the design of the overall research project. This is followed by the presentation of the experimental procedure and the results of the pilot study on cyclic assembly. Based on the stress profiles determined via surface electromyography the sequence of the analysed reference assembly process is reconfigured in order to integrate load changes. Future investigations within the research project are planned to compare both processes in terms of risk surrogate parameters for musculoskeletal disorders.
... To investigate the muscle activation in each forearm muscle, we used amplitude probability distribution function (APDF) analysis for the time series data of %MVC. APDF analysis is a method that expresses the percentage of the total time that the output is below a certain level as the probability of occurrence (P) for that output when the EMG is being measured (Jonsson, 1982). Based on these probability values, the Fig. 1. ...
This study aims to elucidate the relationship between the wrist and finger movements and forearm muscle activation of twelve young people (age: 21.1 ± 0.76 years, nine men and three women) with different typing skills. We hypothesize that skilled typists (STs) could move their wrist and finger joints faster than unskilled typists (UTs) because they could efficiently use their muscles according to the activity characteristics of the flexors and extensors of the wrist joint. We measured wrist and finger movements using a 3D motion capture system and forearm muscle activation using surface electromyography during the typing task. We analyzed the entire task and the time when the U key was entered during the same task. The angular velocity of the wrist and finger flexion/extension and the muscle activation of the wrist flexors was higher in the STs than in the UTs, while the muscle activation of the wrist extensors was higher in the latter than that in the former. Our results showed that STs may have used their forearm muscles to take advantage of the physical characteristics of the keys and the spring characteristics of their muscles and tendons. It was suggested that they placed less me- chanical stress on their finger muscles and tendons when pressing and releasing the keys.
... Finally, the EMG data of LES and TES were averaged over sides and normalised by the peak EMG magnitude (95th percentile) of the data captured from the pre-experimental lifting trial (%baseline). The peak normalised EMG (90th percentile) values of each muscle were extracted and utilised to evaluate the effect of the low-back exoskeleton on back muscle activity (Hwang et al. 2021;Jonsson 1982). ...
This study aimed to establish an ambulatory field-friendly system based on miniaturized wireless flexible sensors for studying the biomechanics of human-exoskeleton interactions. Twelve healthy adults performed symmetric lifting with and without a passive low-back exoskeleton, while their movements were tracked using both a flexible sensor system and a conventional motion capture (MoCap) system synchronously. Novel algorithms were developed to convert the raw acceleration, gyroscope, and biopotential signals from the flexible sensors into kinematic and dynamic measures. Results showed that these measures were highly correlated with those obtained from the MoCap system and discerned the effects of the exoskeleton, including increased peak lumbar flexion, decreased peak hip flexion, and decreased lumbar flexion moment and back muscle activities. The study demonstrated the promise of an integrated flexible sensor-based system for biomechanics and ergonomics field studies as well as the efficacy of exoskeleton in relieving the low-back stress associated with manual lifting.
... The maximal RMS of both MVCs per muscle was used to normalize the RMS of the experiment and expressed as percentage (%MVE). The 10th (static), 50th (median), and 90th percentiles (peak) of the RMS during B 1 , B 3 , B 4 , B 6 , B 7 , and B 9 (cf. Figure 2) were calculated [45]. For localized muscular fatigue, we calculated the slope expressed as change per minute of the median RMS and MPF and plotted them against each other in joint analyses of the EMG spectrum and amplitude (JASA) [46]. ...
Objective
Investigate the effect of passive, active or no intra-operative work breaks on static, median and peak muscular activity, muscular fatigue, upper body postures, heart rate, and heart rate variability.
Background
Although laparoscopic surgery is preferred over open surgery for the benefit of the patient, it puts the surgeons at higher risk for developing musculoskeletal disorders especially due to the less dynamic and awkward working posture. The organizational intervention intraoperative work break is a workplace strategy that has previously demonstrated positive effects in small-scale intervention studies.
Methods
Twenty-one surgeons were exposed to three 90-min conditions: no breaks, 2.5-min passive (standing rest) or active (targeted stretching and mobilization exercises) breaks after 30-min work blocks. Muscular activity and fatigue of back, shoulder and forearm muscles were assessed by surface electromyography; upper body posture, i.e., spinal curvature, by inclination sensors; and heart rate and variability (HRV) by electrocardiography. Generalized estimating equations were used for statistical analyses. This study (NCT03715816) was conducted from March 2019 to October 2020.
Results
The HRV-metric SDNN tended to be higher, but not statistically significantly, in the intervention conditions compared to the control condition. No statistically significant effects of both interventions were detected for muscular activity, joint angles or heart rate.
Conclusion
Intraoperative work breaks, whether passive or active, may counteract shoulder muscular fatigue and increase heart rate variability. This tendency may play a role in a reduced risk for developing work-related musculoskeletal disorders and acute physical stress responses.
... The wrist angles were calculated using instantaneous orientations of the anatomical axes in the forearms and hands. Using the Amplitude Probability Density Function, these kinematic variables were condensed into 10th, 50th, and 90th percentile values (Jonsson, 1982). ...
This study aimed to evaluate the effects of virtual hands in virtual reality (VR) environment on physical demands and task performance during typing tasks. Ten participants (aged 19 to 28; five males) performed typing tasks under three different conditions (typing on a laptop, typing in VR without virtual hands, and typing in VR with virtual hands) in a randomized order. A synchronized virtual keyboard was provided for both VR conditions. The kinematic data of the upper body was measured using an optical motion capture system with eight cameras. For the typing performance, the typing speed (word per minute [WPM]) and accuracy were measured. The results of the upper body angles showed that typing in VR without virtual hands showed lower shoulder adduction (81% decrease) compared to typing on a laptop. Typing in VR with virtual hands did not show significant differences in shoulder flexion/extension and abduction/adduction and wrist flexion/extension compared to typing on a laptop. The results of the hand trajectory showed that typing in VR without virtual hands resulted in significantly lower total distance traveled (49% decrease) and mean hand velocity (47% decrease) relative to typing on a laptop. Typing in VR with virtual hands did not show significant differences in hand coordination compared to typing on a laptop. For the typing performance, both VR without (7.5 WPM) and with virtual hands (19.4 WPM) showed significantly lower performance than typing on a laptop (27 WPM). There was no significant difference in typing accuracy between conditions. The results suggest that the presence of the virtual hands for typing in VR resulted in comparable joint angles of the shoulders and wrists and hand coordination to conventional typing on a laptop. Nonetheless, further design improvement of virtual hands and virtual keyboards would be needed to improve the typing speed.
... The filtered EMG data were normalized relative to the corresponding MVCs (%MVC). Normalized EMG data were summarized with amplitude probability density function: 10th (representing static muscle activity), 50th (representing median muscle activity), and 90th (representing peak muscle activity) percentile (Jonsson, 1982). ...
The aim of this study was to evaluate a passive upper-limb exoskeleton as an ergonomic control to reduce the musculoskeletal load in the shoulders associated with augmented reality (AR) interactions. In a repeated-measures laboratory study, each of the 20 participants performed a series of AR tasks with and without a commercially-available upper-limb exoskeleton. During the AR tasks, muscle activity (anterior, middle, posterior deltoid, and upper trapezius), shoulder joint postures/moment, and self-reported discomfort were collected. The results showed that the exoskeleton significantly reduced muscle activity in the upper trapezius and deltoid muscle groups and self-reported discomfort. However, the shoulder postures and task performance measures were not affected by the exoskeleton during the AR interactions. Given the significant decrease in muscle activity and discomfort without compromising task performance, a passive exoskeleton can be an effective ergonomic control measure to reduce the risks of developing musculoskeletal discomfort or injuries in the shoulder regions.
... Furthermore, some researchers have attempted to reposition controls in the cab with the ultimate goal of reducing muscle activation. However, despite reductions in forearm muscle loading, muscle activation [18] was still well above guidelines [19,20]. Given that joysticks design alterations have not resulted in clear-cut reductions in repetitive strain injury risk, some researchers have chosen to redesign the armrest rather than the joystick. ...
The purpose of this work was to validate an addition to a dynamic armrest design (DA) for use during inward–outward and fore–aft joystick manipulation. The design was validated compared to a stationary armrest (SA) and no armrest (NA) using surface electromyography (EMG) and a questionnaire. The DA was not successful in reducing muscle activation for inward–outward movements when compared to the SA. Furthermore, the addition of inward–outward dynamic portion negated the improvements seen with the fore–aft dynamic armrest design. Despite the lack of significant muscular activation findings, most participants preferred the DA to the SA or NA. However, unlike the fore–aft dynamic armrest, which was found to successfully reduce muscle activation in multiple muscles involved in joystick manipulation, results suggest that the horizontally dynamic support addition may not be necessary for inward and outward joystick movements.
... Through the person-and muscle-specific normalisation of the amplitude parameter RMS (root mean square) calculated from the SEMG signal during physical work in relation to the RMS during maximum voluntary activation (%MVE), work-related muscular stress can be characterised and attributed to a wide range of work activities [21]. An often used characterisation method in ergonomic research is the amplitude probability distribution function with the 10 th percentile, the median and the 90 th percentile as MSC risk indicators [22]. In cyclic assembly work, SEMG assessment therefore indicates muscle-specific peaks or prolonged episodes of muscle stress that would be of interest for a redesign [23]. ...
p>Takt work represents a significant risk factor for the development of musculoskeletal complaints and diseases, especially in short-cycle processes. The increased risk results primarily from a permanent uniform load on the musculoskeletal system. Studies on motor variability suggest that an increase in load variation can have positive effects on reducing the risk.
The research project "Integration of activity-specific load changes to reduce physical stress during takt work" aims to demonstrate the increase in load variation by introducing specific load changes during takt work as a possible means of preventing musculoskeletal disorders without causing negative effects on productivity. For this purpose, a pilot study was already carried out with ten subjects, which is presented in more detail in this paper.
As foundation for the description of this study, the given paper first provides background on the applied theoretical concepts as well as the design of the overall research project. This is followed by the presentation of the experimental procedure and the results of the pilot study on cyclic assembly. Based on the stress profiles determined via surface electromyography the sequence of the analysed reference assembly process is reconfigured in order to integrate load changes. Future investigations within the research project are planned to compare both processes in terms of risk surrogate parameters for musculoskeletal disorders.</p
... Through the person-and muscle-specific normalisation of the amplitude parameter RMS (root mean square) calculated from the SEMG signal during physical work in relation to the RMS during maximum voluntary activation (%MVE), work-related muscular stress can be characterised and attributed to a wide range of work activities [21]. An often used characterisation method in ergonomic research is the amplitude probability distribution function with the 10 th percentile, the median and the 90 th percentile as MSC risk indicators [22]. In cyclic assembly work, SEMG assessment therefore indicates muscle-specific peaks or prolonged episodes of muscle stress that would be of interest for a redesign [23]. ...
p>Takt work represents a significant risk factor for the development of musculoskeletal complaints and diseases, especially in short-cycle processes. The increased risk results primarily from a permanent uniform load on the musculoskeletal system. Studies on motor variability suggest that an increase in load variation can have positive effects on reducing the risk.
The research project "Integration of activity-specific load changes to reduce physical stress during takt work" aims to demonstrate the increase in load variation by introducing specific load changes during takt work as a possible means of preventing musculoskeletal disorders without causing negative effects on productivity. For this purpose, a pilot study was already carried out with ten subjects, which is presented in more detail in this paper.
As foundation for the description of this study, the given paper first provides background on the applied theoretical concepts as well as the design of the overall research project. This is followed by the presentation of the experimental procedure and the results of the pilot study on cyclic assembly. Based on the stress profiles determined via surface electromyography the sequence of the analysed reference assembly process is reconfigured in order to integrate load changes. Future investigations within the research project are planned to compare both processes in terms of risk surrogate parameters for musculoskeletal disorders.</p
This study explored differences in activities and spine kinematics by transient low back pain status throughout a week of their usual office work. Using a 100-mm visual-analogue scale, twenty participants were classified as non-pain (NPD) and pain developers (PD; ≥10 mm). Tri-axial accelerometers measured sitting time and thorax, pelvis, and lumbar spine angles. Amplitude probability distribution functions were constructed for postures and movements. PD (n = 6) exhibited increases in pain daily, with partial or complete recovery overnight and full recovery over the weekend, hence pain did not accumulate. PD sat more than NPD (n = 14), exhibited decreased peak posterior pelvic tilt (10°) and thorax inclination (8°), and tended to demonstrate less frequent spine movements. To decrease the risk of pain with sitting, reducing seated time, reclining on the seatback, and promoting seated movements should be recommended. With habitual exposures, small differences between pain groups could suggest a pathway to sitting-related back pain over time.Practitioner Summary: The biomechanical link between habitual sitting and low back pain remains unclear. Activity, spine kinematics, and pain ratings were collected throughout a week of individuals' seated work at their own workstation. Small differences between those with and without transient low back pain could suggest a pathway to sitting-related back pain.
Studies in the past have yielded that manual construction workers face shoulder injuries (Jonsson, 1982, Singh et al 2019). House painters have been found to suffer from lumbar spine disorders due to postural load (Riihimäki et al, 1985). Awkward Posture., Duration, Prolonged Working Hours, and Age along with poor working posture and static posture lead to musculoskeletal disorders (Buchholz et al, 1996: Rosecrance et al, 2001; Holmstrom, Engholm, 2003; Engholm, Holmstrom, 2005; Bodhare et al, 2011, Singh et al, 2019). Also, studies by Cook et al, 1996, Hsiao et al, 1996; Singh et al, 2016, Singh et al 2017(a) & 2017(b) have concluded that overexertion leads to physical strain on shoulders, back, and thighs among scaffolding workers. Learning newer skills can broaden the horizon of the workers (Singh et al 2017 c). Moreover, with skill enhancement training, the workers get a break from the strenuous job. Exterior wall painters climb on the scaffold and face similar physical ailments as the scaffolding workers. The finishing workers in India are migrant workers. Migrants take low safety measures (Singh et al 2018) and hence are susceptible to health and safety issues (Chakrabarti D., 2008, Singh et al, 2022 a). According to Smallwood, 1997; Smallwood et al, 2000; Smallwood, 2002; Zimmerman et al, 1997; Schneider & Susi, 1994; Gibbons & Hecher, 1999; Remana & Satyanarayana, 2005, causes of physical strain in work posture experienced by workers (20-50 years of age) is mainly due to repetitive physical movement, awkward posture, fixed prolonged posture, heavy load and no breaks. Kroemer (1970) found that muscles fatigue quickly over a period with a static load of even low workload. Conventional ways help the workers invent make-do products (Singh et al 2017 b) that though assist them in completing the tasks do not provide holistic comfort and efficiency. User-centered design methodology as employed in Singh et al, 2022(b), and Singh et al, 2024(b) can prove to be beneficial to the workers as it keeps the workers omnipresent through the product design and testing activity. The article aims to address the gap in research on physical strain experienced by construction finishing workers.
Studies on construction finishing workers are very limited in the literature. Manual construction finishing workers suffer from occupational physical strain due to the nature of their work and poorly designed painting equipment. Therefore, there is a need to study the working postures of the workers and redesign painting equipment. The results will help alleviate the MSDs as well as potentially increase their work efficiency. Musculoskeletal disorders (MSDs) in construction finishing workers are associated with repetitive tasks, sustained similar actions, exertion of force on body parts, and working in awkward postures. These factors lead to muscle strain and impair the functionality of body parts during tasks. Over months and years of daily 8-hour work shifts, workers develop MSDs in various body regions. Effective task design and proper tool and equipment design can significantly reduce MSDs among manual construction finishing workers. This paper analyzes occupational physical strain in the body regions of exterior wall painters, interior wall painters, glass cleaners, and wallpaper applicators. A Nordic questionnaire survey was employed to evaluate the strain, facilitating direct interaction with finishing workers to gather their reported frequency and intensity of pain in different body regions. The pilot study provided valuable insights that influenced the relevance of data collection, leading to modifications in the survey questions. Instead of presenting binary results, the paper offers relative differences in three categories of physical strain: no to low, mild, and medium. The chi-square p-value of .000 indicates that the sample can predict statistically significant variance in the physical strain.
While chronic forearm pain is a common and debilitating condition among cleaners, the most physically demanding tasks remain unidentified. The present field study examines forearm muscle activity during 9 common cleaning tasks in a real working environment. Seven healthy cleaners participated in this study (age: 35.17 ± 9.62 yr; height: 168.17 ± 8.06 cm; weight: 77.14 ± 13.78 kg; experience: 5.60 ± 3.29 yr). Surface wireless electromyography (EMG) was recorded from 2 muscles on both sides of the upper limb, flexor carpi ulnaris (FCU), and extensor carpi radialis (ECR), and normalized to maximal voluntary isometric contractions (MVIC). Top-3 demanding high-force tasks (90th percentile EMG) were the rough floor, dirty rough floor, and office floor mopping for the FCU, and mopping high walls, ceiling mopping, and baize cleaning for the ECR. Top-3 static work tasks (10th percentile EMG) were mopping low walls, ceiling mopping, and dirty rough floors mopping for the FCU and mopping of high walls, low walls, and ceiling for the ECR. The study identified the forearm muscles’ most physically demanding work tasks during cleaning tasks. The development of better working tools is recommended to avoid high-force overload as well as prolonged static overload of these muscles in cleaners.
Background:
The body of literature regarding the use of an upper limb exoskeleton during authentic working conditions is sparse.
Objective:
The aim of this study was to evaluate the effectiveness of an upper limb exoskeleton in reducing muscle strain during authentic industrial construction work.
Methods:
Fifteen male participants, comprising of roofers, scaffolders, builders, bricklayers, and graders performing overhead work participated in the study. During work without (REF) and with exoskeleton (EXO), muscle activity from 8 muscles, heart rate (HR), metabolic equivalent (MET), and upper arm elevation angles were recorded.
Results:
When using the exoskeleton, a significant reduction of 20.2% in average muscle activity of 8 muscles was found. The largest effect focused on m. deltoideus, where 46.2 and 32.2% reduction occurred in medial and anterior parts of the muscle, respectively. HR and MET were unaffected. Upper arm elevation angles were similar between REF and EXO, indicating equal biomechanical loading.
Conclusions:
This study indicates that exoskeletons show great promise in reducing the potential for musculoskeletal strain during authentic overhead construction work.
Background:
There is a lack of information about the optimal setup of multiple screen configurations in virtual reality (VR) office work.
Objective:
The objective of this study was to evaluate the effects of different screen configurations on neck flexion, rotation, neck muscle activity, and simulator sickness symptoms during Virtual Reality (VR) office work.
Methods:
Twelve participants (7 males; 21 to 27 years old) performed copy-paste and drag-drop tasks in three different screen configurations (single screen, primary-secondary screen, and double screen) in a randomized order. Optical motion capture system, electromyography (EMG) device, and simulator sickness questionnaire (SSQ) were used to measure the users' responses.
Results:
Neck rotation angles, muscle activities, and VR sickness were significantly affected by the screen configurations (p < 0.021). The primary-secondary screen showed the highest right rotation angle (median: -33.47°) and left sternocleidomastoid (SCM) muscle activities (median: 12.57% MVC). Both single (median: 22.42) and primary-secondary (median: 22.40) screen showed the highest value of SSQ.
Conclusions:
The screen configurations in VR could be an important design factor affecting the users' physical demands of the neck and VR sickness symptoms. Asymmetric neck rotations caused by the primary-secondary screen conditions should be avoided.
In recent times, learning by demonstration has seen tremendous progress in robotic assembly operations. One of the most prominent trajectory-level task models applied is Dynamic Movement Primitives (DMP). However, it lacks the ability to tackle complex operations as often encountered in industrial assembly. Augmenting low-level models with a high-level framework in which different movement segments are deliberately parameterised is considered promising for such scenarios. This paper investigates the combination of trajectory-level DMPs with Methods-Time Measurement (MTM). We demonstrate how the MTM-1 system is utilised to establish distinguished DMP models for five of its basic elements, paving the way to benefitting from the sophisticated MTM system. The evaluation of the framework is conducted on a generic pick and place operation. Compared to a one-model-fits-all DMP approach for the whole task, the proposed method shows the advantage of appropriate temporal scaling, accuracy levelling and force consideration at adequate times.
Automated handling of technical textiles poses major challenges on modern handling systems. Previous research has shown that using suction grippers is feasible for handling processes involving textiles. However, separating individual sheets of air-permeable materials from a stack using such grippers is a nontrivial task. This paper details an automated stack singulation process using low pressure suction grippers leveraging online data from differential pressure sensors to control the singulation process. Subsystems are analyzed to derive a governing model representation of the process. This model is deployed on a robotic test rig validating the process in experimental analysis. Using this approach, a controlled singulation process for stacked carbon fiber mats has been achieved with a success rate exceeding 99% showing the practicality of controlling the internal suction pressure for advanced handling processes using low pressure suction grippers. Further improvement could be achievable by incorporating and fusing multiple sensor principles.
Synthetic data is an indispensable supplement to the difficult-to-acquire real data in order to meet the substantial demand by machine learning based systems. Data playing the key role in machine learning models, its objective and maintainable quality metrics are vital for quality assurance of the whole system. This paper introduces a systematic and domain-neutral methodology based on formalized scenario variation and experimental digital twins for the generation of synthetic data. The methodology uses human-readable scenarios and semantically meaningful parameter variations to describe possible entities, actions and events to be simulated, whereas experimental digital twins bring the scenarios to life by the integration of various domains of a system such as mechanics, sensors, actuators and communication under one platform that can be simulated as a whole. The scenario description and digital twin simulation is carried out iteratively to derive the optimal distribution of synthetic data. Thus scenarios and experimentable digital twins can together serve as mediums to systematically cover diverse application scenarios, test dangerous situations and find faults within a system.
Introduction:
This study analysed the impact of general purpose progressive addition lenses (GP-PALs) and computer progressive addition lenses (PC-PALs) on the activity of the trapezius muscle during computer operation.
Methods:
In this randomised, single-blinded, crossover study, surface electromyography (SEMG) signals were recorded bilaterally from the trapezius muscle during a 30-min computer task performed wearing different presbyopic corrections. The amplitude probability distribution function and its percentiles, gap frequency, muscular rest time and sustained low-level muscle activity periods were analysed in 32 subjects with artificially induced presbyopia. Subjectively perceived differences in vision and postural load between lenses were evaluated using a seven-item questionnaire (non-standardised, visual analogue scale ranged from 1 [bad] to 100 [good]).
Results:
Considering the SEMG data, no significant difference in the muscular activity of the trapezius muscle was observed when using GP-PALs or PC-PALs for computer operation. However, PC-PALs showed statistically and clinically significantly higher results for subjectively perceived visual quality (78.4-31.3; p < 0.001), spontaneous tolerance (79.2-31.3; p < 0.001) and field of view (75.9-23.5; p < 0.001) compared with GP-PALs.
Conclusions:
Even though the electromyographic approach did not show a significant differentiation between the lenses, the subjective evaluation was clearly in favour of PC-PALs. Eye care practitioners should always take an occupational history of presbyopes, ask about the workplace situation and consider the use of PC-PALs.
Background:
Parachutists are generally recognized as a "high-risk" group among military personnel. However, the findings came mostly from data analysis without soldiers as subjects.
Objective:
This study aimed to investigate the injury prevalence in Chinese paratroopers on-site and determine the relationship between injury and risk factors encountered during parachuting and land-based training.
Methods:
This study consisted of a field study with questionnaire and an experiment on muscle load during the simulated training exercise of platform jumping with surface electromyography (EMG), in which 7230 paratroopers and 38 soldiers were involved respectively. Chi-square test was used for the injury rate analysis, ANOVA and t-test for comparison of EMG data, and logistic regression for the analysis of multiple factors. Taking both intensity and time into consideration, jump-years (J-yrs) was used as a complex indicator for exposure to parachuting. Either injury per 1000 jumps or injured persons per 100 soldiers were calculated as injury prevalence.
Results:
The overall injury rate among Chinese parachutists was found to be 13.9 injuries per 1000 parachute jumps and 24.5% based on personnel. The person-based injury rate increased with the exposure level significantly (χ2 = 142.06, 2-sided, P < 0.05; trend test also significantly). Among the identified risk factors the uneven terrain was ranked as the most important one by logistic analysis. The EMG amplitude in MVE% increased with the platform height of all the 8 measured muscles and even reached 100% in 4 muscles, showing a high impact at landing. In addition, some characteristics of parachuting injury were also revealed by the injury type and site analysis.
Conclusion:
A dose-response relationship between parachuting and injury was observed significantly in the survey of Chinese paratroopers. Their injury rate was found to be relatively higher than the reported internationally. Landing impact as a critical point for injury seemed to be proved by the investigation and also the experiment with EMG measurement. It is suggested for future studies, to use the person-based injury rate, landing studied in work physiology and with consideration of different landing skills.
The traditional wheel loader performs the steering operation by the rotation of the steering wheel, which significantly increases the complexity and fatigue of the operator. This paper presents a dual-mode steering system to solve the afore-mentioned problems, where a pilot control valve with a joystick is connected in parallel with the redirector to control the hydraulic steering system. The steering speed and angle of the loader can be controlled by the swing angle and time of the joystick. Based on the simulation and experimental results, the proposed system has the same trend of pressure variation and good steering performance compared with the traditional steering system. The hydraulic damping diameter matching the steering system is obtained by simulating and optimizing the equivalent model. The experimental results show that the effective control swing angle of the joystick increased from 12.5° to 19.7°, which improves the control accuracy of the steering system.
The relationship between time means of external load and EMG amplitude in long term myoelectric studies was investigated in 10 male subjects. The external loads used were in the range of 0-50 % of the subject's MVC. The investigated relationship was found to be exponential. For lower load levels (less than approximately 30% of the subject's MVC) a linear approximation of this exponential relationship could give a satisfactorily good regression line fit.
The relationship between the time integral of the full wave rectified myoelectric signal amplitude and the performed external work was studied in long term intermittent statical work. A linear relationship was demonstrated.
Electromyographic signs of shoulder muscular fatigue were studied in abduction and forward flexion at right angle in the shoulder joint for seven subjects. The myoelectric signal was recorded by surface electrodes for the upper part of the trapezius muscle, the infraspinatus muscle, the middle and anterior part of the deltoid muscle and the biceps brachialis muscle. Bipolar wire electrodes were used for the supraspinatus muscle. By a moving window t-test the duration to the first significant increase of amplitude (RMS) or decrease of mean power frequency (MPF) were determined. The torque produced by the mass of the arm in the two studied elevated arm positions was found to exceed 10 per cent of the maximal voluntary contraction (MVC) for all subjects. For most subjects the supraspinatus and the upper part of the trapezius muscle, revealed significant signs of fatigue after five minutes in the two positions and short time constants of myoelectric amplitude changes. Furthermore electromyographic signs of fatigue developed within a minute for all subjects in the forward flexion (supraspinatus muscle) and in the abduction position (upper part of the trapezius muscle).
1.1. The integrated electromyogram parallels tension in human muscle contracting isometrically.2.2. No quantitative relation between EMG and tension exists when a muscle is allowed to change in length.3.3. No quantitative relation between EMG and muscle power exists.4.4. The amplitude of the EMG characteristically diminishes in large human muscles when they are stretched. This phenomenon has not been fully explained.5.5. It is shown that a lag of approximately 0.08 ± 0.02 sec. exists between peak electrical activity and peak tension of human muscle, which should be taken into account in the analysis of rapid movements.
Electromyographic methods for analysis of the load on individual muscles and signs of muscular fatigue during long-term work (Swedish text) Arbetarskyddsstyrelsen
- B Ericson
Comparaison des activités électromyographiques globale et élémentaire au cours de la contraction statique voluntaire
- B Bouisset