Physical demands of overhead crane operation

Recent studies have suggested that ergonomic factors may contribute to risks experienced by overhead crane operators. However, there are few studies that provide a comprehensive overview of the physical demands of overhead crane operation. This study aimed to provide this information by quantifying muscular, postural, and upper limb movement demands of overhead crane operation including examination of muscle activation and trunk posture by task. Trunk posture, upper limb movement demands and muscle activation in the trunk and upper limbs were quantified for seven overhead crane operators. Trunk posture was quantified using trunk angle and joystick motion requirements were determined using camera data. Muscle activation was measured bilaterally using surface EMG for the upper trapezii, anterior deltoids, posterior deltoids, biceps brachii, triceps brachii, flexor carpi radialis and erector spinae. Lastly, joystick force requirements were assessed using a spring scale. High upper limb and trunk muscle loading were observed when compared to joystick use in other heavy machinery, in part due to the forward, trunk-flexed position required to adequately view the workspace, and the increased force requirements of the joysticks. Joystick input force requirements were 9–31 N for the right-hand joystick and 11–40 N for the left-hand joystick. Operators maintained a forward trunk flexion (>20°) for all subtasks which suggests that trunk posture might play a role in sustained trunk muscle activation. Results suggest that the primary issue with overhead crane cab operation is upper limb and trunk muscle loading. Results confirm the need to investigate muscle load reduction strategies such as camera systems to help reduce the need for trunk flexion. Other design modification suggestions include reducing the joystick input force and displacement requirements coupled with potentially distributing the machine functions more evenly across the right and left controllers.     

Strengths and limitations of a musculoskeletal model for an analysis of simulated meat cutting tasks

This study assessed the capacity of a musculoskeletal model to predict the relative muscle activation changes as a function of the workbench height and the movement direction during a simulated meat cutting task. Seven subjects performed a cutting task alternating two cutting directions for 20 s at four different workbench heights. Kinematics, electromyography (EMG), and cutting force data were collected and used to drive a musculoskeletal model of the shoulder girdle. The model predicted the muscle forces exerted during the task. Both the recorded and computed activation of the muscles was then compared by means of cross-correlation and by comparison of muscle activation trends with respect to the workstation parameters, i.e. cutting direction and workbench height. The results indicated that cutting movements involving arm flexion are preferable to movement requiring internal arm rotation and abduction. The optimal bench height for meat cutting tasks should be between 20 and 30 cm below the worker's elbow height. The present study underlines a beneficial use of musculoskeletal models for adjusting workstation parameters.     

Simulated motion negatively affects motor task but not neuromuscular performance

The effects of long duration simulated motion on motor task and neuromuscular performance along with time frames required to recover from these effects are relatively unknown. This study aimed to determine (1) how simulated motion affects motor task and neuromuscular performance over one hour of motion and (2) the time course of recovery from any decrements. The dependent variables that were measured included: reaction time; visuomotor accuracy tracking; maximal voluntary contractions; voluntary activation; evoked contractile properties and biceps brachii electromyography of the elbow flexors. Reaction times and error rates of the visuomotor accuracy tracking task were compromised in motion, but maximal force, voluntary activation, evoked contractile properties and rmsEMG responses of the biceps brachii were unaffected by motion. It is concluded that motion causes an increase in attention demands, which have a greater effect on motor task rather than neuromuscular performance.

Practitioner Summary: Minor delays or mistakes can separate life and death at sea. The safety and productivity of most vessels rely on error-free performance of motor tasks. This study demonstrates that human ability to perform motor tasks is compromised by ship motions and may aid in developing training and safety guidelines for seafarers.     

Cocontraction changes in muscular fatigue at different levels of isometric contraction

Ten normal subjects participated in a study designed to contrast results obtained in pre- and post-fatigue states. The measures contrasted were the IEMG ratios of agonist/antagonist pairs of muscles. The experimental task was an 8 s ramp isometric elbow flexion ranging from 0 to 100% of a maximal voluntary contraction (MVC). IEMG ratios were obtained at levels of 20, 40, 60 and 80% MVC. Records from the following muscles were obtained with surface electrodes: biceps brachii (BB), brachioradialis (BR), triceps brachii (TB) and anconeus (SU). The torque at the elbow joint was measured by a Cybex II dynamometer. Fatigue was induced using a 60% MVC of elbow flexion maintained during 5 minutes. The data were collected on-line at a sampling rate of 1 kHz. The results indicated that the IEMG ratios (BB/TB and BR/SU) presented a tendency, across subjects, toward a decrease at the levels of 40%, 60% and 80% MVC at the post- relative to the pre-fatigue state. The BB/BR ratios remained stable. These changes in the post-fatigue ratios disclose a tendency toward a saturation of the agonist occurring concomitantly with an increased level of contraction of the antagonists.     

Forearm posture and grip effects during push and pull tasks

Direction of loading and performance of multiple tasks have been shown to elevate muscle activity in the upper extremity. The purpose of this study was to evaluate the effects of gripping on muscle activity and applied force during pushing and pulling tasks with three forearm postures. Twelve volunteers performed five hand-based tasks in supinated, neutral and pronated forearm postures with the elbow at 90° and upper arm vertical. All tasks were performed with the right (dominant) hand and included hand grip alone, push and pull with and without hand grip. Surface EMG from eight upper extremity muscles, hand grip force, tri-axial push and pull forces and wrist angles were recorded during the 10 s trials. The addition of a pull force to hand grip elevated activity in all forearm muscles (all p < 0.017). During all push with grip tasks, forearm extensor muscle activity tended to increase when compared with grip only while flexor activity tended to decrease. Forearm extensor muscle activity was higher with the forearm pronated compared with neutral and supinated postures during most isolated grip tasks and push or pull with grip tasks (all p < 0.017). When the grip dynamometer was rotated so that the push and pull forces could act to assist in creating grip force, forearm muscle activity generally decreased. These results provide strategies for reducing forearm muscle loading in the workplace.

Statement of Relevance: Tools and tasks designed to take advantage of coupling grip with push or pull actions may be beneficial in reducing stress and injury in the muscles of the forearm. These factors should be considered in assessing the workplace in terms of acute and cumulative loading.     

The role of the biceps and triceps brachii during tennis serving

Abstract

The purpose of this study was to investigate the role of the biceps and triceps in rapid elbow extension during the ‘slice’ service in tennis. Six serves, performed by a top male county player (21 years) were studied. Simultaneous cine film (200 Hz) and electromyography (EMG) were used to collect the service data. Impact provided a sonic synchronizing trigger, with biceps and triceps data recorded for a 1 s period before and after the trigger point.

Inertia data for the racket were directly determined by a pendulum technique and included in a three segment model of the server's arm. Maximum elbow extension velocities, for the six trials, averaged 44·1, (±3·9) rad7sol;s. Angular velocity values, in the range 24 to 52 rad/s have been reported in tennis and volleyball serving and badminton smashing. Values in excess of 20 rad/s are beyond the contractile velocity range of human skeletal muscle. The contribution of the triceps to rapid forearm extension is therefore questioned. Substantial biceps EMG activity was evident throughout the elbow extension phase, with the peak activity commencing just prior to impact. A powerful stabilizing co-contraction rather than a dominant muscle torque was thus evident at the elbow. Inverse dynamic analysis of the data supported this observation with large resultant internal joint forces, averaging 577 (± 57) N, acting across the elbow joint through impact. The current findings indicate that the triceps activity is more related to elbow stabilization than extension.     

Optimal location of the tablet for typing while listening to a song

Tablets are much heavier than smartphones and able to bring more musculoskeletal disorders in the upper extremities. The aim of this study was to understand the effects of tablet location on the recruitment of muscles in the neck and upper extremities. Fifteen healthy volunteers typed the lyrics while listening to a song at three tablet locations for 5 min. An iPad 2 was randomly located at one of the levels with 70, 90, and 130 degrees of elbow flexion in sitting. Typing duration, frequency of typing error, perceived levels of fatigue, and subjective position preferences were recorded and recruitment of muscles in the neck and upper extremities was measured. Muscle recruitment of three parts of the trapezius and biceps brachii decreased and use of the levator scapula increased as the vertical level of the tablet heightened. Self‐reported discomfort increased significantly in the neck, upper back, shoulders, elbows, and wrists over time regardless of the tablet location. The table location affected the self‐reported discomfort only at the elbow joints. Subjective preference was highest at the lowest tablet location with the 130‐degree elbow flexion. The vertical levels of the tablet and typing duration independently affected the muscle recruitment and self‐reported discomfort. Findings of this study can be helpful for tablet users in preventing musculoskeletal disorders in the upper extremities.     

An EMG-based variable impedance control for elbow exercise: preliminary study

As the medical field continues to evolve, the average life expectancy of the people increases. However, due to natural deterioration, the average muscle force of the arm decreases in respect to age. So, there are some needs for the people to exercise his/her body as he/she is getting older. There are many researches about the robotic rehabilitation of the upper limb for patients. However, only a few focus on the system of the upper limb muscle exercise for normal people. So, in this study, an electromyography (EMG)-based variable impedance control method is developed for elbow exercise in normal people. Four EMG sensors were attached to the designated right arm and their average EMG level was controlled by the proposed algorithm during an elbow flexion-extension exercise. A total of twenty nine experiments with 15 subjects were performed to verify the proposed control algorithm with NCCEES, an elbow exercise system developed by the authors for the elbow exercise. The experimental results showed that the proposed control algorithm could control the EMG level in approximately 24.1% percent error during the elbow exercise. However, the proposed control algorithm could not control the EMG level fluctuation which depended on the muscular characteristics of the subject. The effect of training with the proposed algorithm will be future work.     

Work load and fatigue in repetitive arm elevations

Six females performed continuous series of concentric and eccentric flexions in the shoulder between 0 and 90 degrees with 0 to 3.1 kg weights held in a powergrip. Heart rate (H R), perceived exertion (RPE) and myoelectric activity (EMG) from the descending part of the trapezius muscle, the anterior part of the deltoid muscle, and the biceps brachii were measured during the tasks. The increase of RPE was faster than the increase of HR with work load indicating an increased importance of local factors (i.e. strain on muscles and tendons) with load in the perceived exertion. The local muscular load determined by EMG on the trapezius muscle was closely correlated with the external torque produced in the glenohumeral joint. The time constants of EMG amplitude increase were correlated with work load, endurance time and with slope coefficients of RPE-HR linear regression. Symptoms and complaints 24 hours after the task were often localized to the descending part of the trapezius muscle. It is suggested that exertion of the descending part of the trapezius muscle in tasks involving repetitive shoulder flexion may promote discomfort and complaints referred to the neck.     

Total forearm support during a typing task may reduce the risk of Trapezius' Myalgia development

ObjectiveEvaluate the influence of alternating the position of the upper limbs, between fully supported and unsupported forearms, in the Upper Trapezius (UT) activity during a typing task on a straight-edged desk.BackgroundErgonomic barriers, such as reduced desk area, is one of the reasons that force computer users to work without supporting their forearms. Unsupported forearms may lead to increased UT muscle fatigue, increasing the potential for lesions, with Trapezius Myalgia (TM) being a possible outcome.Method15 healthy volunteers were assessed (6 females, average age of 3,7 ± 9,5 years old). The protocol included an alternated position of forearms every 5 min between fully supported and unsupported forearms, with a 20-min total duration of a typing task. Surface electromyography readings were collected from both UTs.ResultsSignificant differences were found in the variation of the EMG signal between the two positions for the non-dominant arm after 10 min (p < .05) of typing. The non-dominant UT registered higher levels of activity than the dominant UT. Supported forearms reduced the electrical activity in both UTs, with a greater difference in the non-dominant.ConclusionThis study consolidates the current knowledge that unsupported upper limb during typing tasks significantly increases UT's electrical activity. By fully supporting the forearm, that activity is reduced. Females and the non-dominant UT showed higher electrical activity, potentially increasing the risk of developing TM.ApplicationHealthcare providers, safety and health professionals, and ergonomists should be mindful of the forearm position when advising computer users to prevent TM.     

Auxilio: A portable cable-driven exosuit for upper extremity assistance

This paper introduces a fully portable, lightweight exosuit-type device for shoulder and elbow assistance. The main motivation of this research was to design a portable upper limb exosuit capable to assist dynamic rehabilitation tasks where patient can involve trunk motions and overground movements (e.g., during pick-and-place tasks). The proposed system provides assistance for shoulder flexion and abduction, as well as for elbow flexion. The mechanism is driven by DC motors which are worn on the wearer’s back, and the power is transferred from the actuators to the arm by means of cable-driven transmission. The unique features of the proposed exosuit are the absence of rigid links or joints around the arm, high compliance and portability. This paper describes operating principle and kinematic model of the proposed exosuit and provides force analysis and experimental evaluation of the manufactured device. As the result of this work, we performed a simulation of rehabilitation scenario with the developed wearable prototype.     

A novel electromyographic signal simulator for muscle contraction studies

Mathematical simulation has been widely used in biomedical and biological sciences. In the case of the surface electromyographic (SEMG) activity, some models have been proposed aiming to study muscle contraction strategies that are used during different tasks and conditions. Most of SEMG simulators are based on energy modulation of a Gaussian noise. This work proposes a novel simulator in which the user-defined parameters are associated with the motor units (MUs) recruitment and their firing rate. Comparison between the mean spectrum of real SEMG signals collected in isometric contraction of the muscle biceps brachii and the mean spectrum obtained from simulated SEMG signals showed a good agreement, pointing the proposed simulator seems to be capable to generate consistent electromyographic signals in time and frequency domains and that can be used in many studies, in particular in the evaluation of automatic methods aimed to detect muscular contraction.     

Quantification of the static load component in muscle work using nonlinear filtering of surface EMG

Prolonged static strain on the muscles of the neck-shoulder region is believed to be linked to the development of musculoskeletal problems. To quantify the static strain on the basis of EMG, the level as well as the duration of the muscle load should be analysed on temporal basis. In this paper, some methods for the temporal analysis of EMG recordings are proposed with an aim of quantifying the long-term static strain on the muscle. The use of nonlinear median prefilters for decomposing the EMG activity according both to amplitude level and duration of the activity at different levels is proposed. The prefiltering methods were also evaluated using laboratory studies. The main aim of the studies was to compare the estimation errors between EMG and force for different types of prefilters especially when the static load component was analysed. The average estimation error for sequences having a duration longer than 1 s was found to be 8% of MVC in the case of trapezius muscle and 14% of MVC in the case of biceps brachii muscle. Linear relation was found on the basis of linear least squares curve fitting to give the largest correlation coefficients between EMG and force, when the static load component was analysed.     

Electromyography in sports and occupational settings: an update of its limits and possibilities

The detection of the electrical signal from human and animal muscle dates from long before L. Galvani who took credit for it. J. Swammerdam had already shown the Duke of Tuscany in 1658 the mechanics of muscular contraction. Even if 'electrology or localised electrisation' - the original terminology for electromyography (EMG) - contained the oldest biological scientific detection and measuring techniques, EMG remained a 'supporting' measurement with limited discriminating use, except in conjunction with other methods. All this changed when EMG became a diagnostic tool for studies of muscle weakness, fatigue, pareses, paralysis. and nerve conduction velocities, lesions of the motor unit or for neurogenic and myogenic problems. In addition to the measurement qualities, the electrical signal could be induced as functional electrical stimulation (FES), which developed as a specific rehabilitation tool. Almost in parallel and within the expanding area of EMG, a speciality developed wherein the aim was to use EMG for the study of muscular function and coordination of muscles in different movements and postures. Kinesiological EMG and therewith surface EMG can be applied in studies of normal muscle function during selected movements and postures; muscle activity in complex sports; occupational and rehabilitation movements; isometric contraction with increasing tension up to the maximal voluntary contraction, evaluation of functional anatomical muscle activity (validation of classical anatomical functions); coordination and synchronization studies (kinematic chain); specificity and efficiency of training methods; fatigue; the relationship between EMG and force; the human-machine interaction; the influence of material on muscle activity, occupational loading in relation to lower back pain and joint kinematics. Within these various applications the recording system (e.g. the signal detection, the volume conduction, signal amplification, impedance and frequency responses, the signal characteristics) and the data-processing system (e.g. rectification, linear envelope and normalization methods) go hand in hand with a critical appraisal of choices, limits and possibilities.     

Electromyography in sports and occupational settings: an update of its limits and possibilities

The detection of the electrical signal from human and animal muscle dates from long before L. Galvani who took credit for it. J. Swammerdam had already shown the Duke of Tuscany in 1658 the mechanics of muscular contraction. Even if ‘electrology or localised electrisation’—the original terminology for electromyography (EMG)—contained the oldest biological scientific detection and measuring techniques, EMG remained a ‘supporting’ measurement with limited discriminating use, except in conjunction with other methods. All this changed when EMG became a diagnostic tool for studies of muscle weakness, fatigue, pareses, paralysis, and nerve conduction velocities, lesions of the motor unit or for neurogenic and myogenic problems. In addition to the measurement qualities, the electrical signal could be induced as functional electrical stimulation (FES), which developed as a specific rehabilitation tool. Almost in parallel and within the expanding area of EMG, a speciality developed wherein the aim was to use EMG for the study of muscular function and coordination of muscles in different movements and postures. Kinesiological EMG and therewith surface EMG can be applied in studies of normal muscle function during selected movements and postures; muscle activity in complex sports; occupational and rehabilitation movements; isometric contraction with increasing tension up to the maximal voluntary contraction, evaluation of functional anatomical muscle activity (validation of classical anatomical functions); coordination and synchronization studies (kinematic chain); specificity and efficiency of training methods; fatigue; the relationship between EMG and force; the human-machine interaction; the influence of material on muscle activity, occupational loading in relation to lower back pain and joint kinematics. Within these various applications the recording system (e.g. the signal detection, the volume conduction, signal amplification, impedance and frequency responses, the signal characteristics) and the dataprocessing system (e.g. rectification, linear envelope and normalization methods) go hand in hand with a critical appraisal of choices, limits and possibilities.     

Electromyographic prosthetic hand using grasping-force-magnification mechanism with five independently driven fingers

This paper proposes an electromyographic (EMG) prosthetic hand that has five independently driven fingers, a flexion drive, and a force-magnification drive. The flexion drive allows for rapid finger motion, and the force-magnification drive allows for a firm grasp. To realize the natural feeling of control similar to that of movements with nonamputated parts, the control system includes the impedance model of human forearms and utilizes the muscle contraction level extracted from a user’s EMG signals. We experimentally verified that the maximum fingertip force of the hand exceeds 20 N, and the time required to fully close the hand by the flexion drive is 0.53 s. We also experimentally verified that in response to EMG signals, the fingers can flex smoothly and the grasping force can be modulated. Furthermore, we show that taking EMG signals as inputs makes it possible to control six operations, including ones that use the five fingers in distinctive ways.     

Alternative computer mouse design and testing to reduce finger extensor muscle activity during mouse use

OBJECTIVE: The purpose of this study was to design and test alternative computer mouse designs that attempted to reduce extensor muscle loading of the index and middle fingers by altering the orientation of the button switch direction and the force of the switch. BACKGROUND: Computer users of two-button mouse designs exhibit sustained lifted finger behaviors above the buttons, which may contribute to hand and forearm musculoskeletal pain associated with intensive mouse use. METHODS: In a repeated-measures laboratory experiment, 20 participants completed point-and-click, steering, and drag tasks with four alternative mouse designs and a reference mouse. Intramuscular and surface electromyography (EMG) measured muscle loading, and movement times recorded by software provided a measure of performance. RESULTS: Changing the direction of the switch from a conventional downward to a forward design reduced (up to 2.5% maximum voluntary contraction [MVC]) sustained muscle activity (10th percentile EMG amplitude distribution) in the finger extensors but increased (up to 0.6% MVC) flexor EMG and increased movement times (up to 31%) compared with the reference mouse (p < .001). Implementing a high switch force design also increased flexor EMG but did not differ in movement times compared with the reference mouse (p < .001). CONCLUSION: The alternative mouse designs with altered switch direction reduced sustained extensor muscle loading; however, trade-offs with higher flexor muscle loading and lower performance existed. APPLICATION: Potential applications of this study include ergonomic and human computer interface design strategies in reducing the exposure to risk factors that may lead to upper extremity musculoskeletal disorders.     

A passive movement method for parameter estimation of a musculo-skeletal arm model incorporating a modified hill muscle model

In this paper we present an experimental method of parameterising the passive mechanical characteristics of the bicep and tricep muscles in vivo, by fitting the dynamics of a two muscle arm model incorporating anatomically meaningful and structurally identifiable modified Hill muscle models to measured elbow movements. Measurements of the passive flexion and extension of the elbow joint were obtained using 3D motion capture, from which the elbow angle trajectories were determined and used to obtain the spring constants and damping coefficients in the model through parameter estimation. Four healthy subjects were used in the experiments. Anatomical lengths and moment of inertia values of the subjects were determined by direct measurement and calculation. There was good reproducibility in the measured arm movement between trials, and similar joint angle trajectory characteristics were seen between subjects. Each subject had their own set of fitted parameter values determined and the results showed good agreement between measured and simulated data. The average fitted muscle parallel spring constant across all subjects was 143 N/m and the average fitted muscle parallel damping constant was 1.73 Ns/m. The passive movement method was proven to be successful, and can be applied to other joints in the human body, where muscles with similar actions are grouped together.