The efforts in the forearm during the use of anti-vibration gloves in simulated work tasks

The objective of this article is to analyze the levels of forearm muscular contraction associated with the use of anti-vibration gloves, in which the contraction levels with gloves and without gloves are compared. Two different vibrating tools - a Bosch Compact Duty Multi-Cutter and a Bosch Rotary Hammer carrying an Ø20 mm bit - were used in a simulated work environment. Standard operations were performed by each subject (n = 14) in an 80 × 40 mm pine bar (cross-sectional cuts with the Multi-Cutter) and on a concrete slab 2 × 2 m, 70 mm thick (20 mm holes with the Rotary Hammer). The forearm muscular efforts were measured by surface electromyography (EMG) in four different muscles: the flexor digitorum superficialis (FDS), flexor carpi ulnaris (FCU), extensor carpi radialis longus (ECRL) and extensor carpi ulnaris (ECU). For the flexor muscles (FDS and FCU), a decrease tendency (p > 0.05) in the measured EMG was observed when the operations are performed with gloves relative to the bare hand (a reduction of 5-23% in the percentage of maximum voluntary exertion (%MVE)). For the extensor muscles (ECU), a tendency toward increased (p > 0.05) muscular contraction was observed when the operations were performed with gloves (an increase of 3-20% in the %MVE). No such tendency was found in the ECRL muscle. The ECU was the muscle with the highest %MVE for 10 and 11 operators (n = 14), during the operations, respectively, with the Multi-Cutter and the Rotary Hammer. As a final conclusion from the study, anti-vibration gloves may increase forearm fatigue in the posterior forearm (ECU muscle) and decrease forearm fatigue in the FDS muscle during operations with the above-mentioned tools.

Relevance to industry

Anti-vibration gloves have been applied in industry to reduce the vibration transmitted into the hand and arms through the palms and fingers. This study analyzed forearm muscular efforts during simulated work tasks performed with two different vibrating tools, operated with the bare hand and with three different gloves, based on the analysis of EMG data.     

Effect of grip span on maximal grip force and fatigue of flexor digitorum superficialis.

The aim of this study was to investigate the effect of grip span on isometric grip force and fatigue of the flexor digitorum superficialis (FDS) muscle during sustained voluntary contractions at 60-65% of the maximal voluntary contraction (MVC). Eighteen subjects performed isometric, submaximal gripping contractions using a grip dynamometer at four different grip span settings while the pronated forearm rested on a horizontal surface. Maximal absolute grip force and median power frequency of FDS surface electromyography (EMG) during the submaximal trials were analyzed. Fatigue of FDS, as inferred from EMG frequency shifts, did not change as a function of grip size. However, middle grip sizes allowed for greater absolute forces than the small or large size. When contractions are at 60-65% MVC and the muscle is allowed to fatigue, however, grip size may be less influential than when maximal absolute force is required.     

A new method for estimating hand internal loads from external force measurements

This study examines using force vectors measured using a directional strain gauge grip dynamometer for estimating finger flexor tendon tension. Fifty-three right-handed participants (25 males and 28 females) grasped varying-sized instrumented cylinders (2.54, 3.81, 5.08, 6.35 and 7.62 cm diameter) using a maximal voluntary power grip. The grip force vector magnitude and direction, referenced to the third metacarpal, was resolved by taking two orthogonal grip force measurements. A simple biomechanical model incorporating the flexor tendons was used to estimate long finger tendon tension during power grip. The flexor digitorum superficialis and the flexor digitorum profundus were assumed to create a moment about the metacarpal phalange (MCP) joint that equals and counteracts a moment around the MCP joint measured externally by the dynamometer. The model revealed that tendon tension increased by 130% from the smallest size handle to the largest, even though grip force magnitude decreased 36% for the same handles. The study demonstrates that grip force vectors may be useful for estimating internal hand forces.     

A new method for estimating hand internal loads from external force measurements

This study examines using force vectors measured using a directional strain gauge grip dynamometer for estimating finger flexor tendon tension. Fifty-three right-handed participants (25 males and 28 females) grasped varying-sized instrumented cylinders (2.54, 3.81, 5.08, 6.35 and 7.62 cm diameter) using a maximal voluntary power grip. The grip force vector magnitude and direction, referenced to the third metacarpal, was resolved by taking two orthogonal grip force measurements. A simple biomechanical model incorporating the flexor tendons was used to estimate long finger tendon tension during power grip. The flexor digitorum superficialis and the flexor digitorum profundus were assumed to create a moment about the metacarpal phalange (MCP) joint that equals and counteracts a moment around the MCP joint measured externally by the dynamometer. The model revealed that tendon tension increased by 130% from the smallest size handle to the largest, even though grip force magnitude decreased 36% for the same handles. The study demonstrates that grip force vectors may be useful for estimating internal hand forces.     

A study of hand grip pressure distribution and EMG of finger flexor muscles under dynamic loads

A matrix of miniature and flexible pressure sensors is proposed to measure the grip pressure distribution (GPD) at the hand-handle interface of a vibrating handle. The GPD was acquired under static and dynamic loads for various levels of grip forces and magnitudes of vibration at different discrete frequencies in the 20–1000 Hz range. The EMG of finger flexor muscles was acquired using the silver-silver chloride surface electrodes under different static and dynamic loads. The measured data was analysed to study the influence of grip force, and magnitude and frequency characteristics of handle vibration on: (i) the local concentration of forces at the hand-handle interface; and (ii) the electrical activity of the finger flexor muscles. The results of the study revealed high interface pressure near the tips of index and middle fingers, and base of the thumb under static grip conditions. This concentration of high pressure shifted towards the middle of the fingers under dynamic loads, irrespective of the grip force, excitation frequency, and acceleration levels. The electrical activity of the finger flexor muscles increased considerably with the grip force under static as well as dynamic loads. The electrical activity under dynamic loads was observed to be 1·5–6·0 times higher than that under the static loads.     

Development of a kinematic model to predict finger flexor tendon and subsynovial connective tissue displacement in the carpal tunnel

Finger flexor tendinopathies and carpal tunnel syndrome are histologically characterised by non-inflammatory fibrosis of the subsynovial connective tissue (SSCT) in the carpal tunnel, which is indicative of excessive and repetitive shear forces between the finger flexor tendons and SSCT. We assessed flexor digitorum superficialis (FDS) tendon and adjacent SSCT displacements with colour Doppler ultrasound as 16 healthy participants completed long finger flexion/extension movements captured by a motion capture system. FDS tendon displacements fit a second-order regression model based on metacarpophalangeal and proximal interphalangeal joint flexion angles (R² = 0.92 ± 0.01). SSCT displacements were 33.6 ± 1.7% smaller than FDS tendon displacements and also fit a second-order regression model (R² = 0.89 ± 0.01). FDS tendon and SSCT displacement both correlated with finger joint thickness, enabling participant-specific anthropometric scaling. We propose the current regression models as an ergonomic method to determine relative displacements between the finger flexor tendons and SSCT.     

基于小波变换和样本熵的假手肌电模式识别方法

提出一种新的模式分类器，利用安置在拇长屈肌、指深屈肌和指伸肌上的3个电极所测得的肌电信号,实现了对3自由度假手手指运动的控制．该分类器采用小波变换和样本熵的方法构造特征矢量．经过由变学习速率算法和RP算法构建的集成3层前馈神经网络的分类，能够成功地分辨出拇指、食指和中指的弯曲与伸展运动，平均识别率可达96％以上．实验结果表明，该分类器为多自由度肌电假手的控制提供了一种有效的方法．     

A laboratory study of the effects of wrist splint orthoses on forearm muscle activity and upper extremity posture

OBJECTIVE: To evaluate the effects of wrist splint orthoses (WSOs) on forearm muscle activity and upper extremity/torso postures. BACKGROUND: WSOs are ubiquitous in industry, but the literature as to their biomechanical effects is limited. METHOD: Study 1: Participants performed single-plane wrist exertions with or without a WSO while the electromyographic (EMG) activity of the flexor carpi radialis, flexor carpi ulnaris, and extensor carpi ulnaris was captured. Study 2: Participants performed simple computer jumper installation tasks with or without a WSO while upper extremity/torso postures were recorded. RESULTS: Study 1: A significant interaction between WSOs and wrist angle was observed in the response of forearm muscles (e.g., normalized EMG of the flexor carpi radialis increased from 4.2% to 15.9% as flexion increased from 0 degree to 36 degrees in the orthosis conditions, whereas in the no-orthosis condition it remained approximately 5% at all wrist flexion angles). Study 2: WSOs were found to effect wrist, torso, and shoulder postures, with the orthoses creating a 48% decrease (36 degrees vs. 18.6 degrees) in wrist flexion and 80% decrease (15 degrees vs. -3 degrees) in ulnar deviation but at a cost of increased shoulder abduction of 22% (36.5 degrees vs. 44.5 degrees) and increased lateral bend of torso of 30% (6 degrees vs. 7.8 degrees). CONCLUSIONS: WSOs increased forearm muscle activity at large wrist deviation angles and induced awkward shoulder postures in tasks requiring significant wrist deviation. APPLICATION: Use of WSOs in occupational settings should be carefully considered relative to task requirements, as orthoses may do more harm than good.     

Prediction of forearm muscle activity during gripping

Occupational exposure is typically assessed by measuring forces and body postures to infer muscular loading. Better understanding of workplace muscle activity levels would aid in indicating which muscles may be at risk for overexertion and injury. However, electromyography collection in the workplace is often not practical. Therefore, a set of equations was developed and validated using data from two separate days to predict forearm muscle activity (involving six wrist and finger muscles) from grip force and posture of the wrist (flexed, neutral and extended) and forearm (pronated, neutral, supinated). The error in predicting activation levels of each forearm muscle across the range of grip forces, using the first day data (root mean square error; RMSEmodel), ranged from 8.9% maximal voluntary electrical activation (MVE) (flexor carpi radialis) to 11% MVE (extensor digitorum communis). Grip force was the main contributor to predicting muscle activity levels, explaining over 70% of the variance in flexor activation levels and up to 60% in extensor activation levels, respectively. Inclusion of gender as a variable in the model improved estimates of flexor but not extensor activity. While posture itself explained minimal variance in activation without grip force (< 10% MVE), wrist and forearm posture were required (with grip force) to explain over 70% of the variance of all six muscles. The validation process indicated good day-to-day reliability of each equation, with similar error for flexor muscle models but slightly higher error in the extensor models when predicting activity levels for the second day of data (RMSEvalid ranging from 8.9% to 12.7% MVE). Detailed error analysis during validation revealed that inclusion of posture in the model effectively decreased error at grip forces above 25% maximum, but was detrimental at very low grip forces. This study presents a potential new tool to estimate forearm muscle loading in the workplace using grip force and posture, as a surrogate to use of a complex biomechanical model.     

The influence of mental load on muscle tension

We examined the differences in muscle tension and in physiological measures depending on the type of mental task. Fifteen participants performed tests for sustained attention, vigilance and maintaining posture only. We analysed electromyogram (EMG) measures of extensor digitorum (ED), flexor carpi ulnaris (FU), deltoideus (DE) and trapezius (TR), and heart rate (HR) and respiratory frequency (RF). Measures indicated higher values for mental tasks than for maintained posture only with significant differences in all measures. The following relationships were also significant: between DE and physiological measures (HR and RF), between ED and the amplitude of EMG of the other three muscles, between FU and TR and between HR and RF. The results of this study showed that the relationship between mental demands and muscle tension was mostly reflected by tension in the arm and shoulder girdle muscles and, to a lesser degree, in forearm muscles.

Practitioner Summary: We focused on physiological and muscle tension measures differentiating work according to the level of mental demands. Differences in sustained attention, vigilance and maintaining posture only proved that mental demands were mostly reflected by tension in arm and shoulder girdle muscles and, to a lesser degree, in forearm muscles.     

Prediction of forearm muscle activity during gripping

Occupational exposure is typically assessed by measuring forces and body postures to infer muscular loading. Better understanding of workplace muscle activity levels would aid in indicating which muscles may be at risk for overexertion and injury. However, electromyography collection in the workplace is often not practical. Therefore, a set of equations was developed and validated using data from two separate days to predict forearm muscle activity (involving six wrist and finger muscles) from grip force and posture of the wrist (flexed, neutral and extended) and forearm (pronated, neutral, supinated). The error in predicting activation levels of each forearm muscle across the range of grip forces, using the first day data (root mean square error; RMSE_model), ranged from 8.9% maximal voluntary electrical activation (MVE) (flexor carpi radialis) to 11% MVE (extensor digitorum communis). Grip force was the main contributor to predicting muscle activity levels, explaining over 70% of the variance in flexor activation levels and up to 60% in extensor activation levels, respectively. Inclusion of gender as a variable in the model improved estimates of flexor but not extensor activity. While posture itself explained minimal variance in activation without grip force (<10% MVE), wrist and forearm posture were required (with grip force) to explain over 70% of the variance of all six muscles. The validation process indicated good day-to-day reliability of each equation, with similar error for flexor muscle models but slightly higher error in the extensor models when predicting activity levels for the second day of data (RMSE_valid ranging from 8.9% to 12.7% MVE). Detailed error analysis during validation revealed that inclusion of posture in the model effectively decreased error at grip forces above 25% maximum, but was detrimental at very low grip forces. This study presents a potential new tool to estimate forearm muscle loading in the workplace using grip force and posture, as a surrogate to use of a complex biomechanical model.     

Interactive effects of acute experimental pain in trapezius and sored wrist extensor on the electromyography of the forearm muscles during computer work

We investigated the interactive effects of shoulder pain and wrist extensor muscle soreness on surface electromyography (EMG) during computer mouse work. On day one, subjects (N = 12) performed computer work with/without acute muscle pain induced in the trapezius muscle. Subsequently, eccentric exercise was performed to induce delayed onset muscle soreness (DOMS) in wrist extensor muscles. In presence of DOMS on day two, computer work recordings with/without pain were repeated. EMG signals were recorded from the descending part of trapezius bilaterally, flexor carpi ulnaris and extensor carpi radialis brevis. Experimental muscle pain in trapezius led to a decrease in the muscular activity of the wrist extensor (P < 0.02) and decreased the relative rest time in the wrist flexor even in presence of DOMS (P < 0.01). The present result suggests that shoulder pain plays a role in the coordination of wrist flexors and extensors during computer work.     

Inward torque and high-friction handles can reduce required muscle efforts for torque generation

OBJECTIVE: The effects of handle friction and torque direction on muscle activity and torque are empirically investigated using cylindrical handles. BACKGROUND: A torque biomechanical model that considers contact force, friction, and torque direction was evaluated using different friction handles. METHODS: Twelve adults exerted hand torque in opposite directions about the long axis of a cylinder covered with aluminum or rubber while grip force, torque, and finger flexor electromyography (EMG) were recorded. In addition, participants performed grip exertions without torque, in which they matched the EMG level obtained during previous maximum torque exertions, to allow us to determine how grip force was affected by the absence of torque. RESULTS: (a) Maximum torque was 52% greater for the high-friction rubber handle than for the low-friction aluminum handle. (b) Total normal force increased 33% with inward torque (torque applied in the direction fingertips point) and decreased 14% with outward torque (torque in the direction the thumb points), compared with that with no torque. Consequently, maximum inward torque was 45% greater than maximum outward torque. (c) The effect of torque direction was greater for the high-friction rubber handle than for the low-friction aluminum handle. CONCLUSION: The results support the proposed model, which predicts a large effect of torque direction when high-friction handles are gripped. APPLICATION: Designing tasks with high friction and inward rotations can increase the torque capability of workers of a given strength, or reduce required muscle activities for given torque exertions, thus reducing the risk of fatigue and musculoskeletal disorders.     

Proposal of a Single-Trocar Assemblable Hand for Laparoscopic Surgery

Large instruments are not suitable for laparoscopic surgery because they cannot pass through trocars, which are typically less than 12 mm in diameter; however, operating on large internal organs with a slender instrument is often difficult. To overcome this limitation, we have proposed an 'assemblable instrument', whose parts are inserted through trocars and assembled inside the abdominal cavity to form a large instrument. We have previously reported the development of assemblable hands that require two trocars for assembly. In this paper, we propose a simple three-fingered hand whose function is limited to retracting or grasping, but whose assembly requires a single trocar. We develop two types of finger units: one for a retracting hand and the other for a grasping hand. The two finger units can be connected to a single main unit of the hand. We conduct in vivo experiments. The retracting hand can retract several large internal organs and lift up the stomach with its three fingers from the bottom. The grasping hand can grasp the spleen stably with its two fingers from the bottom.     

Preliminary study evaluating manual dexterity tests assessing gloves protecting against cuts and stabs by hand knives

The paper presents preliminary results on the research methodology of evaluating the ergonomic properties of gloves protecting against cuts and stabs by hand knives. Four manual dexterity tests were selected for the study: TEST 1: evaluation of fine finger movements pursuant to PN-EN 420; TEST 2: cylinder grip and pull test according to PN-EN 1082 evaluating gross movements of the arms and hands; TEST 3: Purdue Pegboard Test evaluating fine finger movements; TEST 4: evaluation of gross movements of the arms and hands while performing simulated occupational tasks. The tested gloves differed in terms of construction and material (metal mesh or knitwear incorporating a metal yarn) and were selected depending on the scope of work activities performed during meat cutting and boning. The tests were conducted on a homogeneous group of subjects. During the performance of the four dexterity tests, we monitored the loading of four groups of muscles of the upper limb (adductor pollicis, extensor carpi radialis, flexor carpi ulnaris, and biceps brachii) using surface electromyography (EMG). Additionally, subjective sensations concerning the strain on the upper limb were evaluated using a questionnaire survey.The objective of the study was to identify a group of tests that would be characterized by high sensitivity and ensure reliable assessment of gloves protecting against cuts and stabs by hand knives. The results showed that not all of the dexterity captured differences in the way the gloves affected dexterity. This was corroborated by electromyographic measurements, which revealed considerable differences in load of upper limb muscles when using various gloves and further supported by the subjective sensations of the participants, as reported in the questionnaire study. It was concluded that in order to reliably evaluate the ergonomic properties of gloves protecting against cuts and stabs by hand knives it is necessary to design new dexterity tests that would reflect actual workplace conditions, and could simulate occupational activities. Workplace observations helped to identify specific aspects of manual dexterity (fine, medium, gross), and types of hand movement associated with professional activities including different force configurations (finger flexion, wrist abduction, and pressing with the fingers and wrist). Based on those observations three new manual dexterity tests dedicated exclusively to evaluation of the ergonomic properties of gloves protecting against cuts and stabs by hand knives have been proposed.     

Characterisation of forces exerted by the entire hand during the power grip: effect of the handle diameter

The objective of this study was to analyse the effect of the handle diameter on the grip forces exerted by the hand during a maximal power grip task. A handle ergometer, combining six instrumented beams and a pressure map, was used to determine the forces exerted by the palm side of the hand regrouping data from 10 anatomical sites (fingertips, phalanges, thumb, palm…). This methodology provided results giving new insight into the effect of the handle diameter on the forces exerted by the hand. First, it appeared that the relationship between the hand length/handle diameter ratio and the maximal grip force fit a U-inverted curve with maximal values observed for a handle diameter measuring 17.9% of the hand length. Second, it was showed that the handle diameter influenced the forces exerted on the anatomical sites of the hand. Finally, it was showed that the handle diameter influenced the finger force sharing particularly for the index and the little fingers. Practitioner Summary: This study analysed the effect of the handle diameter on the grip forces exerted by the hand during a maximal power grip force. This study showed that measurement of the totality of the forces exerted at the hand/handle interface is needed to better understand the ergonomics of handle tools. Our results could be re-used by designers and clinicians in order to develop handle tools which prevent hand pathologies.     

Power grip force is modulated in repeated elbow movement

The objective of this study was to quantitatively investigate the modulation of power grip force under repeated elbow movement and its relation to muscle cocontraction and potential risk of developing cumulative trauma disorders (CTD). Thirteen right-handed participants without any neuromuscular disorders were recruited. Participants were instructed to hold a digital dynamometer in the hand with three levels of grip forces (20%, 40% and 60% of the maximum grip force) and perform repeated arm movement in the sagittal plane at three speeds (slow, self-paced and fast) with the upper arm voluntarily held by side by the participant. With the increase of motion rate and target force level, the grip force fluctuation, finger flexor muscle activities, elbow muscles cocontraction and apparent stiffness were significantly increased (p < 0.01). This study suggests that the power grip coupled with fast arm movement be avoided as much as possible in the workplace. PRACTITIONER SUMMARY: Power grip is usually accompanied with arm movement in workplaces and the increased physical demand might result in higher muscle activities and potentially higher risk of repetitive musculoskeletal injuries.     

EMG control of a pneumatic 5-fingered hand using a Petri net

This article presents the control method for a 5-fingered artificial hand using electromyography (EMG) signals. Our targeted artificial hand is driven by pneumatic actuators to reduce its weight, and we use ON/OFF solenoid valves instead of electro pneumatic regulators to simplify the control system. The pneumatic hand has 15 degrees of freedom, and it seems difficult to reproduce all the finger motions from the EMG signals only. Therefore, we describe typical hand motions using a Petri net, and control the finger motions efficiently based on this model. Each state of the Petri net indicates one step in the hand posture to complete the intended motion. Simultaneously, this state corresponds to the ON/OFF pattern of the 15 solenoid valves. This enables the operator to control the 5-fingered dexterous hand smoothly, transiting the state in the Petri net according to the EMG motion signals. We conducted an experiment to verify the validity of the proposed method. In the experiment, five typical motions (spherical grasp, power grip, hook grip, key grip, precision grip) were successfully performed using the 6-channel EMG signals measured from the operator’s forearm.     

Surface exploration using laparoscopic surgical instruments: the perception of surface roughness

During laparoscopic surgery video images are used to guide the movements of the hand and instruments, and objects in the operating field often obscure these images. Thus, surgeons often rely heavily on tactile information (sense of touch) to help guide their movements. It is important to understand how tactile perception is affected when using laparoscopic instruments, since many surgical judgements are based on how a tissue 'feels' to the surgeon, particularly in situations where visual inputs are degraded. Twelve na?ve participants used either their index finger or a laparoscopic instrument to explore sandpaper surfaces of various grits (60, 100, 150 and 220). These movements were generated with either vision or no vision. Participants were asked to estimate the roughness of the surfaces they explored. The normal and tangential forces of either the finger or instrument on the sandpaper surfaces were measured. Results showed that participants were able to judge the roughness of the sandpaper surfaces when using both the finger and the instrument. However, post hoc comparisons showed that perceptual judgements of surface texture were altered in the no vision condition compared to the vision condition. This was also the case when using the instrument, compared to the judgements provided when exploring with the finger. This highlights the importance of the completeness of the video images during laparoscopic surgery. More normal and tangential force was used when exploring the surfaces with the finger as opposed to the instrument. This was probably an attempt to increase the contact area of the fingertip to maximize tactile input. With the instrument, texture was probably sensed through vibrations of the instrument in the hand. Applications of the findings lie in the field of laparoscopic surgery simulation techniques and tactile perception.     

Ergonomic design and evaluation of the handle for an endoscopic dissector

The purpose of this study was to design an endoscopic dissector handle and objectively assess its usability. The handles were designed with increased contact area between the fingers and thumb and the eye rings, and the eye rings were modified to have a more perpendicular insertion angle to the finger midline. Four different handle models were compared, including a conventional product. Subjects performed dissection, exclusion, grasping, precision manipulation and precision handling tasks. Electromyography and subjective evaluations were measured. Compared to conventional handles, the designated handle reduced the muscle load in the extensor and flexor muscles of the forearm and increased subjective stability. The activity of the first dorsal interosseous muscle was sometimes influenced by the shape of the other parts. The ergonomically designed endoscopic dissector handle used in this study achieved high usability. Medical instrument designs based on ergonomic concepts should be assessed with objective indices.

Practitioner Summary: The endoscopic dissector handles were designed with increased contact area and more suitable insertion angle between the fingers and thumb and the eye rings. Compared to conventional handles, the designated handle reduced the muscle load in the extensor and flexor muscles of the forearm and increased subjective stability.