Constrained handgrip force decreases upper extremity muscle activation and arm strength

Many industrial tasks require repetitive shoulder exertions to be performed with concurrent physical and mental demands. The highly mobile nature of the shoulder predisposes it to injury. The purpose of this study was to determine the effects of simultaneous gripping, at a specified magnitude, on muscle activity and maximal arm force in various directions. Ten female subjects performed maximal arm exertions at two different heights and five directions using both specified (30% maximum voluntary grip) and preferred (self-selected) grip forces. Electromyography was recorded from eight muscles of the right upper extremity. The preferred grip condition produced grip forces that were dependent on the combination of arm height and force direction and were significantly greater (arm force down), lower (to left, up and push forward), or similar to the specified grip condition. Regardless of the magnitude of the preferred grip force, specifying the grip resulted in decreased maximal arm strength (by 18–25%) and muscle activity (by 15–30%) in all conditions, indicating an interfering effect when the grip force was specified by visual target force-matching. Task constraints, such as specific gripping demands, may decrease peak force levels attainable and alter muscle activity. Depending on the nature of task, the amount of relative demand may differ, which should be considered when determining safety thresholds.     

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.     

Force, frequency and gripping alter upper extremity muscle activity during a cyclic push task

Factors, such as high repetition, high force and gripping play a role in the development of upper extremity work-related musculoskeletal disorders. The purpose of this study was to systematically examine the effects of push load and frequency on muscle activity with and without concurrent gripping. A total of 10 men and 10 women performed a cyclic bimanual pushing task. All combinations of three push loads (1 kg, 2 kg, 4 kg), three frequencies (4/min, 8/min, 16/min) and two grip conditions (no required grip and 30% of maximum grip force) were performed in randomised order. The muscle activity of the upper arm and shoulder complex reflected both frequency and load, often with significant interactions, thus may be better described by workload, the product of force and frequency. In the forearm, muscle activities were generally low but adding a submaximal grip superseded the effects of push load, with the activity reflecting frequency and grip. PRACTITIONER SUMMARY: Force and frequency are important risk factors for upper extremity disorders. We found that upper extremity muscle activity responds to workload (force × frequency) in a complex way which may be superseded if a grip is present. This electromyographic study provides physiological insights to muscular loading as basis for a variety of workplace disorders.     

The influence of rice plow handle design and whole-body posture on grip force and upper-extremity muscle activation

A previous job screening study revealed ergonomics risk factors in rice field plowing. This work motivated the present experimental investigation of the influence of plow handle design and farmer whole-body posture on grip force and arm muscle activity. A total of 24 experienced farmers performed a simulated plowing task, including walking on even and uneven ground while rolling a tiller equipped with conventional horizontal and proposed vertical handles. Results revealed the proposed handles, designed to promote neutral wrist posture, to increase upper-arm muscle use between 47% and 70% across ground types, as compared with conventional handles. The ratio of grip force to forearm muscle activity (or efficiency in muscle use) increased from 1.85 when using conventional handles on uneven ground to 2.16 when using the proposed handles with symmetrical body posture on even ground. However, participants perceived higher discomfort when using the proposed handles, as they were accustomed to the conventional design.     

The size and structure of arm movement variability decreased with work pace in a standardised repetitive precision task

Increased movement variability has been suggested to reduce the risk of developing musculoskeletal disorders caused by repetitive work. This study investigated the effects of work pace on arm movement variability in a standardised repetitive pipetting task performed by 35 healthy women. During pipetting at slow and fast paces differing by 15%, movements of arm, hand and pipette were tracked in 3D, and used to derive shoulder and elbow joint angles. The size of cycle-to-cycle motor variability was quantified using standard deviations of several kinematics properties, while the structure of variability was quantified using indices of sample entropy and recurrence quantification analysis. When pace increased, both the size and structure of motor variability in the shoulder and elbow decreased. These results suggest that motor variability drops when repetitive movements are performed at increased paces, which may in the long run lead to undesirable outcomes such as muscle fatigue or overuse.     

面向智能假肢手臂的生机接口系统与类神经协同控制

针对肢体残障患者的假肢控制问题,搭建了一种基于sEMG（表面肌电信号）的智能假肢手臂系统,实现手臂残障程度较高患者的手－肘协调控制。首先,基于肌肉协同理论,使用非负矩阵分解（NMF）方法提取肌肉协同作用,并进行手部动作识别以及肘关节的连续运动估计。其次,基于意图识别结果构建“前馈－反馈”控制框架,对受试者进行前馈监督与反馈检测;根据前馈－反馈结果调整期望的控制输入,提高假肢系统的舒适性与鲁棒性。然后,针对手部动作,构建一种自适应调整抓握力度的框架,通过力、位信息交替控制,实现不同刚度、不同形状物体的自适应抓握;对于肘部运动,设计一种基于识别结果的阻抗控制算法,实现手－肘一体化假肢的稳定的人机交互控制。最后,由6名健康受试者、1名手臂残障受试者对以上控制策略进行实验验证,对手臂整体运动实现了较为准确的意图识别,同时也完成了稳定的肘部屈伸以及手部抓取,做到了手－肘的一体化协调控制。最终该套系统在北京2022年冬残奥会实现了应用展示。     

A systematic exploration of distal arm muscle activity and perceived exertion while applying external forces and moments

The purpose of this study was to systematically explore and describe the response of selected hand and forearm muscles during a wide range of static force and moment exertions. Twenty individuals with manual work experience performed exertions in power grip, pulp pinch and lateral pinch grips. Electromyography (EMG) from eight sites of the hand and forearm, grip force as well as ratings of perceived exertion (RPE) were monitored as each participant exerted approximately 350 short (5 s) static grip forces and external forces and moments. As expected, strong relationships were found between grip force alone without other actions and muscle activation. When the hand was used to grip and transmit forces and moments to the environment, the relationships between grip force and muscle activation were much weaker. Using grip force as a surrogate for forearm and hand tissue loading may therefore be misleading.     

Measurement of prehensile grasp capabilities by a force and moment wrench: Methodological development and assessment of manual workers

Prehensile grasp capability is typically quantified by pinch and grasp forces. This work was undertaken to develop a methodology to assess complex, multi-axis hand exertions through the measurement of forces and moments exerted by the hand along and about three orthogonal axes originating at the grip centre; termed an external wrench. Instrumentation consisting of a modified pinch/grip dynamometer affixed to a 6?df force cube was developed to simultaneously measure three forces, three moments and the pinch/grip force about the centre of the grip. Twenty right hand dominant manual workers (10 male and 10 female), free of hand or wrist disorders, completed a variety of maximal strength tasks. The randomized block design involved three separate grips?–?power grip, lateral pinch and pulp pinch. Randomized within each block were three non-concurrent repetitions of isolated maximal force and moment generations along and about the three principle orthogonal axes and a maximal grip force exertion. Trials were completed while standing, with the arm abducted and elbow flexed to 90° with a wrist posture near neutral. Where comparable protocols existed in the literature, forces and moments exerted were found to be of similar magnitude to those reported previously. Female and male grip strengths on a Jamar dynamometer were 302.6?N and 450.5?N, respectively. Moment exertions in a power grip (female and male) were 4.7 Nm and 8.1 Nm for pronator, 4.9 Nm and 8.0 Nm for supinator, 6.2 Nm and 10.3 Nm for radial deviator, 7.7 Nm and 13.0 Nm for ulnar deviator, 6.2 Nm and 8.2 Nm for extensor, and 7.1 Nm and 9.3 Nm for flexor moments. Correlations with and between maximal force and moment exertions were only moderate. This paper describes instrumentation that allows comprehensive characterization of prehensile force and moment capability.     

Grip force and force sharing in two different manipulation tasks with bottles

Abstract

Grip force and force sharing during two activities of daily living were analysed experimentally in 10 right-handed subjects. Four different bottles, filled to two different levels, were manipulated for two tasks: transporting and pouring. Each test subject’s hand was instrumented with eight thin wearable force sensors. The grip force and force sharing were significantly different for each bottle model. Increasing the filling level resulted in an increase in grip force, but the ratio of grip force to load force was higher for lighter loads. The task influenced the force sharing but not the mean grip force. The contributions of the thumb and ring finger were higher in the pouring task, whereas the contributions of the palm and the index finger were higher in the transport task. Mean force sharing among fingers was 30% for index, 29% for middle, 22% for ring and 19% for little finger.

Practitioner Summary: We analysed grip force and force sharing in two manipulation tasks with bottles: transporting and pouring. The objective was to understand the effects of the bottle features, filling level and task on the contribution of different areas of the hand to the grip force. Force sharing was different for each task and the bottles features affected to both grip force and force sharing.     

Measurement of prehensile grasp capabilities by a force and moment wrench: methodological development and assessment of manual workers

Prehensile grasp capability is typically quantified by pinch and grasp forces. This work was undertaken to develop a methodology to assess complex, multi-axis hand exertions through the measurement of forces and moments exerted by the hand along and about three orthogonal axes originating at the grip centre; termed an external wrench. Instrumentation consisting of a modified pinch/grip dynamometer affixed to a 6 df force cube was developed to simultaneously measure three forces, three moments and the pinch/grip force about the centre of the grip. Twenty right hand dominant manual workers (10 male and 10 female), free of hand or wrist disorders, completed a variety of maximal strength tasks. The randomized block design involved three separate grips--power grip, lateral pinch and pulp pinch. Randomized within each block were three non-concurrent repetitions of isolated maximal force and moment generations along and about the three principle orthogonal axes and a maximal grip force exertion. Trials were completed while standing, with the arm abducted and elbow flexed to 90 degrees with a wrist posture near neutral. Where comparable protocols existed in the literature, forces and moments exerted were found to be of similar magnitude to those reported previously. Female and male grip strengths on a Jamar dynamometer were 302.6 N and 450.5 N, respectively. Moment exertions in a power grip (female and male) were 4.7 Nm and 8.1 Nm for pronator, 4.9 Nm and 8.0 Nm for supinator, 6.2 Nm and 10.3 Nm for radial deviator, 7.7 Nm and 13.0 Nm for ulnar deviator, 6.2 Nm and 8.2 Nm for extensor, and 7.1 Nm and 9.3 Nm for flexor moments. Correlations with and between maximal force and moment exertions were only moderate. This paper describes instrumentation that allows comprehensive characterization of prehensile force and moment capability.     

The effects of joint torque, pace and work:rest ratio on powered hand tool operations

Repetitive use of hand-held power tools is associated with work-related upper extremity musculoskeletal disorders. Using a pneumatic nutrunner, 21 men completed twelve 360 repetitive fastener-driving sessions on three joints (hard, soft and control) at slow and fast pace, and two different work:rest patterns. Handgrip force and perceived exertions were collected throughout each session. For the control joint, the mean grip force exerted was 39.6% of maximum voluntary exertion (MVE) whereas during hard and soft joint sessions it was 48.9% MVE and 56.9% MVE, respectively. Throughout each session, the grip force decreased, more while operating soft and hard joints as compared with the control joint (regression slope: ?0.022 and ?0.023, compared with ?0.007 N/drive, respectively), suggesting considerable upper extremity muscular effort by participants during torque buildup. Fast work pace resulted in higher average grip forces by participants but a greater decrease in the force as the session progressed. Providing rest breaks reduced perceived exertions. The findings gain additional knowledge for assembly task design to possibly reduce the hand/arm injury risks for the operator.

Practitioner Summary: Powered hand tools are widely used in assembly and manufacturing industries. However, the nature of their repetitive use on human operator biomechanical and perceptual responses is not fully understood. This study examined work-related risk factors such as joint torque, pace and work:rest ratios on powered hand tool performance.     

Power hand tool vibration effects on grip exertions

Operation of vibrating power hand tools can result in excessive grip force, which may increase the risk of cumulative trauma disorders in the upper extremities. An experiment was performed to study grip force exerted by 14 subjects operating a simulated hand tool vibrating at 9.8 m/s² and 49 m/s² acceleration magnitudes, at 40 Hz and 160 Hz frequencies, with vibration delivered in three orthogonal directions, and with 1.5kg and 3.0kg load weights. Average grip force increased from 25.3 N without vibration to 32.1 N (27%) for vibration at 40 Hz, and to 27.1N (7%) for vibration at 160 Hz. Average grip force also increased from 27.4 N at 9.8 m/s² acceleration to 31.8 N (16%) at 49m/s². Significant interactions between acceleration x frequency, and frequency x direction were also found. The largest average grip force increase was from 25.3N without vibration to 35.8N (42%) for 40 Hz and 49 m/s² vibration. The magnitude of this increase was of the same order as for a two-fold increase in load weight, where average grip force increased from 22.5N to 35.0N (56%). A second experiment studied hand flexor and extensor muscle responses using electromyography for five subjects holding a handle vibrating at 8 m/s² using ISO weighted acceleration, with frequencies of 20 Hz, 40 Hz, 80 Hz and 160 Hz, and grip forces of 5%, 10% and 15% of maximum voluntary contraction. Muscle responses were greatest at frequencies where grip force was affected, indicating that the tonic vibration reflex was the likely cause of increased grip exertions.     

Estimation of hand force in ergonomic job evaluations

The aims of the present study were: (1) to collect normative data of pinch and power grip strength with a newer digital dynamometer; (2) to study the ability of hand grip force matching using a hand dynamometer where the validity and reliability issues were studied; and (3) to study the relationship between hand grip force matching and muscle activities of three forearm and hand muscles. This study consisted of two experiments. One hundred and twenty subjects volunteered in the first experiment, where hand grip strength and hand force estimation data were collected. The second experiment had 14 volunteers, where muscle activities of the hand and forearm were collected during the tests of hand grip strength and hand force matching estimations. Results showed that the power grip and pinch grip strengths collected with a newer digital dynamometer were comparable to similar studies using older equipment. At the group level, the force matching method was largely accurate and consistent. Instructions to the subjects about force matching estimation were important to the accuracy and consistency of the estimated forces. Estimation in force matching might depend on perceptions of several major muscle activities.     

Estimation of hand force in ergonomic job evaluations

The aims of the present study were: (1) to collect normative data of pinch and power grip strength with a newer digital dynamometer; (2) to study the ability of hand grip force matching using a hand dynamometer where the validity and reliability issues were studied; and (3) to study the relationship between hand grip force matching and muscle activities of three forearm and hand muscles. This study consisted of two experiments. One hundred and twenty subjects volunteered in the first experiment, where hand grip strength and hand force estimation data were collected. The second experiment had 14 volunteers, where muscle activities of the hand and forearm were collected during the tests of hand grip strength and hand force matching estimations. Results showed that the power grip and pinch grip strengths collected with a newer digital dynamometer were comparable to similar studies using older equipment. At the group level, the force matching method was largely accurate and consistent. Instructions to the subjects about force matching estimation were important to the accuracy and consistency of the estimated forces. Estimation in force matching might depend on perceptions of several major muscle activities.     

Effect of wrist position on grip force sense in healthy adults

To achieve a better understanding of the causes of higher rates of musculoskeletal disorders and to develop preventive strategies to decrease the risk of injury and optimally design hand tools, it is necessary to understand the effects of both wrist position and force level on grip force sense. In this study, the effects of both wrist position and force level on grip force sense in healthy males during an ipsilateral force reproduction task were investigated. Twenty healthy subjects were instructed to produce varying levels of target forces (i.e., 10%, 30%, and 50% of maximal voluntary isometric contraction [MVIC]) for five wrist positions (i.e., neutral position, full radial deviation, full ulnar deviation, full‐extension, and full flexion), and to reproduce these forces using the same hand. The results of our study revealed that the absolute error, constant error, and MVIC decreased as the wrist joint angle deviated from the neutral position. Subjects had a more accurate estimation of medium target force (30% MVIC), while low target force (10% MVIC) was overestimated and high target force (50% MVIC) was underestimated, in contrast to most previous studies.     

Ergonomic evaluation of an alternative tool for cake decorating

AimCake decorating involves several hand intensive steps with high grip force during the application of icing. The purpose of this laboratory study was to evaluate forearm muscle activity, discomfort, productivity, and usability of an alternative tool for cake decorating compared to decorating with the traditional piping bag.MethodsParticipants (n = 17) performed 2 h of cake decorating tasks using the two tools. Subjective hand and arm fatigue, usability, upper extremity posture, and muscle activity from three forearm muscles were assessed for each tool. Outcome measures were evaluated using the Wilcoxon Signed Rank test and the paired t-test.ResultsLess fatigue was reported in the dominant hand (p = 0.001), forearm (p = 0.003) and shoulder (p = 0.02) for the alternative tool when compared to the piping bag. Average median (APDF 50%) and peak (APDF 90%) muscle activity was significantly less for the alternative tool across all three forearm muscles. The alternative tool significantly reduced grip force, an important risk factor for distal upper extremity pain and disorders. Participants rated usability of the alternative tool superior for refill and comfort but the traditional method was rated better for accuracy, stability, positioning and control.ConclusionsThe alternative tool was associated with less dominant arm fatigue, muscle activity, and grip force when compared with the piping bag. However, the alternative tool did not receive the best overall usability rating due to problems with accuracy and overflow, especially with smaller decorating tips. Recommendations were made for addressing these problems with the alternative tool.     

Wrist strength is dependent on simultaneous power grip intensity

The effect of grip activities on wrist flexion/extension strength was examined. Twelve healthy subjects performed maximum wrist flexion/extension exertions with one of five levels of simultaneous grip effort: minimum effort; preferred effort; 30%, 60% and 100% maximum voluntary contraction. As grip force increased from the minimum to the maximum effort, average wrist flexion strength increased 34% and average wrist extension strength decreased 10%. It appears that the finger flexor tendons on the volar aspect of the wrist act agonistically in wrist flexion and act antagonistically to wrist extension. When an object gripped by the hand is fragile or uncomfortable, the reduced finger flexor activity will limit wrist flexion strength. Gripping a slippery object that requires high grip effort will result in reduced wrist extension strength. Grip force should be controlled during measurement of wrist flexion or extension strength. When analysing a task that involves both grip and wrist exertions, use of grip/wrist strength values that were measured during grip exertions only, or wrist exertions only, may incorrectly estimate the true grip/wrist strength, as grip and wrist activities significantly interact with each other as demonstrated in this paper.     

Influence of simultaneous bilateral exertion on muscle strength during voluntary submaximal isometric contraction

The influence of simultaneous bilateral exertion on muscle strength was tested under the conditions in which the same or different levels of strength were exerted by the right and left arm (or hand). Isometric muscle strength of elbow flexion, elbow extension and hand grip was studied. Subjects voluntarily exerted 25%, 50% and 75% of maximal strength based on their subjective judgement without the feedback of the strength actually exerted. Involuntary decrements of muscle strength were caused by the bilateral exertion. Muscle strength of both sides decreased under the condition where the same level of strength was exerted by the right and the left arm (or hand). When different levels of strength were exerted by each arm (or hand), the strength of the weaker side considerably decreased, while the strength of the stronger side did not decrease.     

Influence of simultaneous bilateral exertion on muscle strength during voluntary submaximal isometric contraction

The influence of simultaneous bilateral exertion on muscle strength was tested under the conditions in which the same or different levels of strength were exerted by the right and left arm (or hand). Isometric muscle strength of elbow flexion, elbow extension and hand grip was studied. Subjects voluntarily exerted 25%, 50%, and 75% of maximal strength based on their subjective judgement without the feedback of the strength actually exerted. Involuntary decrements of muscle strength were caused by the bilateral exertion. Muscle strength of both sides decreased under the condition where the same level of strength was exerted by the right and the left arm (or hand). When different levels of strength were exerted by each arm (or hand), the strength of the weaker side considerably decreased, while the strength of the stronger side did not decrease.     

基于运动相关皮层电位握力运动模式识别研究

面向基于脑-机接口（Brain-computer interface,BCI）的脑-机交互控制（Brain-machine interaction control,BMIC）——直接脑控机器人,提出一种新的左、右手握力运动参数范式,在该范式下探索左、右手握力运动相关皮层电位/运动相关电位（Movement-related potentials,MRPs）的时域特征表示并识别握力运动模式.在涉及左、右手4个不同任务的实验中采集了11个健康被试的脑电信号,任务期间要求被试以2种握力变化模式之一完成自愿握力运动,每种任务随机重复30次.不同握力任务之间具有显著差异的运动相关电位特征用于识别握力运动模式.分别用基于核的Fisher线性判别分析和支持向量机识别4个不同的握力运动任务.研究结果进一步证实运动相关电位可以表征握力运动规划、运动执行和运动监控的脑神经机制过程.基于核的Fisher线性判别分析和支持向量机分别获得24±4%和21±5%的平均错误分类率.最小误分类率是12%,所有被试平均最小误分类率为20.9±5%.与传统的仅仅识别参与运动的肢体类型以及识别单侧肢体运动参数的研究相比,本研究可望为脑-机交互控制/脑控机器人接口提供更多的力控制意图指令,奠定了后续的对比研究基础.