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Studies of animal weaponry and defensive structures rarely take into consideration their underlying mechanical properties. We measured the compressive strength and thickness of the exoskeleton of the claw (chela) in two North American crayfish species, Faxonius virilis and F. limosus. We performed similar measures on the carapace, a body region not directly involved in agonistic contests. Males of both species generated significantly stronger maximum pinch forces than females. However, these differences can be attributed to differences in claw size between the sexes. The thickness (ultrastructure) of the claw exoskeleton was a significant predictor of its compressive strength and likely explained the difference in compressive strength we observed between the two species. Neither claw thickness nor claw compressive strength was correlated with maximum pinch force. Additionally, we found that crayfish body size was a strong predictor of carapace compressive strength and thickness, whereas sex was not. The claw had greater compressive strength and thickness than the corresponding values for the carapace. Our study shows that the mechanical properties of the crayfish exoskeleton are largely a function of size and highlights the need to integrate mechanical properties into studies of animal morphology and performance. [ABSTRACT FROM AUTHOR]

Objective: The objective of this review was to examine the impact of instrument designs on pinch force generation during scaling by dental professionals. Methods: Three databases were utilized from September 2019 to November 2021 in addition to hand‐searching specific journals and reference lists. Research articles that examined pinch force generation in dental professionals during scaling with manual instruments only were included. Bias was assessed in the individual articles. Results: Six research articles were included with sample populations that varied from 12 to 24 participants. Four articles evaluated instrument designs in relation to pinch force generation during scaling by dental professionals. Two articles evaluated the clinicians' experience levels and the impact on pinch force generation. Results of three articles revealed instruments with large diameters and low weights produced the least amount of pinch force (p < 0.05). Additionally, two articles found instruments with a round, tapered shape produced less pinch force and instrument handles made of silicone produced higher pinch strength post‐scaling (p < 0.05). One study indicated instrument designs associated with modified scaling techniques may reduce thumb and index finger pinch force (p < 0.05). Conclusion: The findings from this review indicate weak evidence for instrument choices to reduce pinch force during scaling. Dental professionals should consider lightweight and large diameter instruments for manual scaling. Clinicians may also want to consider round, tapered handles and instrument designs with modified scaling techniques. This systematic review further identified the need for clinical research studies with rigorous research designs that examine the ergonomic impacts of instrument designs. [ABSTRACT FROM AUTHOR]

This study compares and correlates young and elderly people's pinch force and endurance, and proposes inventive solutions contextualised from these statistical evaluations using TRIZ techniques. An experiment was performed with 64 young and old adults who were required to pinch an apparatus while wearing a glove with pressure sensors. Participants held their pinch until they could no longer sustain it. Pinch force and endurance time were measured and analysed using Pearson's correlation and T-Tests. The analyses confirmed that pinch force decreases with lower endurance and vice versa. Apart from the significant difference in elderly and young people's pinch force and endurance, researchers found that young people sustained pinches longer and at a higher force than elderly people. TRIZ strategies suggested that it is better for objects to 'grasp' the elderly's fingers in pinch activities rather than the usual way. Elderly people could attempt pinching periodically to conserve endurance and reduce injury risks from highly sustained exertions. This study provides an explicit pathway in developing innovative solutions that help prevent finger-related musculoskeletal risks among elderly people. These solutions have the potential in contributing to advances in ergonomics, mechanical design and biomechanics in the form of hand prosthetics and hand exoskeletons. [ABSTRACT FROM AUTHOR]

Animal weapons are diverse and often exaggerated structures associated with sexual selection and male–male combat. Despite their diversity, our knowledge of these structures comes primarily from studies that focus on the size of the weapons and neglect other components, such as their shape or performance. Furthermore, weapons can exhibit species-level plasticity based on nutrition and other ecological variables, but few studies have documented seasonal variation in weapon plasticity. Here, we investigate how weapon size, shape and performance differ across adult male reproductive and non-reproductive Allegheny crayfish, Faxonius obscurus. Given that F. obscurus and other cambarid crayfishes exhibit cyclical moulting between reproductive and non-reproductive states, they provide an ideal system in which to investigate such questions. We found that claws of reproductive and non-reproductive male F. obscurus differ in all three weapon components we investigated; claws from reproductive males were longer, stronger and different in shape compared with claws from non-reproductive males. Wielding longer and stronger claws is likely to confer greater competitive success during the mating season, which demonstrates an unexplored pattern of seasonal weapon plasticity. We discuss these results considering our knowledge of the seasonality of weapon phenotypes and propose several avenues of future research using cambarid crayfish as a model system. [ABSTRACT FROM AUTHOR]

In this study, the authors used the Fujifilm Prescale Pressure Measuring System to measure the contact pressure and distribution at the jaws of laparoscopic grasping forceps. This data was then correlated with measured pressures at the forceps handles to understand the relationship between the surgeon’s actuating pressure and that on the organ being manipulated. The purpose of this study is to create a database of tactile information to provide guidelines in defining minimally invasive surgery (MIS). This is expected to be important as today's society continues to progress in the use of automation, IoT, AI and MIS. In order to achieve the above, the authors developed an experimental device consisting of an actuator, a load cell and an MCU to stably actuate and control the handle side of grasping forceps. Target organs were simulated using triangular prisms of various silicone rubber materials. The experimental method involved actuating the handle side with preset pressure values for fixed time periods and using sensitive film to measure the pressure at the forceps tip. The film data was then scanned, processed and analyzed.

Production of functional forces by human motor systems require coordination across multiple muscles. Grip and pinch are two prototypes for grasping force production. Each grasp plays a role in a range of hand functions and can provide an excellent paradigm for studying fine motor control. Despite previous investigations that have characterized muscle synergies during general force production, it is still unclear how intermuscular coordination differs between grip and pinch and across different force outputs. Traditional muscle synergy analyses, such as non-negative matrix factorization or principal component analysis, utilize dimensional reduction without consideration of nonlinear characteristics of muscle co-activations. In this study, we investigated the novel method of multiplex recurrence networks (MRN) to assess the inter-muscular coordination for both grip and pinch at different force levels. Unlike traditional methods, the MRN can leverage intrinsic similarities in muscle contraction dynamics and project its layers to the corresponding weighted network (WN) to better model muscle interactions. Twenty-four healthy volunteers were instructed to grip and pinch an apparatus with force production at 30%, 50%, and 70% of their respective maximal voluntary contraction (MVC). The surface electromyography (sEMG) signals were recorded from eight muscles, including intrinsic and extrinsic muscles spanning the hand and forearm. The sEMG signals were then analyzed using MRNs and WNs. Interlayer mutual information (${I}$) and average edge overlap ($\omega $) of MRNs and average shortest path length (${L}$) of WNs were computed and compared across groups for grasp types (grip vs. pinch) and force levels (30%, 50% and 70% MVC). Results showed that the extrinsic, rather than the intrinsic muscles, had significant differences in network parameters between both grasp types (${p} < 0.05$), and force levels (${p} < 0.05$), and especially at higher force levels. Furthermore, ${I}$ and $\omega $ were strengthened over time (${p} < 0.05$) except with pinch at 30% MVC. Results suggest that the central nervous system (CNS) actively increases cortical oscillations over time in response to increasing force levels and changes in force production with different sustained grasping types. Muscle coupling in extrinsic muscles was higher than in intrinsic muscles for both grip and pinch. The MRNs may be a valuable tool to provide greater insights into inter-muscular coordination patterns of clinical populations, assess neuromuscular function, or stabilize force control in prosthetic hands. [ABSTRACT FROM AUTHOR]

In this paper, the effects of different grasp types, grasp widths, coupling types, and wearing gloves on pinch-insertion force have been studied using the discrete wavelet transform method, which was proposed for extracting features from the force-time curves during the experiment that simulates the snap-fit assembly procedure. This paper uses collected Salmanzadeh and Landau [4] experiments data as an application for proposed methodology. This method allows to use of all information obtained from the experiment and considers the whole force exertion process instead of one point of curves and at the same time reduce the number of variables without losing information. The results obtained by applying multivariate analysis of variance (MANOVA) on the wavelet coefficients are more sensible and more precise than the results of the conventional method based on only one point of the curve. The results show that both wearing glove and grasp type significantly affect the pinch-insertion forces. The second series of results show that the effects of both grasp width and grasp type on pinch force are significant. The third result series show that both pinch-insertion forces are significantly affected by coupling type with/without wearing gloves. Further analysis was performed on the average wavelet coefficients curves that can explain the cause of MANOVA test results. The results of this paper can be used for ergonomic designing of snap-fits to reduce the potential damage of the assembly process.

To investigate how sensory symptoms impact the motor control of hands, in this study we examined the differences in conventional sensibility assessments and pinch force control in the pinch-holding-up activity (PHUA) test between carpal tunnel syndrome (CTS) patients and healthy controls. CTS patients (n = 82) with 122 affected hands and an equal number of control subjects were recruited to participate in the threshold, discrimination, and PHUA tests. The patients showed significantly poorer hand sensibility and lower efficiency of force adjustment in the PHUA test as compared with the control subjects. Baseline pinch strength and the percentage of maximal pinch strength for the PHUA were significantly higher for the subgroup of sensory nerve action potential (SNAP) of <16 μV than for the subgroup of SNAP of ³16 μV. Using a PHUA perspective to analyze the efficiency of force-adjustment could assist the clinical detection of sensory nerve dysfunction. [ABSTRACT FROM AUTHOR]

Featured Application: This work was conducted to develop an automated data acquisition system to monitor the pinch grip in rehabilitation and assessment applications after a stroke. The Upper Extremity Fugl Meyer Assessment (UE-FMA) is the most comprehensive assessment for pinch impairment after stroke. The pinch test of UE-FMA is manually performed by pulling a pincer object away from the patient's fingers while providing a visual observation that results in a subjective assessment. In this study, an automated data acquisition system that consists of a linear electric actuator applying automatic pulling to the customized pincer object held by the volunteer was developed. The pinch force was measured such that a strain gauge was placed on the pincer object while pulling force was measured using pulling force load cell connected in between the linear electric actuator and customized pincer object. The pincer object's slip onset was detected using a displacement slip sensor. The mean pinch and pulling force values at the slip onset were 12.17 and 6.25 N for right hands, while mean pinch and pulling force values were 11.67 and 5.92 N for left hands of 50 healthy volunteers, respectively. Based on the paired t-test, there is no significant difference between right and left hands. The automated data acquisition system can objectively apply a pulling force, detect the slip onset, and measure the pinch and pulling forces. [ABSTRACT FROM AUTHOR]

• Pinch force strength is accurately predicted using sEMG. • Different pinch movements are accurately classified using sEMG. • Similarity of EMG features is evaluated. • An EMG feature-to-image method is proposed. The movement of intelligent EMG-driven prosthesis mainly relies on the synergy of different fingers to achieve function of grasping objects. The paper proposes a novel scheme for force prediction and movement classification about pinch between different fingers based on surface electromyography (sEMG) using machine learning. The pinch force and sEMG signals are recorded synchronously by a data acquisition device. Eight features are extracted, which are proven to have better performance in the estimation of sEMG-to-force. We present a novel feature selection method that uses the one-dimensional time series similarity assessment based on Manhattan distance to eliminate the repetitive information between features. Three optimal features carrying less repetitive information are retained. Seven machine learning algorithms are used to predict force strength. The results show that the Long Short Term Memory (LSTM) has the best performance of force prediction, achieving a R 2 of 0.9517 and RMSE of 3.2723. The paper proposes a novel method of converting EMG feature sequences to the normalized gray image in order to classify the finger movement. Five classifiers based on image feature extraction and the Convolutional Neural Network (CNN) are developed respectively. The experimental results indicate that the CNN performs best, achieving an accuracy of 97.66%. In this way, it not only realizes the accurate force prediction, but also realizes the movement classification between different fingers. The proposed methodology has the potential to realize simultaneous force and movement control of prosthetic hand. [ABSTRACT FROM AUTHOR]

As people age, their finger function deteriorates due to muscle, nerve, and brain degeneration. While exercises might delay this deterioration, an invention that enhances elderly people’s pinching abilities is essential. This study aims to design and develop a finger grip enhancer that facilitates the day-to-day pinching activities of elderly people. This research is an extension of a previous study that conceptualised a finger grip enhancer. The device facilitates finger flexion on the thumb and index finger, and weighs 520 g, allowing for improved portability and sufficient force exertion (13.9 N) for day-to-day pinching. To test for usability, eleven subjects aged 65 years and above performed a pinch-lift-hold test on various household objects. The pinch force before and after utilising the device was measured. Using Minitab 18, the statistical significance of using this device was analysed with a paired-samples t-test. With this device, the elderly people’s pinching abilities significantly improved in both pinch force and pinch force steadiness (p < 0.05). The proposed device has the potential to enhance elderly people’s quality of life by supporting a firm pinch in the handling of everyday objects. This research has applicational value in developing exoskeleton devices for patients who require rehabilitation.

Morphological differences between the sexes are a common feature in many groups of animals and can have important ecological implications for courtship, mating, access to prey and, in some cases, intersex niche partitioning. In this study, we evaluated the role of sexual dimorphism in the performance of the two structures that mediate the ability to access prey, the pinchers or chelae and the venomous stinger, in two species of scorpions with contrasting morphologies: Chactas sp. which has marked sexual dimorphism in the chelae, and Centruroides sp. which does not have such marked dimorphism in the chelae. We evaluated aspects such as chela pinch force, toxicity to prey (LD50) and the volume of venom in males and females of each species. We found significant differences between males and females of Chactas sp. in the chela pinch force, volume of venom and LD50. In contrast, for Centruroides sp. no differences between males and females were found in any of these traits. We discuss several potential selective regimes that could account for the pattern observed. [ABSTRACT FROM AUTHOR]

In this study, the authors used the Fujifilm Prescale Pressure Measuring System to measure the contact pressure and distribution at the jaws of laparoscopic grasping forceps. This data was then correlated with measured pressures at the forceps handles to understand the relationship between the surgeon's actuating pressure and that on the organ being manipulated. The purpose of this study is to create a database of tactile information to provide guidelines in defining minimally invasive surgery (MIS). This is expected to be important as today's society continues to progress in the use of automation, IoT, AI and MIS. In order to achieve the above, the authors developed an experimental device consisting of an actuator, a load cell and an MCU to stably actuate and control the handle side of grasping forceps. Target organs were simulated using triangular prisms of various silicone rubber materials. The experimental method involved actuating the handle side with preset pressure values for fixed time periods and using sensitive film to measure the pressure at the forceps tip. The film data was then scanned, processed and analyzed. [ABSTRACT FROM AUTHOR]

The Upper Extremity Fugl Meyer Assessment (UE-FMA) is the most comprehensive assessment for pinch impairment after stroke. The pinch test of UE-FMA is manually performed by pulling a pincer object away from the patient’s fingers while providing a visual observation that results in a subjective assessment. In this study, an automated data acquisition system that consists of a linear electric actuator applying automatic pulling to the customized pincer object held by the volunteer was developed. The pinch force was measured such that a strain gauge was placed on the pincer object while pulling force was measured using pulling force load cell connected in between the linear electric actuator and customized pincer object. The pincer object’s slip onset was detected using a displacement slip sensor. The mean pinch and pulling force values at the slip onset were 12.17 and 6.25 N for right hands, while mean pinch and pulling force values were 11.67 and 5.92 N for left hands of 50 healthy volunteers, respectively. Based on the paired t-test, there is no significant difference between right and left hands. The automated data acquisition system can objectively apply a pulling force, detect the slip onset, and measure the pinch and pulling forces.

To improve our understanding on the neuromechanics of finger movements, a comprehensive musculoskeletal model is needed. The aim of this study was to build a musculoskeletal model of the hand and wrist, based on one consistent data set of the relevant anatomical parameters. We built and tested a model including the hand and wrist segments, as well as the muscles of the forearm and hand in OpenSim. In total, the model comprises 19 segments (with the carpal bones modeled as one segment) with 23 degrees of freedom and 43 muscles. All required anatomical input data, including bone masses and inertias, joint axis positions and orientations as well as muscle morphological parameters (i.e. PCSA, mass, optimal fiber length and tendon length) were obtained from one cadaver of which the data set was recently published. Model validity was investigated by first comparing computed muscle moment arms at the index finger metacarpophalangeal (MCP) joint and wrist joint to published reference values. Secondly, the muscle forces during pinching were computed using static optimization and compared to previously measured intraoperative reference values. Computed and measured moment arms of muscles at both index MCP and wrist showed high correlation coefficients (r = 0.88 averaged across all muscles) and modest root mean square deviation (RMSD = 23% averaged across all muscles). Computed extrinsic flexor forces of the index finger during index pinch task were within one standard deviation of previously measured in-vivo tendon forces. These results provide an indication of model validity for use in estimating muscle forces during static tasks. [ABSTRACT FROM AUTHOR]

The authors sought to explore the impact of tactile sensation on manual dexterity and the validity of the strength-dexterity test in subjects with chronic impairments after stroke in a cross-sectional study of 24 patients with impaired hand function after stroke. Dexterity was assessed by the strength-dexterity test, Box and Blocks, and Nine-Hole Peg Test, and the ABILHAND questionnaire. Sensation was measured by pinprick, cotton-wool, graphesthesia, and 2-point discrimination tests. Sensation in the paretic hand had strong association with paretic hand performance in the strength-dexterity test and Nine-Hole Peg Test and explained 13% of the variance. Sensation in the nonparetic hand was associated with the results of the ABILHAND questionnaire. Among sensory tests, 2-point discrimination had the strongest association with dexterity tests. No significant correlations between sensation, pinch force, and dexterity tests were found for the nonparetic hand. The strength-dexterity test exhibited strong correlations with the other dexterity measures and with pinch force. There is an association between tactile sensation and dexterous performance in the paretic hand; activity level performance is associated with sensation in the nonparetic hand. The study supports the validity of the strength-dexterity test when applied in subjects in the chronic stage after stroke. [ABSTRACT FROM PUBLISHER]

Individuals often pinch with preferred pinch techniques based on their experience and familiarity. However, researchers believe that pinch force exertions are not comparable across different pinch techniques. Hence, it is possible to pinch objects with incompatible pinch techniques during manual handling. This increases risks of developing musculoskeletal disorders. The preceding problem substantiates the need for a comprehensive understanding of definitions, categorisations and capacities of different pinch techniques. Nevertheless, the knowledge on pinch techniques appears to be highly dispersed and not compiled to a level systematic enough for further research. Thus, this review aims to develop a consolidated theoretical groundwork on pinch techniques. It presents an anthology of terminologies, previous findings and concepts underpinning different pinch techniques. While much research is still required, it is believed that an improved understanding on pinch techniques is now within sight, due to, in part, a structured review of their definitions, classifications and capacities. [ABSTRACT FROM PUBLISHER]

Although studies show that torque and sensation are important factors to consider in grip force, there appears to be few frameworks that focus on their roles in pinch force. This study proposes a framework that potentially explains the roles of torque and sensation in pinch force. A review was done on these factors followed by a literature synthesis which categorised them into sub-factors. The sub-factors were combined to output a framework that explains the mechanisms of their interactions. This framework enriches the knowledge on pinch force levels for reduced injury risks by identifying preliminary factors that may influence pinch force. It can potentially be used to improve the effectiveness of manufacturing tasks. Although further research on it is required, it still provides researchers with more factors to consider for studies on occupational risks and injuries. With this framework, researchers can potentially improve predictions on functional outcomes in precision manufacturing tasks. [ABSTRACT FROM PUBLISHER]

The aim of this study was to examine the hypothesis that Japanese female nurses with a reduced total power (TP) component of heart rate variability (HRV) will show an imbalance in sympathovagal activity during night-time work. We carried out this study on 10 healthy female nurses (30.9 ± 3.1 years) working a night shift from 16:00 to 09:00. Heart rate (HR) and the different frequency power components of HRV were measured to estimate individual patterns of sympathovagal activity. A latent imbalance of sympathovagal activity was defined as higher HR and reduced TP, and subjects were divided into two groups based on TP values taken before the night shift. To evaluate central fatigue, we performed three different fatigue tests before and after night work in all subjects. Our results suggest that nurses with reduced HRV have an imbalance of sympathovagal activity but do not suffer from the effects of central fatigue. [ABSTRACT FROM PUBLISHER]

Heart rate is associated with work hardness and increase linearly with its increasing. In the average of energy consumption, heart rate measurement is simple but non-accurate method for calculation of work hardness. Our purpose in this research was to evaluate the relationship between heart rate and dynamometry results with hypothesis of work hardness effectiveness on the human power. This study was conducted on 102 porcelain workers. Participants were selected randomly. The research tools include stethoscope, the dynamometer. Heart rate, and pinch, grip, and back-leg-chest force were measured and relationships between variables were analyzed with Pearson correlation test and independent T-test using Spss16 software. The average heart rate of participants were 4.11±1.79 with minimum 60 and maximum120. The average force of pinch, grip, and back-leg-chest were 8.9±3.20, 4.2±4.5 and 9.36±6.55, respectively. Work hardness for 3.86% of workers were light, 7.12% were moderate and 1% were heavy. Pinch, grip, and back-leg-chest force relation with heart rate were not significant (r=0.01, p=0.85), (r=-0.03, p=0.74), and (r=0.05, p= 0.59), respectively. There was no correlation between heart rate and work hardness. So we can't use the dynamometry results to determine of work hardness. [ABSTRACT FROM AUTHOR]

As people age, their finger function deteriorates due to muscle, nerve, and brain degeneration. While exercises might delay this deterioration, an invention that enhances elderly people's pinching abilities is essential. This study aims to design and develop a finger grip enhancer that facilitates the day-to-day pinching activities of elderly people. This research is an extension of a previous study that conceptualised a finger grip enhancer. The device facilitates finger flexion on the thumb and index finger, and weighs 520 g, allowing for improved portability and sufficient force exertion (13.9 N) for day-to-day pinching. To test for usability, eleven subjects aged 65 years and above performed a pinch-lift-hold test on various household objects. The pinch force before and after utilising the device was measured. Using Minitab 18, the statistical significance of using this device was analysed with a paired-samples t-test. With this device, the elderly people's pinching abilities significantly improved in both pinch force and pinch force steadiness (p < 0.05). The proposed device has the potential to enhance elderly people's quality of life by supporting a firm pinch in the handling of everyday objects. This research has applicational value in developing exoskeleton devices for patients who require rehabilitation. [ABSTRACT FROM AUTHOR]

This study aimed to define the effect of object width on spontaneous grasp. Participants held objects of various masses (0.75 to 2.25 kg) and widths (3.5 to 9.5 cm) between thumb and index finger. Grip force, maximal grip force and corresponding finger postures were recorded using an embedded force sensor and an optoelectronic system, respectively. Results showed that index finger joints varied to accommodate the object width, whereas thumb posture remained constant across conditions. For a given object mass, grip force increased as a function of object width, although this result is not dictated by the laws of mechanics. Because maximal grip force also increased with object width, we hypothesise that participants maintain a constant ratio between grip force and their maximal grip force at each given width. Altogether we conclude that when the task consists in manipulating objects/tools, the optimal width is different than when maximal force exertions are required. [ABSTRACT FROM AUTHOR]

Abstract: One of the factors associated with the high prevalence of upper extremity musculoskeletal disorders, such as carpal tunnel syndrome, among dental practitioners is the repeated high pinch force applied during periodontal scaling. The goal of this study was to determine the relationship between the pinch force applied during periodontal scaling and the forces generated at the tip of the tool. A linear biomechanical model that incorporated tool reaction forces and a calculated safety margin was created to predict the pinch force applied by experienced and inexperienced dentists during periodontal scaling. Six dentists and six dental students used an instrumented scaling tool while performing periodontal scaling on patients. Thumb pinch force was measured by a pressure sensor, while the forces developed at the instrument tip were measured by a six-axis load cell. A biomechanical model was used to calculate a safety factor and to predict the applied pinch force. For experienced dentists, the model was moderately successful in predicting pinch force (). For inexperienced dentists, the model failed to predict peak pinch force (). The mean safety margin was higher for inexperienced (4.88±1.58) than experienced (3.35±0.55) dentists, suggesting that students apply excessive force during scaling. [Copyright &y& Elsevier]

Abstract: The transient data of the pinch force produced between the human forefinger and thumb have been shown to fit the functional form of the well-known lognormal density function. Isometeric force generation is achieved by the stochastic recruitment of individual motor units, which sum together. Evidence from animal and human experiments demonstrates that the force generation can be modelled by underdamped terms. It is shown that a lognormal time series (distribution) can be fitted to a sum of exponential decaying sinusoidal terms. [Copyright &y& Elsevier]

Normative data of the grip force distribution necessary to complete functional tasks are limited. Small force sensors have been specially designed for accurate measurement of the dynamic handgrip force distribution by attaching them to the palmar surface of the hand. Seventeen healthy participants performed three different tasks, each requiring a different functional prehension pattern. When cylindrical objects were manipulated, the highest average grip forces were found at the fingertips and the thumb, followed by the middle finger. In a spherical grasp pattern, the contributions by the thumb, ring and small fingers always exceeded 71% of the total grip force. The highest local forces of 9.9 N were measured when a zip was closed with a tip pinch. Individual finger forces were found to differ by gender, but not by hand dimension and age. The results are useful for biomechanical modelling of the hand, for designing ergonomic tool grips, and for evaluating hand function. [ABSTRACT FROM AUTHOR]

Purpose: Surgical transfers of muscles are used to restore lateral pinch in tetraplegia; however, outcomes are variable. The purpose of this study was to compare activation of the brachioradialis (Br) after transfer to the flexor pollicis longus during maximum effort in its primary function (elbow flexion) with maximum effort in its postoperative function (lateral pinch) and to record Br activation during functional tasks. Methods: Fine-wire electrodes recorded activation of the Br in 11 arms with tetraplegia. Subjects produced maximum lateral pinch force with and without elbow stabilization and were classified according to elbow strength. The elbow was stabilized by supporting the arm and limiting elbow motion. A force sensor mounted on a custom grip recorded the pinch force. Electromyographic (EMG) signals recorded during lateral pinch were expressed as a percentage of the maximum voluntary contraction recorded during maximum-effort elbow flexion. Results: The EMG activation was significantly lower during lateral pinch compared with resisted elbow flexion. The mean EMG during lateral pinch in the self-supported elbow condition was 34% of the maximum voluntary contraction; with the elbow stabilized the EMG increased to 55% of the maximum voluntary contraction. Postoperative pinch-force magnitude was 14 N with self-support and 20 N with the elbow stabilized. Subjects with weak elbow extension strength produced significantly lower pinch forces compared with subjects with strong elbow extension but had similar ability to activate the Br. The Br activation was higher when the pinch tasks were performed successfully. Conclusions: These findings suggest a reduced ability to activate the transferred muscle fully in lateral pinch function after surgery, even with the addition of elbow support. The Br activation is linked to successful performance of lateral pinch tasks. The subjects’ inability to activate the transferred muscle fully may be affected by postoperative muscle re-education and contribute to postoperative weakness. [Copyright &y& Elsevier]

OBJECTIVES: The purpose of this study was to quantify age-induced changes in handgrip and finger-pinch strength, ability to maintain a steady submaximal finger pinch force and pinch posture, speed in relocating small objects with finger grip, and ability to discriminate two identical mechanical stimuli applied to the finger tip. DESIGN: A cross-sectional study. SETTINGS: Greater Cleveland area of Ohio. PARTICIPANTS: Healthy, independent, young (n = 27, range 20–35 years) and older (n = 28, range 65–79 years) subjects. MEASUREMENTS: Handgrip strength, maximum pinch force (MPF), ability to maintain a steady pinch force at three relative force levels (5%, 10%, and 20% MPF) and three absolute force levels (2.5 Newtons (N), 4 N, and 8 N), ability to maintain a precision pinch posture, speed in relocating pegs from a nearby location onto the pegboard, and the shortest distance for discriminating two stimuli were measured in both young and older groups. RESULTS: Compared with young subjects, the older group's handgrip force was 30% weaker (P < .001), MPF was 26% lower (P < .05), and ability to maintain steady submaximal pinch force and a precision pinch posture was significantly less (P < .05). The time taken to relocate the pegs and the distance needed to discriminate two identical stimuli increased significantly with age (P < .01). The decrease in the ability to maintain steady submaximal pinch force was more pronounced in women than men. CONCLUSION: Aging has a degenerative effect on hand function, including declines in hand and finger strength and ability to control submaximal pinch force and maintain a steady precision pinch posture, manual speed, and hand sensation. [ABSTRACT FROM AUTHOR]

The effect of friction and load on pinch force was studied in a simple hand transfer task using a repeated measures design and ten men. Subjects moved a container between two targets, 450 mm apart, at a slow, self-paced speed. The levels of mass in the container were set at 0·8, 2·5 and 4·2 kg (7·5, 24·5 and 41·5 N respectively). The handle materials were sandpaper and smooth aluminium. Applied pinch force was measured via a strain gauge mounted in a specially-designed handle attached to the container. Dependent variables were peak and ‘steady-state’ pinch force. The main and interaction effects of load and friction were significant. The friction effect was significant only for the highest load which, on average, elicited peak pinch forces of 16-70% of maximum voluntary force. This suggests that these men were not sensitive to friction effects at the lower loads. Results suggest that the use of tool handle friction enhancements may reduce required pinch forces for objects requiring upwards of 50% or more of maximum pinch strength [ABSTRACT FROM PUBLISHER]

Disparities in load stiffness were used to differentiate and characterize pinch-force, finger-span, and pinch-effort matching in two experiments. All subjects squeezed a spring-loaded manipulandum in each hand using three-finger pinch. Subjects in the first experiment were instructed explicitly to match one of the three continua. Subjects matching force or span were told to attend carefully to sensations from the hand or arm and to ignore differences in the effort required to make the sensations equal. They had to achieve and hold a particular target force with the reference hand and then match force or span with the opposite hand, usually against a spring with a different stiffness. These subjects were given as much time as necessary to make their matches and were told which hand was serving as the reference in each trial. Effort-matching subjects were told to ignore peripheral sensations and to match effort or motor commands. These subjects were not told which hand was the reference and were given only 1 s to make a match, so they made matches by rapidly squeezing both manipulanda simultaneously and, presumably, with the same voluntary motor command. The matching behaviors of the three groups were clearly distinguishable and were consistent with instructions. Results were similar whether different subjects were assigned different instructions or the same subjects performed all three match types. In a second experiment, naïve subjects were given purposely ambiguous instructions without reference to a specific continuum and had no time or accuracy constraints. Subjects produced the same three sensorimotor behaviors obtained with explicit instructions, showing that the different behaviors were not artifacts of strict protocols. Taken together, the results show that force, span, and effort are distinct sensorimotor continua that can be judged reliably. [ABSTRACT FROM AUTHOR]

• We evaluated the hand strength required to operate an inhaler with a lever aid. • Use of the lever aid greatly reduced the pinch force required for pMDI operation. • Use of the lever aid reduced the force needed to use SMI, not but the torque. • Using a lever aid increases the contact area between the fingertip and the pMDI. • Using a lever aid will increase the number of patients who can use their inhalers. In the treatment of asthma and chronic obstructive pulmonary disease, using a lever aid to improve drug delivery from an inhaler is recommended for patients with poor muscle strength. However, no studies have investigated the effect on hand strength of using a lever aid. Here, we measured hand strength before and after operating a lever aid and tried to predict the required strength. We compared the pinch force required to activate a pressurized metered dose inhaler (pMDI) and a dry powder inhaler as well as the rotational torque required to activate a soft mist inhaler (SMI) before and after attaching a lever aid. We then assessed the correlation between the theoretical and measured pinch force after fitting the lever aid. Use of the lever aid significantly reduced the pinch force required for pMDI operation from 26.13–48.74 N to 4.90–16.87 N. In contrast, using a lever aid significantly reduced the force needed to rotate SMI, although the rotational torque required to operate did not change. There was a significant positive correlation between the theoretical and measured pinch forces required to activate a pMDI fitted with a lever aid. Using a lever aid will increase the number of patients who can use this device. [ABSTRACT FROM AUTHOR]