Biomed Mater Eng

The rehabilitation squeeze ball is a popular device to help strengthen the hand, fingers and forearm muscles. The distributions of the contact pressure in the interface between the therapy ball and hand/fingers can affect the joint moment of each of the individual fingers, thereby affecting rehabilitation effects. In the current study, we evaluated the contact force distributions on the fingers when gripping a spherical object. Eight female adults [age 29 (9.1) years, mass 64.6 (7.1)\ua0kg, height 163.5 (1.9)\ua0cm, hand length 17.2 (0.7)\ua0cm] participated in the study. Contact force sensors were attached to the middle of the palmar surfaces of the distal, middle, and proximal phalanges of the four fingers in the longitudinal direction. In order to evaluate the effects of the ball stiffness on the contact force distributions on the fingers, subjects were requested to perform quasi-static gripping on a standard tennis ball and on a rehabilitation ball. The tennis ball is much stiffer and experiences smaller deformation under compression compared to the rehabilitation ball. We analyzed the force share among the distal, middle, and proximal finger segments, when subjects gripping balls of different stiffnesses (tennis ball vs. rehabilitation ball) and at three different grip efforts. Our results indicated that the grip force is contributed about 60% and 40% by the middle/ring fingers and by the index/little fingers, respectively. These characteristics are independent of the grip force levels and stiffness of the contact surface.CC999999/Intramural CDC HHS/United States2019-02-25T00:00:00Z30400076PMC6388416vault:3156

Influences Of Tactile Sensation On Pinch Force Under Loaded And Unloaded Conditions

Although researchers have studied various parameters that affect grip force, few studies investigate the effects of tactile sensation on pinch force. This study aims to determine the influences of tactile sensation on pinch force with a special emphasis on screw knobs under loaded and unloaded conditions. The participants included 32 manual workers who were required to pinch and turn the knobs to generate pinch force under reduced and increased sensations simulated using cotton and nitrile gloves. The data were analysed using the analysis of variance via Minitab 16. Results show that the pinch force exerted for reduced sensations is higher than that of increased sensations because the reduced friction increased skin-object slippages, which caused participants to spontaneously increase their force to prevent slippages. This study serves as a guideline to potentially improve the design of objects operated with pinch grips to be safe and suitable for manual, sedentary or general tasks

J Biomech

This study developed biomechanical models for hand breakaway strength that account for not only grip force but also hand-handle frictional coupling in generation of breakaway strength. Specifically, models for predicting breakaway strength for two commonly-used handle shapes (circular and rectangular handles) and varying coefficients of friction (COF) between the hand and handle were proposed. The models predict that (i) breakaway strength increases with increasing COF and (ii) a circular handle with a 50.8 mm-diameter results in greater mean breakaway strength than a handle with a rectangular cross-section of 38.1 by 38.1 mm for COFs greater than 0.42. To test these model predictions, breakaway strengths of thirteen healthy young adults were measured for three frequently-encountered COF conditions (represented by three glove types of polyester (COF=0.32), bare hand (COF=0.50), and latex (COF=0.74) against an aluminum handle) and for the two handle shapes. Consistent with the model predictions, mean breakaway strength increased with increasing COF and was greater for the circular than rectangular handle for COFs of 0.50 and 0.74. Examination of breakaway strength normalized to body weight reveals that modification of COF and handle shapes could influence whether one can hold his/her body using the hands or not (thus must fall), highlighting the importance of considering these parameters for fall prevention. The biomechanical models developed herein have the potential to be applied to general handle shapes and COF conditions. These models can be used to optimize handle design to maximize breakaway strength and minimize injuries due to falls from ladders or scaffolds.T42 OH008672/OH/NIOSH CDC HHSUnited States/2022-03-01T00:00:00Z22281405PMC888781511030vault:4099

Ergonomics

Statement of Relevance:Desirable handle features for torque generation may be different from those for grip only. Design of handles per advantageous handle features (e.g., shape, size, surface) may help increase people\u2019s torque strength and contribute to increased physical capacity of people.20112022-02-18T00:00:00ZT42 OH008455/OH/NIOSH CDC HHSUnited States/21973007PMC88565631099

Med Eng Phys

Contact interactions between the hand and handle, such as the contact surface softness and contact surface curvature, will affect both physical effort and musculoskeletal fatigue, thereby the comfort and safety of power tool operations. Previous models of hand gripping can be categorized into two groups: multi-body dynamic models and finite element (FE) models. The goal of the current study is to develop a hybrid FE hand gripping model, which combines the features of conventional FE models and multi-body dynamic models. The proposed model is applied to simulate hand-gripping on a cylindrical handle with covering materials of different softness levels. The model included three finger segments (distal, middle, and proximal phalanxes), three finger joints (the distal interphalangeal (DIP), proximal interphalangeal (PIP), and metacarpophalangeal (MCP) joint), and major anatomical substructures. The model was driven by joint moments, which are the net effects of all passive and active muscular forces acting about the joints. The finger model was first calibrated by using experimental data of human subject tests, and then applied to investigate the effects of surface softness on contact interactions between a finger and a cylindrical handle. Our results show that the maximal compressive stress and strain in the soft tissues of the fingers can be effectively reduced by reducing the stiffness of the covering material.CC999999/Intramural CDC HHS/United States2015-09-17T00:00:00Z24736020PMC457353

Quantification des paramètres biomécaniques qui affectent le système main-bras lors de la simulation de la tenue d'outils exerçant différentes vibrations et moments de force

Les vibrations main-bras sont spécifiquement reconnues pour être la cause du syndrome des vibrations, une maladie atteignant les doigts et la main à des niveaux vasculaires, musculo-squelettiques et neurosensoriels. De longues durées et de fortes intensités de vibration peuvent accélérer l'apparition des symptômes. De plus, des muscles soumis à la vibration ont tendance se contracter involontairement de façon plus intense que sans vibration : c'est le réflexe tonique vibratoire. Or, une plus grande rigidité musculaire est associée à une plus grande transmission de vibration aux structures corporelles. Le but de cette étude était de mesurer la transmission de vibration et mesurer le taux de contraction des muscles par électromyographie en fonction de différents paramètres de force de poussée, de moment de force, de fréquence et d'amplitude de vibration. De plus, les somatotypes ectomorphes et mésomorphes ont été comparés afin de déterminer si des gens de avec plus ou moins de masse musculaire obtenaient des résultats différents. Douze participants (six ectomorphes et six mésomorphes) ont participé à cette expérimentation. Cette expérimentation durait environ 3h et comportait 81 essais en fonction d'une combinaison des trois niveaux de chacune des quatre variables (poussée, moment de force, amplitude de vibration et fréquence de vibration). Le somatotype n'a pas eu d'effet notable ni sur la vibration et peu sur le réflexe tonique vibratoire. Les variables biomécaniques (moment de force, force de poussée) ont généralement eu pour effet d'augmenter la transmission de vibration ainsi que les scores d'EMG. Les variables de vibration ont permis de déceler la présence d'un réflexe tonique vibratoire significatif mais de faible importance.\ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : Électromyographie, outils vibrants, réflexe tonique vibratoire, somatotype, moment de force

Statistical Power in Ergonomic Intervention Studies

As awareness of the costs of workplace injury and illness continues to grow, there has been an increased demand for effective ergonomic interventions to reduce the prevalence of musculoskeletal disorders (MSDs). The goal of ergonomic interventions is to reduce exposures (mechanical and psychosocial); however there is conflicting evidence about the impact of these interventions as many studies produce inconclusive or conflicting results. In order to provide a clearer picture of the effectiveness of these interventions, we must find out if methodological issues, particularly statistical power, are limiting this research. The purpose of this study was to review and examine factors influencing statistical power in ergonomic intervention papers from five peer reviewed journals in 2008. A standardized review was performed by two reviewers. Twenty eight ergonomic intervention papers met the inclusion criteria and were fully reviewed. Data and trends from the reviewed papers were summarized specifically looking at the research designs used, the outcome measures used, if statistical power was mentioned, if a rationale for sample size was reported, if standardized and un-standardized effect sizes were reported, if confidence intervals were reported, the alpha levels used, if pair-wise correlation values were provided, if mean values and standard deviations were provided for all measures and the location of the studies. Also, the studies were rated based on the outcomes of their intervention into one of three categories (shown to be effective, inconclusive and not shown to be effective). Between these three groupings comparisons of post hoc power, standardized effect sizes, un-standardized effect sizes and coefficients of variation were made. The results indicate that in general, a lack of statistical power is indeed a concern and may be due to the sample sizes used, effect sizes produced, extremely high variability in some of the measures, the lack of attention paid to statistical power during research design and the lack of appropriate statistical reporting guidelines in journals where ergonomic intervention research may be published. A total of 69.6% of studies reviewed had a majority of measures with less than .50 power and 71.4% of all measures used had CVs of > .20