Med Eng Phys

Inverse dynamics models used to investigate musculoskeletal disorders associated with handle gripping require accurate phalangeal kinetics. Cylindrical handles wrapped with pressure film grids have been used in studies of gripping kinetics. We present a method fusing six degree-of-freedom hand kinematics and a kinematic calibration of a cylinder-wrapped pressure film. Phalanges are modeled as conic frusta and projected onto the pressure grid, automatically segmenting the pressure map into regions of interest (ROIs). To demonstrate the method, segmented pressure maps are presented from two subjects with substantially different hand length and body mass, gripping cylinders 50 and 70 mm in diameter. For each ROI, surface-normal force vectors were summed to create a reaction force vector and center of pressure location. Phalangeal force magnitudes for a data sample were similar to that reported in previous studies. To evaluate our method, a surrogate was designed for each handle such that when modeled as a phalanx it would generate a ROI around the cells under its supports; the classification F-score was above 0.95 for both handles. Both the human subject results and the surrogate evaluation suggest that the approach can be used to automatically segment the pressure map for quantifying phalangeal kinetics of the fingers during cylindrical gripping.CC999999/Intramural CDC HHS/United States2017-02-01T00:00:00Z26709291PMC483042

Mapping kinematic functional abilities of the hand to three dimensional shapes for inclusive design

Loss of hand function can have adverse effects on an individual\u27s ability to maintain independence. The ability to perform daily activities, such as food preparation and medication delivery, is dependent on the hand\u27s ability to grasp and manipulate objects. Therefore, the goal of this research was to demonstrate that three dimensional (3D) modeling of hand function can be used to improve the accessibility of handheld objects for individuals with reduced functionality through informed design. Individual models of hand functionality were created for 43 participants and group models were developed for groups of individuals without (Healthy) and with reduced functionality due to arthritis (RFA) of the hand. Cylindrical models representative of auto-injectors of varying diameters were analyzed in 3D space relative to hand function. The individual model mappings showed the cylinder diameter with the highest mapped functional values varied depending on the type of functional weighting chosen: kinematic redundancy of fingertip pad positional placement, fingertip pad orientation, or finger force directionality. The group mappings showed that for a cylinder to be grasped in a power grasp by at least 75% of the Healthy or RFA groups, a diameter of 40 mm was required. This research utilizes a new hand model to objectively compare design parameters across three different kinematic factors of hand function and across groups with different functional abilities. The ability to conduct these comparisons enables the creation of designs that are universal to all – including accommodation of individuals with limits in their functional abilities

Using kinematic reduction for studying grasping postures. An application to power and precision grasp of cylinders

The kinematic analysis of human grasping is challenging because of the high number of degrees of freedom involved. The use of principal component and factorial analyses is proposed in the present study to reduce the hand kinematics dimensionality in the analysis of posture for ergonomic purposes, allowing for a comprehensive study without losing accuracy while also enabling velocity and acceleration analyses to be performed. A laboratory study was designed to analyse the effect of weight and diameter in the grasping posture for cylinders. This study measured the hand posture from six subjects when transporting cylinders of different weights and diameters with precision and power grasps. The hand posture was measured using a Vicon® motion-tracking system, and the principal component analysis was applied to reduce the kinematics dimensionality. Different ANOVAs were performed on the reduced kinematic variables to check the effect of weight and diameter of the cylinders, as well as that of the subject. The results show that the original twenty-three degrees of freedom of the hand were reduced to five, which were identified as digit arching, closeness, palmar arching, finger adduction and thumb opposition. Both cylinder diameter and weight significantly affected the precision grasping posture: diameter affects closeness, palmar arching and opposition, while weight affects digit arching, palmar arching and closeness. The power-grasping posture was mainly affected by the cylinder diameter, through digit arching, closeness and opposition. The grasping posture was largely affected by the subject factor and this effect couldn't be attributed only to hand size. In conclusion, this kinematic reduction allowed identifying the effect of the diameter and weight of the cylinders in a comprehensive way, being diameter more important than weight.We are grateful to the Universitat Jaume I for financial support through project P1·1B2013-33, and the Spanish Ministry of Research and Innovation and the EU (FEDER funds) jointly through projects DPI2010-18177 and DPI2014-52095-P

The Influence of Hand Tool Design on Hand Grip Strength: A Review

Hand is made up of bones, tendons, ligaments, nerves and blood vessels that can be easily debilitated and injured if the hand tool is not design ergonomically. Recently researchers have examined the effects of individual, environmental and occupational factors on hand grip strength. However, information on the influence of hand tool design on hand grip strength is still lacking. The aim of this paper is to provide a comprehensive review of factors influencing hand grip strength focusing more towards hand tool design factors. The authors searched the journal articles, book and guidelines from the online databases of Google Scholar, ScienceDirect and Pubmed. Fourteen factors of hand tools design were found to have significant effect on the hand grip strength.  The handle size shows the most significant factor for hand grip strength

تأثیر قطر ابزار دستی غیر قدرتی در میزان راحتی و حداکثر گشتاور تولید شده دست

مقدمه: ضعف طراحی ابزار دستی و عدم تناسب آن با کاربر یکی از اصلی‌ترین ریسک فاکتورهای اختلالات اسکلتی-عضلانی اندام فوقانی شناخته شده است. آسیب­های ناشی از ابزارهای دستی تقریباً 9% از کل آسیب­های ناشی از کار را شامل می­شود. هدف از انجام این مطالعه بررسی تأثیر قطر ابزار در میزان راحتی و حداکثر گشتاور تولید شده دست و برآورد قطر بهینه ابزار دستی بوده است. مواد و روش ­ها: شرکت‌کنندگان شامل 12 نفر (6 مرد و 6 زن) با میانگین سنی 7/24 و انحراف معیار 84/5 سال می‌باشد. روش پژوهش بدین صورت بوده که هریک از شرکت‌کنندگان با 7 دسته ابزار با قطرهای متنوع به‌وسیله ابزار محقق ساخته سنجش گشتاور دست شروع به اعمال نیرو و چرخاندن دسته ابزار با تمام نیرو می‌کردند. سپس مدت زمان آزمون، حداکثر گشتاور و میزان راحتی دسته ابزار سنجیده و در نهایت آنالیز واریانس و آزمون تی صورت گرفته است. یافته‌ها: میانگین حداکثر گشتاور 88/1 و انحراف معیار 95/0 نیوتن متر، مدت زمان رسیدن به حداکثر گشتاور 96/13 و انحراف معیار 03/9 ثانیه، میانگین راحتی 27/3 و انحراف معیار 48/1 در بازه 1-7 نمره‌ای به دست آمده است. تفاوت معنی­دار بین حداکثر گشتاور تولید شده بین دو گروه مردان و زنان مشاهده شد (001/0 P <). میانگین حداکثر گشتاور 034/3 نیوتن متر و حداکثر سطح راحتی با میانگین 67/4 در قطر چنگش 38 میلی‌متر به دست آمد

Investigation of Factors Influencing Ergonomic Characteristics of Water Bottle Handles

Increasingly competitive market environment pushes products and their packaging to meet functional and aesthetic requirements and expectations of consumers. Ergonomic features are one of the most important features for fulfilling consumer expectations and achieving a satisfying user experience. Drinking water in retail is commonly packaged in PET bottles ranging from 0.2 up to 6 litres. The weight of the 6-litre bottle is roughly 6 kilos which can produce strain on the hand while carried from the place of purchase to the place of usage. The goal of this research was to investigate the influence of water bottle handles and to determine how much does handle length, width, and curvature of the grip\u27s edges affect the comfort of product use. This research presents objective experimental measurements and subjective judgment regarding ergonomic characteristics of the 5-6 litre water bottle handles, based on the variations in their shape and dimensions

Differences in muscle activation while gripping a sandbag versus an Olympic weightlifting bar

The purpose of this study was to compare the myoelectric activity of the extensor carpi ulnaris, flexor carpi ulnaris, flexor carpi radialis, and opponens pollicis muscles while gripping a 50 lb Olympic weightlifting bar to the myoelectric activity of the same muscles while gripping a sandbag of the same weight. Myoelectric activity was measured as the average root mean square (RMS) of the surface electromyography (sEMG) values. The hypothesis was that gripping a sandbag would result in greater muscle activation of the extensor carpi ulnaris, flexor carpi ulnaris, flexor carpi radialis, and opponens pollicis muscles than gripping an Olympic weightlifting bar of the same weight. The participants were seven healthy males who performed a six second lift with the sandbag as well as a six second lift with the Olympic weightlifting bar. The order of the lifts was random. The Olympic weightlifting bar was lifted using a traditional overhand grip and the sandbag was lifted using an overhand pinching grip. In both trials the bar or sandbag was positioned at thigh height and the participant then leaned over and gripped it with both hands in front of the body. The participant then lifted the implement off its support and assumed an upright position while holding the implement in a position so that it did not touch the body other than the hands. Surface EMG electrodes detected the myoelectric activity of the extensor carpi ulnaris, flexor carpi ulnaris, flexor carpi radialis, and opponens pollicis muscles. The electrodes preamplified the myoelectric signals by a factor of 35. The sEMG signals of the four muscles were treated with a 20 Hz low cut/high pass filter, amplified by a factor of 2000, and the RMS of the filtered signals were derived using a 2.5 ms time window. The analog RMS sEMG was sampled at 1000 Hz and converted to digital form. Each muscle’s RMS sEMG was averaged over a six second period of the lift. The results of a within-subject one-tailed t-test iv indicated that the means of the subjects’ RMS sEMG for each of the four muscles were significantly larger for the sandbag lift than the Olympic bar lift. This result supported the hypothesis that gripping a sandbag produces significantly higher myoelectric activity in the extensor carpi ulnaris, flexor carpi ulnaris, flexor carpi radialis, and opponens pollicis muscles than gripping an Olympic bar of the same weight. Athletic trainers, physical therapists, strength and conditioning coaches, fitness professionals, and other health professionals can use this information to improve grip strength when designing and implementing training programs for their clients, athletes, or patients

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

A kinematic model of the human hand to evaluate its prehensile capabilities

A kinematic model has been developed for simulation and prediction of the prehensile capabilities of the human hand. The kinematic skeleton of the hand is characterized by ideal joints and simple segments. Finger-joint angulation is characterized by yaw (abduction-adduction), pitch (flexion-extension) and roll (axial rotation) angles. The model is based on an algorithm that determines contact between two ellipsoids, which are used to approximate the geometry of the cutaneous surface of the hand segments. The model predicts the hand posture (joint angles) for power grasp of ellipsoidal objects by `wrapping' the fingers around the object. Algorithms for two grip types are included: (1) a transverse volar grasp, which has the thumb abducted for added power; and (2) a diagonal volar grasp, which has the thumb adducted for an element of precision. Coefficients for estimating anthropometric parameters from hand length and breadth are incorporated in the model. Graphics procedures are included for visual display of the model. In an effort to validate the predictive capabilities of the model, joint angles were measured on six subjects grasping circular cylinders of various diameters and these measured joint angles were compared with angles predicted by the model. Sensitivity of the model to the various input parameters was also determined. On an average, the model predicted joint flexion angles that were 5.3% or 2.8[deg] +/- 12.2[deg] larger than the measured angles. Good agreement was found for the MCP and PIP joints, but results for DIP were more variable because of its dependence on the predictions for the proximal joints.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30224/1/0000616.pd