The effect of torque direction and cylindrical handle diameter on the coupling between the hand and a cylindrical handle

Pheasant and O'Neill's torque model (1975) was modified to account for grip force distributions. The modified model suggests that skin friction produced by twisting an object in the direction of fingertips causes flexion of the distal phalanges and increases grip force and, thus, torque. Twelve subjects grasped a cylindrical object with diameters of 45.1, 57.8, and 83.2 mm in a power grip, and performed maximum torque exertions about the long axis of the handle in two directions: the direction the thumb points and the direction the fingertips point. Normal force on the fingertips increased with torque toward the fingertips, as predicted by the model. Consequently, torque toward the fingertips was 22% greater than torque toward the thumb. Measured torque and fingertip forces were compared with model predictions. Torque could be predicted well by the model. Measured fingertip force and thumb force were, on average, 27% less than the predicted values. Consistent with previous studies, grip force decreased as the handle diameter increased from 45.1 to 83.2 mm. This may be due not only to the muscle length-strength relationship, but also to major active force locations on the hand: grip force distributions suggest that a small handle allows fingertip force and thumb force to work together against the palm, resulting in a high reaction force on the palm, and, therefore, a high grip force. For a large handle, fingertip force and thumb force act against each other, resulting in little reaction force on the palm and, thus, a low grip force.     

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 degrees +/- 12.2 degrees 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.     

Biodynamic response of human fingers in a power grip subjected to a random vibration

BACKGROUND: Knowledge of the biodynamic response (BR) of the human hand-arm system is an important part of the foundation for the measurement and assessment of hand-transmitted vibration exposure. This study investigated the BR of human fingers in a power grip subjected to a random vibration. METHOD: Ten male subjects were used in the experiment. Each subject applied three coupling actions to a simulated tool handle at three different finger grip force levels. RESULTS AND CONCLUSIONS: The BR is practically independent of the hand coupling actions for frequencies at or above 100 Hz. Above 50 Hz, the BR is correlated to finger and hand sizes. Increasing the finger coupling force significantly increases the BR. Therefore, hand forces should be measured and used when assessing hand-transmitted vibration exposure. The results also show that under a constant-velocity vibration, the finger vibration power absorption at frequencies above 200 Hz is approximately twice that at frequencies below 100 Hz. This suggests that the frequency weighting specified in the current ISO 5349-1 (2001) may underestimate the high frequency effect on vibration-induced finger disorders.     

Evolution of the power ("squeeze") grip and its morphological correlates in hominids.

The "squeeze" form of power grip is investigated for the purposes of clarifying the hand posture and activities associated with the grip, assessing the potential in chimpanzees for using the grip, and identifying morphological correlates of an effective power grip that may be recognized in fossil hominid species. Our approaches include: (1) the analysis of the human grip, focusing on both the hand posture involved and hand movements associated with use of the grip in hammering; (2) the analysis of similar chimpanzee grips and associated movements; (3) comparative functional analysis of regions in the hand exploited and stressed by the grip and its associated movements in humans; and (4) a review of the literature on the power grip and its morphological correlates. Results of the study indicate that humans use a squeeze form of power grip effectively to wield cylindrical tools forcefully as extensions of the forearm. Several morphological features occur in high frequency among humans which facilitate the grip and are consistent with the large internal and external forces associated with it in hammering and in other tool-using activities. Chimpanzee hand postures resembling this form of human power grip are not fully comparable and lack some of these morphological correlates that facilitate its use. The hand of Australopithecus afarensis does not appear to have been stressed by use of the grip, but there is some evidence for this type of stress in the metacarpals from Sterkfontein Member 4. Hands from Olduvai and Swartkrans do not provide sufficient evidence for assessment of power grip capabilities.     

Characteristics and lateral dominance of hand grip and elbow flexion powers in young male adults

This study aimed to clarify the characteristics and the lateral dominance of hand grip power and elbow flexion power. The subjects were 15 healthy young males (mean age 22.1+/-0.7 yr, mean height 171.3+/-3.4 cm, mean mass 64.5+/-4.1 kg). All subjects were right-handed. Peak power was measured by both hands with 6 different loads of 20%-70% of maximum voluntary contraction. The maximum voluntary contraction of hand grip movement and elbow flexion movement was significantly larger in the dominant hand. Peak power of the dominant hand was larger in all loads in hand grip movement and in loads of 20% and 30% of maximum voluntary contraction in elbow flexion movement. In short, lateral dominance was confirmed. Peak power was significantly larger in hand grip movement than in elbow flexion movement in both hands. Peak velocity decreased with increasing loads in both movements, but peak power increased until about 50% of maximum voluntary contraction and then decreased. The peak power ratio of the dominant hand to the nondominant hand was significantly larger in hand grip movement than in elbow flexion movement in all loads and the peak power ratio in elbow flexion movement was more marked in light loads. In conclusion, both powers showed lateral dominance. Lateral dominance is more marked in hand grip power.     

Grasping behavior in tufted capuchin monkeys (Cebus apella): grip types and manual laterality for picking up a small food item

This study investigates prehension in 20 tufted capuchins (Cebus apella) in a reaching task requiring individuals to grasp a small food item fixed to a tray. The aim was twofold: 1) to describe capuchins' grasping techniques in detail, focusing on digit movements and on different areas of contact between the grasping fingers; and 2) to assess the relationship between grip types and manual laterality in this species. Capuchins picked up small food items using a wide variety of grips. In particular, 16 precision grip variants and 4 power grip variants were identified. The most frequently used precision grip involved the distal lateral areas of the thumb and the index finger, while the most preferred kind of power grip involved the thumb and the palm, with the thumb being enclosed by the other fingers. Immature capuchins picked up small food items using power grips more often than precision grips, while adult individuals exhibited no significant preference for either grip type. The analysis performed on the time capuchins took to grasp the food and withdraw it from the tray hole revealed that 1) precision grips were as efficient as power grips; 2) for precision grips, the left hand was faster than the right hand; and 3) for power grips, both hands were equally quick. Hand preference analysis, based on the frequency for the use of either hand for grasping actions, revealed no significant hand bias at group level. Likewise, there was no significant relationship between grip type and hand preference.     

Precision grips in young chimpanzees

A precision grip, thumb-finger opposition, has been regarded as an uniquely human trait. Napier's conclusion that chimpanzees were incapable of precision grip was based on two subjects and prehension of a single object (i.e., a grape). The purpose of the present study was to specify grip type and hand use by 13 young chimpanzees to prehend three different-sized food objects. The subjects were laboratory raised (eight males and five females) and ranged in age from 27 to 58 months. An ethogram was devised that comprised 43 different grip types: ten configurations of precision grips were found, in addition to imprecise or inefficient grip types (nine types), thumb-to-finger opposition (10 types), power grips (two types), and a variety of other grips (12 types). Subjects most often prehended were very small-sized (5 mm × 5 mm × 3 mm) or small-sized (10 mm × 10 mm × 3 mm) food objects with precision and imprecise grips. An analysis of latency to prehend, i.e., efficiency, revealed (1) precision grips were equally efficient for all object sizes; (2) power grips were most efficient with the largest object (a grape); (3) with imprecise grips, the left hand was more efficient than the right with small objects, and with power grips the right hand was more efficient than the left for medium-sized objects. No population handedness was observed, but individual handedness was seen in nine subjects for some grip types and some object sizes. This study provides evidence that young chimpanzees preferentially use a true precision grip to prehend small and very small objects. © 1996 Wiley-Liss, Inc.     

Modeling of biodynamic responses distributed at the fingers and the palm of the human hand-arm system

The objective of this study is to develop analytical models for simulating driving-point biodynamic responses distributed at the fingers and palm of the hand under vibration along the forearm direction (z(h)-axis). Two different clamp-like model structures are formulated to analyze the distributed responses at the fingers-handle and palm-handle interfaces, as opposed to the single driving point invariably considered in the reported models. The parameters of the proposed four- and five degrees-of-freedom models are identified through minimization of an rms error function of the model and measured responses under different hand actions, namely, fingers pull, push only, grip only, and combined push and grip. The results show that the responses predicted from both models agree reasonably well with the measured data in terms of distributed as well total impedance magnitude and phase. The variations in the identified model parameters under different hand actions are further discussed in view of the biological system behavior. The proposed models are considered to serve as useful tools for design and assessment of vibration isolation methods, and for developing a hand-arm simulator for vibration analysis of power tools.     

Form of the hand and designing of the handle

The usefulness of a handle is greatly dependent upon the correlation of grip circumference to the diameter of the hand. Since up to now, industry has produced handles primarily to fit men's hands, the question as to what extent women can use a normal hammer with a 20 to 30 mm shaft diameter without disadvantage, has remained open. The research results show that grip circumferences measured on a Herig cone show a much smaller sexual dimorphism than many other body measurements. Sexual differentiation is shown to be so small that it can be neglected in practice.     

Experimental study on the grip and hold strength for stanchions and handrails in buses

The purpose of this study was to investigate the effective use of stanchions and handrails in buses. We constructed experimental equipment resembling bus stanchions and handrails and examined the grip and hold strength exerted when used. The total number of subjects was 80: 30 elderly and 19 young males, and 22 elderly and 9 young females. The experimental equipment comprised four parts: a handle part to imitate safety devices in buses such as stanchions, handrails, and straps, which was pulled by a winch at a constant speed; and a load cell wired with an analyzing processor, which output the strength exerted. The handle part was designed to measure grip and hold strengths against pulling forces in three directions, that is, forward, in the direction of the back of the hand, and in the direction of the palm. The subjects were asked to grasp the handle part against a pulling force. The maximum grip and hold strengths were recorded and analyzed. The strengths when pulled forward were the largest independent of the sex and age of the subjects. The results indicate that standing bus passengers should grip the fixtures, such as a stanchion, with their right hand when they are standing on the right side in a bus facing the windows.     

Lower median nerve block impairs precision grip.

The purpose of this study was to investigate precision grip impairment caused by a lower median nerve block at the wrist. The median nerve block was achieved by injecting bupivacaine hydrochloride into the carpal tunnel, which acutely simulated a median neuropathy. Seven healthy male subjects were instructed to grip, lift, and hold an instrumented handle within 60s using precision grip. The same tasks were performed before and after the nerve block. Force and torque data were recorded using two miniature 6-component force/torque transducers. The precision grip was quantified by the safety margin (i.e. the difference between the actual grip force and the minimal grip force to keep the object from dropping), the variation of grip force, and the migration area of center of pressure (i.e. the area defined by the center of pressure at a digit-transducer surface while holding the handle). Two subjects were unable to complete the precision grip tasks after the nerve block, and their data were excluded from the analyses. The median nerve block caused significant increases (P<0.05) in the safety margin of the grip force (>50%), the grip force variation (>80%), and the area of center of pressure migration (>250%). Median nerve block at the wrist impairs the fine motor control during precision grip. Our results corroborate the important role played by sensory function in hand fine motor control. Clinically, the measures related to precision grip have the potential to quantify impairment of hand function caused by neuromuscular disorders, to monitor the progress of a hand disorder, and to evaluate the efficacy of a treatment or rehabilitation procedure.     

Hand breakaway strength model-effects of glove use and handle shapes on a person's hand strength to hold onto handles to prevent fall from elevation

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.     

A novel force transducer for the measurement of grip force.

A new strain gauge transducer has been developed to measure functional grip forces. The gripping area is a cylinder of diameter 30 mm and length 150 mm and simulates the handle of a number of devices, allowing a range of activities to be studied. The device measures radial forces divided into six components and forces of up to 250 N per segment can be measured with an accuracy of +/- 1%. The device therefore gives information about the magnitude and distribution of force around the cylinder during gripping, and has been shown to be a valuable research tool in a study of four different types of grip, providing valuable input data for biomechanical models.     

Object Grasping using the Minimum Variance Model

Reaching-to-grasp has generally been classified as the coordination of two separate visuomotor processes: transporting the hand to the target object and performing the grip. An alternative view has recently been formed that grasping can be explained as pointing movements performed by the digits of the hand to target positions on the object. We have previously implemented the minimum variance model of human movement as an optimal control scheme suitable for control of a robot arm reaching to a target. Here, we extend that scheme to perform grasping movements with a hand and arm model. Since the minimum variance model requires that signal-dependent noise be present on the motor commands to the actuators of the movement, our approach is to plan the reach and the grasp separately, in line with the classical view, but using the same computational model for pointing, in line with the alternative view. We show that our model successfully captures some of the key characteristics of human grasping movements, including the observations that maximum grip size increases with object size (with a slope of approximately 0.8) and that this maximum grip occurs at 60–80% of the movement time. We then use our model to analyse contributions to the digit end-point variance from the two components of the grasp (the transport and the grip). We also briefly discuss further areas of investigation that are prompted by our model.     

Cardiovascular Responses to Isometric Hand grip vs. Relaxed Hand Grip in Sustained Cycling Efforts

ABSTRACT: Canivel, RG, Wyatt, FB, and Baker, JS. Cardiovascular responses to isometric hand grip vs. relaxed hand grip in sustained cycling efforts. J Strength Cond Res 26(11): 3101-3105, 2012-Peripheral isometric contractions may lead to enhanced performance. Previous research using hand grip protocols indicates increased stabilization and peak power outputs. Research is lacking with the grip vs. no-grip protocol during sustained efforts. The purpose of this study is to determine cardiovascular reactions (i.e., heart rate [HR], blood pressure [BP], and rate pressure product [RPP]) during sustained cycling via an isometric and relaxed hand grip. Nine (n = 9) recreational cyclists participated in this study. After signing a medical and physical readiness questionnaire, the subjects were randomly assigned to 1 of 2 different protocols. Preexercising values of the HR (beats per minute), BP (miilimeters of mercury), height (centimeters), weight (kilograms), and age (years) were assessed before testing. A Monark bicycle ergometer was used for testing. Grip was substantiated through the use of a hand grip dynamometer at 20 kg of tension. Protocol 1 used an isometric "Hand Grip" scenario at 150 W for 20 minutes. Protocol 2 used a "Relaxed Hand Grip" at the same power and time. During the 20-minute exercise test, HR (POLAR), BP (stethoscope and sphygmomanometer), and calculated RPP (HR × systolic BP [SPB]/100) were recorded every minute. Statistical measures included mean and SDs between protocols, and dependent samples t-tests were used to examine differences between grip and no-grip protocols. At an alpha of ≤0.05, SBP did show a significant increase when using no grip, 161.4 (5.1) mm Hg vs. grip, 154.1 (6.6) mm Hg. However, rate pressure product and heart rate showed no significant differences between protocols. Our data suggested that the use of an isometric hand grip is transient and diminishes over time.     

Alteration of period and amplitude of circadian rhythms in shift workers. With special reference to temperature, right and left hand grip strength

48 male shift workers in various industries volunteered to document circadian rhythms in sleeping and working, oral temperature, grip strength of both hands, peak expiratory flow and heart rate. All physiological variables were self-measured 4 to 5 times a day for 2 to 4 weeks. Individual time series were analyzed according to several statistical methods (power spectrum, cosinor, chi squares, ANOVA, correlation, etc.) in order to estimate rhythm parameters such as circadian period (tau) and amplitude (A), and to evaluate subgroup differences with regard to tolerance to shift work, age, duration of shift work, speed of rotation and type of industry. The present study confirms for oral temperature and extends to other variables (grip strength of both hands, heart rate) that intolerance to shift work is frequently associated with both internal desynchronization and small circadian amplitude. The internal desynchronization among several circadian rhythms supports the hypothesis that these latter are driven by several oscillators. Many differences were observed between circadian rhythms in right and left hand grip strength: circadian tau in oral temperature was correlated with that in the grip strength of the dominant hand but not with that of the other hand; changes in tau s of the non-dominant hand were age-related but did not correlate with temperature tau; only the circadian A of the non-dominant hand was associated with a desynchronization. Thus, circadian rhythms in oral temperature and dominant hand grip strength may be driven by the same oscillator while that of the non-dominant hand may be governed by a different one. Internal desynchronization between both hand grip rhythms as well as desynchronization of performance rhythms reported by others provide indirect evidence that circadian oscillator(s) may be located in the human cerebral cortex.     

Development and evaluation of an optimization-based model for power-grip posture prediction

An optimization-based model for power-grip posture prediction was proposed. The model was based on the premise that the hand prehensile configuration in a power grip best conforms to the object shape. This premise was embodied by an optimization procedure that minimized the sum of distances from the finger joints to the object surface. The model was evaluated against data from an experiment that measured the grasp postures of 28 subjects having diverse anthropometry. The intra- and inter-person variabilities in grip postures were empirically assessed and used as benchmark values for model evaluation. The evaluation showed that the root-mean-square (RMS) values of angle differences between the predicted and measured postures had a 13.7 degrees grand mean (across all joints, subjects, and two cylindrical handles grasped), whereas the RMS values of the inter- and intra-person variabilities in measured postures had grand means of 13.0 degrees and 4.4 degrees , respectively. The model can be readily generalized to the prediction of postures in power-grasping objects of different shapes, and adapted for testing alternative prehensile strategies or performance criteria.     

Toward a realistic optoelectronic-based kinematic model of the hand: representing the transverse metacarpal arch reduces accessory rotations of the metacarpophalangeal joints

A kinematic model representing the versatility of the human hand is needed to evaluate biomechanical function and predict injury risk in the workplace. We improved upon an existing optoelectronic-based kinematic hand model with grouped metacarpals by defining segmented metacarpals and adding the trapeziometacarpal joint of the thumb. Eight participants performed three static postures (neutral pose, cylinder grip, cap grip) to evaluate kinematic performance of three different models, with one, two, and four metacarpal segment(s). Mean distal transverse metacarpal arch angles in the four-segment metacarpal model were between 22.0° ± 3.3° (neutral pose) and 32.1° ± 3.7° (cap grip). Representation of the metacarpals greatly influenced metacarpophalangeal joint rotations. Both the two- and four-segment metacarpal models displayed significantly lower metacarpophalangeal joint ‘supination’ angles (than the one-segment model) for the fourth and fifth fingers. However, the largest reductions were for the four- versus one-segment models, with mean differences ranging from 9.3° (neutral pose) to 17.0° (cap grip) for the fourth finger and 16.3° (neutral pose) to 33.0° (cylinder grip) for the fifth finger. MCP joint abduction/adduction angles of the fourth and fifth fingers also decreased with segmentation of the metacarpals, although the lowest magnitudes generally occurred in the four-segment model. Overall, the four-segment metacarpal model produced the lowest accessory rotations in non-dominant axes, and best matched previous radiological studies that found MCP joint pronation/supination angles were typically less than 10°. The four-segment metacarpal model, with improved anatomic fidelity, will better serve future studies of detailed actions of the hand in clinical or work applications.     

Functional Corticospinal Projections from Human Supplementary Motor Area Revealed by Corticomuscular Coherence during Precise Grip Force Control

The purpose of the present study was to investigate whether corticospinal projections from human supplementary motor area (SMA) are functional during precise force control with the precision grip (thumb-index opposition). Since beta band corticomuscular coherence (CMC) is well-accepted to reflect efferent corticospinal transmission, we analyzed the beta band CMC obtained with simultaneous recording of electroencephalographic (EEG) and electromyographic (EMG) signals. Subjects performed a bimanual precise visuomotor force tracking task by applying isometric low grip forces with their right hand precision grip on a custom device with strain gauges. Concurrently, they held the device with their left hand precision grip, producing similar grip forces but without any precision constraints, to relieve the right hand. Some subjects also participated in a unimanual control condition in which they performed the task with only the right hand precision grip while the device was held by a mechanical grip. We analyzed whole scalp topographies of beta band CMC between 64 EEG channels and 4 EMG intrinsic hand muscles, 2 for each hand. To compare the different topographies, we performed non-parametric statistical tests based on spatio-spectral clustering. For the right hand, we obtained significant beta band CMC over the contralateral M1 region as well as over the SMA region during static force contraction periods. For the left hand, however, beta band CMC was only found over the contralateral M1. By comparing unimanual and bimanual conditions for right hand muscles, no significant difference was found on beta band CMC over M1 and SMA. We conclude that the beta band CMC found over SMA for right hand muscles results from the precision constraints and not from the bimanual aspect of the task. The result of the present study strongly suggests that the corticospinal projections from human SMA become functional when high precision force control is required.     

Prediction of handgrip forces using surface EMG of forearm muscles.

Evaluation of handgrip forces constitutes an essential component of ergonomic evaluation (e.g. of hand tools), but is difficult to perform at the workplace. The present study describes a series of experiments on 8 healthy male subjects to determine the validity of linear regression models using the surface electromyography (EMG) of up to 6 forearm muscles to predict handgrip forces. For isometric gripping tasks, normalized EMG to grip force calibrations using a series of dynamic force bursts up to 300 N resulted in a valid prediction of grip forces based on the EMG of 6 forearm muscles. Absolute differences between observed and predicted grip force were small (between 27 and 41 N) which shows that the proposed method might be used for the ergonomic evaluation of the use of hand tools. The EMG - handgrip force model appeared to be minimally affected by grip width, i.e. a model for 67 mm grip width was able to validly predict grip forces for 59 and 75 mm grip widths. Furthermore, it was shown that of the 6 forearm muscles studied at least 3 have to be assessed to arrive at a sufficient level of validity, while it seems to be irrelevant which 3 of those 6 forearm muscles are assessed.