Increase In Grip Force Research Articles

Effects of wrist posture and stabilization on precision grip force production and muscle activation patterns.

Most of the power for generating forces in the fingers arises from muscles located in the forearm. This configuration maximizes finger joint range of motion while minimizing finger mass and inertia. The resulting multiarticular arrangement of the tendons, however, complicates independent control of the wrist and the digits. Actuating the wrist impacts sensorimotor control of the fingers and vice versa. The goal of this study was to systematically investigate interactions between isometric wrist and digit control. Specifically, we examined how the need to maintain a specified wrist posture influences precision grip. Fifteen healthy adults produced maximum precision grip force at 11 different wrist flexion/extension angles, with the arm supported, under two conditions: 1) the participant maintained the desired wrist angle while performing the precision grip and 2) a robot maintained the specified wrist angle. Wrist flexion/extension posture significantly impacted maximum precision grip force (P < 0.001), with the greatest grip force achieved when the wrist was extended 30° from neutral. External wrist stabilization by the robot led to a 20% increase in precision grip force across wrist postures. Increased force was accompanied by increased muscle activation but with an activation pattern similar to the one used when the participant had to stabilize their wrist. Thus, simultaneous wrist and finger requirements impacted performance of an isometric finger task. External wrist stabilization can promote increased precision grip force resulting from increased muscle activation. These findings have potential clinical significance for individuals with neurologically driven finger weakness, such as stroke survivors.NEW & NOTEWORTHY We explored the interdependence between wrist and fingers by assessing the influence of wrist posture and external stabilization on precision grip force generation. We found that maximum precision grip force occurred at an extended wrist posture and was 20% greater when the wrist was Externally Stabilized. The latter resulted from amplification of muscle activation patterns from the Self-Stabilized condition rather than adoption of new patterns exploiting external wrist stabilization.

Effect of Segment Types on Characterization of Soft Sensing Textile Actuators for Soft Wearable Robots.

The use of textiles in soft robotics is gaining popularity because of the advantages textiles offer over other materials in terms of weight, conformability, and ease of manufacture. The purpose of this research is to examine the stitching process used to construct fabric-based pneumatic bending actuators as well as the effect of segment types on the actuators' properties when used in soft robotic glove applications. To impart bending motion to actuators, two techniques have been used: asymmetry between weave and weft knit fabric layers and mechanical anisotropy between these two textiles. The impacts of various segment types on the actuators' grip force and bending angle were investigated further. According to experiments, segmenting the actuator with a sewing technique increases the bending angle. It was discovered that actuators with high anisotropy differences in their fabric combinations have high gripping forces. Textile-based capacitive strain sensors are also added to selected segmented actuator types, which possess desirable properties such as increased grip force, increased bending angle, and reduced radial expansion. The sensors were used to demonstrate the controllability of a soft robotic glove using a closed-loop system. Finally, we demonstrated that actuators integrated into a soft wearable glove are capable of grasping a variety of items and performing various grasp types.

Early Adaptation To Increased Mechanical Loading After Disuse: Muscle Response In Male And Female Rats

On top of musculoskeletal alterations during spaceflight, reloading upon return induces muscle deterioration and prolongs recovery. Astronauts will return to the lunar surface by 2024, and plan for a future landing on Mars, where they will experience gravity shifts. PURPOSE: To understand the impact of acute gravitational reloading following disuse in both sexes. METHODS: 141 Adult Wistar rats were unloaded for 14d to establish muscle deconditioning, and then exposed to either 4 h or 24 h or partial weight-bearing (PWB) at 20, 40, or 100% of normal loading to simulate early adaptation to the Moon, Mars, and Earth’s gravity, respectively. Muscle strength, function and composition were assessed. Gene expression was performed in the soleus muscle using RTqPCR. RESULTS: After 14d of unloading, males lost more weight and displayed a greater decline in grip strength than females (-53.7% vs -35.9%, p < 0.0001), which was associated with greater atrophy of the soleus (p = 0.009). After 4 h of reloading, males displayed increased grip force while females did not. After 24 h, only males reloaded at PWB100 and PWB20 had a significant increase in grip strength but no change in gastrocnemius mass. Soleus mass decreased in females but increased in all males. In the soleus, myofiber size was greater in reloaded animals compared to HLS, but more so in males reloaded at PWB40 (p = 0.0002). Compared to HLS animals, gastrocnemius, myofiber size was higher in reloaded males but identical in reloaded females, regardless of the PWB level. Interestingly, reloaded males showed an increased proportion of type 1 myofibers, while females displayed an increase in hybrid myofibers. Gene expression highlighted that males were able to significantly upregulate several genes involved in muscle regeneration, including Pax7, MyoD, MyoG, Ubr5, as early as after 4 hr of reloading, while females did not. CONCLUSION: Early adaptation to PWB after unloading results in a rapid increase in grip strength in males, but not in females. Moreover, the ability for males to induce gene expression immediately following reloading might contribute to the improve muscle function. Muscle composition during recovery seems to be plastic and sex-dependent, suggesting a complex set of influences on muscle recovery after disuse. This work was supported by NASA (80NSSC19K1598).

Effect of a single proximal interphalangeal Joint Fusion of the Index, Middle or Ring Finger on the Grip and Finger Force and Load Distribution in the Hand

Due to the functional coupling of adjacent finger joints and the quadriga effect, arthrodesis of the proximal interphalangeal joint (PIPJ) can be assumed to lead to a different grip pattern resulting in altered force distribution of the hand. Ten patients with isolated arthrodesis of the PIPJ due to posttraumatic osteoarthritis (4×PIPJ II, 4×PIPJ III, 2×PIPJ IV) were assessed 59 (17-121) months postoperatively on average. The angle of arthrodesis was assessed by radiographs. Grip force and load distribution of both hands were measured by manugraphy using 3 differently sized cylinders. Grip force was separately assessed and compared for the whole hand as well as for each of the fingers and each phalanx. Average total grip force of the affected hand compared to the uninjured opposite side was 74% (38-136%) for the small cylinder, 104% (68-180%) for the mid-sized cylinder and 110% (69%-240%) for the large cylinder. Arthrodesis of the PIPJ of the index finger led to a reduction of the grip force (91%) for the small cylinder, but increased grip force for the mid-sized (120%) and large cylinder (139%). Grip force was reduced for all cylinder sizes by arthrodesis of the PIPJ of the middle finger (56%, 88% and 91%). Arthrodesis of the PIPJ of the ring finger resulted in a grip force of 76%, 105% and 91%, respectively, for the different cylinder sizes.The finger force of the affected finger was reduced after arthrodesis of the PIPJ, with the exception of the index finger, which was stronger than the unaffected opposite finger when using the large cylinder. The force of the healthy fingers on the affected side was greater when compared with the same finger on the opposite side, which led to increased grip force for the mid-sized and the large cylinder of the affected hand. A reduction in load distribution was measured mostly for the middle phalanx but also for the distal phalanx of the operated-on finger. Arthrodesis of the PIPJ almost always led to force reduction in the middle and distal phalanx of the affected finger. However, the total grip force of the hand was compensated by a higher force of the adjacent healthy fingers. In many cases, total grip force was even higher on the affected side. However, arthrodesis of the PIPJ resulted in a noticeable force reduction when smaller objects were gripped.

Beneficial effects of denosumab on muscle performance in patients with low BMD: a retrospective, propensity score-matched study

SummaryThis study examined the effects of denosumab compared to bisphosphonates and vitamin D alone on muscle performance in patients with low BMD. While grip force improved in both the denosumab and bisphosphonate group, a superior increase in chair rising test force was observed in the denosumab group.IntroductionThe aim of this study was to investigate the effect of the anti-resorptive agent denosumab (Dmab) on upper and lower limb muscle performance compared to bisphosphonate (BP) treatment and vitamin D supplementation alone (i.e., basic therapy) in patients with low BMD.MethodsThis retrospective, propensity score-matched (sex, age, BMI, follow-up time) cohort study included 150 osteopenic or osteoporotic patients receiving basic (n = 60), BP (n = 30) or Dmab (n = 60) therapy. All patients underwent a musculoskeletal assessment at baseline and follow-up, including DXA, laboratory bone metabolism parameters, grip force, and chair rising test mechanography. Mean annual percentage changes were calculated and compared between study groups.ResultsAfter a mean follow-up period of 17.6 ± 9.0 months, a significantly higher increase in grip force in both the Dmab (p < 0.001) and BP group (p = 0.001) compared to the vitamin D group was observed (vitamin D = − 6.1 ± 10.2%; BP = + 0.8 ± 8.2%; Dmab = + 5.1 ± 25.5%). The Dmab group showed a significantly higher increase in chair rising test force compared to the BP group (vitamin D = + 5.8 ± 12.7%; BP = + 0.9 ± 8.6%; Dmab = + 8.2 ± 14.4%; Dmab vs. BP p = 0.03). Neither the changes in BMD nor in bone metabolic parameters were associated with changes in muscle performance.ConclusionDmab resulted in increased muscle strength in the upper and lower limbs, indicating systemic rather than site-specific effects as compared to BP. Based on these findings, Dmab might be favored over other osteoporosis treatments in patients with low BMD and poor muscle strength.

An Experimental Study of the Influence of Hand-Arm Posture and Grip Force on the Mechanical Impedance of Hand-Arm System

In order to investigate the effects of hand-arm posture, grip force, push force, and vibration excitation intensity on the mechanical impedance of human hand-arm system, a test system with a self-developed vibration handle has been prepared. Based on the testing system, the mechanical impedance of the hand-arm system of seven Chinese adult males were tested and calculated under the random vibration excitation with the frequency of 10–1000 Hz. The results reveal that when the frequency is lower (&lt;40 Hz), the hand-arm system with an elbow angle of 180o produces a higher mechanical impedance; when the frequency ranges from 40 Hz to 100 Hz, the hand-arm system with an elbow angle of 90o generates a higher mechanical impedance; while when the frequency is higher (&gt;100 Hz), the hand-arm posture seems to have no obvious effect on the mechanical impedance. Higher grip or push force would increase the frequency corresponding to the peak value of the mechanical impedance and often correspond to a higher mechanical impedance in a specific frequency range (30–200 Hz). When the frequency is lower (&lt;140 Hz), vibration intensity has certain effects on the mechanical impedance of the hand-arm system. In conclusion, vibration intensity does not directly affect the mechanical impedance, but an increase in grip or push force often causes an increase in mechanical impedance and a higher frequency that corresponds to the peak of mechanical impedance.

New device with force sensors for laparoscopic liver resection – investigation of grip force and histological damage

Introduction As the benefits of minimally invasive surgery are recognized, the rate of laparoscopic liver resection (LLR) is rapidly increasing. Liver tissue is fragile compared to tissue of the stomach and colon. In endoscopic and robotic surgery, sufficient tactile sensation is yet to be obtained. Therefore, it is necessary to measure and indicate the grip force of forceps during surgery. We developed a new device consisting of force sensors and investigated its grip force and the resulting histological damage to liver tissue. Material and methods We measured the grip force generated during laparoscopic surgery in pigs using the forceps with pressure sensors developed by us. Throughout the hepatectomy, we measured the grip force generated by the forceps in real time. We investigated the histological damage to the liver caused by using the forceps with different grip forces. Results The subject produced a mean grip force of 1.75 N during the procedures. The maximum grip force was 3.38 N. By grasping the tissues of the liver with forceps, bleeding and destruction of the hepatic lobules were observed in a manner dependent on increasing grip force. Conclusion The new device is necessary for preventing liver damage in laparoscopic hepatic resection.

A Bio-Inspired Slip Detection and Reflex-Like Suppression Method for Robotic Manipulators

Robotic manipulators face significant challenges when handling objects of different sizes and shapes. Incorporating a sense of touch into these devices has the potential to improve performance and dexterity. In this paper, a bio-inspired approach is presented for slip detection and suppression during object manipulation. The method was inspired by the behavior of FA-I afferents located in the glabrous skin that encode sliding motion of objects over the skin. The proposed slip detection method encodes object motion captured by a slip sensor into spikes, following principles of neuromorphic sensing. The spikes are used as the feedback signal for an event-based closed-loop control system. The controller behaves in a reflex-like manner and actively engages the robotic fingers to increase grip force and suppress slip. A Dynamic Adaptive Threshold method was designed to improve slip detection for different surface properties of grasped objects. The performance of the method was evaluated following situations of dynamic slip caused by a sudden or gradual increase in object weight. The results demonstrated the feasibility of the proposed method. Slip events were suppressed before complete object slippage in 80% of all experimental trials. The response time ( $\Delta {\text {t}} ms) was compatible with the time for grip force adjustments in humans. This paper explored event-based touch applicable to the problem of manipulation, which is less explored than event-based tactile perception and shows promising prospects for both robotics and prosthetics.

Impaired force control contributes to car steering dysfunction in chronic stroke

Purpose Precise control of a car steering wheel requires adequate motor capability. Deficits in grip strength and force control after stroke could influence the ability steer a car. Our study aimed to determine the impact of stroke on car steering and identify the relative contribution of grip strength and grip force control to steering performance. Methods Twelve chronic stroke survivors and 12 controls performed three gripping tasks with each hand: maximum voluntary contraction, dynamic force tracking, and steering a car on a winding road in a simulated driving environment. We quantified grip strength, grip force variability, and deviation of the car from the center of the lane. Results The paretic hand exhibited reduced grip strength, increased grip force variability, and increased lane deviation compared with the non-dominant hand in controls. Grip force variability, but not grip strength, significantly predicted (R 2 = 0.49, p < 0.05) lane deviation with the paretic hand. Conclusion Stroke impairs the steering ability of the paretic hand. Although grip strength and force control of the paretic hand are diminished after stroke, only grip force control predicts steering accuracy. Deficits in grip force control after stroke contribute to functional limitations in performing skilled tasks with the paretic hand. Implications for rehabilitation Driving is an important goal for independent mobility after stroke that requires motor capability to manipulate hand and foot controls. Two prominent stroke-related motor impairments that may impact precise car steering are reduced grip strength and grip force control. In individuals with mild-moderate impairments, deficits in grip force modulation rather than grip strength contribute to compromised steering performance with the paretic hand. We recommend that driving rehabilitation should consider re-educating grip force modulation for successful driving outcomes post stroke.

Left–Right Interaction during Anticipatory Motor Adjustment

The interaction of anticipatory and reflexive changes in the grip force of the right hand was tested for the effect on the grip force developed by the thumb and index finger of the left hand. The test task for the right hand was the same in all test variants, to hold a cup where a weight fell (with the thumb and index finger). Three different tasks were chosen for the left hand. In the first task, the left fingers touched a sensor with a negligible grip force. In the second task, the subject had to hold a force sensor loaded with a 200-g load. In the third task, the subject was instructed to slowly increase the grip force by fingers of both hands. In response to the impact of the falling weight, an involuntary increase was observed in the grip force of the right-hand fingers, depending on the available visual information of the falling weight and being independent of the motor task performed by left hand. When the subject’s eyes were closed, the grip force increased in all tasks as a response to the impact of the weight fall. When the subject’s eyes were open, an automatic increase in the right-hand grip force occurred 200–300 ms before the impact. The left-hand grip force changed in different ways. In the first and second tasks, the grip force of the left hand did not change despite the changes in the grip force of the right hand in response to the impact of the falling weight. In case of a coordinated slow increase in the grip forces of both hands, an increase in the grip force was observed in the unaffected left hand before the impact and during the response to the impact, like in the right hand. Thus, a common motor task for both hands led to similar changes in grip force, which were recorded in both right and left hands not only during the response to an external stimulus, but also during anticipation. Movement planning was assumed to involve the organization of left–right interaction at the supraspinal level, probably, at the level of motor cortex interactions between the left and right hemispheres.

Pre-operative grip force as clinical predictor for weakness after transversal carpal ligament release

Temporary or long-lasting loss of grip force after open carpal tunnel release (CTR) in carpal tunnel syndrome (CTS) patients is well known and caused by changes in biomechanical conditions through sectioning of the transverse carpal ligament. We hypothesize to find predicting factors for loss of grip strength. We performed dynamometer testing of overall hand grip, tip pinch, and key pinch grip prior, 3 and 6 months after open CTR in 42 CTS subjects. Changes in these three main variables related to pre-operative grip, tip pinch and key pinch forces as well as gender and age were analyzed for significant results (t test, Pearson and Spearman correlations, descriptive statistics; 2-tailed p = .05). At 3-month post-CTR, overall hand grip force decreased significantly by 11.7% (p = .006), whereas key pinch and tip pinch only decreased by 5.6 and 3.5% (p < .0004). At 6-month post-CTR our subjects showed, compared to pre-operative level, an increase of overall grip force to 94.6% (p = .242) and an improvement of tip pinch to even 107% (p = .169) and key pinch to 102% (p = .675). Further investigation showed that subjects with a strong grip prior to the operation seem to lose more strength 3 and 6 months after operation than subjects with average or low strength results (3 months: Spearman −.522.; 6 months: Spearman −.569, p = .000). Pre-operative dynamometer assessment can predict loss of grip force and therefore create realistic post-operative expectations. Patients at risk for prolonged weakness after surgery (especially male subjects with high pre-operative grip force), could, instead of early surgical transversal carpal ligament release, profit from enrolling into an extended conservative therapy (immobilization and anti-inflammatory medication). Additionally, these patients undergoing CTR could enroll into an intensive post-operative occupational therapy with focus on grip force training to improve their recovery. Level of Evidence: Level III, risk / prognostic study

Adaptation to the absence of tactile and proprioceptive feedback in object handling

Dextrous manipulation necessitates efficient sensorimotor feedback mechanisms to orientate handheld objects, adjust for movement dynamics and respond to perturbations. In particular, cutaneous receptors and proprioception are paramount in the regulation of hand-object interactions (Johansson, 1991; Nowak et al., 2004). This study further examined the object handling skills of a person with massive peripheral deafferentation (consequent to sensory neuropathy) in order to improve knowledge of how people adapt/compensate for the loss of tactile/proprioceptive feedback. Object handling abilities of a deafferented woman (GL) were compared to eight age-matched control subjects using three experimental tasks: – discrete vertical movements; – functional grasp and place and; – static holding with perturbations (taps) applied to the top of the object—firstly by the person themselves and secondly by the experimenter. Tasks 1 and 3 were performed under full vision and blinded conditions. Grip force and object acceleration/orientation were recorded using a portable, instrumented object. When compared to control subjects, GL demonstrated a global increase in grip force with diminished temporal coupling to changes in object acceleration and limited ability to maintain orientation of the handheld object in the absence of visual feedback. All phases of the grasp and place task were of greater duration for GL and a qualitatively distinct acceleration profile was observed. In the hold perturbation tasks, GL exhibited greater time delays between perturbation and grip force response but proved efficient at gauging grip force response with respect to the magnitude of the perturbation. Whilst proprioceptive deficits limit temporal precision of grip force adjustments in object handling, visuomotor strategies and auditory feedback may assist in regulating object orientation during functional tasks and grip force scaling during perturbations. Future studies might investigate the feasibility of augmented visual/auditory feedback devices to optimise object handling for people with somatosensory deficits.

Manual action verbs modulate the grip force of each hand in unimanual or symmetrical bimanual tasks.

Manual action verbs modulate the right-hand grip force in right-handed subjects. However, to our knowledge, no studies demonstrate the ability to accomplish this modulation during bimanual tasks nor describe their effect on left-hand behavior in unimanual and bimanual tasks. Using load cells and word playlists, we evaluated the occurrence of grip force modulation by manual action verbs in unimanual and symmetrical bimanual tasks across the three auditory processing phases. We found a significant grip force increase for all conditions compared to baseline, indicating the occurrence of modulation. When compared to each other, the grip force variation from baseline for the three phases of both hands in the symmetrical bimanual task was not different from the right-hand in the unimanual task. The left-hand grip force showed a lower amplitude for auditory phases 1 and 2 when compared to the other conditions. The right-hand grip force modulation became significant from baseline at 220 ms after the word onset in the unimanual task. This moment occurred earlier for both hands in bimanual task (160 ms for the right-hand and 180 for the left-hand). It occurred later for the left-hand in unimanual task (320 ms). We discuss the hypothesis that Broca’s area and Broca’s homologue area likely control the left-hand modulation in a unilateral or a bilateral fashion. These results provide new evidence for understanding the linguistic function processing in both hemispheres.

Mind Your Grip: Even Usual Dexterous Manipulation Requires High Level Cognition.

Simultaneous execution of cognitive and sensorimotor tasks is critical in daily life. Here, we examined whether dexterous manipulation, a highly habitual and seemingly automatic behavior, involves high order cognitive functions. Specifically, we explored the impact of reducing available cognitive resources on the performance of a precision grip-lift task in healthy participants of three age groups (18–30, 30–60 and 60–75 years). Participants performed a motor task in isolation (M), in combination with a low-load cognitive task (M + L), and in combination with a high-load cognitive task (M + H). The motor task consisted in grasping, lifting and holding an apparatus instrumented with force sensors to monitor motor task performance. In the cognitive task, a list of letters was shown briefly before the motor task. After completing the motor task, one letter of the list was shown, and participants reported the following letter of the list. In M + L, letters in the list followed the alphabetical order. In M + H, letters were presented in random order. Performing the high-load task thus required maintaining information in working memory. Temporal and dynamic parameters of grip and lift forces were compared across conditions. During the cognitive tasks, there was a significant alteration of movement initiation and a significant increase of grip force (GF) throughout the grip-lift task. There was no interaction with “age”. Our results demonstrate that planning and the on-line control of dexterous manipulation is not an automatic behavior and, instead, that it interacts with high-level cognitive processes such as those involved in working memory.

A preliminary study on characterisation of finger interface kinetics using a pressure and shear sensor system.

Our hands constantly handle objects throughout our lives, where a crucial component of this interaction is the detection of grasping (pressure) and slipping (shear) of the object. While there have been a large amount of studies using pressure sensors for grasping detection, synchronised pressure and shear detection at the finger/object interface is still needed. This study aims to assess the feasibility of a sensor system designed to detect both pressure and shear at the fingertip/object interface via a single subject test. Descriptive study, proof of concept. One healthy subject participated in the study and was asked to perform a single finger test protocol and a simple hand test protocol. The corresponding multidirectional loads at the fingertip/object interface were measured in real time using a pressure and shear sensor system. Results from the finger test protocol show peak values of up to approximately 50 kPa (5 N) and 30 kPa (3 N) of pressure for each test, respectively. Results from the hand test protocol show a pressure and shear profile that shows a large increase in grip force during the initial grasping of the object, with a peak pressure of approximately 50 kPa (5 N). The pressure and shear profile demonstrates that the load is not evenly distributed across all digits. This study provides evidence that the reported sensor system has sufficient resolution, dynamic response and load capability to capture biomechanical information during basic protocols and hand-grasping tasks. Clinical relevance The presented sensor system could be potentially used as a tool for measuring and evaluating hand function and could be incorporated into a prosthetic hand as a tactile feedback system.

Methylphenidate Enhances Grip Force and Alters Brain Connectivity.

A central fatigue theory proposes that force output during fatiguing exercise is limited to maintain homeostasis. The self-awareness of the body's homeostatic state is known as interoception. Brain regions thought to play a role in interoception, such as the insular and orbital frontal cortex, have been proposed as sites for the upstream regulation of fatiguing exercise. Methylphenidate (MPH) can improve force output during exercise and may alter central processes during fatiguing exercise. However, the ergogenic neural underpinnings of MPH are unknown. This study examines the effect of MPH on force output and brain functional connectivity during a muscle-fatiguing handgrip task. In a double-blind, crossover design, 15 subjects (mean age = 28.4 ± 5.2; 9 males and 6 females) ingested MPH or placebo before performing a muscle-fatiguing handgrip task during functional magnetic resonance imaging. We examined force output and brain connectivity (psychophysiological interactions and functional connectivity) throughout the task as well as in the few seconds just before releasing the grip dynamometer (i.e., pretask failure). We show that in the MPH condition, subjects increased grip force throughout but not during pretask failure. Brain connectivity was altered throughout the task between the insular and the hand motor cortex, as well as between the insular and the orbital frontal cortex. There were no differences in connectivity during pretask failure. For the first time, we show that brain connectivity can be influenced by MPH during muscle-fatiguing exercise. This study provides additional support that the CNS acts to regulate motor drive subservient to homeostasis.

Modeling of the interaction between grip force and vibration transmissibility of a finger

It is known that the vibration characteristics of the fingers and hand and the level of grip action interacts when operating a power tool. In the current study, we developed a hybrid finger model to simulate the vibrations of the hand–finger system when gripping a vibrating handle covered with soft materials. The hybrid finger model combines the characteristics of conventional finite element (FE) models, multi-body musculoskeletal models, and lumped mass models. The distal, middle, and proximal finger segments were constructed using FE models, the finger segments were connected via three flexible joint linkages (i.e., distal interphalangeal joint (DIP), proximal interphalangeal joint (PIP), and metacarpophalangeal (MCP) joint), and the MCP joint was connected to the ground and handle via lumped parameter elements. The effects of the active muscle forces were accounted for via the joint moments. The bone, nail, and hard connective tissues were assumed to be linearly elastic whereas the soft tissues, which include the skin and subcutaneous tissues, were considered as hyperelastic and viscoelastic. The general trends of the model predictions agree well with the previous experimental measurements in that the resonant frequency increased from proximal to the middle and to the distal finger segments for the same grip force, that the resonant frequency tends to increase with increasing grip force for the same finger segment, especially for the distal segment, and that the magnitude of vibration transmissibility tends to increase with increasing grip force, especially for the proximal segment. The advantage of the proposed model over the traditional vibration models is that it can predict the local vibration behavior of the finger to a tissue level, while taking into account the effects of the active musculoskeletal force, the effects of the contact conditions on vibrations, the global vibration characteristics.

The influence of wrist posture, grip type, and grip force on median nerve shape and cross-sectional area.

During grasping, the median nerve undergoes mechanical stress in the carpal tunnel which may contribute to carpal tunnel syndrome. This study investigated the effects of wrist posture, grip type, and grip force on the shape and cross-sectional area of the median nerve. Ultrasound examination was used to obtain cross-sectional images of the dominant wrist of 16 healthy subjects (8 male) at the proximal carpal tunnel during grasping. The cross-sectional area, circularity, and axis lengths of the median nerve were assessed in 27 different conditions (3 postures × 3 grip types × 3 force levels). There were no significant changes in median nerve cross-sectional area (P > 0.05). There were significant interactions across posture, grip type, and grip force affecting nerve circularity and axis lengths. When the wrist was flexed, increasing grip force caused the median nerve to shorten in the mediolateral direction and lengthen in the anteroposterior direction (P < 0.04), becoming more circular. These effects were significant during four finger pinch grip and chuck grip (P < 0.05) but not key grip (P > 0.07). With the wrist extended, the nerve became more flattened (less circular) as grip force increased during four finger pinch grip and chuck grip (P < 0.04) but not key grip (P > 0.3). Circularity was lower during the four finger pinch compared to chuck or key grip (P < 0.03). The findings suggest that grip type and wrist posture significantly alter the shape of the median nerve. Clin. Anat. 30:470-478, 2017. © 2017 Wiley Periodicals, Inc.

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

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

Predictive and Reactive Grip Force Responses to Rapid Load Increases in People With Multiple Sclerosis

ObjectivesTo determine the effects of multiple sclerosis (MS) on predictive and reactive grip force control in a catching task and on clinical tests of hand function. DesignCase-control study with matched-pairs control group. SettingUniversity prevention and rehabilitation center. ParticipantsParticipants (N=30) consisted of people with multiple sclerosis (PwMS) (n=15) and healthy controls (n=15), matched for sex, age, and hand dominance. InterventionsNot applicable. Main Outcome MeasuresPerformance on the Expanded Disability Status Scale (EDSS), Nine-Hole Peg Test (9-HPT), Jebsen-Taylor Hand Function Test (JTHFT), and 2-point discrimination (2PD) was evaluated. To analyze grip force control, blindfolded subjects held a receptacle equipped with grip force and acceleration sensors in their hand. In a catching task, a weight was dropped from (1) the experimenter's hand unexpectedly into the receptacle (reactive force control); and (2) from the subject's opposite hand (predictive force control). Grip forces and time lags were analyzed. ResultsPwMS (mean EDSS ± SD, 4.2±1.86) had impairments in the 9-HPT and JTHFT (P<.001). The 2PD did not differ significantly between PwMS and controls. During reactive force control (catching task 1), PwMS showed significantly higher grip forces immediately after impact (P<.05), and a significant prolongation of the time from grip force increase until reaching the peak of grip force (P<.001). PwMS and controls did not differ during predictive force control (catching task 2; P>.1). ConclusionsExaggerated grip force responses and alterations of timing after an unpredictable perturbation, combined with preserved grip force control during predictable conditions, is a characteristic pattern of fine motor control deficits in MS. Measures of reactive grip force responses may be used to complement neurologic assessments. Further studies exploring the usefulness of these measures should be performed in a broader community of PwMS.