Pinch Grip per SE Is Not an Occupational Risk Factor for the Musculoskeletal System: An Experimental Study on Field

Introduction: Some ergonomic evaluation methods define pinch grip as a risk factor independent of the exerted force. The present experimental study was performed with the main aim of objectively measuring the muscle engagement during the execution of pinch grip. Methods: the participants of the study were healthy workers occupationally involved in a high-intensity repetitive job related to the sorting of letters and small packages. Surface electromyography (sEMG) was used to study the activity of the abductor pollicis brevis and first dorsal interosseous fibers related to the execution of the required working tasks, while the force exerted during voluntary muscle contraction for pinch grip was measured by a portable acquisition system. The subjects were specifically asked to exert the maximum voluntary isometric contraction (MVIC) and further voluntary isometric contractions with a spontaneous force (SF) equal to 10%,20% and 50% of the MVIC; finally, the workers were asked to hold in pinch grip two types of envelopes, weighing 100 g and 500 g, respectively. Results: The force required to pinch 100 and 500 g envelopes by the fifteen subjects of the study corresponded to 4 and 5% MVIC, respectively. The corresponding sEMG average rectified values (ARV) were approximately 6% of that at MVIC for first dorsal interosseus (FDI) fibers and approximately 20-25% of MVIC for abductor pollicis brevis (ABP) fibers. Bivariate correlation analysis showed significant relationships between force at MVIC and FDI ARV at MCV. Conclusions: The obtained results demonstrate that muscle recruitment during pinch grip varies as a function of the SF: not only the position but also the exerted force should be considered when assessing the pinch grip as risk factor for biomechanical overload of the upper limb

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

Role of Sensation in Altered Phalanx Grip Force in Persons with Stroke

Many individuals experience hand impairment after stroke leading to decreased ability to perform daily living activities. Previous research studies have investigated how stroke survivors\u27 pinch grip control differs from healthy individuals, even though many individuals can only grasp with power grip after stroke. Furthermore, many stroke survivors experience tactile sensory deficit in their paretic limb in addition to motor deficit. It is currently unknown how stroke induced tactile sensory deficit affects power grip force directional control, which is important in terms of preventing object slippage and power grip normal force generation. Additionally it is unknown if power grip could be improved through tactile sensory enhancement. This dissertation investigated how stroke survivors\u27 power grip force control is different from healthy individuals. Also, the effect of stroke induced tactile sensory deficit on power grip force control and the benefits of a sensory enhancement method using remote subsensory vibrotactile noise on power grip phalanx force deviation was assessed. In addition, the effect of noise on the tactile sensation for stroke survivors with tactile sensory deficit and their performance on two dynamic gripping tasks, the Box and Block Test (`BBT\u27, number of blocks moved in 60 seconds) and the Nine Hole Peg Test (`NHPT\u27, time to pick up, place, and remove 9 pegs from 9 holes), were investigated. The theoretical framework of this dissertation is that tactile sensation is critical for grip control and impairment or enhancement of tactile sensation impacts power grip force control post stroke. Results showed that stroke survivors, especially those with tactile sensory deficit, gripped with increased phalanx force deviation compared to healthy individuals, showing reduced directional force control and increasing their chances of dropping objects. Remote subsensory vibrotactile noise improved fingertip and upper palm tactile sensation for stroke survivors with tactile sensory deficit. The noise also improved phalanx force directional control during power grip (reducing phalanx force deviation) for stroke survivors with and without tactile sensory deficit and age-matched healthy controls and improved the BBT score and time to complete the NHPT for stroke survivors with tactile sensory deficit. Overall, stroke survivors, particularly those with tactile sensory deficit, appear to have reduced phalanx force control during power grip, which may biomechanically result from a muscle activation pattern. Remote subsensory vibrotactile noise may have enhanced tactile sensation and hand motor control via stochastic resonance and interneuronal connections and could have potential as a wearable rehabilitation device for stroke survivors. This dissertation contributes to the long term goal of increasing stroke survivors\u27 independence in completing daily living activities

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

The Trapeziometacarpal Joint: Tissue Characterization and Surgical Techniques for Treatment of Osteoarthritis

The trapeziometacarpal (TMC) joint is one of the most important joints in the human body. It provides the thumb with the ability to cross over the palm of the hand, thus enabling motions of pinch and grip essential in performing routine daily activities. In the case of repeated use of this joint, the articular cartilage may wear through a progressive joint disease known as osteoarthritis (OA). This disease is characterized by pain at the base of the thumb, decreased range of motion, thumb instability, and decreased grip and pinch strength leading to impairment in vocational activities, significantly affecting quality of life. Much of the research surrounding the TMC joint has focused on development of non-surgical and surgical options for treatment of early and late stage OA. Unfortunately, the extent of research on characterizing the biophysical properties of the TMC joint and surrounding tissue is limited. The following research will seek to identify the ligamentous structures hypothesized to act as primary stabilizers of the TMC joint through advanced, high-resolution motion analyses. Mechanical properties of the primary ligamentous stabilizers will be obtained through uniaxial tensile testing of ligamentous tissue. This tissue will be further characterized through histology, staining for identification of the presence and orientation of essential proteins which may serve to support the argument for primary stabilizing tissue. Using results from the tissue characterization studies, two techniques are presented for the treatment of early and late stage TMC joint osteoarthris, which are designed to maintain and/or regain stability of this joint. The final section introduces a methodology for development of patient-specific computational finite element models of the hand and thumb. Input properties of these models are based on computed tomography data and outputs from the motion analysis and mechanical testing studies

Measurement of grip force and evaluation of its role in a golf shot

This study was conducted with the aim of establishing a method to measure time-varying forces at multiple locations at the hand-grip interface, using this method to record how golfers of varying abilities grip the club during a standard tee shot and investigating a potential link between the variations in vibration seen at the grip and the grip force applied near impact. It is hoped that additional knowledge about grip force during a golf shot will lead to improved training techniques and grip design in the future. An assortment of technologies were available for the measurement of grip force, but thinflexible sensors were chosen as they could be applied to the grip or gloves without altering the characteristics of the club. Reliability and performance for these sensors were not well established and, therefore, a novel set of tests were developed to evaluate their capabilities. Thin-film force sensor performance was examined under controlled laboratory conditions to give an indication of each sensor's quasi-static accuracy, hysteresis, repeatability and drift errors, dynamic accuracy and drift errors, and the effects of shear loads and surface curvature. With this newly developed set of tests, five varieties of thin-film force sensor utilizing four different technologies were assessed. The sensors had varying levels of success under the controlled conditions of the evaluation tests. Three of the sensors performed well under static and quasi-static loading conditions, with accuracy errors of 10% or less, hysteresis errors near 6%, repeatability near 6% or below, and drift at 60 s after load application under 15%. Two of these sensors were further tested and demonstrated little change in sensor output to loads applied over curved surfaces, although shear sensitivity and dynamic accuracy errors were more substantial. It was also found that some of the sensors lost sensitivity with repeated loading. Even with these drawbacks, the potential of these sensors to provide useful grip force information was clear. With an understanding of sensor performance in controlled laboratory settings, one sensor type was used to determine regions of peak pressure at the hand-grip interface and three others were used in player tests to obtain time-varying measurements of grip force during a swing. During the player tests, grip force was measured for 10-12 tee shots and impact time was determined Total force was computed for each shot taken by summing the force output of all the sensing elements positioned on either the grip or gloves. When these total force traces were aligned by impact and plotted for each of the golfers tested, an interesting and previously unreported phenomenon became apparent. Each player appeared to have their own grip force 'signature', i.e. total grip force for a particular golfer was very repeatable, but varied considerably between golfers. A grip force signature existed for all players tested regardless of ability, and the level of consistency for an individual golfer and the similarities between golfers was analysed using a cross correlation. It was found that nearly all of the golfers tested had swings that were dominated by the left hand, and that the most notable contributions of the right hand occurred after impact. Variations in grip force were also related to key phases of the swing using high speed video footage. Previously it has been noted that for the same ball, club, and impact location that the vibration on the shaft is remarkably consistent for many different golfers but there is a much greater variation in the vibration at the grip. It was hypothesized that the way a golfer grips the club affects the way vibration is transmitted into their hands and arms. A final set of player tests was therefore conducted with the aim of identifying how grip force affects vibration transmission from the shaft to the hands and the players' perceptions of this vibration. Vibration was measured on the shaft just below the grip and on the golfer'S left thumbnail, force was monitored at 18 locations on the hands, and impact location and clubhead speed were recorded. Each golfer's perceptions of the vibration caused by impact were also noted for two standard drivers. It was found that changes in the amount of vibration travelling from the shaft into the hands is affected by the grip force applied by the golfer. This is the first study to analyse the effects of grip force on vibration transmission into the hands and arms due to a golf impact

An evaluation of modern day kitchen knives: an ergonomic and biomechanical approach

The focus of this study was to evaluate how different knife characteristics affect the consumer\u27s ability to slice vegetables. There are many variables to a knife and there are beliefs about what makes for a better knife. There are two common multipurpose knives used for slicing vegetables, the chef knife and the santoku knife. The aim of the first portion of the study was to investigate if there is a difference in cutting between a chef knife and a santoku knife, a ceramic knife and a stainless steel knife, and a sharp and dull knife in terms of muscle activation, body part discomfort, time, and slice performance. In order to test these variables, four different knives were used. 50 participants sliced two pounds of vegetables with two knives each, each on a different day. The results show that for the consumer, the type of knife, material, and level of sharpness do not affect the user\u27s muscle activation, discomfort, time, or slice performance. In the second portion of the study the Pinch Cinch grip was designed to be placed on the knife to create an affordance for users to hold the knife in a pinch grip. This grip aligns the wrist and forearm and decreases fatigue and increases stability and control while cutting. The designed grip, the Pinch Cinch, is to be used as a training mechanism for the consumer to easily adjust to using the pinch grip. The grip was tested with 16 participants against a previously tested knife to ensure it did not require more muscle activation, time, discomfort, or cause lower slice performance. The results showed this grip did not have any significant difference from the knife with out the grip. The Pinch Cinch did not have any negative effect on the task compares to the other knife tested. The Pinch Cinch can ensure the consumer is maintaining the pinch grip, and allows them to become accustomed to it by having the affordance present. With the use of the Pinch Cinch, the consumer will feel the pinch grip is natural and retain the benefits of more control and stability

Effect of Remote Vibrotactile Noise on Pinch Force Maintenance Ability and Brain Activity

Noise has been used to enhance detection of signals thereby improving performance of nonlinear systems (referred to as stochastic resonance ). In biological systems, the noise and signal integration may occur not only at the receptor level but also in the central nervous system, thereby allowing noise remotely applied from a signal to enhance the system\u27s response to the signal. However, integration of tactile signal and noise within the central nervous system has not been demonstrated in humans. In addition, whether the enhanced detection of tactile signals with remote noise results in changes in motor behavior is unknown. The objectives of this thesis were to elucidate the effect of remote vibrotactile noise on hand motor control (Aim 1) and to demonstrate feasibility for quantifying the effect of remote vibrotactile noise on electroencephalography (EEG) activity (Aim 2). Aim 1 found that remote vibrotactile noise had little effect on young, healthy persons\u27 ability to maintain a target pinch force level. While remote noise may have enhanced people\u27s ability to detect very weak signals such as the monofilament stimulation in a previous study, it appears that remote noise was not effective during pinching activity involving strong tactile signals in this thesis. Aim 2 developed methods for quantifying the effect of remote vibrotactile noise on the somatosensory cortex EEG activity in response to monofilament stimulation at the fingertip. A pilot data from one subject showed a trend for strengthened sensation/sensory feedback and sensorimotor information processing, as evidenced by increased peak-to-peak amplitude of event-related potentials and changes in power spectral densities with remote vibrotactile noise at 60% of sensory threshold, but not at 80% and 120% of the sensory threshold. In conclusion, this thesis demonstrated that remote vibrotactile noise did not influence young healthy adults\u27 ability to maintain pinch force. This thesis also demonstrated the ability for quantifying the effect of remote vibrotactile noise on EEG activity in response to fingertip stimulation, with a trend for improved sensory information processing. The results of this thesis may guide future investigation regarding the use of remote vibrotactile noise to influence brain activity, tactile sensing, and motor control