Voluntary Grip Research Articles

Kinetic measurements of hand motor impairments after mild to moderate stroke using grip control tasks.

BackgroundThe aim of this study is to investigate quantitative outcome measurements of hand motor performance for subjects after mild to moderate stroke using grip control tasks and characterize abnormal flexion synergy of upper extremities after stroke.MethodsA customized dynamometer with force sensors was used to measure grip force and calculate rotation torque during the sub-maximal grip control tasks. The paretic and nonpartic sides of eleven subjects after stroke and the dominant sides of ten healthy persons were tested. Their maximal voluntary grip force was measured and used to set sub-maximal grip control tasks at three different target force levels. Force control ability was characterized by the maximal grip force, mean force percentage, coefficient of variation (CV), target deviation ratio (TDR), and rotation torque ratio (RTR). The motor impairments of subjects after stroke were also evaluated using the Fugl-Meyer assessment for upper extremity (FMA-UE) and Wolf Motor Function Test (WMFT).ResultsMaximal grip force of the paretic side was significantly reduced as compared to the nonparetic side and the healthy group, while the difference of maximal grip force between the nonparetic side and the healthy group was not significant. TDR and RTR increased for all three groups with increasing target force level. There were significant differences of CV, TDR and RTR between the paretic side and the healthy group at all the force levels. CV, TDR and RTR showed significant negative correlations with FMA-UE and WMFT at 50% of maximum grip force.ConclusionsThis study designed a customized dynamometer together with an innovative measurement, RTR, to investigate the hand motor performance of subjects after mild to moderate stroke during force control tasks. And stroke-induced abnormal flexion synergy of wrist and finger muscles could be characterized by RTR. This study also identified a set of kinetic parameters which can be applied to quantitatively assess the hand motor function of subjects after mild to moderate stroke.

Facilitation of corticospinal tract excitability by transcranial direct current stimulation combined with voluntary grip exercise

Previous studies have established that transcranial direct current stimulation (tDCS) is a powerful technique for the deliberate manipulation of the activity of human cerebral cortex. Moreover, it has also been shown that the non-exhausted voluntary motor exercise increases the excitability of corticospinal tract. We conducted this study to define the facilitation effect following anodal tDCS combined with the voluntary grip exercise as compared with single use of tDCS or voluntary grip exercise. Our result showed that the combination of anodal tDCS with voluntary grip exercise produced a 2-fold increase in the amplitude of MEP as compared with single use of anodal tDCS or voluntary grip exercise. In conclusion, our result could indicate that the treatment outcomes of brain and neurorehabilitation using tDCS would be better when tDCS is combined with the appropriate method of voluntary exercise as compared with single use of tDCS.

Frequency specific activity in subthalamic nucleus correlates with hand bradykinesia in Parkinson's disease

Local field potential recordings made from the basal ganglia of patients undergoing deep brain stimulation have suggested that frequency specific activity is involved in determining the rate of force development and the peak force at the outset of a movement. However, the extent to which the basal ganglia might be involved in motor performance later on in a sustained contraction is less clear. We therefore recorded from the subthalamic nucleus region (STNr) in patients with Parkinson's disease (PD) as they made maximal voluntary grips. Relative to age-matched controls they had more rapid force decrement when contraction was meant to be sustained and prolonged release reaction time and slower rate of force offset when they were supposed to release the grip. These impairments were independent from medication status. Increased STNr power over 5–12Hz (in the theta/alpha band) independently predicted better performance—reduced force decrement, shortened release reaction time and faster rate of force offset. In contrast, lower mean levels and progressive reduction of STNr power over 55–375Hz (high gamma/high frequency) over the period when contraction was meant to be sustained were both strongly associated with greater force decrement over time. Higher power over 13–23Hz (low beta) was associated with more rapid force decrement during the period when grip should have been sustained, and with a paradoxical shortening of the release reaction time. These observations suggest that STNr activities at 5–12Hz and 55–375Hz are necessary for optimal grip performance and that deficiencies of such activities lead to motor impairments. In contrast, increased levels of 13–25Hz activity both promote force decrement and shorten the release reaction time, consistent with a role in antagonising (and terminating) voluntary movement. Frequency specific oscillatory activities in the STNr impact on motor performance from the beginning to the end of a voluntary grip.

Radiostereometric Analysis in Measurements of Migration and Inducible Micromotion in Intra-Articular Distal Radius Fractures Treated With a Volar Plate

This study examined the use of radiostereometric analysis (RSA) in the assessment of fixation stability and healing characteristics in intra-articular fractures of the distal radius treated with a volar locking plate. Prospective cohort study. University hospital. Fifteen patients between 39 and 67 years of age with OTA type C distal radius fractures. All fractures were treated with a locked volar plate, and tantalum markers were inserted into fracture fragments. RSA was performed at 2, 6, 12, 18, and 52 weeks postoperatively. RSA measurements were also performed using maximal voluntary grip to create inducible micromotion at the fracture site at 6, 12, 18, and 52 weeks. Interfragmentary migration and inducible micromotion in terms of translation and rotation in 3 orthogonal axes were determined. The total translation and rotation were also calculated. Precision of measurements along individual axes was between 0.08 and 0.17 mm and 0.70-0.94 degrees for migration and between 0.04 and 0.07 mm and 0.29 and 0.86 degrees for inducible micromotion. Fractures underwent significant translational and rotational migration (P = 0.004 for both) during the first 2 weeks after surgery. This permanent migration was not detectable on conventional radiographs. Inducible fracture micromotion, measured during maximal grip, was detectable up to 18 weeks, even after achievement of radiographic union. RSA seems to have the potential to be a unique tool in redefining the biologic progress of fracture union. In plated fractures of the distal radius, the method is technically challenging due to difficulties in achieving a good scatter and visibility of tantalum RSA markers. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Phototherapy and Grip Muscle Performance

Background: Grip strength and endurance has been shown to be an overall indicator of physical strength, function, and health. Previous research has provided evidence that phototherapy may increase muscle endurance. The purpose of this study was to investigate the effects of red/infrared light and blue/infrared light on grip endurance, lactic acid accumulation, and delayed onset muscle soreness (DOMS). Materials and Methods: Fourteen subjects, seven men, and seven women (mean age 23.2 ± 1.7) took part in this randomized crossover double-blinded study. The subjects received either phototherapy (red/infrared probe with 4 red light emitting diodes (LEDs); λ= 670nm; 5 infrared laser diodes; λ= 850nm; 540mW power output; 65 seconds of irradiation, applied in 3 locations over the forearm and hand of the dominant arm; 35.1 J of total energy per site), phototherapy (blue/infrared probe with 28 blue LEDs emitting λ= 405nm; 8 infrared LEDs emitting λ= 880nm; 500mW of power output; 80 seconds, applied to the same points for a 40.0 J total energy per site) or placebo phototherapy using an identical cluster probe. The dosage in energy density units for the phototherapy treatments were 8 J/cm2 per site. Each intervention was applied immediately before performance of the grip endurance exercise. All subjects performed voluntary grip strength repetitions until they reached 50% of their initial maximal voluntary contraction. The number of repetitions performed was utilized for data analysis. Lactic acid (La) accumulation was measured five minutes after the exercise has been completed. A visual pain analog scale measured DOMS at 24 and 48 hours post exercise. Results: There were no significant differences between any of the three conditions on muscle endurance, La accumulation and pain scores as analyzed by Repeated Measures ANOVA. Conclusion: The application of a standard therapeutic dosage of phototherapy did not improve grip endurance.

Acute Effect of Vibration Exercise on Grip Strength and Physiological Recovery from High-Intensity Intermittent Grip Exercise

The purpose of this study was to investigate the physiological effects of the vibration exercise during the recovery phase after high-intensity intermittent grip exercise. Twelve female college students voluntarily participated in this repeated measured and randomly crossover experiment. After maximum voluntary intermittent grip test (5 × 20 reps, 1-min rest interval), all subjects were asked to immediately place their forearms on the vibration platform to perform the non-vibration (5 min, 0 Hz, 0 mm) or low-frequency vibration (5 min, 12 Hz, ± 3 mm) treatments. Immediately after the treatments, each subject was requested to perform 1 set of maximum voluntary grip test (6th set) again to examine the acute recovery effects of vibration. The blood lactate concentrations and ratings of perceived exertion (RPE) were measured throughout the experiment. The peak force, mean force and percent fatigue at each set of maximum voluntary grip test were also analyzed by grip dynamometer. The results showed no significant differences on the peak force, mean force and percent fatigue in the 6 sets of grip test between two treatments. However, the RPE (vibration vs. non-vibration, 13.6 ± 2.1 vs. 14.3±2.1, p＜.05) and lactate increase ratio (vibration vs. non-vibration, 125.8 ± 31.1 vs. 161.3 ± 46.0%, p ＜ .05) at the 6th set of grip test in the vibration treatment were significantly lower than those in the non-vibration treatment. These results demonstrated that the direct, local and low frequency vibration exercise could not improve the grip performance immediately after the high-intensity intermittent grip exercise, however, could ameliorate the perception of fatigue and the metabolic stress.

Examination of Older Females' Grip Characteristics

Loss of grip strength due to aging has been widely reported by researchers but other factors may also be influential in age-related hand function declines. For instance, older adults have demonstrated a propensity to orient fingertip forces in a manner different from younger adults. Additionally, a slowing in the maximal rate of force development due to aging has been found in muscle groups ranging from the biceps to the quadriceps. These grip characteristics may independently, or concurrently, affect hand function. Using the Multi-axis (MAP) dynamometer, we evaluated the ability of younger and older adult female participants to rapidly generate a maximal voluntary grip exertion. The maximum grip force, rate of force development (N/sec) and grip force vector orientation were measured. Older female participants had 69% the grip force, 62% the rate of force development, and had grip force vector orientations shifted 5.9 degrees as compared to younger female participants. The ability to use one's hands is critical for completing activities of daily living and retaining independence. The differences in grip characteristics measured in this study may improve our understanding of the loss of function in older adults' hands more than the decline in grip strength alone.

Influence of Instruction Conditions on the Evaluation of Muscular Endurance Based on Muscle Oxygenation

Proper instruction is essential for evaluating muscular endurance with high reliability. This study aimed to examine the influence of instruction conditions on the evaluation of rhythmic repeated muscular endurance based on muscle oxygenation kinetics. Fifteen healthy young men performed repeated maximal rhythmic grips for 6 minutes under the following 3 instruction conditions: (1) "Squeeze as hard as you can during 2 seconds freely (Ex1)"; (2) "Squeeze as hard as you can quickly at the cue of a beep every 2 seconds (Ex2)"; and (3) "Squeeze as hard as you can quickly at the cue of a beep every 2 seconds, and then hold the exertion for 1 second (Ex3)". In the start phase of measurement during which larger exertion (above 80% maximal voluntary grip contraction) of grip strength is possible, the exertion values and muscle oxygenation kinetics were not significantly different among the 3 instruction conditions. However, a significant difference was found in muscle oxygenation kinetics after the middle phase (3 minutes) of measurement and also in the peak forces. Particularly, oxygen supply to the skeletal muscle as compared with oxygen consumption was greater in Ex2 than in Ex3. This study found that the evaluated muscle endurance differs considerably under various instruction conditions. The following instruction may be useful in the assessment of muscular endurance: "Squeeze as hard as you can quickly at the cue of a beep and then immediately relax". The present findings suggest that proper instructions are essential in various physical function tests and in the dynamometer handgrip test for occupational therapists and strength and conditioning professionals to obtain accurate measurements.

S-27 Radiostereometric Analysis Detects Interfragmentary Micromotion in Healed Intra-Articular Fractures of the Distal Radius Treated with a Volar Locking Plate

A large number of different volar plate designs have emerged into the market without evidence-based data on their relative efficacy in the stabilization of unstable fractures of the distal end of the radius. One of the obstacles is the lack of suitable methods for quantitative assessment of fracture union. The aim of this study was to perform a critical evaluation of radiostereometric analysis (RSA) in the measurement of three-dimensional interfragmentary micromotion in patients with intra-articular fractures of the distal radius treated with a volar locking plate. Fifteen consecutive adult patients with AO type-C fractures of the distal end of the radius were recruited into the study. All fractures were treated with one type of volar fixed-angle plate. During operative treatment, tantalum RSA markers were inserted into proximal and distal fracture fragments of the radius. Assessment of the treatment outcome included functional tests, Patient-Rated Wrist Evaluation questionnaire (PRWE), conventional radiography and static RSA imaging performed at two, six, twelve, eighteen, and fifty-two weeks postoperatively. In order to study inducible interfragmentary micromotion, dynamic RSA imaging was performed during maximal voluntary grip at the follow-up visits starting at six weeks. Interfragmentary migration and inducible micromotion were measured for three axes of translation and rotation, and the total translation and rotation were calculated. The precision of measurements along individual axes was between 0.08–0.17mm and 0.70–0.94° for migration and between 0.04– 0.07mm and 0.29–0.86° for inducible micromotion. The fractures underwent significant translational and rotational migration (p =0.004 for both) during the first two weeks after surgery, but not thereafter. Maximal grip caused significant translational and rotational interfragmentary micromotion (p < 0.03 for both). Inducible micromotion was detectable up to eighteen weeks even after achievement of radiographic union. Application of RSA in the measurement of fracture fragment migration and inducible interfragmentary micromotion is feasible but technically demanding. RSA may be a unique tool for randomized clinical trials in defining the progress of fracture union.

Accuracy of the Borg CR10 Scale for Estimating Grip Forces Associated with Hand Tool Tasks

The gripping of tools is required by many industrial operations, and an important aspect of exposure assessment is determining the grip force output of operators. Ratings of perceived exertion can provide an indirect measure of grip force; however, reports in the literature of the use of Borg CR10 scale ratings as a surrogate measure of grip force have been mixed. During a laboratory study with 16 participants, power grip forces were measured directly during three hand tool task simulations: (1) a screwdriver task, (2) a ratchet task, and (3) a lift and carry task, each performed at four force/load levels. Borg scale ratings reported following each trial were compared with mean, peak, and integrated grip forces for the respective trials. Pearson correlations conducted on an individual basis were greatest for the screwdriver task, r∼ 0.9. Correlations for integrated grip force were generally better than for mean or peak force. Correlations were also performed on data pooled for all participants, simulating a cross-sectional sampling approach. Correlations made with pooled data were weaker than when conducted on an individual basis, ranging from r = 0.26 for peak grip force for the lift and carry task, to r = 0.79 for the screwdriver task. When the pooled data were normalized to individual maximum voluntary grip exertions, correlation generally improved but not to the level of the “individually scaled” data. Based on these findings, a protocol is proposed that could improve the strength of correlations between direct measures of grip force and ratings of perceived exertion. Differences in strength of correlation between task simulations are discussed with respect to differences observed in force distributions about the handle for the three tasks.

Constrained handgrip force decreases upper extremity muscle activation and arm strength

Many industrial tasks require repetitive shoulder exertions to be performed with concurrent physical and mental demands. The highly mobile nature of the shoulder predisposes it to injury. The purpose of this study was to determine the effects of simultaneous gripping, at a specified magnitude, on muscle activity and maximal arm force in various directions. Ten female subjects performed maximal arm exertions at two different heights and five directions using both specified (30% maximum voluntary grip) and preferred (self-selected) grip forces. Electromyography was recorded from eight muscles of the right upper extremity. The preferred grip condition produced grip forces that were dependent on the combination of arm height and force direction and were significantly greater (arm force down), lower (to left, up and push forward), or similar to the specified grip condition. Regardless of the magnitude of the preferred grip force, specifying the grip resulted in decreased maximal arm strength (by 18–25%) and muscle activity (by 15–30%) in all conditions, indicating an interfering effect when the grip force was specified by visual target force-matching. Task constraints, such as specific gripping demands, may decrease peak force levels attainable and alter muscle activity. Depending on the nature of task, the amount of relative demand may differ, which should be considered when determining safety thresholds.

Dependence of safety margins in grip force on isometric push force levels in lateral pinch

This study examined the relationship between safety margin and force level during an isometric push task in a lateral pinch posture. Ten participants grasped an object with an aluminium- or rubber-finished grip surface using a lateral pinch posture and exerted 20%, 40%, 60%, 80% and 100% of maximum push force while voluntary grip force was recorded. Then minimum required grip force was measured for each push force level. Mean safety margin, the difference between voluntary and minimum required grip forces, was 25% maximum voluntary contraction (MVC) when averaged for all push levels. Safety margin significantly increased with increasing push force for both grip surfaces. Grip force used during maximum push exertion was only 74% lateral pinch grip MVC. Possible underlying mechanisms for increasing safety margin with increasing push force are discussed as well as the implication of this finding for ergonomic analysis. This study demonstrates that ergonomic analyses of push tasks that involve friction force should account for safety margin and reduced grip strength during the push. Failure to consider these can result in overestimation of people's push capability.

Design and Evaluation of a Functional Electrical Stimulation System for Hand Sensorimotor Augmentation

The aim of this study was to perform a preliminary evaluation of a new method for therapeutic exercise of grasping in patients with upper limb disability. The new method combines active voluntary exercise augmented with electrical stimulation and controlled by using force feedback. The feedback has two functions: automatic control of the intensity of electrical stimulation by minimizing the tracking error, and biofeedback to the patient on the computer screen. The force feedback is realized by the use of a newly designed adjustable hand force measuring device, which comprises two force sensors. The therapy requires from patients to volitionally try to open and close the hand while tracking the target on the screen. The system was evaluated in a pilot study in five healthy and two chronic incomplete tetraplegic subjects. Results in healthy subjects were used for reference and for stimulation controller evaluation. The therapy in incomplete tetraplegic subjects of 45-min daily session delivered during four weeks. The results of pilot study show that augmentation of voluntary grip force control with presented system is possible.

A new method for estimating hand internal loads from external force measurements

This study examines using force vectors measured using a directional strain gauge grip dynamometer for estimating finger flexor tendon tension. Fifty-three right-handed participants (25 males and 28 females) grasped varying-sized instrumented cylinders (2.54, 3.81, 5.08, 6.35 and 7.62 cm diameter) using a maximal voluntary power grip. The grip force vector magnitude and direction, referenced to the third metacarpal, was resolved by taking two orthogonal grip force measurements. A simple biomechanical model incorporating the flexor tendons was used to estimate long finger tendon tension during power grip. The flexor digitorum superficialis and the flexor digitorum profundus were assumed to create a moment about the metacarpal phalange (MCP) joint that equals and counteracts a moment around the MCP joint measured externally by the dynamometer. The model revealed that tendon tension increased by 130% from the smallest size handle to the largest, even though grip force magnitude decreased 36% for the same handles. The study demonstrates that grip force vectors may be useful for estimating internal hand forces.

Pain relief after intratendinous injections in patients with tennis elbow: results of a randomised study

Background:“Tennis elbow” is a difficult condition to treat. Ultrasonography (US) and colour Doppler (CD) guided injections with polidocanol targeting the area with increased blood flow in the extensor origin have...

Associated reactions after stroke: A randomized controlled trial of the effect of botulinum toxin type A

To measure the impact of botulinum toxin A on associated reactions in patients following stroke. Randomized placebo-controlled trial. Forty patients with spasticity in their paretic arm (median time since stroke: 2.7 years) were randomized to botulinum toxin A (Dysport; 1000 mouse units (MU) divided between elbow, wrist and finger flexors) or placebo. Associated reactions were measured using hand dynamometry. The effort used was measured using maximum voluntary grip in the unaffected arm. Measurements were recorded at 2 pre-treatment and 3 post-intervention times. Activities that patients felt caused associated reactions and activities that were affected by associated reactions were recorded. Peak associated reactions force was reduced at week 6 with botulinum toxin A compared with placebo (mean group difference 19.0 N; 95% confidence interval (CI): 7.2, 30.9; p < 0.01) and week 2 (p = 0.005), with the effect wearing off by week 12 (p = 0.09). Thirty-one patients noted associated reactions on a regular basis and 24 said that these movements interfered with daily activities. Ten of 12 patients receiving botulinum toxin A and 2 of 12 receiving placebo reported reduction in interference with daily activities (p = 0.02). Botulinum toxin A reduces associated reactions and may be a useful adjunct to other rehabilitation interventions. The impact of associated reactions on daily activities may also be reduced.

Power grip strength as a function of tool handle orientation and location

Thirty male volunteers participated in a study evaluating the effect of workspace envelope (work height and reach distance) and handle orientation on grip force capacity. Maximum voluntary power grip exertions were recorded using instrumented tool handles under three conditions: a pistol grip tool handle oriented horizontally and vertically and a right angle tool handle oriented horizontally. Significant main effects of handle height and reach location on normalized grip force capacity were observed with the horizontally oriented pistol grip and right angle handles, whereas only an interaction effect was observed with the vertically oriented pistol grip handle. Comparison of results to scores produced with a job assessment tool (RULA) is included as an appendix. The proposed methodology can provide information useful to job, workstation or tool design directed toward best accommodating the physical capacities of workers performing hand tool tasks.

Optimal work–rest cycles for an isometric intermittent gripping task as a function of force, posture and grip span

The aim of this study was to investigate the maximum acceptable contraction frequencies (i.e. work–rest cycles) for an isometric-intermittent handgrip task as a function of grip span, applied force and shoulder posture using psychophysical and physiological approaches. Twelve healthy males served as subjects. The three grip spans investigated were the optimal, 2 cm narrower than the optimal, and 2 cm wider than the optimal. The grip force levels studied were 15% and 30% of maximum voluntary grip force and the two shoulder postures were 25° flexion and 30° abduction. The psychophysical results indicate that subjects work faster with the narrower grip span at 15% of maximum voluntary grip force level in comparison to working with the optimal and the wider spans. However, when the task required 30% of maximum grip force level, the subjects worked faster with the optimal grip span. These findings were supported by the results of electromyography, heart rate, blood pressure and perceived discomfort. The study suggests that grip span of a tool is an important factor to be considered in predicting optimal work–rest cycles for hand grip tasks, and the optimum setting of grip span of the hand-tool depends on the required task force level. That is, the optimality is relative rather than absolute. In addition, it appears that weaker subjects can work at a higher rate than stronger ones at the same relative force level.

A fatigue resistance test for elderly persons based on grip strength: reliability and comparison with healthy young subjects

Although a wide variety of protocols are available for evaluating skeletal muscle fatigue resistance, they often necessitate important technological resources or are too complicated for elderly subjects. We present here a new test, designed for elderly persons, based on maintaining maximal voluntary grip strength as long as possible. The aim of the study was to determine the reliability of this test procedure in hospitalized geriatric patients and in young healthy persons. Fatigue resistance was considered as the time in which grip strength decreases to 50% of its maximum value. Twenty geriatric, hospitalized patients (age 83 +/- 6 yrs) and thirty-nine young, healthy persons (age 23 +/- 4 yrs) were evaluated for fatigue resistance by two different observers. Height, weight and body mass index were determined for each participant and the current amount of sports activity was recorded in the young subjects. All participants were able to perform the test. Inter- and intra-rater reliability in both subgroups was good to excellent, with ICC(3,1) values ranging from 0.77 to 0.94. No significant differences in inter- and intra-rater measurements were found, except for inter-observer evaluations of the dominant hand in hospitalized geriatric patients. No significant relationships were found between fatigue resistance and maximal grip strength, anthropometrics or gender. The proposed fatigue resistance test is a reliable tool to evaluate geriatric hospitalized patients as well as young, active and healthy persons. Fatigue resistance scores are not related to gender, maximal strength or anthropometrics within the observed subgroups.

Force tracking system for the assessment of grip force control in patients with neuromuscular diseases

Background. The majority of hand functionality assessment methods consist of the maximal voluntary grip force measurement. Additional knowledge on sensory-motor control can be obtained by capturing functional grip force in a time frame. Tracking methods have been successfully used for the assessment of grip force control in stroke patients and patients with Parkinson’s disease. Methods. A novel tracking system for the evaluation of grip force control is presented. The system consists of a grip-measuring device with the end-objects of different shapes which was used as input to a tracking task where the patient applied the grip force according to the visual feedback. The grip force control was assessed in 20 patients with neuromuscular diseases and 9 healthy subjects. The performance of two tracking tasks was analysed in five grips. The ramp-tracking task was designed to assess the grip strength and muscle fatigue. The sinus-tracking task was used to evaluate grip force control during periodic muscle activation. Findings. The results suggest that in some patients the disease did not affect their grip force control despite evident muscular weakness. Most patients produced larger tracking errors in precision grip while the healthy subjects showed less significant differences in performance among the grips tested. Interpretation. The current study investigated force control in patients with neuromuscular diseases where detection of small changes in motor performance is important when following the progress of disease. The presented evaluation method can provide additional information on muscle activation and fatigue as compared to traditional grip strength testing.