ABSTRACT
In the present research study 4 shoulder muscles-the supraspinatus, infraspinatus, the middle deltoid and the upper part of the trapezius-were assessed for muscle thickness using real time ultrasonography (RUSI) in various degrees of abducted and flexed arm positions, in 30 patients with acute and sub-acute shoulder pain and 30 asymptomatic healthy subjects (N=60). The symptomatic and asymptomatic subjects were further subdivided according to affection of dominant (n=15) and non-dominant (n=15) shoulder joint. Muscle thickness (mm) was measured using real time ultrasonography of dominant and non-dominant shoulder in different range of movement of shoulder abduction and flexion in symptomatic patients and asymptomatic subjects with and without gripping action on the dynamometer. The subjects were asked to produce a static handgrip force of in 8 different arm positions. In all positions, the subjects held a dynamometer in the hand. The activity in the shoulder muscles was assessed using RUSI while the participating subjects produced a handgrip with maximal force. Muscle thickness and changes with activity was similar in symptomatic and asymptomatic individuals. Muscle activity increased in the middle deltoid muscle in humeral flexion and abduction from 0 0 through 800, whereas supraspinatus and lower trapezius showed increased muscle thickness only in the initial ranges of movement of shoulder flexion, whereas, infraspinatus did not show exhibit any significant change. Our findings imply that high static hand grip force, particularly in elevated arm positions, increases the load on some shoulder muscles, independent of presence of pain in the shoulder. Handgrip activity is important to evaluate while assessing shoulder load in manual work and in clinical evaluations of patients with shoulder pain. Also, while rehabilitation it would be possible to make use of hand gripping activity and load the shoulder muscles differently and distinctly throughout the ranges of movement of shoulder joint.
ABSTRACT
Objective To study the relationship between handgrip level and characteristics of surface electromyogram(sEMG)signal from forearm muscles.Methods Nine healthy volunteers were asked to do a specific grip test with three force levels of maximum volunteer contraction(MVC),80% MVC and 40% MVC.sEMG signal was recorded from flex digitorum superficial(FDS)and extensor carpi radialis longus(ECRL)simultaneously.The amplitude characteristics of sEMG signal were calculated by the means of root mean square(RMS)and wavelet analysis.Furthermore,to compare the relationship of sEMG and force level between different participants,SPSS was applied to analyze the relative value that was defined as the ratio between sEMG characteristics of MVC condition and that of different grip levels.Results There existed positive correlation between grip level and sEMG activity,stronger grip corresponded the greater sEMG characteristics for every participant,and this correlation revealed significant coherence between different volunteers.Conclusion There is significant correlation between grip force and forearm muscle activities represented as sEMG characteristics.The result suggests that sEMG can be used to predict grip force noninvasively for measuring motor function and assessing the motor function rehabilitation.
ABSTRACT
The effects of the surface friction of a grasped object on the regulation of grip force during holding tasks using a precision grip were investigated. Using a force transducer-equipped grip apparatus, the grip force and load force acting on the object were measured continuously while surface materials (silk, wood, suede and sandpaper) and load weights (0.98N, 1.96N, 2.94N, 4.90N and 9.81N) were varied. From the recorded data, the average static grip force, slip force, safety margin force and static friction coefficient were evaluated.<BR>It was found that both the slip force and safety margin force increased as the slipperiness of the object surface increased. Significant interactions between surface type and weight were observed in the slip force and static friction coefficient. The interaction effect resulted from the fact that the frictional relationships with the fingers changed according to both weight and surface conditions. This was considered due to the viscoelastic nature of finger skin. An increase in the safety margin force with surface slipperiness was considered due to psychological reaction, probably fear of dropping the object. Unexpected changes in surface conditions caused a greater safety margin force than trials without a surface change, which might also have been associated with psychological reaction to uncertainty of the new surface condition. A relatively large inter-subject variation was found in the slip force and safety margin force relative to slippery surfaces.
ABSTRACT
Recent studies reveal that grip forces during the hand-arm vibration are most significant for the genesis of vibration-induced white finger syndrome. Therefore, exerted grip forces and skin temperatures or fingers were regarded as dependent variables in experiments and the effects of grip temperature, noise, pushing force, vibration and the combined effect of vibration and pushing force were studied. The objectives or the present study were, first, to varify and compare the changes of grip force affected by grip temperature, noise, pushing force, vibration and the combined effect of vibration and pushing force and, second, to observe the reaction of finger skin temperature affected by above factors. Forty-six healthy male students(25.07+/-2.85) participated in five systematically permuted trials, which endured 4 minutes each other. Experiments were executed in a special chamber with an air temperature of 21 C. In each experiments, the subjects were exposed to five experiment types: (l) grip force of 25 N only, (2) pushing force of 50 N, (3) acceleration of vibration 7.1m/sec2(z-direction), (4) pink noise or 95 dB(A) and (5) combination of pushing force 50 N and acceleration of vibration 7.1m/sec2. A repeated-measures analysis of variance(ANOVA) was performed on the grip force to test whether it was affected by noise, pushing force, vibration and pushing force. The present results show that vibration was significantly related to the increase of grip force, but the other factors, such as pushing force, noise and grip temperature had no significant influence on the increase of grip force and that the reaction of finger skin temperature were significantly affected by the skin temperature at start of experiment and grip temperature, not grip force and other experimental conditions. Therefore, we suggest that the management for decreasing the grip force is meaningful to prevent the occurrence of Hand-arm vibration syndrome (HAVS).
Subject(s)
Humans , Male , Acceleration , Fingers , Hand Strength , Hand-Arm Vibration Syndrome , Noise , Skin Temperature , Skin , VibrationABSTRACT
A study was conducted to investigate the effects of object weight on the regulation of grip force during holding tasks using a precision grip. In addition, variations in grip force among individuals were examined. Using a force transducer-equipped grip apparatus, grip force, load force and the vertical position of the object were measured continuously while using load weights of 0.98N, 1.96N, and 2.94N under sandpaper grip surface conditions. From the recorded data, peak grip force, average static grip force, slip force, safety margin force (average static grip force-slip force), and time to stabilize the grip force from the peak grip force were evaluated.<BR>It was found that both the slip force and safety margin force increased with object weight. The static friction coefficient, estimated from the slip force and load force, deviated from Amonton's law at a lower load force. The deviation was believed to be due to the influence of the viscoelastic nature of finger skin. An increase in safety margin force with object weight was considered to be related to the psychological reaction to the increased heaviness of the object. Indeed, in trials that included unexpected changes in object weight, the safety margin force was increased, which also seemed to be associated with the psychological reaction to uncertainty about the object's weight. A relatively large inter-subject variation was revealed for both the slip force and safety margin force.