Distribution of mechanical impedance at the fingers and the palm of the human hand

A comprehensive understanding of the complex biodynamic response of the human fingers-hand-arm system may help researchers determine the causation of injuries arising from hand-transmitted vibration. This study theoretically demonstrates that the mechanical impedance (MI) in a hand power grip, as a measure of the biodynamic response of the system, can be divided into finger MI and palm MI. A methodology is developed to measure them separately and to investigate their distribution characteristics. This study involves 6 adult male subjects, constant-velocity sinusoidal excitations at 10 different discrete frequencies (16, 25, 40, 63, 100, 160, 250, 400, 630, 1000 Hz), and three different hand-handle coupling conditions. Our results suggest that at low frequencies (40 Hz), the palm MI is substantially higher than the finger MI; the majority of the hand MI remains distributed at the palm up to 100 Hz; and at frequencies higher than 160 Hz, the finger MI is comparable to or higher than the palm MI. Furthermore, at frequencies equal to or above 100 Hz, the finger MI is practically independent of the palm-handle coupling conditions. Knowledge of the MI distribution pattern may increase the understanding of vibration transmission to the hand and aid in the development of effective isolation devices.     

Estimation of vibration power absorption density in human fingers

The absorption of hand-transmitted vibration energy may be an etiological factor in vibration-induced disorders. The vibration power absorption density (VPAD) may be a better measure of energy than the total power absorption of the hand-arm system. The objectives of the present study are to develop a method to estimate the average absorption density in the fingers and to investigate its basic characteristics. Ten healthy male subjects were used in this study. The biodynamic response of the fingers in a power grip subjected to a broad-band random excitation was measured under three grip forces (15, 30, 50 N) and three push forces (35, 45, 50 N). The response was used to estimate the total finger energy absorption. The response, together with the finger volume, was also used to estimate the amount of tissue effectively involved in the absorption. Then, the average VPAD under constant-acceleration, constant-power density, constant-velocity vibration spectra, and 20 tool vibration spectra were calculated. The correlations between the VPAD and the unweighted and weighted accelerations (ISO 5349-1, 2001) were also examined. The VPAD depends on both the characteristics of the vibration spectrum and the biodynamic response of the finger-hand-arm system. The biodynamic response generally plays a more important role in determining the VPAD in the middle frequency range (31.5-400 Hz) than those at the low and high ends. The applied force significantly affected the VPAD. The finger VPAD was highly correlated to the unweighted acceleration. The average VPAD can be determined using the proposed experimental method. It can serve as an alternative tool to quantify the severity of the vibration exposure for studying vibration-induced finger disorders.     

Independent responses of Pacinian and Non-Pacinian systems with hand-transmitted vibration detected from masked thresholds

This study was designed to identify psychophysical channels responsible for the detection of hand-transmitted vibration. Perception thresholds for vibration (16, 31.5, 63 and 125?Hz sinusoidal for 600?ms) at the distal phalanx of the middle finger and the whole hand were determined with and without simultaneous masking stimuli (1/3 octave bandwidth Gaussian random vibration centered on either 16?Hz or 125?Hz for 3000?ms, varying in magnitude 0 to 30?dB above threshold). At all frequencies from 16 to 125?Hz, absolute thresholds for the hand were significantly lower than those for the finger. Changes in threshold as a function of masker level were used to estimate the thresholds of three psychophysical channels (i.e. P, NP I, and NP II channels). Increased vibrotactile sensitivity of the hand compared to the finger seems to be not entirely due to increased spatial summation via the Pacinian system (P channel); non-Pacinian system (NP I and NP II channels) also contributed to perception. Differing transmission of vibration between the hand and the finger may have also influenced the thresholds.     

Independent responses of Pacinian and Non-Pacinian systems with hand-transmitted vibration detected from masked thresholds

This study was designed to identify psychophysical channels responsible for the detection of hand-transmitted vibration. Perception thresholds for vibration (16, 31.5, 63 and 125 Hz sinusoidal for 600 ms) at the distal phalanx of the middle finger and the whole hand were determined with and without simultaneous masking stimuli (1/3 octave bandwidth Gaussian random vibration centered on either 16 Hz or 125 Hz for 3000 ms, varying in magnitude 0 to 30 dB above threshold). At all frequencies from 16 to 125 Hz, absolute thresholds for the hand were significantly lower than those for the finger. Changes in threshold as a function of masker level were used to estimate the thresholds of three psychophysical channels (i.e. P, NP I, and NP II channels). Increased vibrotactile sensitivity of the hand compared to the finger seems to be not entirely due to increased spatial summation via the Pacinian system (P channel); non-Pacinian system (NP I and NP II channels) also contributed to perception. Differing transmission of vibration between the hand and the finger may have also influenced the thresholds.     

Frequency weighting derived from power absorption of fingers-hand-arm system under z(h)-axis vibration

The objectives of this study are to derive the frequency weighting from three vibration power absorption (VPA) methods (finger VPA, palm VPA, and total or hand VPA), and to explore whether these energy methods are better than the currently accepted acceleration method. To calculate the VPA weightings, the mechanical impedance of eight subjects exposed to a broadband random vibration spectrum in the z(h)-axis using 18 combinations of hand couplings and applied forces was measured. The VPA weightings were compared with the frequency weighting specified in ISO 5349-1 [2001. Mechanical Vibration--Measurement and Evaluation of Human Exposure to Hand--Transmitted Vibration--Part 1: General Requirements. International Organization for Standardization, Geneva, Switzerland]. This study found that the hand and palm VPA weightings are very similar to the ISO weighting but the finger VPA weighting for the combined grip and push action is much higher than the ISO weighting at frequencies higher than 25 Hz. Therefore, this study predicted that the total power absorption of the entire hand-arm system is likely to be correlated with psychophysical response or subjective sensation. However, if the ISO weighting method cannot yield good predictions of the vibration-induced disorders in the fingers and hand, the hand and palm energy methods are unlikely to yield significantly better predictions. The finger VPA is a vibration measure between unweighted and ISO weighted accelerations. The palm VPA method may have some value for studying the disorders in the wrist-arm system.     

Thresholds for the perception of hand-transmitted vibration: dependence on contact area and contact location

The detection of vibration applied to the glabrous skin of the hand varies with contact conditions. Three experiments have been conducted to relate variations in the perception of hand-transmitted vibration to previously reported properties of tactile channels. The effects of a surround around the area of contact, the size of the area of contact, the location of the area of contact, the contact force, and the hand posture on perception of thresholds were determined for 8-500 Hz vibration. Removal of a surround around a contact area on the fingertip elevated thresholds of the NP II channel (FA I fibres) at frequencies less than 31.5 Hz and reduced thresholds of the Pacinian channel (FA II fibres) at frequencies greater than about 63 Hz. When no surround was present, thresholds reduced systematically as the contact area increased from the fingertip to the whole hand at frequencies from 16 to 125 Hz, although the decrease was not inversely proportional to the increase in contact area. The results are partly explained by spatial summation in the Pacinian channel (FA II fibres) and the involvement of the NP II channel (SA II) with some influence of biodynamic responses and contact pressures. There were regional differences in sensitivity over the hand within the NP I channel but not within the Pacinian channel: the NP I thresholds (less than 31.5 Hz) decreased from proximal to distal regions of the hand, whereas the Pacinian thresholds (125 Hz) were independent of contact location over the hand.     

Study of Biomechanical Response of Human Hand-Arm to Random Vibrations of Steering Wheel of Tractor

This paper reports a study on the biomechanical response of a human hand-arm model to random vibrations of the steering wheel of a tractor. An anatomically accurate bone-only hand-arm model from TurboSquidTM was used to obtain a finite element (FE) model to understand the Hand-arm vibration syndrome (HAVS), which is a neurological and vascular disorder caused by exposure of the human hand-arm to prolonged vibrations. Modal analysis has been done to find out the first few natural frequencies and mode shapes of the system. Coupling of degrees of freedom (DOF) had to be done in the FE idealization to do modal analysis, as the bones were not attached to each other in the TurboSquidTM model. The shoulder bone, scapula, has been constrained at one end for eigenvalue analysis. It was observed that the first five natural frequencies were in the range of 0-250 Hz, which is the range in which the effect of HAVS is the highest. Harmonic analysis was done by giving a swept sine excitation in the frequency range 0 to 200 Hz. For this, a force input of 25 N was imparted at nodes perpendicular to the hand, the force value chosen being the nominal force in most applications involving powered hand-held tools and steering wheels of tractors. The nodes chosen for force application were determined experimentally from observations made by gripping the steering wheel. The frequency response function (FRF) plots were obtained in the x, y and z directions. Random vibration analysis was done next by giving force power spectral densities (PSD) in the form of nodal excitation as input to the FE model of hand-arm, and computing the output acceleration PSDs. The input force PSDs were measured using FlexiForce® sensors along the three axes. The acceleration responses at the steering wheel were also measured using tri-axial accelerometers for validating the computed results. The output acceleration PSDs were then weighted using the frequency weighting curves for hand-arm vibration and the total daily exposure A(8), computed using ISO 5349-1 standards, was compared with the vibration action and limit values. The A(8) values obtained are found to be higher than the vibration limit values.     

Effect of Tendon Vibration on Hemiparetic Arm Stability in Unstable Workspaces

Sensory stimulation of wrist musculature can enhance stability in the proximal arm and may be a useful therapy aimed at improving arm control post-stroke. Specifically, our prior research indicates tendon vibration can enhance stability during point-to-point arm movements and in tracking tasks. The goal of the present study was to investigate the influence of forearm tendon vibration on endpoint stability, measured at the hand, immediately following forward arm movements in an unstable environment. Both proximal and distal workspaces were tested. Ten hemiparetic stroke subjects and 5 healthy controls made forward arm movements while grasping the handle of a two-joint robotic arm. At the end of each movement, the robot applied destabilizing forces. During some trials, 70 Hz vibration was applied to the forearm flexor muscle tendons. 70 Hz was used as the stimulus frequency as it lies within the range of optimal frequencies that activate the muscle spindles at the highest response rate. Endpoint position, velocity, muscle activity and grip force data were compared before, during and after vibration. Stability at the endpoint was quantified as the magnitude of oscillation about the target position, calculated from the power of the tangential velocity data. Prior to vibration, subjects produced unstable, oscillating hand movements about the target location due to the applied force field. Stability increased during vibration, as evidenced by decreased oscillation in hand tangential velocity.     

Applying support vector regression analysis on grip force level-related corticomuscular coherence

Voluntary motor performance is the result of cortical commands driving muscle actions. Corticomuscular coherence can be used to examine the functional coupling or communication between human brain and muscles. To investigate the effects of grip force level on corticomuscular coherence in an accessory muscle, this study proposed an expanded support vector regression (ESVR) algorithm to quantify the coherence between electroencephalogram (EEG) from sensorimotor cortex and surface electromyogram (EMG) from brachioradialis in upper limb. A measure called coherence proportion was introduced to compare the corticomuscular coherence in the alpha (7–15Hz), beta (15–30Hz) and gamma (30–45Hz) band at 25 % maximum grip force (MGF) and 75 % MGF. Results show that ESVR could reduce the influence of deflected signals and summarize the overall behavior of multiple coherence curves. Coherence proportion is more sensitive to grip force level than coherence area. The significantly higher corticomuscular coherence occurred in the alpha (p?p?p?相似文献   

Muscular forearm activation in hand-grip tasks with superimposition of mechanical vibrations

The purpose of this paper is to evaluate the muscular activation of the forearm, with or without vibration stimuli at different frequencies while performing a grip tasks of 45 s at various level of exerted force. In 16 individuals, 9 females and 7 males, the surface electromyogram (EMG) of extensor carpi radialis longus and the flexor carpi ulnari muscles were assessed. At a short latency from onset EMG, RMS and the level of MU synchronization were assessed to evaluate the muscular adaptations. Whilst a trend of decay of EMG Median frequency (MDF_d) was employed as an index of muscular fatigue. Muscular tasks consists of the grip of an instrumented handle at a force level of 20%, 30%, 40%, 60% of the maximum voluntary force. Vibration was supplied by a shaker to the hand in mono-frequential waves at 20, 30, 33 and 40 Hz. In relation to EMG, RMS and MU synchronization, the muscular activation does not seem to change with the superimposition of the mechanical vibrations, on the contrary a lower MDF_d was observed at 33 Hz than in absence of vibration. This suggests an early muscular fatigue induced by vibration due to the fact that 33 Hz is a resonance frequency for the hand-arm system.     

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

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

Experimental studies on the effects of vibration and noise on sympathetic nerve activity in skin

Multi-unit sympathetic activity was recorded at elbow level from median nerve fascicles supplying glabrous skin of the left hand in five healthy subjects. The resultant vasomotor responses accompanying the neural activity were monitored by simultaneous recordings of skin blood flow using the laser doppler method and skin temperature in the innervation zones. No significant change in sympathetic activity was observed during handgrip exercise of the right hand under a constant gripping force of 2 kg. Subjects maintained the same gripping force of the right hand during exposure in random order to local vibration and/or noise, each type of exposure lasting 5 min with intervals of 20 min. A two-peaked significant increase in outflow from sympathetic nerves was observed during local exposure of the right hand to vibration with a frequency of 60 Hz and an acceleration of 50 m.s-2, followed by a postexposure period which revealed a relative suppression of sympathetic nerve activity and a significant increase in blood flow. Noise at 100 dB(A) showed only an initial effect on skin sympathetic nerve activity (SSA), whereas when combined with local vibration at 60 Hz, a pronounced increase in neural activity was noticed, indicating a combined effect of vibration and noise. These results from direct recordings of SSA suggest a sympathetic vasomotor reflex mechanism triggered by local vibration stimuli to the hand.     

Effects of acute upper-body vibration on strength and power variables in climbers

Whole-body vibration training has recently received a lot of attention with reported enhancements of strength and power qualities in athletes. This study investigated whether upper-body vibration would be able to augment muscular attributes for climbing performance. Twelve healthy active climbers volunteered for the study. All participants underwent 3 treatments--arm cranking (AC), upper-body vibration (UBV), and non-UBV (NUBV)--in a balanced random order, conducted on separate days. Upper-body vibration was generated via a commercialized electric-powered dumbbell with a rotating axis that delivered oscillatory movements to the shoulders and arms. The UBV treatment consisted of performing 5 upper-body exercises for a total duration of 5 minutes. The UBV frequency was set at 26 Hz, amplitude 3 mm. For the NUBV treatment, the participants performed the exact exercises and time constraints as UBV; however, the vibration dumbbell was set at 0 Hz and 0 mm amplitude. The third treatment consisted of AC, which was performed at 75 k.min(-1) for 5 minutes. Pre- and postmuscular performance measures of medicine ball throw, hand grip strength, and a specific climbing maneuver were performed after each treatment. There were no significant treatment differences on medicine ball throw, hand grip strength, and the specific climbing maneuver. Acute UBV exposure did not demonstrate the expected potential neuromuscular enhancements on the climbing performance tests selected for this study.     

Reductions in finger blood flow in men and women induced by 125-Hz vibration: association with vibration perception thresholds

Vibration of one hand reduces blood flow in the exposed hand and in the contralateral hand not exposed to vibration, but the mechanisms involved are not understood. This study investigated whether vibration-induced reductions in finger blood flow are associated with vibrotactile perception thresholds mediated by the Pacinian channel and considered sex differences in both vibration thresholds and vibration-induced changes in digital circulation. With force and vibration applied to the thenar eminence of the right hand, finger blood flow and finger skin temperature were measured in the middle fingers of both hands at 30-s intervals during seven successive 4-min periods: 1) pre-exposure with no force or vibration, 2) pre-exposure with force, 3) vibration 1, 4) rest with force, 5) vibration 2, 6) postexposure with force, and 7) recovery with no force or vibration. A 2-N force was applied during periods 2-6 and 125-Hz vibration at 0.5 and 1.5 ms(-2) root mean square (r.m.s.; unweighted) was applied during periods 3 and 5, respectively. Vibrotactile thresholds were measured at the thenar eminence of right hand using the same force, contact conditions, and vibration frequency. When the vibration magnitude was greater than individual vibration thresholds, changes in finger blood flow were correlated with thresholds (with both 0.5 and 1.5 ms(-2) r.m.s. vibration): subjects with lower thresholds showed greater reductions in finger blood flow. Women had lower vibrotactile thresholds and showed greater vibration-induced reductions in finger blood flow. It is concluded that mechanoreceptors responsible for mediating vibration perception are involved in the vascular response to vibration.     

Neuromuscular fatigue during maximal concurrent hand grip and elbow flexion or extension.

The objective was to investigate muscle fatigue measuring changes in force output and force tremor and electromyographic activity (EMG) during two sustained maximal isometric contractions for 60s: (1) concurrent hand grip and elbow flexion (HG and EF); or (2) hand grip and elbow extension (HG and EE). Each force tremor amplitude was decomposed into four frequency bands (1-3, 4-10, 11-20, and 21-50Hz). Surface EMGs were recorded from the flexor digitorum superficialis (FDS), extensor digitorum (ED), biceps brachii (BB) and lateral head of triceps brachii (TB). The HG and EF forces for the HG and EF and the HG force for the HG and EE declined rapidly, whereas the EE force remained almost constant near to the initial value for the first 40s and then declined. The decrease in EMG amplitude was observed not for the FDS muscle but for the ED muscle. The HG tremor amplitude for each frequency band showed similar decreasing rate, whereas the decreases in EF and EE tremor amplitudes for the lower band (below 10Hz) were slower than those for the higher band (above 11Hz). The neuromuscular mechanisms underlying muscle fatigue during sustained maximal concurrent contractions of hand grip and elbow flexion or extension are discussed.     

Tetanic force development of adductor pollicis muscle in anesthetized man.

The tetanic force development of the human adductor pollicis muscle was studied under light anesthesia with nitrous oxide, oxygen, and Demerol, by the use of tetanic stimulation of the ulnar nerve at frequencies ranging from 10 to 100 Hz. The time necessary for the tetanic contraction to reach a plateau was longest at frequencies between 15 and 20 Hz. Fusion of tetanus occurred between 40 and 45 Hz. The mean maximal force of 6.92 kg was developed at a mean frequency of approximately 75 Hz. The maximal force was well maintained up to a stimulation frequency of 100 Hz. The results indicate that in lightly anesthetized man, the maximal force is developed at higher stimulation frequencies than those observed in conscious man and that it is well sustained at higher frequencies.     

Apparent mass of the standing human body when using a whole-body vibration training machine: Effect of knee angle and input frequency

Several studies have investigated the transmission of vibration from the vibrating plate of a whole-body vibration training machine (WBVTM) to different locations on the human body. No known work has investigated the interface force between the vibrating plate of the machine and the human body. This paper investigates the effect of bending the knees and the vibration frequency on the interface force (presented as apparent mass (AM)) between the vibrating plate and the body. Twelve male subjects stood with four different knee angles (180, 165, 150 and 135°) and were exposed to sinusoidal vertical vibration at eight frequencies in the range of 17–42 Hz. The vertical acceleration and the interface force between the body and the vibrating plate were measured and used to calculate the AM. The acceleration and force depended on the frequency and were found to vary with both the adopted posture and subject. The AM generally decreased with increasing the frequency but showed a peak at 24 Hz which was clearer when the knees were bent. Bending the knees showed an effect similar to increasing the damping of a system with base excitation; increasing the damping reduced the AM in the resonance region but increased the AM at higher frequencies. Users of WBVTMs have to be careful when choosing the training posture: although, as shown in previous studies, bending the knees reduces the transmission of vibration to the spine, it increases the interface forces which might indicate increased stresses on the lower legs and joints.     

Increased Force Variability in Chronic Stroke: Contributions of Force Modulation below 1 Hz

Increased force variability constitutes a hallmark of arm disabilities following stroke. Force variability is related to the modulation of force below 1 Hz in healthy young and older adults. However, whether the increased force variability observed post stroke is related to the modulation of force below 1 Hz remains unknown. Thus, the purpose of this study was to compare force modulation below 1 Hz in chronic stroke and age-matched healthy individuals. Both stroke and control individuals (N = 26) performed an isometric grip task to submaximal force levels. Coefficient of variation quantified force variability, and power spectrum density of force quantified force modulation below 1 Hz with a high resolution (0.07 Hz). Analyses indicated that force variability was greater for the stroke group compared with to healthy controls and for the paretic hand compared with the non-paretic hand. Force modulation below 1 Hz differentiated the stroke individuals and healthy controls, as well as the paretic and non-paretic hands. Specifically, stroke individuals (paretic hand) exhibited greater power ∼0.2 Hz (0.07–0.35 Hz) and lesser power ∼0.6 Hz (0.49–0.77 Hz) compared to healthy controls (non-dominant hand). Similarly, the paretic hand exhibited greater power ∼0.2 Hz, and lesser power ∼0.6 Hz than the non-paretic hand. Moreover, variability of force was strongly predicted from the modulation of specific frequencies below 1 Hz (R ² = 0.80). Together, these findings indicate that the modulation of force below 1 Hz provides significant insight into changes in motor control after stroke.     

An improved biomechanical model for simulating the strain of the hand-arm system under vibration stress

In order to define relationships between the vibration stress and the strain of the human hand-arm system a biomechanical model was developed. The four masses of the model representing the hand, the forearm and the upper arm were connected by dampers and springs in two perpendicular directions. Simulating muscle activity, damped torsion springs were included additionally. The motions of the model were described by a differential matrix equation which was solved by using a ‘transfer matrix routine’ as well as by numerical integration. Thus, functions with harmonic or transient time courses could be selected as an excitation. The simulated vibrations were compared with those of other hand-arm models. The forces and torques transmitted between the masses, and the energy dissipated by the dampers were computed for several combinations of exciter frequencies and accelerations. The dependence of torques upon excitation agreed fairly well with the behaviour of the arm muscles under vibration as described by various investigators. At frequencies above 100 Hz the energy was dissipated mainly by the dampers between the masses near to the exciter. Transferring this result to the hand-arm system it shows that at high frequencies energy is dissipated by the hand and its palmar tissues and this might be one cause for the incidence of vibration-induced white finger disease.     

Effects of vibration on arm and shoulder muscles in three body postures

The electromyographic responses of arm and shoulder muscles to vibrations were studied in three postures similar to the postures of drilling in a ceiling, drilling in a wall and drilling in a floor. This experiment was performed within the defined parameters of: vibrational frequency at 30 Hz, acceleration level 40 m.s-2 (rms), pushing force expressed as percentage maximal voluntary contraction, and gripping force which was set at 100 N. The exposure time for each test was 5 min. The general findings from these three body postures show that all the examined muscles were affected by exposure to vibration. The EMG index increased as follows: trapezius muscle 39% (p less than 0.05), lower-arm flexor muscles 23% (p less than 0.05), infraspinatus muscle 14% (p less than 0.05), lower-arm extensor muscles 14% (p less than 0.1) and biceps muscle 6% (p less than 0.1). The muscle most affected by vibration was found to be the trapezius muscle. It should be taken into consideration that vibration can be a contributing factor in neck/shoulder disorders among power handtool operators. The general conclusion from this study is that changes in working posture give different transmissions of vibration in the upper extremities. It seems as if the prime movers and muscles with an increased muscle length or increased degree of contraction are most affected by vibration.