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At least 397 records · Page 22Linked to original sources
PubMed1990

Prolonged muscle vibration reducing motor output in maximal voluntary contractions in man.

1. We observed in a previous study on the human foot dorsiflexor muscles that the fatigue-induced decline in motor output during sustained maximal voluntary contractions (MVCs) was temporarily counteracted during the initial phase of superimposed high-frequency (150 Hz) muscle vibration, whereas prolonged muscle vibration seemed to accentuate the fatigue-induced decline in gross EMG activity and motor unit firing rates. A more extensive investigation of this late effect of muscle vibration on MVCs was performed in the present study. 2. Prolonged periods of superimposed muscle vibration caused a reduction of EMG activity, motor unit firing rates and contraction force in both intermittent and sustained MVCs. This vibration-induced effect had the following main characteristics: (i) it developed slowly during the course of about 1 min of sustained vibration and subsided within 10-20 s after the end of vibration; (ii) it was much more pronounced in some subjects than in others (not age-dependent) and it was accentuated by preceding muscle exercise; (iii) it affected primarily the subject's ability to generate and/or maintain high firing rates in high-threshold motor units. 3. Since the effect developed while vibration at the same time exerted a tonic excitatory influence on the alpha-motoneurone pool (as evidenced by the presence of a tonic vibration reflex) it is argued that the vibration-induced suppression of motor output in MVCs probably does not depend on alpha-motoneurone inhibition, but on a reduced accessibility of these neurones to the voluntary commands. It is suggested that contributing mechanisms might be vibration-induced presynaptic inhibition and/or 'transmitter depletion' in the group Ia excitatory pathways which constitute the afferent link of the gamma-loop.

Adolescent↗
PubMed1995

Dose-response relation for vascular disorders induced by vibration in the fingers of forestry workers.

OBJECTIVES: To study the relation between the prevalence of vascular disorders (white finger) and vibration exposure in a group of 222 forestry workers, of whom 164 (73.9%) had work experience limited to antivibration (AV) chain saws only and 58 (26.1%) had operated both non-AV and AV chain saws. METHODS: The chain saw operators and 195 control workers never exposed to hand transmitted vibration were interviewed with health and workplace assessment questionnaires. The diagnosis of vibration induced white finger (VWF) was made on the basis of subjective symptoms of finger blanching and the results of a cold test with plethysmographic measurement of systolic blood pressure of the finger. Vibration was measured on a representative sample of AV and non-AV chain saws. Daily vibration exposure was assessed as eight hour energy equivalent frequency weighted acceleration (A(8)). A lifetime vibration dose was estimated for each of the forestry workers. RESULTS: The overall prevalence of VWF among the forestry workers was 23.4%. The diagnosis of VWF was made in 13.4% of the forestry workers who handled only AV chain saws and in 51.7% of those who had also operated non-AV chain saws in the past. Raynaud's phenomenon was found in 2.6% of the controls. In the forestry workers, the risk for VWF showed positive increments with each increment of vibration dose, suggesting a monotonic dose-response relation. The responsiveness to cold in the digital arteries of the forestry workers was also found to increase with increasing vibration dose and severity of VWF. The estimated relation between VWF and vibration exposure showed that the expected prevalence of VWF increased almost linearly to either A(8) (with exposure duration unchanged) or the number of years of exposure (with equivalent acceleration unchanged). CONCLUSIONS: In this study of VWF among forestry workers, the estimated dose-response relation showed that if the magnitude of vibration acceleration is doubled, the total duration of exposure should be halved to produce an equivalent effect. On the basis of the assessment of vibration exposure, the estimated risk for VWF in the study population was found to be lower than that predicted by the international standard ISO 5349. These findings suggest a revision of the risk estimates for VWF currently provided by ISO 5349.

Case-Control Studies↗
PubMed1996

Acute effects of vibration on peripheral blood flow in healthy subjects.

OBJECTIVES: The main objective was to study the acute vascular effects in the hands of normal healthy subjects of a complex vibration spectrum similar to that generated by many industrial hand held tools. The effects of repeated bouts of vibrations and alterations in the intensity of vibration were also studied. METHODS: Blood flow was measured by venous occlusion plethysmography with strain gauges. Vibration across a frequency range of 0.4 to > 4000 Hz was generated by a pneumatic chisel and applied to the right hand. Blood flow was measured in both middle fingers, both big toes, or both forearms before, during, and after a two minute period of vibration. Systolic pressure of a finger and heart rate were also measured. RESULTS: Vibration was associated with a significant bilateral reduction in finger and toe blood flow (P < 0.01 and P < 0.03) and a significant increase in heart rate (P < 0.05) but had no effect on forearm blood flow. The finger response was not abolished by repeated bouts of the vibration but was initially most notable during the first minute of vibration. Increasing the intensity of vibration delayed recovery. CONCLUSIONS: Hand vibration causes a generalised increase in sympathetic tone in the heart and extremities. This may be a factor in the development of vasospastic disease in habitual users of hand held industrial vibrating tools.

Adolescent↗
PubMed1997

Diagnostics of hand-arm system disorders in workers who use vibrating tools.

A hand-arm vibration syndrome occurs in some workers who use hand held vibrating tools. It is recognised to consist of white fingers, diffusely distributed finger neuropathy, pain in the arm and hand, and a small excess risk of osteoarthrosis from percussion to the wrist and elbow. Carpal tunnel syndrome is mainly due to ergonomic factors other than vibration, but certain factors related to vibration may contribute to its development. A decrease in muscle power induced by vibration, and excessive hearing deficit have been postulated. The assessment of a disorder suspected of being induced by vibration includes deciding whether there is a disorder and, if so, whether the symptoms can be caused by vibration. To decide whether the symptoms can be caused by vibration epidemiological documentation and pathogenically reasonable theories must exist. A causal diagnosis finally requires and epidemiological decision whether or not the factual exposure has elicited the patient's symptoms. Epidemiological data on the quantitative association between vibration and excessive risks of white fingers and diffusely distributed neuropathy are incomplete. The symptomatic diagnosis of white fingers is still mainly based on anamnestic information. Available laboratory tests are incapable of grading the severity of individual cases. Recording the finger systolic blood pressure during cold provocation is a method of symptomatic diagnosis with reasonable levels of specificity, sensitivity, and predictive value. For diffusely distributed neuropathy these levels are lower than desired. Electrodiagnostic tests for carpal tunnel syndrome have sufficient validity. Proper exposure evaluation must be based on an appreciation of the character of the vibration as well as effective duration and intermittency. If this is not taken into account, the number of hours of exposure and intensity of vibration are likely to be non-commensurable variables, and the simple product of them is a questionable dose measure. Separate models for risk evaluation of vascular and neurological disorders related to work with different tools and processes will have to be established. Ongoing research to obtain further data on exposure-response relations for neurological disturbances begins to yield encouraging results.

Arm↗
PubMed1997

Nerve injury induced by vibration: prevention of the effect of a conditioning lesion by D600, a Ca2+ channel blocker.

OBJECTIVES: Exposing a hind leg of a rat to vibration induces an injury to the sciatic nerve--a so called conditioning lesion. After such injury induced by vibration the regenerative capacity of the nerve is improved and can be detected as an increased axonal outgrowth from a test crush lesion to the same nerve. The purpose was to study whether the effect of a conditioning lesion induced by vibration can be prevented by local treatment with a Ca2+ channel blocker D600. METHODS: D600 (methoxyverapamil) or Ringer's solution was locally applied to the sciatic nerve on one side through a silicone tube connected to a miniosmotic pump, which was implanted subcutaneously. During the same period the hind leg was exposed to vibration (80 Hz; 32 m/s2 root mean squared) for five hours daily for five consecutive days. The other hind leg was not vibrated. After the end of exposure to vibration the sciatic nerves were crushed bilaterally (test crush lesions) and three or six days later the regeneration distances of sensory axons were measured by the pinch reflex test. RESULTS: Nerves in the control animals (without implanted miniosmotic pumps and nerves on to which Ringer's solution was locally applied) that were exposed to vibration showed a significantly increased outgrowth length of sensory axons from the test crush lesion compared with the non-vibrated side. Such an effect of a conditioning lesion from the exposure to vibration was suppressed by local application of D600. CONCLUSIONS: Local administration of a Ca2+ channel blocker D600 can prevent the effect of a conditioning lesion-that is, the nerve injury induced by vibration can be inhibited by D600. This may have implications for the treatment of patients with neuropathy of the hand induced by vibration.

Animals↗
PubMed2004

Dorsal neck muscle vibration induces upward shifts in the endpoints of memory-guided saccades in monkeys.

Producing a movement in response to a sensory stimulus requires knowledge of the body's current configuration, and spindle organs embedded within muscles are a primary source of such kinesthetic information. Here, we sought to develop an animal model of kinesthetic illusions induced by mechanically vibrating muscles as a first step toward a mechanistic understanding of how kinesthesia is integrated into neural plans for action. We elected to examine the effects of mechanical vibration of dorsal neck muscles in head-restrained monkeys performing memory-guided saccades requiring them to look to the remembered location of a flashed target only after an imposed delay. During the delay on one-half of all trials, mechanical vibration (usually 1,500 ms in duration, 200 microm in amplitude, 100 Hz in frequency) was applied to the dorsal aspect on one side of the monkey's neck. We compared the metrics of such vibration saccades to control saccades without vibration during the delay interval. Relative to control saccades, the endpoints of vibration saccades were shifted consistently upward, even though the variability in saccadic endpoints was unaltered. Although the stability of the eye was compromised during the delay interval of vibration trials, as evidenced by an increased incidence of upward drifts and downward microsaccades, vibration saccades displayed different metrics than control saccades, including an upwardly deviated radial direction and increased vertical amplitude. The influence of variations in the duration (500-2,500 ms), amplitude (100-300 microm), or frequency (75-125 Hz) of vibration scaled well with the presumed change in spindle activity entrained by vibration. Comparisons of the profile of these results are made to the human literature. We conclude that neck muscle vibration induces alterations in oculomotor performance in monkeys consistent with a central interpretation of illusory neck flexion and downward gaze deviation due to increased activation in the spindles of neck extensor muscles.

Animals↗
PubMed1991

Effect of imposed head vibration on the stability and waveform of flagellar beating in sea urchin spermatozoa.

The heads of live spermatozoa of the sea urchin Hemicentrotus pulcherrimus were held by suction in the tip of a micropipette mounted on a piezoelectric device and vibrated either laterally or axially with respect to the head axis. Within certain ranges of frequency and amplitude, lateral vibration of the pipette brought about a stable rhythmic beating of the flagella in the plane of vibration, with the beat frequency synchronized to the frequency of vibration [Gibbons et al. (1987), Nature 325, 351-352]. The sperm flagella, with an average natural beat frequency of 48 Hz, showed stable beating synchronized to the pipette vibration over a range of 35-90 Hz when the amplitude of vibration was about 20 microns or greater. Vibration frequencies below this range caused instability of the beat plane, often associated with irregularities in beat frequency. Frequencies above about 90 Hz caused irregular asymmetrical flagellar beating with a marked decrease in amplitude of the propagated bends and a skewing of the flagellar axis towards one side; the flagella often stopped in a cane shape. In flagella that were beating stably under imposed vibration, the wavelength was reduced at higher frequencies and increased at lower frequencies. When the beat frequency was equal to or lower than the natural beat frequency, the apparent time-averaged sliding velocity of axonemal microtubules, obtained as twice the product of frequency and bend angle, decreased with beat frequency in both the proximal and distal regions of the flagella. However, at vibration frequencies above the natural beat frequency, the sliding velocity increased with frequency only in the proximal region of the flagellum and remained essentially unchanged in more distal regions. This apparent limit to the velocity of sliding in the distal region may represent an inherent limit in the intrinsic velocity of active sliding, while the faster sliding observed in the proximal region may be a result of passive sliding or elastic distortion of the microtubules induced by the additional energy supplied by the vibrating pipette. Axial vibration with frequencies either close to or twice the natural beat frequency induced cyclic changes in the waveform, compressing and expanding the bends in the proximal region, but did not affect bends in the distal region or alter the beat frequency.

Animals↗
PubMed2003

Electromyography activity of vastus lateralis muscle during whole-body vibrations of different frequencies.

The aim of this study was to analyze electromyography (EMG) responses of vastus lateralis muscle to different whole-body vibration frequencies. For this purpose, 16 professional women volleyball players (age, 23.9 +/- 3.6 years; height, 182.5 +/- 11.1 cm; weight, 78.4 +/- 5.6 kg) voluntarily participated in the study. Vibration treatment was administered while standing on a vibrating platform with knees bent at 100 degrees (Nemes Bosco-system, Rome, Italy). EMG root mean square (rms) and was recorded for 60 seconds while standing on the vibrating plate in the following conditions: no vibrations and 30-, 40-, and 50-Hz vibration frequencies in random order. The position was kept for 60 seconds in each treatment condition. EMGrms was collected from the vastus lateralis muscle of the dominant leg. Statistical analysis showed that, in all vibration conditions, average EMGrms activity of vastus lateralis was higher than in the no-vibration condition. The highest EMGrms was found at 30 Hz, suggesting this frequency as the one eliciting the highest reflex response in vastus lateralis muscle during whole-body vibrations in half-squat position. An extension of these studies to a larger population appears worthwhile to further elucidate the responsiveness of the neuromuscular system to whole-body vibrations administered through vibrating platforms and to be able to develop individual treatment protocols.

Adult↗
PubMed2003

Physiological and functional effects of acute low-frequency hand-arm vibration.

The effects of low frequency of vibration have not been widely studied in the scientific literature, yet humans are exposed to such environmental stress everyday. The purpose of this investigation was to examine the physiological responses to low-frequency upper-body limb vibration. Fourteen healthy men were exposed to 1 hour of bilateral hand-arm vibration and control (no vibration) conditions in a counter-balanced, cross-over design separated by 2 days. Subjects gripped handles that were coupled to a vibrating device, which oscillated in an anterior to posterior direction at a constant frequency of 7.5 Hz and a displacement of 0.38 cm. A series of tests were performed prior to and following the vibration to assess cardiovascular response, visual acuity, tremor of the hand and fingers, grip strength, anticipation response, limb girths, and a movement repositioning task. There were significantly (p < or = 0.05) more visual errors postvibration compared with postcontrol on a standardized vision chart. Tremor was significantly reduced during the vibration compared with the control condition. There were no significant changes in grip strength. Mean anticipation response time was significantly increased during the control condition (+3.3%) but not after vibration (+1.0%). There was a significant improvement in the movement repositioning task after vibration compared with control. Heart rates during the vibration protocol were not significantly higher than the control condition. No significant increases in limb size representative of swelling were observed. These data indicate that exposure to 1 hour of low-frequency hand-arm vibration has only minor effects on physiological function.

Adult↗
PubMed1985

[The response of monoamines in the rat brain to local vibration exposure].

An experimental study was performed to investigate the effects of local vibration on the brain monoamines of rats. The rats' hind limbs were exposed to vertical sinusoidal vibration at frequencies of 20-960 Hz under constant acceleration of 50 m/S2 for 240 min. Rats were decapitated immediately after the exposure, the brains were quickly removed from the cranium and blood was collected in a heparinized beaker. The brain was divided into seven regions on an ice plate, and the changes of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in the whole brain or regional brains were examined. Furthermore, to investigate the mechanism of the appearance of peripheral effects induced by local vibration, the response of plasma dopamine-beta-hydroxylase (DBH) activity was observed with and without pretreatment by 6-hydroxydopamine (6-OHDA), known as a drug for chemical sympathectomy. The amines were determined by fluorometry and DBH activity was by radioimmunoassay. The results obtained were as follows: NE level in the whole brain showed a tendency to decrease compared with the controls at a frequency of 120 Hz and an acceleration of 50 m/S2. Levels of DA and 5-HT in the whole brain showed no particular changes at any frequencies used in the present study. In the study of regional brains, NE showed a tendency to decrease at a frequency of 60 Hz and a significant decrease at a frequency of 120 Hz in the hypothalamus. In the hippocampus, NE showed significant decreases at frequencies of 60 Hz, 120 Hz and 240 Hz, especially at 120 Hz. DA showed a tendency to decrease in the striatum at a frequency of 20 Hz and a significant increase at a frequency of 60 Hz in the medulla oblongata and pons. 5-HT showed a significant increase in the hypothalamus at frequencies of 20 Hz and 120 Hz. The changes in brain amines induced by local vibration were compared with those by whole body vibration. By exposure to local vibration at a frequency of 20 Hz and acceleration of 50 m/S2, the amines in the whole brain were not meaningfully affected, whereas in whole body vibration at the same frequency and acceleration significant effects were observed. NE level was decreased significantly to 57% of that of the control in whole body vibration (20 Hz, 50 m/S2) and showed a tendency to decrease to 79% of that of the control in local vibration (120 Hz, 50 m/S2). Thus the effect of whole body vibration was much greater than that by local vibration.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Influence of vibration on work performance during ergometer cycling.

With a view to investigating how vibration affects dynamic working capacity, exercise tests were performed both with and without superimposed vibration. The performance of 8 healthy, non-smoking 20-year-old males exercising on a cycle ergometer at a constant load was studied on four occasions, with and without vibration in a randomly chosen order. The frequency of the vibration, which was applied vertically through the pedals, was 20 Hz and the acceleration was 20 m/s2 RMS. The handlebars and saddle of the cycle were insulated from the vibration. The exercise time averaged 47 min with vibration and 60 min without. The vibratory stress reduced the exercise time by 13 +/- 2.9 min (mean +/- SEM) (P less than 0.005). The average heart rate when the exercise was stopped was 180.3 beats/min with vibration and 180.7 beats/min without. The systolic blood pressure after 20 min averaged 188 mm Hg with vibration and 187 mm Hg without vibration. Both with and without vibration, 6 of the 8 subjects stated that leg fatigue was the cause of their inability to continue pedalling longer. Our conclusion is that in the performance of dynamic muscular work endurance may decrease under the influence of vibration.

Adult↗
PubMed1991

[Effects of the perforation of the tympanic membrane on its vibration--with special reference to an experimental study by holographic interferometry].

Using canine temporal bone, perforations were surgically prepared at the anterior, inferior and posterior parts of the tympanic membrane, and the influences of these perforations on the tympanic vibration were observed and analyzed by holographic interferometry. Normal canine tympanic membrane had its respective single maximum amplitude points at its anterior and posterior parts at a frequency from the low compass to 2 kHz or so and showed a concentric circular vibration pattern centering mainly there around. At 3 and 4 kHz or so, the posterior and anterior parts began to show their respective sectional vibrations and with an increase in frequency, showed their further complicated multi-sectional vibrations. Resonance frequency was 1 or 2 kHz or so. The tympanic vibration following the preparation of perforations was as follows: 1) For the posterior perforation, the frequency at which the anterior sectional vibration began passed to a higher frequency, while for the other perforations, no change was noted in vibration pattern of the remaining tympanic membrane. 2) Comparative examination of the vibration amplitude at the mallear tip revealed that for a small perforation, no change in resonance frequency was noted regardless of the location of perforation and an increase in vibration amplitude was noted near the resonance frequency. 3) For the anterior perforation, no change in resonance frequency was noted even with an expansion of perforation and an increase in vibration amplitude was noted near the resonance frequency. 4) For the posterior and inferior perforations, the resonance frequency passed to a higher frequency with an expansion of perforation and an increase in vibration amplitude was noted near the resonance frequency.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1976

Transmission of vibration in the hand-arm system with special reference to changes in compression force and acceleration.

The transmission of longitudinal vibration in the hand-arm system of five subjects was investigated. Altogether 405 individual tests were made. Vibration was measured with an accelerometer (weight 0.4 g) fixed in turn to the wrist, the elbow, and the upper arm by means of a supporting device (weight 34 g). A handle with strain gauges attached was used to study the effect of compression force (10, 20 and 40 N) and constant acceleration (1, 3 and 10 g) on the transmission of vibration at frequencies from 20 to 630 Hz. In the curves recorded, sharp dips appeared which were evidently caused by resonances from the soft tissues of the hand. However in the hand-arm system no common resonance frequency was observed that would harmfully affect the health of workers. Vibration in the hand-arm system was attenuated at an average of 3 dB per octave at the frequencies between 20 and 100 Hz. Between 100 and 630 Hz the attenuation was about 6 dB per octave in the wrist and 10 dB per octave in the elbow and upper arm. At the frequency of 630 Hz the attenuation was hence about 35 dB in the wrist and about 45 DB in the elbow. The attenuation of vibration in the elbow joint was 2 to 4 dB at all frequencies. The hand-arm system appears to be linear at the acceleration range considered; the increase in handle vibration by, e.g., 10 dB also increased vibration in the hand by 10 dB. When the grip strength was increased fourfold, i.e., 12 dB, vibration increased only 3 to 5 dB in the hand-arm system. Thus changing the weight of a vibrating tool does not reduce vibration enough. Therefore attempts to reduce vibration should concentrate on the mechanical parts of the engines.

Acceleration↗
PubMed2001

Human postural responses to different frequency vibrations of lower leg muscles.

We analyzed human postural responses to muscle vibration applied at four different frequencies to lower leg muscles, the lateral gastrocnemius (GA) or tibialis anterior (TA) muscles. The muscle vibrations induced changes in postural orientation characterized by the center of pressure (CoP) on the force platform surface on which the subjects were standing. Unilateral vibratory stimulation of TA induced body leaning forward and in the direction of the stimulated leg. Unilateral vibration of GA muscles induced body tilting backwards and in the opposite direction of the stimulated leg. The time course of postural responses was similar and started within 1 s after the onset of vibration by a gradual body tilt. When a new slope of the body position was reached, oscillations of body alignment occurred. When the vibrations were discontinued, this was followed by rapid recovery of the initial body position. The relationship between the magnitude of the postural response and frequency of vibration differed between TA and GA. While the magnitude of postural responses to TA vibration increased approximately linearly in the 60-100 Hz range of vibration frequency, the magnitude of response to GA vibration increased linearly only at lower frequencies of 40-60 Hz. The direction of body tilt induced by muscle vibration did not depend on the vibration frequency.

Adult↗
PubMedDate not supplied

[Hand-arm vibration syndrome and upper limb disorders associated with forestry work].

BACKGROUND: Occupational exposure to hand-transmitted vibration in forestry workers is associated with an increased risk for vascular, neurological and musculo-skeletal disorders of the upper limbs. OBJECTIVES: To carry out a cross-sectional study of the hand-arm vibration syndrome and soft-tissue disorders of the upper limb in a group of forestry workers employed in the Forestry Service of the Province of Trento (Italy). In the forestry worker group, usage of anti-vibration chain-saws was intermittent over a typical work year (16 weeks/yr, on average). METHODS: To investigate vascular, neurological and musculo-skeletal disorders of the upper limbs, the forestry workers (n=159) and a control group of manual workers, unexposed to hand-transmitted vibration, employed in the same Forestry Service (n=146) underwent a structured medical interview and a complete physical examination. The clinical diagnoses of vibration-induced white finger (VWF) and carpal tunnel syndrome were made according to internationally recognised consensus criteria. Occupational exposure to hand-transmitted vibration was assessed according to the recommendations of the International Standard ISO 5349-1 (2001). RESULTS: The forestry workers showed an increased prevalence of peripheral sensory-neural disturbances (33.3%), musculo-skeletal disorders of the upper limbs (37.7%), and carpal tunnel syndrome (21.4%) compared to those observed in the control group. There was no significant difference in the prevalence ofRaynaud' sphenomenon between the forestry workers (6.3%) and the controls (4.1%). After adjustment for confounding factors (age, body mass index, tobacco and alcohol consumption), a significant association was observed between peripheral neuropathies (peripheral sensory-neural disorders, carpal tunnel syndrome) and several indices of vibration exposure such as 8-hr energy-equivalent frequency-weighted acceleration [A(8) in m/s2 r.m.s.], duration of exposure (years), and lifetime vibration dose (m2/s4 hr). An excess, although not significant, risk for VWF was observed only in the forestry workers with A(8) > or = 4 m/s2 r.m.s.. In the forestry workers, there was no significant association between VWF and sensory-neural disorders, and between VWF and carpal tunnel syndrome. This finding seems to support the hypothesis that the vascular and neurological components of the hand-arm vibration syndrome develop independently of each other. Within the forestry worker group, the variable "years of tool usage" showed the strongest association with peripheral sensory-neural symptoms, carpal tunnel syndrome, and soft-tissue disorders of the upper limbs. It is likely that in the forestry workers the variable "years of tool usage" represents an overall index of duration of exposure to several adverse ergonomic and mechanical risk factors. CONCLUSIONS: The results of this study suggest a tendency for a decrease in the occurrence of VWF among forestry workers, and this finding seems to be associated with the use of anti-vibration chain saws, the reduction of exposure duration, and the improvement of work organization. On the other hand, the forestry workers showed an increase in the occurrence of peripheral sensory neuropathies, carpal tunnel syndrome, and upper-extremity musculo-skeletal disorders. This finding seems to support the view that there is epidemiological evidence for a positive association between exposure to a combination of risk factors (segmental vibration, forcefulness, awkward posture) and the occurrence of soft-tissue disorders of the upper limb in working populations.

Adult↗
PubMed2006

Influence on operator's health of hand-transmitted vibrations from handles of a single-axle tractor.

The operators of the single-axle tractors are especially exposed to hand-arm transmitted vibrations. These vibrations can cause the complex of vascular, neurological and musculoskeletal disorders, collectively named hand-arm vibration syndrome. Among these, the most common disorder is vibration-induced white finger (Raynaud's phenomenon). The vibration levels were measured in three tractor's working conditions, namely idling, transportation and soil tillage. The vibration level on the handles was measured and analysed and the frequency spectra for the chosen working conditions were obtained. The frequency-weighted acceleration, given in m/s2, was calculated and the obtained values are graphically presented. The measured vibration levels are then discussed with regard to the operator's daily exposure limits recommended by the ISO 5349. The vibration levels were much higher in the x and y directions than the z-direction in all working conditions. The vibration total values in idling, transportation and soil tillage were 3.37, 8.37 and 9.62 m/s2, respectively. Results showed that the 10% of workers are exposed to a risk of vibration-induced white finger disorder of the hands after relatively short periods (3-4 years), if the tractor is used 8 hour per day in soil tillage and transportation at full load. Considering the criteria of the ISO 5349, the daily working time with the single-axle tractor should be limited in order to protect the operator and work schedules should be arranged to include vibration-free periods.

Acceleration↗
PubMed1986

[Vibration of neck muscles changes the apparent position of a visual target].

The discharge rate of muscle spindle afferents normally provides a precise signal of muscle length. Vibration of a muscle or its tendon induces an increase in afferent discharge which then no longer represents true muscle length; however, this increased proprioceptive input is interpreted in the central nervous system as a lengthening of the muscle. The incremented signal gives rise to illusions of displacement, or movement, of a fixed, vibrated limb. A visual target attached to such a vibrated limb also appears to move. We now report that vibration of the neck muscles influences visual localisation by inducing illusory movement of targets in visual space. Subjects were seated in a totally dark room and viewed a light-emitting diode (LED). The LED was placed at eye level approximately in the body midline at a distance of 70 cm. They held a physiotherapy vibrator in the left hand with its tip against the left side of the neck. When vibration was initiated the LED appeared to move rightward. The position of the tip of the vibrator was adjusted to produce the maximum apparent displacement to the right. In some subjects the illusion had a vertical component. Subjects maintained the vibrator in position and described the illusion when vibration began, during vibration and at its end. They reported that, initially, the target moved to the right but this displacement ceased after a second or two. The target then appeared to continue in motion without changing its position. When vibration ended the target returned to its initial position.(ABSTRACT TRUNCATED AT 250 WORDS)

Central Nervous System↗
PubMed1982

Discomfort judgements of translational and angular whole-body vibrations.

In a previous series of experiments the subjective intensities of translational (Z-axis) and angular (roll, pitch, and yaw) vibrations were compared, using a psychophysical matching technique. To test the validity and generality of the matching results, an independent set of similar data was obtained in the present experiment, using the method of category production. Seated subjects set levels of translational vibrations, in the X-, Y-, and Z-axes, and angular vibrations, in roll and pitch, that they judged to be "uncomfortable" on a scale of vibration discomfort. Frequencies of 2.5, 3.15, 4.0, 5.0, 6.3, and 8.0 Hz were presented in each vibration direction. As frequency increased the mean acceleration judged to be uncomfortable increased for Y-axis and roll vibrations, decreased for Z-axis vibrations, and was essentially constant for X-axis and pitch vibrations. The Y- and Z-axis results correspond well to equal intensity contours in existing vibration exposure criteria, and the roll results show good agreement with data from the roll matching experiment. The X-axis and pitch results are similar to the results from the pitch matching experiment and indicate the importance of the backrest in determining the effects of X-axis translational vibrations and angular vibrations in pitch.

Acceleration↗