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PubMed2004

Evaluation of selected sidewalk pavement surfaces for vibration experienced by users of manual and powered wheelchairs.

BACKGROUND: Obstacles such as bumps, curb descents, and uneven driving surfaces cause vibrations that affect the wheelchair, and in turn, the wheelchair user. Chronic exposure can cause low-back pain, disk degeneration, and other harmful effects. Little research has been conducted to assess the vibrations experienced by wheelchair users. OBJECTIVE: The purpose of this study was to conduct an evaluation of the vibration exposure during electric-powered wheelchair driving and mechanical energy requirements for manual wheelchair propulsion over selected sidewalk surfaces. The goal was to determine the criteria for a wheelchair-pedestrian access route that does not require excessive propulsive work or expose wheelchair users to potentially harmful vibrations. METHODS: Ten unimpaired individuals participated in this study. Six sidewalk surfaces were tested. Measured variables included power of the acceleration per octave, mechanical work to propel over surfaces, peak acceleration, and frequency at which peak acceleration occurs. RESULTS: For both the manual and electric-powered wheelchair, at 1 m/s, significant differences were found in peak accelerations between the seat and footrest (P < 0.0001) and between the sidewalk surfaces (P = 0.004). The greatest risk for injury caused by shock and vibration exposure occurs at frequencies near the natural frequency of seated humans (4-15 Hz). The values for work required to propel over the surfaces tested were not statistically significantly different. Besides appearance and construction, the only distinguishing characteristic was surface roughness caused by the joints. CONCLUSION: When treating the poured concrete sidewalk as the standard, surfaces 2, 3, 5, and 6 compared most favorably in terms of vibration exposure, whereas surface 4 produced mixed results. Surfaces 2, 3, 5, and 6 yielded results that were similar to the poured concrete sidewalk and could be considered acceptable for wheelchair users. In conclusion, surfaces other than the traditional poured concrete can be used for pedestrian access routes without adding vibration exposure or reducing propulsion efficiency.

Adult↗
PubMed2003

The effect of seat design on vibration comfort.

A field study was done to evaluate different seat designs in the aspect of minimizing vibration transmission and reducing the level of discomfort experienced by drivers subjected to transient vibration. Two seat designs (sliding or fixed in the horizontal direction) were compared in an experiment based on variation of sitting posture, speed, and type of obstacle. The comparison was done by assessing discomfort and perceived motion and by vibration measurement. Ten professional drivers were used as participants. Maximum Transient Vibration Value and Vibration Dose Value were used in the evaluation. The results showed that a sliding seat is superior in attenuating vibration containing transient vibration in the horizontal direction. It was also perceived as giving less overall and low back discomfort compared to a fixed seat.

Automobile Driving↗
PubMed1992

High-frequency vibration in flagellar axonemes with amplitudes reflecting the size of tubulin.

Flagellar axonemes of sea urchin sperm display high-frequency (approximately 300 Hz) vibration with nanometer-scale amplitudes in the presence of ATP (Kamimura, S., and R. Kamiya. 1989. Nature (Lond.). 340:476-478). The vibration appears to represent normal mechanochemical interaction between dynein and microtubules because the dependence of the frequency on MgATP concentration is similar to that of the axonemal motility, and because it is inhibited by micromolar concentrations of vanadate. In this study a two-dimensional photo-sensor was used to characterize this phenomenon in detail. Several new features were revealed. First, the vibration was found to be due to a back-and-forth movement of the doublet microtubules along the axonemal length. Two beads attached to different parts of the same axoneme vibrated in unison, i.e., synchronized exactly in phase. This suggested that the outer doublet can be regarded as a stiff rod in vibrating axonemes. Second, evidence was obtained that the amplitude of the vibration reflected the number of active dynein arms. Third, under certain conditions, the vibration amplitude took stepwise values of 8 x N + 4 nm (N = 0, 1, 2, 3, or 4), indicating that the amplitude of microtubule sliding was limited by the size of tubulin dimer (8 nm) or monomer (4 nm). To explain this phenomenon, a model is presented based on an assumption that the force production by dynein is turned off when dynein is subjected to tensile force; i.e., dynein is assumed to be equipped with a feedback mechanism necessary for oscillation.

Adenosine Triphosphate↗
PubMed2006

Vibration syndrome diagnosis using a cooling test verified by computerized photoplethysmography.

This study addresses the problem of vibration syndrome diagnosis by means of a cooling test verified by photoplethysmography. Measurement was taken on a small area on the fingertip plexus in which many arterio-venous anastomoses are present. In the opinion of many authors, flow disorders in this area are more typical for developing vibration syndrome than changes in the micro vessels. The study group comprised 128 subjects (58 women aged 40.9 +/- 5.4 years and 70 men aged 38.7 +/- 8.8 years) exposed to vibration. The control group consisted of 41 people (20 women aged 39.6 +/- 7.3 years and 21 men aged 39.3 +/- 6.4 years) who were not exposed to vibration. The patients were examined by a questionnaire and then a vibration perception threshold test and a cooling test were performed. The cooling test was verified both visually and using the computer method. Measurement data (S1, S2 and A) for each patient were obtained from averaging three pulse graphs. We departed from an average of 60 graphs (and more), the standard established in the literature, because of the cooling test specification, which causes huge thermodynamic parameter changeability in the plexus mass of the small finger under pulse waves coming one after another. A longer measurement time will reflect the thermal drift of the tested area in a direction to compensate for the reduced temperature. In the control group, all subjects showed an increase in planimetric indicators during the cooling test verified by computerized photoplethysmography. In the study group visual verification of the cooling test was positive in eight cases (6.2%) and the vibration perception threshold test was positive in seven cases (5.5%), but in computerized photoplethysmography the planimetric indicators decreased after cooling in 87 (67.4%) cases. Computer photoplethysmography is highly specific and shows greater sensitivity in detecting preclinical forms of vascular-type vibration syndrome when compared with palesthesiometry, the visually verified cooling test and the questionnaire. The proposed test enables the detection of vascular disorders in the prodromal period and gives time for preventive measures to be taken.

Adult↗
PubMed2003

Effects of adjunctive Swedish massage and vibration therapy on short-term postoperative outcomes: a randomized, controlled trial.

OBJECTIVE: To examine the effects of adjunctive postoperative massage and vibration therapy on short-term postsurgical pain, negative affect, and physiologic stress reactivity. DESIGN: Prospective, randomized controlled trial. The treatment groups were: (1) usual postoperative care (UC); (2) UC plus massage therapy; or (3) UC plus vibration therapy. SETTING: The University of Virginia Hospital Surgical Units, Gynecology-Oncology Clinic, and General Clinical Research Center. SUBJECTS: One hundred and five (N = 105) women who underwent an abdominal laparotomy for removal of suspected cancerous lesions. INTERVENTIONS: All patients received UC with analgesic medication. Additionally, the massage group received standardized 45-minute sessions of gentle Swedish massage on the 3 consecutive evenings after surgery and the vibration group received 20-minute sessions of inaudible vibration therapy (physiotones) on the 3 consecutive evenings after surgery, as well as additional sessions as desired. OUTCOME MEASURES: Sensory pain, affective pain, anxiety, distress, analgesic use, systolic blood pressure, 24-hour urine free cortisol, number of postoperative complications, and days of hospitalization. RESULTS: On the day of surgery, massage was more effective than UC for affective (p = 0.0244) and sensory pain (p = 0.0428), and better than vibration for affective pain (p = 0.0015). On postoperative day 2, massage was more effective than UC for distress (p = 0.0085), and better than vibration for sensory pain (p = 0.0085). Vibration was also more effective than UC for sensory pain (p = 0.0090) and distress (p = .0090). However, after controlling for multiple comparisons and multiple outcomes, no significant differences were found. CONCLUSIONS: Gentle Swedish massage applied postoperatively may have minor effects on short-term sensory pain, affective pain, and distress among women undergoing an abdominal laparotomy for removal of suspected malignant tissues.

Abdomen↗
PubMed1993

The effect of seat suspension on exposure to whole-body vibration of professional drivers.

In this study the effectiveness of the seat suspension on the transmission of whole-body vibration through the driver's seat has been determined. Eleven types of seat frequently used in lorries, agricultural tractors and fork-lift trucks were selected. The transmissibility coefficient of each seat was measured by the ratio of the acceleration (weighted root-mean-square in the vertical axis) at the interface between the seat surface and the human body to the vibration at the attachment points of the seat on the vehicle floor. Measurements in the laboratory, using standardized representative vehicle vibration spectra and two volunteers of different weights, showed transmissibility coefficients of 0.34-1.28. Attenuation of the vibration input spectrum was obtained in 20 out of 24 (83%) measurements. Measurements in the field, conducted in vehicles under representative working conditions, showed transmissibility coefficients of 0.60-1.45. Attenuation of the vibration spectrum was obtained in 17 out of 24 (71%) vehicle-seat combinations. No significant differences were observed between seats with conventional suspension and those with air suspension. Laboratory measurements of the dynamic response of the seat suspension did not provide an adequate basis for predicting its performance in the field. In most work situations the magnitude and duration of vibration-exceeded the 8 h fatigue-decreased proficiency boundary of 0.32 m s-2 in the vertical axis, which indicates that in many working situations with a daily exposure of 8 h or more suspended seats will not protect professional drivers from harmful exposure to whole-body vibration.

Humans↗
PubMed1988

Neck muscle vibration modifies the representation of visual motion and direction in man.

The retinal coordinates of an image are normally insufficient to define the direction of an object in body-centred visual space. Gaze direction, specified by information on the position of eye-in-head and on the position of head-on-torso, is also required. While the source of the eye-in-head signal is controversial, it is clear that proprioceptive signals from neck muscles are sufficient to provide head-on-torso information. Observations by Goodwin et al., beginning in 1972, that vibration of limb muscles modifies proprioception from them, and induces illusory motion and false perception of limb position, suggested this study of the effects of neck muscle vibration on the representation of visual space. Verbal reports, supported by objective measures, revealed that vibration of muscles on one side of the neck induces a visual illusion: contralateral displacement of a small visual target viewed in the dark. Pointing movements towards the target are similarly affected, confirming that the representation of directions in visual space is modified by neck muscle vibration. A second vibration-induced illusion was uncovered when apparent displacement ceased. This is an illusion of pure target motion in the same direction as the previously observed displacement. The magnitudes of both the displacement and pure motion illusions were dependent on vibration amplitude and were unrelated to real or apparent movements of eyes or head. Taken together these observations indicate that vibration of neck muscles can modify independently (1) the central representation of the instantaneous direction of gaze and (2) the signal of the velocity with which this direction is changing.

Adult↗
PubMed1990

Abnormal vibration-induced cerebral blood flow responses in idiopathic dystonia.

Regional cerebral blood flow responses to vibrotactile stimulation were studied in 11 patients with predominantly unilateral idiopathic focal dystonia and 18 normal subjects using PET and H2(15)O. Stimulation produced a consistently localized and robust peak response in primary sensorimotor cortex contralateral to hand vibration in normal subjects (averaged hemisphere response 10.97 ml/(100 g.min) +/- 2.53). The sensorimotor response in dystonic patients was also consistently localized to the same area, but significantly reduced in magnitude whether vibrating the affected (8.35 ml/(100 g.min) +/- 2.29) or unaffected hand (8.40 ml/(100 g.min) +/- 2.15). Furthermore, vibration induced a dystonic cramp in the stimulated arm/hand in 6 patients, but not in any normal subjects. To determine whether the cocontraction of agonist and antagonist muscles could, in itself, attenuate the regional blood flow response, 10 normal subjects were studied with vibration during voluntary cocontraction of appropriate hand and forearm muscles, as well as with vibration alone. Vibration with voluntary cocontraction (mean = 12.57 ml/(100 g.min) +/- 2.13) produced a significantly greater response than vibration alone (mean = 10.30 ml/(100 g.min) +/- 2.20, P less than 0.00008). This abnormal sensorimotor response may have important implications for understanding the pathophysiology of idiopathic dystonia.

Adult↗
PubMed1989

Effect of high-frequency vibration on experimental pain threshold in young women when applied to areas of different size.

The purpose of this study was to compare the effects of high-frequency vibration when applied to two areas of different size. Subjects were 30 right-handed Caucasian women, aged 19-38 years, with a negative history of upper extremity dysfunction. The experimental cutaneous pain threshold was determined by stimulating the skin over the pisiform bone on the palmar surface of the hand. Pain threshold measurements were taken before, during, and 2 and 5 min after vibration. Group A received vibration to an area 12.5 cm2 on the ulnar aspect of the palm of the hand 1 cm distal to the pisiform bone. Group B received vibration to an area 25 cm2, also on the ulnar aspect of the palm of the hand. Results of the mixed design analysis of variance performed on the mean pain thresholds indicate that there was no significant main effect for group (size of area vibrated), p greater than 0.05, or interaction effect between group by trial (size of area vibrated and time of pain threshold measurement), p greater than 0.05. There was a significant main effect for trial (time of pain threshold measurement), p less than 0.001. Pain threshold values were greatest for both groups during the period of vibration.

Adult↗
PubMed1998

Kappa Delta Award. Low back pain and whole body vibration.

The investigators describe their multifaceted approach to the study of the relationship between whole body vibration and low back pain. The epidemiologic study was a two center study of drivers and sedentary workers in the United States and Sweden. The vibration exposure was measured in the vehicles. It was found that the career vibration exposure was related to low back, neck, and shoulder pain. However, disability was related to job satisfaction. In vivo experiments, using percutaneous pin mounted accelerometers have shown that the natural frequency is at 4.5 Hz. The frequency response is affected by posture, seating, and seat back inclination. The response appears to be determined largely by the rocking of the pelvis. Electromyographic studies have shown that muscle fatigue occurs under whole body vibration. After whole body vibration exposure the muscle response to a sudden load has greater latency. Vehicle driving may be a reason for low back pain or herniated nucleus pulposus. Prolonged seating exposure, coupled with the whole body vibration, should be reduced for those recovering from these problems. Vibration attenuating seats and correct ergonomic layout of the cabs may reduce the risks of recurrence.

Acceleration↗
PubMed2000

Ventilatory support by tracheal gas insufflation and chest vibration during bronchoconstriction.

OBJECTIVE: To determine whether chest wall vibration with tracheal gas insufflation during bronchoconstriction maintains gas exchange at lower airway and intrathoracic pressures than those that occur during positive pressure ventilation. DESIGN: Prospective study. SETTING: Experimental laboratory. SUBJECTS: Six anesthetized, paralyzed mongrel dogs (mean weight, 24.7+/-3.8 kg). INTERVENTIONS: Dogs were ventilated by two methods: mechanical ventilation (7 breaths/min, 25 mL/kg tidal volume); and tracheal oxygen insufflation at 0.15 L x kg(-1) x min(-1) delivered with external chest wall vibration (29 Hz, 2 mm amplitude) of the dependent hemithorax. Bronchoconstriction was induced by methacholine infusion adjusted to double and quadruple the baseline airway resistance. Proximal mean airway pressure was kept equal for both modes of ventilation. MEASUREMENTS AND MAIN RESULTS: Airway pressure and flow, esophageal pressure, hemodynamic variables (cardiac output, systemic and pulmonary arterial pressures, pulmonary artery occlusion pressure) and gas exchange variables (PaO2, PaCO2, pH, shunt fraction, VO2) were measured. Peak airway pressure was lower (p < .05) with insufflation and vibration than with mechanical ventilation by 83.6% at baseline resistance, by 76.9% at twice baseline resistance, and by 76.8% at four times baseline resistance. Peak esophageal pressure was lower (p < .05) during insufflation with vibration by 68.5% at baseline resistance, by 87.5% at twice baseline resistance, and by 107% at four times baseline resistance. During insufflation with vibration, mild hypercapnia (PaCO2 58+/-3 torr (7.7+/-0.4 kPa) and pH 7.28+/-0.02) developed with moderate bronchoconstriction; more profound respiratory acidosis (PaCO2 137+/-41 torr (18.2+/-5.5 kPa) and pH 6.87+/-0.11) developed with severe bronchoconstriction. CONCLUSIONS: Tracheal gas insufflation with chest vibration supports gas exchange with permissive hypercapnia only during moderate, not severe, bronchoconstriction. Gas exchange was achieved at lower airway and intrathoracic pressures than those that developed during mechanical ventilation. The alveolar hypoventilation that occurred during insufflation with vibration indicates impaired CO2 elimination and suggests increased resistance to CO2 transport. This ventilation technique may confer therapeutic advantages over mechanical ventilation in the treatment of asthma.

Animals↗
PubMed1998

The influence of traffic vibrations on the radon potential.

The influence of traffic vibrations on the radon potential is analyzed in this study. Generally, the radon concentration in soil-gas increases through traffic vibrations. The influence of the vibrations is determined near railway tracks and heavy-traffic roads. Soils above natural, in-place, bedrock (solid and unconsolidated rocks) and backfills were studied. The type of vibrations, as well the soil material, have a pronounced influence on the amount of increase of the radon concentration. The spatial radius of influence is wider with railway traffic (>30 m) than with motor vehicle traffic (<25 m). Close to the traffic lanes the increase of the radon concentration by motor vehicle traffic is significantly higher (37%) than that by railway traffic (11.5%). There are no differences between locations, which lay above unconsolidated rock (11.1%), and locations above solid rock (11.8%). In addition to the increased radon concentrations, the averaged radon concentration decreases with increasing distance to the vibration source, but only at locations that lay above solid rock. Both phenomena can be explained by a "pump effect": the mechanical vibration of soil and mineral particles leads to an upward motion of the whole volume of soil-gas. During the vibrations the topmost soil layers lose radon to the atmosphere and as a result the upward transport is increased.

Automobiles↗
PubMedDate not supplied

Vibration and the human spine.

Vibrational effects have been found to be associated with increased frequency of low-back pain in various industries, and because of this the study herein reported was conducted to assess the physiologic response of the spinal system to sinusoidal vibrations. A device replicating industrial vibration was constructed and employed on healthy human volunteers to determine the stiffness, impedence, and resonant characteristics of the subjects. Three peaks of enhanced transmissibility corresponding to the resonant frequency of the spinal system were found. The greatest transmissibility of vibratory input occurs at the first resonant frequency (5Hz) where marked enhancement of vibrational input occurs as vibrations pass through the spinal system. A progressive stiffening of the system occurs in response to vibrational inputs of increasing frequency. The effects of posture, the Valsalva maneuver, and fatigue alter the normal response. Structures vibrated at the first resonant frequency have greater potential for damage.

Adolescent↗
PubMed1990

Changes in spine length during and after seated whole-body vibration.

The authors examined the relation between exposure to seated whole-body vibration (WBV) and an increase in the loss of height of the spine over and above normal diurnal changes. A device for measuring sitting height is described (SD, 1.4 mm for repeated measures). The mean change in body height (diurnal reduction) during two normal days in five men aged 23 to 25 years was 10.6 mm, (SD, 3.2 mm). On the third day, the change in sitting height was measured before and after vertical vibration (5 Hz with a peak-to-peak amplitude of 3 mm, and peak acceleration less than 2 m/s2) and again at the end of the day. The mean reduction in sitting height over the half hour of vibration exposure was 9.0 mm versus less than 1 mm for the control condition. The mean height loss over the third day (the day of 30 minutes of vibration exposure) was only 3.6 mm (compared with 10.6 mm lost over a control day with no vibration exposure). Hence, exposure to vibration increased the creep response in all subjects during exposure but, at the end of the day, there was a recovery in height, such that subjects were taller at the end of the day of vibration exposure. It is hypothesized that this "rebound" effect is due to an inflammatory response in the spine.

Adult↗
PubMed1997

Bony vibration stimulation test combined with magnetic resonance imaging. Can discography be replaced?

STUDY DESIGN: The results of two noninvasive methods, magnetic resonance imaging and a bony vibration test, were compared with discographic pain provocation findings. OBJECTIVES: To evaluate whether the combination of magnetic resonance imaging and vibration pain provocation tests could be used to replace discography in low back pain diagnostics. SUMMARY OF BACKGROUND DATA: Magnetic resonance imaging gives a wealth of visual information on anatomic changes of the spine with often unknown clinical significance. Discographic examination of the spine is still the only widely accepted diagnostic method that can relate the pathoanatomic changes to the patient's clinical pain. Internal anular rupture has been shown to be one of the sources of back pain. The bony vibration test of the spinal processes has been shown correlate well with discographic pain provocation tests in cases of internal anular rupture. METHODS: The three lowest lumbar discs of 33 patients with back pain were examined by means of magnetic resonance imaging and a bony vibration stimulation test, and the results were compared with those from computed tomography-discography. RESULTS: In cases of intradiscal magnetic resonance imaging findings, the vibration provocation test showed a sensitivity of 0.88 and a specificity of 0.50 compared with the discographic pain provocation test. If the patients with previous back surgery were excluded, the specificity was 0.75. In the cases of total anular rupture, the sensitivity was 0.50, and the specificity was 0.33. CONCLUSION: The combination of the two noninvasive methods, vibration stimulation and magnetic resonance imaging, gives more information on the origin of the back pain than magnetic resonance imaging alone. The pathoanatomic changes seen in magnetic resonance imaging can be correlated with the patient's disorder more reliably using the vibration provocation test in the cases of partial anular ruptures. The use of discography can be limited mostly to cases with total anular ruptures detected by magnetic resonance imaging.

Adult↗
PubMed2006

Influence prediction of injury and vibration on adjacent components of spine using finite element methods.

OBJECTIVES: A three-dimensional finite element (FE) model of the lumbar spine L3-L5 segment, the ligaments of which were assumed to be nonlinear materials, was established based on the actual vertebra geometry to investigate the influence of the injury lumbar spine on its adjacent components on the condition of whole-body vibration. Several injury conditions of the spine components were assumed, such as facetectomy, nucleotomy, and removal of bony posterior elements. METHODS: The dynamic FE analyses were carried out for those FE conditions under cyclic compression loads at the frequencies of 5 and 10 Hz. Then a comparison between the dynamic results and the static results was conducted to analyze the influence of both the nucleus injury and the facet joint injury on the adjacent intervertebral discs. RESULTS AND CONCLUSIONS: The results indicate that the lumbar spine exhibits not only vertical vibration but also the flexion--extension motion during vibration. The denucleation will cause high stress and large disc bulge on the disc annulus under vibration. The facet joints of lumbar spine can limit the motion amplitude of flexion-extension and protect both the posterior regions and the posterolateral regions of disc annulus from large strain and stress during vibration. The facet joint removal will increase the stress of disc annulus by around 15% at the posterior region for the conditions of nucleotomy or no vibration. The stress of annulus circumference is higher at the posterolateral region than that of other regions of annulus circumference, and the facet joint removal may exacerbate the intervertebral disc degeneration on the condition of whole-body vibration.

Compressive Strength↗
PubMed2000

Vibration arthrometry in the patients with failed total knee replacement.

This is a preliminary research on the vibration arthrometry of artificial knee joint in vivo. Analyzing the vibration signals measured from the accelerometer on patella, there are two speed protocols in knee kinematics: 1) 2 degrees/s, the signal is called "physiological patellofemoral crepitus (PPC)", and 2) 67 degrees/s, the signal is called "vibration signal in rapid knee motion". The study has collected 14 patients who had revision total knee arthroplasty due to prosthetic wear or malalignment represent the failed total knee replacement (FTKR), and 12 patients who had just undergone the primary total knee arthroplasty in the past two to six months and have currently no knee pain represent the normal total knee replacement (NTKR). FTKR is clinically divided into three categories: metal wear, polyethylene wear of the patellar component, and no wear but with prosthesis malalignment. In PPC, the value of root mean square (rms) is used as a parameter; in vibration signals in rapid knee motion, autoregressive modeling is used for adaptive segmentation and extracting the dominant pole of each signal segment to calculate the spectral power ratios in f < 100 Hz and f > 500 Hz. It was found that in the case of metal wear, the rms value of PPC signal is far greater than a knee joint with polyethylene wear and without wear, i.e., PPC signal appears only in metal wear. As for vibration signals in rapid knee motion, prominent time-domain vibration signals could be found in the FTKR patients with either polyethylene or metal wear of the patellar component. We also found that for normal knee joint, the spectral power ratio of dominant poles has nearly 80% distribution in f < 100 Hz, is between 50% and 70% for knee with polyethylene wear and below 30% for metal wear, whereas in f > 500 Hz, spectral power ratio of dominant poles has over 30% distribution in metal wear but only nonsignificant distribution in polyethylene wear, no wear, and normal knee. The results show that vibration signals in rapid knee motion can be used for effectively detecting polyethylene wear of the patellar component in the early stage, while PPC signals can only be used to detect prosthetic metal wear in the late stage.

Aged↗
PubMed2000

Neck muscle vibration makes walking humans accelerate in the direction of gaze.

We studied the effect of the continuous vibration of symmetrical dorsal neck muscles in seven normal subjects during (a) quiet standing, (b) stepping in place movements and (c) walking on the treadmill. The experiments were performed in a darkened room and the subjects were given the instruction not to resist the applied perturbation. In one condition the velocity of the treadmill was controlled by feedback from the subject's current position. Head, trunk and leg motion were recorded at 100 Hz. In normal standing, neck vibration elicited a prominent forward body sway. During stepping in place, neck vibration produced an involuntary forward stepping at about 0.3 m s-1 without modifying the stepping frequency. If the head was turned horizontally 45 and 90 deg to the right or to the left, neck muscle vibration caused stepping approximately in the direction of the head naso-occipital axis. For lateral eye deviations, the direction of stepping was roughly aligned with gaze direction. In treadmill locomotion, neck vibration produced an involuntary step-like increase of walking speed (by 0.1-0.6 m s-1), independent of the initial walking speed. During backward locomotion, the walking speed tended to decrease during neck vibration. Thus, continuous neck vibration evokes changes in the postural reference during quiet standing and in the walking speed during locomotion. The results suggest that the proprioceptive input from the neck is integrated in the control of human posture and locomotion and is processed in the context of a viewer-centred reference frame.

Acceleration↗