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At least 1,207 records · Page 67Linked to original sources
PubMed1974

Modification of the postural response of the normal dog by blindfolding.

1. Normal dogs were trained to stand quietly upon a movable platform. The animals' postural adjustments in response to sinusoidal motion of the platform were assessed in both the normal and the blindfolded condition. The induced postural adjustments were described by the Fourier coefficients for the fundamental of the input together with the coefficients which were integral multiples of the fundamental.2. All of the output variables, including motion at the hind limb joints and of the body, showed modifications when the dogs were blindfolded. The body motion increased in amplitude, as measured by the fundamental Fourier coefficient, and further lagged the input motion. Motion at the knee and phalangeal joints also increased in amplitude and the timing of these movements shifted from the normal in characteristic patterns for different frequencies of input motion.3. The modifications of the postural response due to blindfolding were most pronounced at the lower input frequencies: 0.2-1.0 Hz. At 1.4 Hz or above the fundamental coefficients of most of the output measures resembled those of the normal condition. Even at the higher input frequencies, however, the postural response of the blindfolded dog was more distorted than that of the normal dog.4. It is hypothesized that relatively slow movement of the visual surround provides the dog with information which is essential to normal operations of the postural control system.

Animals↗
PubMed2006

Startle responses elicited by whiplash perturbations.

The human startle response produces muscle contractions throughout the body but the most brisk and synchronized contractions appear in the neck muscles. This response, which is greatest with the first exposure to a startling stimulus, could produce excessive and inappropriately directed muscle contractions that could explain the higher incidence of whiplash injuries in people who are unprepared for the collision. This study seeks neurophysiological evidence of startle responses in the neck muscles of 120 healthy subjects exposed to between 1 and 16 rear-end impacts or forward perturbations of different speeds. Startle responses were quantified by the synchronous electromyographic (EMG) activity between 10 and 20 Hz in bilaterally homologous sternocleidomastoid, scalene and cervical paraspinal neck muscles. Coherence analyses of EMGs from the left and right muscles were used to estimate synchrony for: (i) the first unexpected trial, (ii) subsequent habituated trials, and (iii) the superposition of habituated trials and a loud acoustic stimulus (40 ms, 124 dB sound). The peak in coherent EMG activity between contralateral muscle pairs in the 10-20 Hz bandwidth was related to startle. Synchrony in this bandwidth was observed between the left and right muscles during the first impact or whiplash-like perturbation. This synchrony decreased significantly in the habituated trials, but reappeared when the loud acoustic stimulus was introduced. Its presence in the first trial indicates that startle is part of the neuromuscular response to an unexpected rear-end impact. This startle component of the neuromuscular response could play a role in the aetiology of whiplash injuries.

Acceleration↗
PubMed2006

Craniocentric body-sway responses to 500 Hz bone-conducted tones in man.

Whole-body responses evoked by bone-conducted sound, a stimulus known to activate vestibular afferents, were recorded in standing subjects deprived of vision. With the head facing forward, unilateral mastoid vibration (500 Hz, 2 s, 136 dB force level) produced an oblique body sway with a consistent lateral component away from the stimulated ear and an average forward component. The side of stimulation had a powerful influence on the direction but not the magnitude of sway. Individuals' mean response directions were significantly clustered between subjects, as well as within subjects for 12 of 16 subjects when tested on five occasions. Single trial analysis did not reveal any habituation of the response. To investigate whether muscle spindle activation might be responsible for the response, vibration was applied directly over posterior and anterior neck muscles and tendons. This generally produced responses that were smaller and with different direction characteristics than with mastoid vibration. In contrast, stimulation over the temporal fossa produced responses similar in magnitude and direction to mastoid stimulation. When the head was turned in yaw to face in different directions the sway response changed direction by the same amount but with no change in magnitude, suggesting response organization in a craniocentric reference frame. Whole-body sway evoked by 500 Hz vibration delivered over sites close to the ear is thus likely to represent a vestibular-evoked balance response. When compared with sway responses evoked by 500 Hz vibration of the left temporal fossa, responses to 1 mA left cathodal galvanic vestibular stimulation were of similar magnitude, yet significantly different in direction, suggesting differences in the end organ afferents activated by these two stimuli. This may enable investigation of previously inaccessible aspects of vestibular function in intact freely behaving human subjects.

Acoustic Stimulation↗
PubMed2003

Dynamics of the human head-neck system in the horizontal plane: joint properties with respect to a static torque.

The vestibular system has often been studied by perturbing the position of the head. This study was conducted to identify the dynamic properties of the head-neck system in response to horizontal plane perturbations. A quasilinear approach was used to quantify the dynamics of the head-neck system at different levels of static torque. An operating point was established by applying a static torque to the head with a helmet-based perturber. The head-neck dynamics were then probed with a rich spectrum, stochastic, torque perturbation. Impulse response functions (IRFs) were estimated from correlation measures, and parametric models were fit to the IRFs. The results indicated that when the mean torque was held constant, the head-neck system behaved like a second-order, underdamped, passive system between 0.5 and 10.0 Hz. The system was not strictly linear, however. The properties of the system were sensitive to the static component of the torque. As the mean torque increased, the effective stiffness and damping progressively increased, and did so such that the system's damping ratio remained essentially constant. The findings of the study will assist in designing stimuli that are well tolerated by subjects and can induce head motions that span the performance capabilities of the vestibular system.

Atlanto-Axial Joint↗
PubMed2006

An adaptive system identification model of the biomechanical response of the human trunk during sudden loading.

Sudden loading injuries to the low back are a concern. Current models are limited in their ability to quantify the time-varying nature of the sudden loading event. The method of approach used six males who were subjected to sudden loads. Response data (EMG and kinematics) were input into a system identification model to yield time-varying torso stiffness estimates. The results show estimates of system stiffness in good agreement with values in the literature. The average root mean square error of the model's predictions of sagittal motion was equal to 0.1 deg. In conclusion, system identification can be implemented with minimal error and used to gain more insight into the time-dependent trunk response to sudden loads.

Abdomen↗
PubMed2006

Age-related differences in muscle power during single-step balance recovery.

The purpose of this study was to investigate age-related differences in muscle power during a surrogate task of trip recovery. Participants included 10 healthy young men (19-23 years old) and 10 healthy older men (65-83). The task involved releasing participants from a forward-leaning posture. After release, participants attempted to recover their balance using a single step of the right foot. Muscle power at the hip, knee, and ankle of the stepping limb were determined from the product of joint angular velocity and joint torque. Muscle powers during balance recovery followed a relatively consistent pattern in both young and older men, and showed effects of both lean and age. Interestingly, the effects of age did not always involve smaller peak power values in the older men as expected from the well-documented loss of muscle power with aging. Older men exhibited smaller peak muscle power at the knee and larger peak muscle power at the ankle and hip compared to young men. The increases in muscle power at the ankle and hip may result from a neuromuscular adaptation aimed at improving balance recovery ability by compensating for the age-related loss of muscle function.

Adult↗
PubMed1975

Cardiovascular control in diabetes mellitus.

Heart rate variability and the changes in heart rate and blood pressure which occur on standing were measured in 21 diabetics. These simple measures distinguished four groups of patients, with loss of parasympathetic activity being commoner than loss of sympathetic activity.

Adolescent↗
PubMed1983

Quantitative analysis of stance in ataxic myxoedema.

Postural abnormalities in a 66-year-old woman with ataxic myxoedema were recorded by stabilography during treatment. After replacement therapy, 3 Hz power in the sagittal plane was greater than before treatment; this peak shifted to a higher frequency and finally its ratio became normal. This is the first report of recovery of a 3 Hz body oscillation in ataxic myxoedema.

Aged↗