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Results for “REFLEX, POSTURAL”

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At least 595 records · Page 33Linked to original sources
PubMed2000

Postural modulation of soleus H-reflex under simulated hypogravity by head-out water immersion in humans.

To test our hypothesis that somatosensory inputs would influence postural modulation of soleus H-reflex, eleven subjects were investigated under the head-out water immersion (HOWI) conditions. Subjects were supine or standing on a tilting bed in each condition. They were instructed to maintain an upright posture with both legs. The water was filled to the subject's neck level in a test tank to reduce 95% of the gravitational effect by buoyancy. Surface electromyography of the soleus and tibialis anterior was measured. The soleus H-reflex was elicited at a stimulation intensity of 1.05 times the motor threshold. The recruitment profile of the motor response was unchanged between the conditions. The background activities of the soleus and tibialis anterior were not detected in any condition. The peak-to-peak amplitude of the H-reflex was significantly different between the conditions while the stimulation intensity (small M size) was not different. The soleus H-reflex during standing was significantly decreased compared with being supine in the control condition, whereas it did not in the HOWI condition. It was concluded that somatosensory inputs due to gravity exert an influence on postural modulation of the soleus H-reflex to maintain static posture in humans.

Adult↗
PubMed2004

Physical activity after retirement enhances vestibulo-ocular reflex in elderly humans.

Vestibular information decreases in sensitivity with ageing, and its role becomes less important in the regulation of postural control. In addition, the practice of physical activity (PA) helps to improve vestibular sensitivity. This study aimed to evaluate PA-related benefit on vestibular function in 36 subjects split into four groups according to the period of practice. Caloric and rotatory vestibular testings showed that the performance of subjects who had begun practising PA recently were close to those of subjects active for a long time, whereas those of subjects who had stopped practising at an early age were close to those of inactive subjects. Although starting to practise PA has immediate beneficial effects on the vestibule, in terms of vestibular stimulation mechanisms these effects soon disappear if this activity is stopped.

Aged↗
PubMed1992

Interaction of tonic labyrinth and neck reflexes in man.

Interaction of tonic labyrinth and neck reflexes was studied in 3 healthy volunteers by analyzing changes in Soleus H-Reflex (SHR) area in relation to both lateral tiltings and neck rotations. By using a Kermath chair each subject was tilted laterally from the vertical to the left and to the right up 15 degrees in steps of 5 degrees and at the same time the longitudinal body axis, keeping the head fixed, was rotated to the right and to the left up to 15 degrees in steps of 5 degrees. All combinations of lateral tiltings and neck rotations were tested. Each test position was followed by a return to 0 degree for both rotation and tilting (control position). Twelve H-reflexes of right soleus muscle were recorded in each test and control position and the changes in RSHR area were expressed as percentage variations from the mean value absorbed in the pretest and post-test control position. Our data indicate that in man, as in animals, labyrinth and neck reflexes act in the opposite direction, and that in the static condition their contribution to postural stabilization is equal.

Adult↗
PubMed1989

The role of stretch and vestibulo-spinal reflexes in the generation of human equilibrating reactions.

Equilibrating reactions in standing humans were examined for evidence that either vestibulo-spinal or proprioceptive long loop stretch reflexes from ankle muscles, or both, are responsible for the control and organization of rapid postural responses. Specifically, the hypothesis was tested that the same postural response could be evoked by rotation of the support surface that mimics the ankle rotation occurring during support surface translations. Rotation perturbations evoked postural responses in leg and trunk muscles that were different in strategy, synergy and coactivation from translation responses, even though the short-latency response in the stretched triceps surae muscles was equal in latency and size. Movement patterns consisted of a stiffening strategy and hardly any compensating ankle rotation for rotation stimuli, and a multi-link strategy with motion focused about the neck, hip and ankle joints for translation stimuli. Dorsiflexion rotations caused earlier and stronger responses in tibialis anterior and quadriceps muscles just post to the onset of paraspinal muscles, whereas rearward translation activated soleus and abdominals strongest, both just prior to hamstring muscles. Correlated activation strengths of agonist and antagonist activity was a common feature for both types of perturbation, albeit, only in the ankle muscles for rotations and only in the trunk muscles for translations. These data suggest that sensory inputs, other than those generated in the lower leg predominate, in the triggering and modulation of equilibrating reactions. Possible candidates are those of the vestibular system or proprioceptive inputs from the trunk.

Humans↗
PubMed2000

Blood distribution adaptations in paraplegics during posture changes: peripheral and central reflex responses.

The veno-arteriolar reflex (VAR) in spinal-cord-injured subjects (SCI) has been attributed little interest, although it might contribute substantially to their blood redistribution. This peripheral reflex response, which is based on an axon reflex, consists of a reduction in limb blood flow following an increase in venal transmural pressure. The purpose of the present investigation was to assess the peripheral and central cardiovascular adaptations of paraplegics with high (HP) and low (LP) spinal lesions to subsequent, passive posture changes involving leg dependency and upright sitting, and to compare them to able-bodied (AB) subjects. Lower-limb cutaneous vascular conductance (CVC) was evaluated from skin blood flow measurements (laser Doppler flowmetry) taken from the dorsal foot, and from ankle blood pressure. Cardiac stroke volume, heart rate and myocardial performance were assessed using impedance cardiography and brachial blood pressure. During leg dependency, a significant vasoconstriction was noted in all three groups. The initial decrease in CVC was higher in HP (-76.82%) than in AB (-45.82%), the values for LP (-67.08%) lying in between these two (significant group x time interaction: F = 2.832; P = 0.042). There were no differences for parameters of central hemodynamics. No between-group differences were noted in any parameter tested during upright sitting. CVC remained at a similar low level as compared to leg dependency, stroke volume decreased, heart rate and blood pressure increased, and myocardial performance remained constant. The present results suggest that paraplegics have a peripheral VAR in their paralyzed lower limbs, and that this contributes to their cardiovascular stability.

Adaptation, Physiological↗