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Results for “REFLEX, POSTURAL”

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At least 631 records · Page 35Linked to original sources
PubMed2005

Effects of static flexion-relaxation on paraspinal reflex behavior.

BACKGROUND: Static trunk flexion working postures and disturbed trunk muscle reflexes are related to increased risk of low-back pain. Animal studies conclude that these factors may be related; passive tissue strain in spinal ligaments causes subsequent short-term changes in reflex. Although studies have documented changes in the myoelectric onset angle of flexion-relaxation following prolonged static flexion and cyclic flexion we could find no published evidence related to the human reflex response of the trunk extensor muscles following a period of static flexion-relaxation loading. METHODS: Eighteen subjects maintained static lumbar flexion for 15 min. Paraspinal muscle reflexes were elicited both before and after the flexion-relaxation protocol using pseudorandom stochastic force disturbances while recording EMG. Reflex gain was computed from the peak value of the impulse response function relating input force perturbation to EMG response using time-domain deconvolution analyses. FINDINGS: Reflexes showed a trend toward increased gain after the period of flexion-relaxation (P < 0.055) and were increased with trunk extension exertion (P < 0.021). Significant gender differences in reflex gain were observed (P < 0.01). INTERPRETATIONS: Occupational activities requiring extended periods of trunk flexion contribute to changes in reflex behavior of the paraspinal muscles. Results suggest potential mechanisms by which flexed posture work may contribute to low-back pain. Significant gender differences indicate risk analyses should consider personal factors when considering neuromuscular behavior.

Adaptation, Physiological↗
PubMed2004

Neurological examination in healthy term infants aged 3-10 weeks.

OBJECTIVES: The neurodevelopmental progress of newborn term infants is checked routinely at around 6 weeks of postnatal age. The maturation of neurological signs in this age range however has not been systematically studied and normative data are not available. The aim of this study was to document any changes in posture, tone, reflexes, behaviour and movements in low-risk full-term infants between 3 and 10 weeks of postnatal age. STUDY DESIGN: We performed a structured neurological examination previously standardised in full-term newborns in the first 48 h after birth. In the current study, a total of 76 examinations were performed between 3 and 10 weeks of age in low-risk full-term infants. RESULTS: The results of the examinations were divided according to postnatal age. In most items, the scores changed with time, with a definite shift in their distribution occurring around 6 weeks. At this age, a reduction in flexor tone of the limbs was observed, together with an increase in active neck tone. Visual orientation in contrast had already improved by 3 weeks when all infants were able to follow a target in a full circle compared to newborns that are often only able to follow a target in an arc. CONCLUSIONS: Our results suggest that 6 weeks post-term birth is an important milestone for changes in neurological signs, particularly those related to muscle tone and posture, probably reflecting maturation of the nervous system. These findings provide important guidelines for the interpretation of the neurological examination performed at this age.

Child Development↗
PubMed1984

Autonomic function in cholinergic urticaria and atopic eczema.

Autonomic function in patients with cholinergic urticaria and atopic eczema was compared with that in patients with chronic idiopathic urticaria and non-atopic allergic contact dermatitis, respectively. Forty-nine patients were studied. The following specific tests of sympathetic and parasympathetic function were used to assess the integrity of autonomic control: pupillary reflex amplitude in response to pulsed light stimulation and response to topical arecoline hydrobromide (parasympathetic); the speed of pupillary dilatation following a large light reflex (sympathetic); pupillary resting diameter (sympathetic and parasympathetic); sweat gland response to forearm intradermal injection of acetylcholine chloride; and the effect of postural change and deep breathing on blood pressure and heart rate (sinus arrhythmia indicating parasympathetic function). No significant difference in autonomic function was found between the four groups of patients.

Acetylcholine↗
PubMed2006

Effects of postural anxiety on the soleus H-reflex.

Previous research has proposed that spinal reflex modulation may mediate anxiety-related changes in postural control. This study investigated how soleus H-reflex amplitude was influenced by standing at heights that induced different levels of anxiety. H-reflexes were elicited in 15 participants standing at the center and edge of a platform raised from a low to a high height (with and without vision). Increased skin conductance confirmed the anxiety effect of elevated surface heights. When standing at the edge of the platform with vision, H-reflex amplitude was attenuated in the high compared to low height condition. Changes in background muscle activity could not explain observed H-reflex changes, suggesting the potential involvement of pre-synaptic inhibition or fusimotor drive on anxiety-related changes in reflex modulation. This study reveals that healthy participants reduce spinal reflex excitability in the presence of increased postural anxiety and a postural threat imposed by standing at the edge of a raised platform. These findings have implications for understanding control of standing balance in individuals with postural instability and/or fear of falling, such as the elderly or stroke.

Adult↗
PubMed2006

Influence of posture and muscle length on stretch reflex activity in poststroke patients with spasticity.

OBJECTIVE: To investigate the influence of different positions on stretch reflex activity of knee flexors and extensors measured by electromyography in poststroke patients with spasticity and its expression in the Ashworth Scale. DESIGN: Crossover trial with randomized order of positioning. SETTING: Outpatient rehabilitation center in the Netherlands. PARTICIPANTS: Poststroke patients (N = 19) with lower-limb spasticity. INTERVENTION: Changing position: sitting versus supine. MAIN OUTCOME MEASURES: Root mean square (RMS) values of muscle activity and goniometric parameters, obtained during the pendulum test and passive knee flexion and extension, and Ashworth scores. RESULTS: RMS values of bursts of rectus femoris activity were significantly higher in the supine compared with the sitting position (P = .006). The first burst of vastus lateralis activity during the pendulum test (P = .049) and semitendinous activity during passive stretch (P = .017) were both significantly higher in the supine versus the sitting position. For both the pendulum test and passive movement test, the duration and amplitude of the cyclic movement of the lower leg changed significantly as well. In the supine position, we found significantly higher Ashworth scores for the extensors (P = .001) and lower scores for the flexors (P = .002). CONCLUSIONS: The outcome of clinical and neurophysiologic assessment of spasticity is influenced considerably by subject positioning.

Cross-Over Studies↗
PubMed1988

Fast head tilt has only a minor effect on quick compensatory reactions during the regulation of stance and gait.

Sudden tilts of the head to the front or rear were induced during stance, balancing, gait and during perturbations of gait. The most prominent response in the leg muscle electromyogram (e.m.g.) to head tilt occurred in the tibialis anterior muscle (latency about 55 ms) following a backward tilt induced during balancing. During stance and gait, the e.m.g. activity related to head tilt was only a minor component of the leg muscle activity normally occurring during gait. When the head tilt was induced shortly after a perturbation of gait (treadmill acceleration impulse), the compensatory reaction in the leg muscles did not significantly differ from that seen after the gait perturbation alone. In addition, the rate of acceleration of the head was tested against the compensatory e.m.g. responses: No correlation of influence could be discerned. The results indicate that sudden head tilts and the resulting head acceleration have little influence on the e.m.g. patterns that occur during gait and perturbations of gait. It is assumed that these patterns are regulated by central programs, and that the compensation for leg perturbation is achieved mainly by spinal reflex mechanisms. It is discussed whether the lack of head tilt responses is the result of an antagonistic vestibular-neck interaction, or whether it indicates a reduced effectiveness of vestibulo- and cervico-spinal reflexes during gait.

Adult↗
PubMed1993

Recovery of stretch reflex responses following mechanical stimulation.

The recovery behaviour of mechanically evoked stretch responses was investigated. Stimuli which promoted identical dorsiflexing movements around the ankle joint were applied to ten subjects in two positions, seated and upright. The experimental sets comprised single as well as double dorsiflexing displacements. In the latter the stimuli were elicited for durations of either 100, 200 or 400 ms. Stretch responses following the first displacements were related to the stretch velocity but not to the amplitude. The responses of the plantar flexors following the second mechanical dorsiflexion were reduced with respect to the delay time between the first and second displacement. In addition, the magnitudes of these responses depended on the functional task: the stretch responses recovered much faster in the standing position when the triceps surae muscle was only slightly activated, whereas in the relaxed sitting position the reflexes remained suppressed. Both reciprocal inhibition, as well as the time course of the reformation of intrafusal cross-bridge links, may help to explain the depression of the monosynaptic stretch reflex.

Adult↗
PubMed1977

[Changes in the bioelectrical activity of the biceps femoral muscles in the diplegic form of infantile cerebral palsy].

The author performed an EMG study of the biceps femoris muscle and their proximal and distal parts in 15 normals and 42 patients with diplegic forms of infantile cerebral palsy. In patients with infantile cerebral palsy there were significant coordinational disturbances in the bioelectric activity of the muscles of the thigh during walking and an orthostatic position. These changes had characteristic traits depending upon the influence of preserved primitive tonic reflexes.

Cerebral Palsy↗