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Results for “voluntary activation”

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At least 19 recordsLinked to original sources
PubMed1979

Voluntary activation of spindle endings in human muscles temporarily paralysed by nerve pressure.

1. In normal human subjects, the afferent activity from muscle spindle endings in the pretibial muscles was recorded while a pressure block was applied to the peroneal nerve proximally in the popliteal fossa. 2. In five of ten blocks, spindle activity increased in attempted isometric voluntary contractions when the receptor-bearing muscles were completely paralysed. In the remaining five blocks, voluntary effort still increased spindle activity when maximum voluntary power was reduced by more than 90%, but the ability to activate spindles voluntarily was lost with or slightly before block of the last motor units. When the ability to activate spindle endings in an attempted voluntary contraction was lost sympathetic efferent fibres remained unblocked. 3. It is concluded that the fusimotor effects seen during a voluntary contraction are mediated by myelinated fibres of small calibre which probably innervate intrafusal structures exclusively (gamma fusimotor fibres). There is no necessity to postulate that skeleto-fusimotor (beta) fibres are responsible for the tight 'alpha-gamma co-activation' seen in man during voluntary contractions.

Humans↗
PubMed1978

Reflexes evoked in human thenar muscles during voluntary activity and their conduction pathways.

Responses evoked by an electrical stimulus to the median nerve in a small muscle of the human hand during a voluntary contraction have been examined. Two of these responses have been shown to be evoked through reflex pathways. The first, with a mean afferent conduction velocity of 64 m/s and estimated central delay of about 0.8 ms, is identified as an H reflex. The second response, which has an undefined central pathway, has a mean afferent conduction velocity of 43 m/s and an estimated central delay of about 17 ms.

Adult↗
PubMed1978

Dynamic load in the human knee joint during voluntary active impact to the lower leg.

The aim of the study was to get an insight into the nature of the dynamic load in a joint caused by impacts of physiological magnitude to the distal part of an extremity of normal, live human subjects. A method was developed for the calculation of two components of the impulse reaction (parallel and perpendicular to the lower leg) as a measure of the dynamic load in the knee. A theoretical model regarding the lower limb as a double pendulum was chosen and equations developed. Five subjects were studied during kicking situations and the components of the impulse reaction were calculated. With a normal kicking motion pattern the direction of the components of the impulse reaction in the knee joint caused by the impact to the lower leg are usually distal and anterior. The impulse reaction thus tends to cause a traction of the lower leg from the thigh and an anterior displacement of the proximal part of the lower leg in relation to the distal part of the thigh. Anatomical structures which can prevent this displacement are discussed.

Biomechanical Phenomena↗
PubMed1978

Reflex and voluntary electromyographic activity in patients with hemiparesis.

The purpose of this study was to quantify the effect of combining voluntary effort with passive muscle stretch in the major flexors and extensors of the elbow and knee joints in order to test the validity of the assumption that stretching a muscle in conjunction with voluntary effort enhances the production of muscle activity more than muscle stretch or voluntary effort alone. This was accomplished by using a computer-controlled test instrument to produce the conditions necessary for measuring stretch reflex activity, voluntary effort, and stretch reflex activity plus voluntary effort, and then quantitatively examining the EMG activity associated with each test condition. In general, greater EMG activity was produced by the combination of muscle stretch and voluntary effort than by either muscle stretch or voluntary effort alone. Clinical implications of these findings are discussed.

Adolescent↗
PubMed1979

Contribution of growth, fatness, and activity to weight disturbance after septohypothalamic cuts in adult hamsters.

The mechanism responsible for weight stability in adult hamsters was investigated by (a) transecting the dorsoventrally oriented nerve pathways between the septal area and hypothalamus (SH cuts) and (b) partitioning the observed increases in the rate of weight gain into three contributory components: changes in somatic growth, in body fatness, and in energy expended as voluntary activity on horizontal disks. Between 60% and 70% of the weight increase after SH cuts was due to acquisition of lean body mass, and 30%-40% of weight increase consisted of excess body fat. After SH cuts, serum growth hormone and insulin concentrations were increased on Day 14, food intake was increased between Day 2 and Day 42, skeletal lengths were greater on Day 77, and voluntary activity levels were 84% lower on Days 10-45, relative to control hamsters. It is concluded that dorsoventrally oriented nerve pathways in the septal area are involved in the control of growth, maintenance of body fat reserves, and voluntary activity and that they contribute to the maintenance of stable body weight in adult hamsters.

Adipose Tissue↗
PubMed1978

Brain and liver aldehyde dehydrogenase activity and voluntary ethanol consumption by rats: relations to strain, sex, and age.

Voluntary ethanol consumption and brain and liver aldehyde dehydrogenase (ALDH) activity were measured in male and female rats of the Tryon Maze-Bright (S1), Tryon Maze-Dull (S3), and Wistar strains. The levels of brain ALDH measured in the different groups, corresponded well to the levels of ethanol consumption, while differences in liver ALDH corresponded well to only the strain differences in ethanol intake. Within individual groups, levels of ethanol consumption correlated better with levels of brain and liver aldehyde-oxidizing capacity. Age affected both voluntary ethanol intake and liver ALDH levels, but there were no systematic relations between the two effects. Age did not significantly affect the cerebral-aldehyde oxidizing capacity. It is argued that inherent variation in brain ALDH activity may be a principal biochemical counterpart of the differences in ethanol intake amoung different strains and sexes of laboratory rats.

Aging↗
PubMed1976

Physiological and pharmacological aids in the differential diagnosis of tremor.

Physiological and pharmacological studies of more than 150 patients with movement disorders are reported. Particular attention is paid to the differentiation of various types of tremor on the basis of rate, rhythm, and pattern of EMG activity in antagonistic muscles. The typical 'tremor-at-rest' of Parkinson's disease--3-7 Hz activity which alternates between antagonistic muscles--is suppressed, at least briefly, during voluntary activity, at which time typical 8--12 Hz 'physiological tremor' may be seen. Essential tremor and its familial or senile variants also have a characteristic EMG pattern during voluntary activity--5-8 Hz bursts of activity which are synchronous in antagonistic muscles. This type of tremor may also be present in patients with Parkinson's disease and in certain kinships with a Charcot-Marie-Tooth polyneuropathy. Other tremors in association with polyneuropathy ('neuropathic tremor') have different physiological characteristics. Myoclonus is of essentially two types ('positive' with EMG bursts and 'negative' with brief pauses in ongoing activity, as with asterixis) and may, at times, mimic tremor. Certain specific tremors respond predictably to specific pharmacological therapy.

Ataxia↗
PubMed1977

Interactions between unloading reflex and voluntary muscle activity under different instructions.

Changes in the instantaneous firing frequency of a separate motor unit (MU) in the unloading reflex and voluntary movement according to instruction, triggered by external mechanical disturbance in the position of the arm, were studied. The activity of m. biceps brachii and m. pronator teres was recorded using surface bipolar electrodes with small area and small interelectrode distance. The correct position of the electrode with respect to the MU was controlled vectorelectromyographically. The probabilities of the appearance of an impulse in successive 10 ms intervals before and after the unloading were determined. The effect of the voluntary movement performed by the subject according to instruction on the reflex response is demonstrated, as well as the opposite effect, i.e. of the type of the external disturbing action on the voluntary movement. Certain problems related to the transcortical reflex response are discussed. It is assumed that some maxima in the summated electromyogram (EMG) which correspond in time to transcortical reflex influences are not due to a higher excitability of the alpha-motoneurones, but they are obtained by grouping of the impulses of many activated tonic MUs whose activity is recorded by recording the summated EMG.

Action Potentials↗
PubMed1979

Response to sudden torques about ankle in man: myotatic reflex.

1. Sudden dorsiflexions and plantarflexions of the foot were imposed on normal human subjects under various states of voluntary activity. 2. Under conditions of constant muscle contraction, the myotatic reflex in soleus and lateral gastrocnemius muscles is linearly and highly correlated with the rate of muscle stretch. The slope of this curve characterizes part of the reflex arc "gain." 3. The gain is linearly proportional to the level of tonic voluntary activation. 4. The gain is reduced by tonic contraction of antagonists. 5. The above statements can be summarized by the following equation (formula: see text), where d theta/dt is the rate of joint rotation. Ts and Tat are measures of voluntary contraction (tension) of all the extensor and flexor muscles acting at the ankle. The term S represents the level of preexisting spinal excitability that can be altered by prior instruction to the subject. 6. A phasic voluntary contraction of the soleus muscle, which leads to muscle shortening, will alter the reflex gain. The gain initially increases with increasing rates of shortening, but at higher rates the gain is reduced. This is in contradiction to the observation for tonic activation as stated above and may be due to an inability of the coactivated fusimotor system to produce sufficiently rapid cocontraction of the spindle fibers. 7. During lengthening of a muscle caused by voluntary contraction of its antagonists, the myotatic reflex gain is reduced. 8. The above facts are interpreted to imply that a functional role for the myotatic reflex in the leg extensors is limited to conditions of postural maintenance or slow, precise movement. During rapid movement, the myotatic reflex is ineffective and load-compensating reactions are mediated by longer latency loops. 9. The duration of the myotatic reflex EMG is from 10 to 40 ms, too brief to be a simple response to a velocity-sensing receptor organ. Either the response is in large measure due to the initial burst of spindle activity that occurs at the start of a ramp stretch, or motoneuron pool dynamics act as a high-pass filter on afferent inputs. 10. In the anterior tibial muscle, the relationships between stretch velocity and reflex amplitude and tonic voluntary contraction and reflex gain are qualitatively similar to those found in the ankle extensors.

Ankle↗
PubMedDate not supplied

[Effect of mental work on the efficiency and reliability of voluntary motor activity].

By means of reflexometry 200 students were divided into three groups -- with high, medium and low work efficiency (WE) and mobility of cortical processes (MCP) and into three initial variations within each group. After studies WE and MCP change in the direction opposite to the initial in extreme variations and remain at the initial level in the mean variation. Direct correlation between WE and MCP and work reliability (WR) is found which is independent of the degree of their pronouncement. MCP is the decisive factorial parameter of WE, and WR--a significant one. In its turn MCP is in an inverse significant correlation with WR determined by the intensity of the internal inhibition. The latency and duration of motor reflexes are in weak correlation with MCP and WE.

Adult↗