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Results for “Neuromuscular adaptability”

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At least 235 records · Page 13Linked to original sources

PubMed1986

Mechanisms of toxicity and tolerance to diisopropylphosphorofluoridate at the neuromuscular junction of the rat.

Diisopropylphosphorofluoridate (DFP), an irreversible inhibitor of acetylcholinesterase (AChE) activity, when given as an acute dose (1.5 mg/kg, sc) caused fasciculations and induced necrosis in rat skeletal muscle fibers. No adaptation was seen to daily dosing of DFP (1.5 mg/kg, sc) since all rats died after the second or third injection. Daily dosing of DFP in a concentration (0.5 mg/kg, sc) that as a single dose did not cause symptoms, produced onset of fasciculations on the third day associated with a reduced number of muscle fiber lesions. Further administration of DFP (14 days) caused disappearance of fasciculations and loss of sensitivity to the necrotizing actions in all muscles tested (diaphragm, soleus, and extensor digitorum longus). Activity of all molecular forms of AChE was reduced to 20-24% of control when symptoms of cholinergic hyperactivity appeared. Continuous injections of DFP (0.5 mg/kg/day, sc) up to 14 days did not cause greater inhibition of AChE activity. Instead, recovery of enzyme activity, especially of the 4S and 10S forms, was seen. During this period choline acetyltransferase activity (ChAT) was increased in muscle (intramuscular nerves) while the postsynaptic nicotinic acetylcholine receptor (nAChR) density (Bmax) was decreased to 44% without a change in the affinity constant (KD). It is concluded that neuromuscular adaptation to DFP is caused by recovery of AChE activity due to de novo synthesis and reduction in the number of nAChR.

Acetylcholinesterase↗

PubMed2004

Juvenile hormone-dependent motor activation in the adult locust Locusta migratoria.

Abdominal motoneurones of the locust Locusta migratoria were investigated in immature, mature and allatectomised females to compare their response characteristics during reproductive development. These motoneurones were chosen because they control muscles which are involved in extreme lengthening during egg-laying behaviour. The study focused on changes in motoneurone firing activity and its possible regulation by juvenile hormone. In isolated nerve-muscle preparations, increased resting motor activity was found in mature (>14 days) but not in immature females (<5 days). Removing the corpora allata, the gland producing juvenile hormone in insects, prevented increased motor activity. Stimulus evoked activation of the motor system led to a characteristic burst of action potentials which lasted for a few seconds. The time-course and amount of activation changed significantly during reproductive development. Mature females displayed longer lasting and higher activity than immature or allatectomised females, but only those segments involved in egg-laying were found to express the altered firing properties. Single cell analysis of motoneurone dendritic morphology or membrane properties revealed no evidence that could be causative for the activity changes seen during reproductive development. The results suggest that altered motoneurone activity serves to adapt females to the neuromuscular requirements of egg-laying behaviour.

Action Potentials↗

PubMed2001

Adaptive control of cyclic movements as muscles fatigue using functional neuromuscular stimulation.

For individuals with spinal cord injuries, functional neuromuscular stimulation (FNS) systems can be used to activate paralyzed muscles in order to restore function, provide exercise, or assist in movement therapy. In previous work, the pattern generator/pattern shaper (PG/PS) adaptive controller was evaluated on subjects with spinal cord injuries and was able to automatically adjust stimulation parameters to account for individual subject differences and system response nonlinearities. In this study, the PG/PS control system was utilized in extended trials. Results indicated that the controller adapted stimulation patterns in an online manner to account for changes in system properties due to fatigue.

Adult↗

PubMed2005

Impedance control and internal model use during the initial stage of adaptation to novel dynamics in humans.

This study investigated the neuromuscular mechanisms underlying the initial stage of adaptation to novel dynamics. A destabilizing velocity-dependent force field (VF) was introduced for sets of three consecutive trials. Between sets a random number of 4-8 null field trials were interposed, where the VF was inactivated. This prevented subjects from learning the novel dynamics, making it possible to repeatedly recreate the initial adaptive response. We were able to investigate detailed changes in neural control between the first, second and third VF trials. We identified two feedforward control mechanisms, which were initiated on the second VF trial and resulted in a 50% reduction in the hand path error. Responses to disturbances encountered on the first VF trial were feedback in nature, i.e. reflexes and voluntary correction of errors. However, on the second VF trial, muscle activation patterns were modified in anticipation of the effects of the force field. Feedforward cocontraction of all muscles was used to increase the viscoelastic impedance of the arm. While stiffening the arm, subjects also exerted a lateral force to counteract the perturbing effect of the force field. These anticipatory actions indicate that the central nervous system responds rapidly to counteract hitherto unfamiliar disturbances by a combination of increased viscoelastic impedance and formation of a crude internal dynamics model.

Adaptation, Physiological↗

PubMed1984

[Effect of cold adaptation on the transmission of excitation in a myoneural synapse].

In cold-adapted rats, synaptic excitability of single muscle fibers of fast (m. gastrocneiraus ) and slow (m. soleus) muscles as well as lability of their synapses were studied with the intracellular recording of APs. A decrease of thresholds of the synaptic excitability both in fast and in slow muscle fibers was found in cold-adapted rats. The lability of neuromuscular synapses in both types of muscles was also higher in the cold-adapted rats than in the control group. Cold adaptation seems to induce changes of synaptic transmission of excitation in fast and slow muscle fibers which reduces their excitability difference.

Action Potentials↗

PubMed1995

Applied physiology of ice hockey.

Today's elite hockey players are physically bigger and have improved levels of physiological fitness when compared with their predecessors. Correspondingly, previous ice hockey studies that have become widely referenced may have little relevance to current players and the way the game is presently played. A great need exists to apply exercise science to the game of ice hockey. Although much has been written about the physiology of ice hockey, there is little information based on well controlled studies. Particularly, there is a paucity of knowledge concerning optimal training schedules, training specificity, recovery profiles and seasonal detraining. Moreover, the reports that do exist have attempted to make comparisons across all levels of skill and talent. Thus, fundamental questions remain as to actual physiological exercise response and specialised training programmes for ice hockey players, particularly at the elite level. There is a demand for new properly designed experiments to find answers pertaining to the appropriate training methods for today's ice hockey players. Future research directions should consider the relationships between performance and such variables as neuromuscular skills, strength, power, peripheral adaptations, travel, hydration, detraining and sport-specific training programmes. Incidence and severity of injury among ice hockey players in relation to fatigue and fitness must also be investigated. Much of the information currently used in ice hockey will remain speculative and anecdotal until these studies are conducted.

Adaptation, Physiological↗

PubMed1990

Expression of long-term adaptation of synaptic transmission requires a critical period of protein synthesis.

The crayfish claw closer muscle is innervated by 2 distinct excitatory motoneurons, one tonic and the other phasic. The phasic motoneuron is relatively inactive and generates large EPSPs that normally depress rapidly with repetitive stimulation at moderate frequencies. Stimulation of the phasic motoneuron in vivo for 3 d at 5 Hz (2 hr/d) produced a marked adaptive shift in the neuromuscular synaptic response properties of the motoneuron: average initial EPSPs and depression of EPSPs were significantly reduced. We tested the hypothesis that neuronal protein synthesis is required for full expression of long-term adaptation (LTA). A reversible inhibitor of neuronal protein synthesis, cycloheximide (CHX), was injected into intact crayfish at various times prior to, during, or after each stimulation period. At a dosage of 5 micrograms/gm body weight, CHX inhibited the incorporation of [35S]-methionine into abdominal nerve cord protein for approximately 2 hr after administration (greater than 80% inhibition). Full expression of LTA was selectively blocked when CHX was administered 6 hr or 2 hr prior to each stimulation period. Both the reduction in initial EPSP amplitude and the resistance to synaptic depression were significantly attenuated. CHX administered at the onset of or at the end of each stimulation period did not affect the expression of LTA. Control experiments using unstimulated animals showed that neither chronic nor acute administration of CHX adversely affected the phasic axon's synaptic response properties. Our results suggest that full expression of neuronal LTA requires the presence of a pool of preexisting, short-lived (or rapidly utilized) protein(s). Depletion of such a pool prior to each stimulation period appears to interfere with subsequent induction of LTA.

Adaptation, Physiological↗

PubMed1986

Neuronal experience modifies synaptic long-term facilitation.

In a crayfish phasic neuromuscular junction, we have demonstrated low-frequency depression (LFD), high-frequency depression (HFD), and long-term facilitation (LTF) in response to different regimens of stimulation. Chronic stimulation of the phasic axon supplying the closer muscle of the claw in Procambarus clarkii resulted in diminished expression of HFD and LTF. Conversely, when impulse production in the phasic motoneuron was reduced by claw immobilization, both HFD and LTF were enhanced. LFD was insensitive to these manipulations. These results provide further evidence for long-term adaptation of the phasic neuromuscular junction to ongoing levels of impulse activity and illustrate the importance of a neuron's past history for synaptic plasticity. The ability of the neuron to adjust its short-term plasticity in response to altered experience constitutes an adaptive response that could be of general significance.

Adaptation, Physiological↗

PubMed2006

Differences in gait between children with and without developmental coordination disorder.

In the present study the walking pattern of 10 children with developmental coordination disorder (DCD) was investigated and compared to that of 10 typically developing, matched control children. All children walked at a similar velocity that was scaled to the length of the leg on a motor-driven treadmill. Three-dimensional kinematics were recorded with a motion capture digital camera system. The spatiotemporal parameters of the gait pattern revealed that children with DCD walked with shorter steps and at a higher frequency than the typically developing children. In addition, the children with DCD exhibited a body configuration that demonstrated increased trunk inclination during the entire gait cycle and enhanced during the entire gait cycle. At toe-off a less pronounced plantar flexion of the ankle was observed in children with DCD. In conclusion, it appeared that children with DCD make adaptations to their gait pattern on a treadmill to compensate for problems with neuromuscular and/or balance control. These adaptations seem to result in a safer walking strategy where the compromise between equilibrium and propulsion is different compared to typically developing children.

Biomechanical Phenomena↗

PubMed2003

Motoneuron and sensory neuron plasticity to varying neuromuscular activity levels.

The size and phenotypic properties of the neural and muscular elements of the neuromuscular unit are matched under normal conditions. When subjected to chronic decreases or increases in neuromuscular activity, however, the adaptations in these properties are much more limited in the neural compared with the muscular elements.

Case-Control Studies↗

PubMed2001

Automated tracking of facial features in patients with facial neuromuscular dysfunction.

Facial neuromuscular dysfunction severely impacts adaptive and expressive behavior and emotional health. Appropriate treatment is aided by quantitative and efficient assessment of facial motion impairment. We validated a newly developed method of quantifying facial motion, automated face analysis (AFA), by comparing it with an established manual marking method, the Maximal Static Response Assay (MSRA). In the AFA, motion of facial features is tracked automatically by computer vision without the need for placement of physical markers or restrictions of rigid head motion. Nine patients (seven women and two men) with a mean age of 39.3 years and various facial nerve disorders (five with Bell's palsy, three with trauma, and one with tumor resection) participated. The patients were videotaped while performing voluntary facial action tasks (brow raise, eye closure, and smile). For comparison with MSRA, physical markers were placed on facial landmarks. Image sequences were digitized into 640 x 480 x 24-bit pixel arrays at 30 frames per second (1 pixel congruent with0.3 mm). As defined for the MSRA, the coordinates of the center of each marker were manually recorded in the initial and final digitized frames, which correspond to repose and maximal response. For the AFA, these points were tracked automatically in the image sequence. Pearson correlation coefficients were used to evaluate consistency of measurement between manual (the MSRA) and automated (the AFA) tracking methods, and paired t tests were used to assess the mean difference between methods for feature tracking. Feature measures were highly consistent between methods, Pearson's r = 0.96 or higher, p < 0.001 for each of the action tasks. The mean differences between the methods were small; the mean error between methods was comparable to the error within the manual method (less than 1 pixel). The AFA demonstrated strong concurrent validity with the MSRA for pixel-wise displacement. Tracking was fully automated and provided motion vectors, which may be useful in guiding surgical and rehabilitative approaches to restoring facial function in patients with facial neuromuscular disorders.

Adult↗

PubMed1997

Two artificial neural systems for generation of gait swing by means of neuromuscular electrical stimulation.

A three-layer artificial neural network was used for adaptive control of gait swing generated by neuromuscular electrical stimulation (NMES) in a spinal cord injured subject. Network inputs consisted of knee and ankle goniometer signals for System 1, and knee and hip angular data for System 2. Controller output was proportional to changes in applied NMES pulse width (PW). Stimulation was applied to the left femoral and common peroneal nerves. The neural networks were trained off-line and on-line. Network performance was assessed by applying a number of different stimulation PWs and later comparing the resulting motion to a sample good step observed during the same test session. On-line training consisted of negative and positive reinforcement applied at chosen times. Both on-line and off-line training algorithms consisted of an enhanced supervised backpropagation scheme. Performance evaluation results favour the use of System 1 over System 2. Also, a network trained off-line and later submitted to on-line punishment appears to be more reliable (in automatic mode) than the same network after it is submitted to on-line reward or to off-line training alone. Finally, the systems' immediate response to on-line learning was favourable in all cases. Based on the results, a version of System 1 was used to generate walking in the test subject. This test indicated that the system is promising.

Adult↗

PubMed1994

Neuromuscular performance of lower limbs during voluntary and reflex activity in power- and endurance-trained athletes.

Neural, mechanical and muscle factors influence muscle force production. This study was therefore, designed to compare possible differences in the function of the neuromuscular system among differently adapted subjects. A group of 11 power-trained athletes and 10 endurance-trained athletes volunteered as subjects for this study. Maximal voluntary isometric force and the rate of force production of the knee extensor and the plantar flexor muscles were measured. In addition, basic reflex function was measured in the two experimental conditions. The power athletes produced higher voluntary forces (P < 0.01-0.001) with higher rates for force production (P < 0.001) by both muscle groups measured. Unexpectedly, however, no differences were noticed in the electromyogram time curves between the groups. During reflex activity, the endurance group demonstrated higher sensitivity to the mechanical stimuli, i.e. the higher reflex amplitude caused a higher rate of reflex force development, and the reflex amplitude correlated with the averaged angular velocity. The differences in the isometric conditions could be explained by obviously different muscle fibre distribution, by different amounts of muscle mass, by possible differences in the force transmission from individual myofibrils to the skeletal muscle and by specificity of training. In addition, differences in nervous system structure and muscle spindle properties could explain the observed differences in reflex activity between the two groups.

Adult↗

PubMed2003

[Rehabilitation guidelines after total knee arthroplasty].

Rehabilitation programs after total knee arthroplasty vary as much as do the surgical procedures employed. The postoperative range of motion of the knee is considered to be one of the primary indicators of the success of arthroplasty surgery. Protocols focusing on improving range of motion have been widely investigated: the end result does not seem to depend on using specific devices or exercises. There are no prospective randomized clinical trials evaluating the differences in outcome after total knee arthroplasty between patients following different rehabilitation programs. What are the needs of the patient after this surgery? Rehabilitation should focus on physical and functional limitations, and guidance of the patient during this process is important. The patient follows an individual program comprising a sensorimotor progression in weight-bearing positions to allow for improved functional knee stabilization. In knee osteoarthritis, and also after total knee arthroplasty, the neuromuscular system undergoes various adaptations during gait and other activities. Because of this, rehabilitation should not attempt to achieve hypothetical norms, but to help the patient in the motor learning process of acquiring improved motion patterns and stabilization strategies.

Arthroplasty, Replacement, Knee↗

PubMed2005

Potential advantages of patient-ventilator synchrony.

During conventional mechanical ventilation, fixed set pressure, flow, and tidal volume result in a mismatch between patient and ventilator inspiratory time and in a patient's inability to adapt to changing ventilatory demand. Synchrony between the patient and ventilator improves neuromuscular coupling and the ability to adapt to increased ventilatory demand or loading. The sensation of dyspnea prevents ineffective inspiratory efforts and attenuates periodic breathing during sleep.

Humans↗

PubMed2004

Making muscles "stronger": exercise, nutrition, drugs.

As described in this review, maximal muscle strength is strongly influenced by resistive-types of exercise, which induce adaptive changes in both neuromuscular function and muscle morphology. Further, timed intake of protein in conjunction with resistance training elicit greater strength and muscle size gains than resistance training alone. Creatine supplementation amplifies the hypertrophic response to resistance training, although some individuals may not respond positively. Locally produced muscle growth factors are upregulated during creatine supplementation, which contributes to increase the responsiveness of muscle cells to intensive training stimuli. Usage of anabolic steroids boosts muscle hypertrophy beyond inherent genetical limits, not only by increasing the DNA transcription rate for myofibrillar proteins but also by increasing the nucleus-to-cytoplasm ratio due to accelerated activation of myogenic satellite cells. However, severe tissue damaging effects exist with anabolic steroids, some of which are irreversible.

Anabolic Agents↗

PubMed2000

The effect of endurance training on parameters of aerobic fitness.

Endurance exercise training results in profound adaptations of the cardiorespiratory and neuromuscular systems that enhance the delivery of oxygen from the atmosphere to the mitochondria and enable a tighter regulation of muscle metabolism. These adaptations effect an improvement in endurance performance that is manifest as a rightward shift in the 'velocity-time curve'. This shift enables athletes to exercise for longer at a given absolute exercise intensity, or to exercise at a higher exercise intensity for a given duration. There are 4 key parameters of aerobic fitness that affect the nature of the velocity-time curve that can be measured in the human athlete. These are the maximal oxygen uptake (VO2max), exercise economy, the lactate/ventilatory threshold and oxygen uptake kinetics. Other parameters that may help determine endurance performance, and that are related to the other 4 parameters, are the velocity at VO2max (V-VO2max) and the maximal lactate steady state or critical power. This review considers the effect of endurance training on the key parameters of aerobic (endurance) fitness and attempts to relate these changes to the adaptations seen in the body's physiological systems with training. The importance of improvements in the aerobic fitness parameters to the enhancement of endurance performance is highlighted, as are the training methods that may be considered optimal for facilitating such improvements.

Adaptation, Physiological↗

PubMed2000

Myosin heavy chain isoform expression following reduced neuromuscular activity: potential regulatory mechanisms.

In this review, the adaptations in myosin heavy chain (MHC) isoform expression induced by chronic reductions in neuromuscular activity (including electrical activation and load bearing) of the intact neuromuscular unit are summarized and evaluated. Several different animal models and human clinical conditions of reduced neuromuscular activity are categorized based on the manner and extent to which they alter the levels of electrical activation and load bearing, resulting in three main categories of reduced activity. These are: 1) reduced activation and load bearing (including spinal cord injury, spinal cord transection, and limb immobilization with the muscle in a shortened position); 2) reduced loading (including spaceflight, hindlimb unloading, bed rest, and unilateral limb unloading); and 3) inactivity (including spinal cord isolation and blockage of motoneuron action potential conduction by tetrodotoxin). All of the models discussed resulted in increased expression of fast MHC isoforms at the protein and/or mRNA levels in slow and fast muscles (with the possible exception of unilateral limb unloading in humans). However, the specific fast MHC isoforms that are induced (usually the MHC-IIx isoform in slow muscle and the MHC-IIb isoform in fast muscle) and the degree and rate of adaptation are dependent upon the animal species and the specific model or condition that is being studied. Recent studies designed to elucidate the mechanisms by which electrical activation and load bearing alter expression of MHC isoforms at the cellular and genetic levels are also reviewed. Two main mechanisms have been proposed, the myogenin:MyoD and calcineurin:NF-AT pathways. Collectively, the data suggest that the regulation of MHC isoform expression involves a complex interaction of multiple control mechanisms including the myogenin:MyoD and calcineurin:NF-AT pathways; however, other intracellular signaling pathways are likely to contribute.

Animals↗