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PubMed1997

[Electromyography-controlled muscle rehabilitation--knee injuries].

Surface is a noninvasive, mostly nonreactive, objective measuring procedure for evaluation of the degree of muscle activation. It allows for accurate assessments of the neuromuscular system and description of adaptations resulting from injury. Decreases in torque, EMG amplitude and EMG frequency occur as a result of knee joint injuries. Efficiency checks and evaluations of training programs and neuromuscular treatment can be done. Decreases in torque, EMG amplitude and EMG frequency found after knee joint injury (cruciate ligament, meniscus) are due to intraarticular and periarticular afferent processes. 12 weeks postoperatively, the neuromuscular deficits from cruciate ligament injury have increased. While complete recovery can be achieved following meniscus fixation (more than 1 year postoperatively), cruciate ligament injuries lead to chronically reduced EMG median frequencies.

Athletic Injuries↗
PubMed2002

The adaptive potential of skeletal muscle fibers.

Mammalian skeletal muscle fibers display a great adaptive potential. This potential results from the ability of muscle fibers to adjust their molecular, functional, and metabolic properties in response to altered functional demands, such as changes in neuromuscular activity or mechanical loading. Adaptive changes in the expression of myofibrillar and other protein isoforms result in fiber type transitions. These transitions occur in a sequential order and encompass a spectrum of pure and hybrid fibers. Depending on the quality, intensity, and duration of the alterations in functional demand, muscle fibers may undergo functional transitions in the direction of slow or fast, as well as metabolic transitions in the direction of aerobic-oxidative or glycolytic. The maximum range of possible transitions in either direction depends on the fiber phenotype and is determined by its initial location in the fiber spectrum.

Adaptation, Physiological↗
PubMed1992

Compensatory plasticity of aging at the neuromuscular junction.

Several age-related phenomena observed at the neuromuscular junction (NMJ) can be viewed as adaptations to cellular deficits. These compensatory mechanisms, which maintain functional and morphologic integrity, are those present in the adult animal. In the study of compensatory mechanisms with age, the choice of an appropriate animal model is important. Three adaptations are discussed: maintenance or increase of transmitter release despite reduced supply of synaptic vesicles; functional reactive sprouting after partial denervation despite reduced axonal transport; and maintenance of nerve terminal integrity in the face of increased outgrowth and retraction. In all cases, successful adaptation in old animals is obtained at the expense of a more fragile system. Either the compensations themselves or the resulting vulnerability may alter the reactions of the aging nervous system to changes in external and internal milieu.

Adaptation, Physiological↗
PubMed2004

Synaptic vesicle cycling at type-identified diaphragm neuromuscular junctions.

Differences in neuromuscular transmission and neuromuscular junction morphology exist across muscle fiber types. We hypothesized that these fiber-type differences are reflected in the size of the cycling synaptic vesicle pool. Synaptic vesicle cycling at type-identified rat diaphragm neuromuscular junctions was examined by fluorescently labeling presynaptic vesicles with FM4-64. We found that FM4-64 fluorescence uptake was higher at presynaptic terminals of type I/IIa fibers than type IIx/IIb fibers. However, no fiber-type differences in the rate of FM4-64 destaining were found with repetitive nerve stimulation. Synaptic vesicle density at active zones was examined by transmission electron microscopy. In accordance with FM4-64 uptake, synaptic vesicle density was greater at type I/IIa than IIx/IIb fibers. These results demonstrate differences in synaptic vesicle cycling across diaphragm muscle fiber types, which may underlie previously observed differences in neuromuscular transmission across diaphragm muscle fiber types. In the diaphragm, motor units comprising type I and type IIa fibers are most frequently recruited with a duty cycle of approximately 40%. Motor units comprising IIx/IIb fibers are infrequently recruited and only for short durations. The capacity for synaptic vesicle release and cycling at different muscle fiber types matches the functional requirements of these motor units. If the demand for recruitment of motor units comprising IIx/IIb fibers increases, for example, with mechanical loading, there is an increased risk for neuromuscular transmission failure that my relate to the capacity for synaptic vesicle release and cycling. Muscle fiber type-specific adaptations should be considered when examining neuromuscular disorders.

Animals↗
PubMed1991

Use of a pharmacokinetic-dynamic model for the automatic feedback control of atracurium.

A control algorithm for the closed-loop control of atracurium-induced neuromuscular blockade based on pharmacokinetic-dynamic model-based adaptive feedback is described. Mean offset from setpoint at 90% neuromuscular block was 0.04% and the mean standard deviation from mean neuromuscular block was 1.9%. The mean average atracurium requirement was 0.37 mg.kg-1.h-1. The model-based adaptive closed-loop control of atracurium infusion provided reasonable control of muscle relaxation. It offers a solution to the problem of adapting pharmacokinetic and pharmacodynamic data to individuals when using mean data as starting values for drug therapy.

Adult↗
PubMed1992

Maintenance of long-term adaptation of synaptic transmission requires axonal transport following induction in an identified crayfish motoneuron.

Motoneurons can adapt to altered levels of electrical activity by effecting semi-permanent changes in their neuromuscular synaptic physiology. In the present study, we tested the hypothesis that maintenance of activity-dependent long-term adaptation of synaptic transmission in a crayfish abdominal extensor motoneuron (phasic axon 3) required axonal transport following induction. Intact crayfish were chronically wired for periodic in vivo stimulation of axon 3. Periodic unilateral stimulation for 3-5 consecutive days (2 h/day) induced long-term adaptation (LTA) of neuromuscular synaptic transmission in axon 3. Initial EPSP amplitudes (measured at 0.1 Hz) were significantly reduced to approximately 40% of contralateral control amplitudes over a 7-day poststimulation period. Additionally, synaptic depression during 5 Hz test stimulation of axon 3 was significantly less in chronically stimulated neurons: excitatory postsynaptic potential (EPSP) amplitudes measured after 20 min of 5 Hz test stimulation (final EPSPs) were significantly larger in conditioned neurons than in unstimulated controls. The depression of initial EPSP amplitudes persisted for 7 days postinduction, while the increased synaptic stamina persisted for 4 days but was absent at 7 days postinduction. Axotomy of axon 3 following induction of LTA had no effect on long-term maintenance of the activity-induced reduction in initial EPSP amplitudes. Initial EPSP amplitudes in conditioned, axotomized neurons were still reduced to 42% of control amplitudes over the 7-day postinduction period. In contrast, postinduction axotomy of axon 3 elicited an accelerated decay of the enhanced synaptic stamina. Following axotomy, final EPSP amplitudes were significantly larger in conditioned neurons for only 1 day poststimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed2001

[Controlled dynamic weight training in patients with neuromuscular disorders].

The question posed was whether individually adapted, controlled dynamic weight training, in accordance with training principles and methods from sports science, applied for a limited time, can lead to an improvement in the stimulation and release of muscular strength in patients with neuromuscular disorders. The muscles of the pelvic girdle and the lower extremity of 10 patients (5 with dystrophic muscle disease and 5 with neurogenic muscular atrophy) were exercised provisionally for a period of 6 weeks on various weight training machines. The training routine was 3 sessions (TS) per week at an intensity range of 40-60% of the respective best performance for the exercise (One Repetition Maximum; ORM), at 8-12 repetitions/set and 2-4 sets/exercise. Body weight and ORM were determined before, during and after the training period (TP), the different load criteria/TS were documented. It was possible to train the patients in accordance with principles of training known from sports science. Over the entire TP it was possible to increase the load criteria significantly (p < 0.01). The ORM had increased considerably in all exercises after the TP (p < 0.01). The changes in strength lay between 11 and 95%. Correlation analyses demonstrated that the percentage changes in strength correlated significantly (p < 0.01) and positively (r = 0.87) with the training load in terms of quality. No significant changes in development of strength could be ascertained between the two groups of patients (dystrophic versus atrophic). The individually adjusted, controlled dynamic weight training described above, leads to an increase in the stimulation and release of strength and can be conducted according to principles of training science. Applied in clinical rehabilitation, it represents a supplementary form of therapy in the symptomatic treatment of neuromuscular disorders.

Adult↗
PubMed2005

Electromyographic evaluation of neuromuscular co-ordination during chewing in a subject with organic occlusion.

The neuromuscular co-ordination of the anterior masseter and temporal muscles during chewing has been studied. The subject analysed was 24 years old female with organic occlusion, molar and canine class 1, with 2 mm overbite and overjet, frontal disocclusion and canine protection, with no cranio-mandibular disorders. Masticatory cycles and electromyographic activity were recorded with a K6 I kinesiograph (Myotronics Inc., Seattle, WA, USA). The chewing cycles were recorded with a soft bolus and a hard bolus, on 3 consecutive days. Electromyographic analysis during masticatory cycles showed that electromyographic activity was higher in the masseter muscle homolateral to the chewing side than in the contralateral muscle, whereas the anterior temporal muscles achieved similar voltages. When chewing the hard bolus, versus the soft bolus, activity in the contralateral masseter muscle increased to a greater extent than in the homolateral masseter muscle. The results were analogous at all 3 recordings. When chewing, the subject showed good muscle co-ordination, which was constant over the 3 recordings made on 3 consecutive days. Increased activity of the contralateral masseter muscle when chewing the hard versus the soft bolus indicates the stomatognathic system's capability to adapt to load and its neuromuscular equilibrium.

Adult↗
PubMedDate not supplied

Comparison of heteronymous monosynaptic Ia facilitation in young and elderly subjects in supine and standing positions.

BACKGROUND: The control of posture and balance is a primary concern among the elderly. Postural instability has been identified as a contributor to the greater incidence of falling among this segment of the population. One important neuromuscular mechanism identified as important in the control of posture and balance is the segmental reflex system. The purpose of this study was to examine the role of presynaptic inhibition in modulating the reflex system in young and elderly subjects. METHODS: To estimate the influence of body position on presynaptic inhibition to the soleus motor pool between young and elderly subjects, 11 young (mean age=23.9 yrs.) and 9 elderly (mean age=72.1 yrs.) subjects were examined in two different body positions: supine and standing. This study utilized the heteronymous facilitation protocol, as described by Hultborn et al. (1987), to estimate presynaptic inhibition of the Ia afferent pathway onto the soleus alpha-motoneuron pool. Maximal soleus H-reflex (H-max) and motor response (M-max) amplitudes were determined prior to testing at each condition, and the H-max/M-max ratio at each body position was determined. To estimate presynaptic inhibition at each body position, subjects received 24 test soleus H-reflex stimuli ( approximately 15% M-max), and 24 soleus H-reflexes conditioned by stimulation of the ipsilateral femoral nerve. RESULTS: Results demonstrated a significant decrease in H-max/M-max ratio from supine (66.1%) to standing (56.8%) for the young subjects, whereas the elderly subjects demonstrated no changes in the H-max/M-max ratio between body positions (39.8% supine; 39.8% standing). The conditioning stimulus produced a significant change in the test reflex for the young subjects during supine testing (51.1% increase) but not standing (3.4% increase). The elderly subjects demonstrated no significant changes in the test reflex produced by the heteronymous conditioning at either condition (17.6% increase supine; 4.9% increase standing). CONCLUSIONS: These results demonstrate differential effects of both H-reflex modulation and heteronymous conditioning for elderly subjects when compared with young adults. These differences may be an adaptive phenomenon of the aging neuromuscular system, exemplified by a decreased ability to modulate the reflex system in the elderly group.

Adult↗
PubMed1984

The influence of extra load on the mechanical behavior of skeletal muscle.

Eleven international jumpers and throwers engaged in year round training were divided into experimental (n = 6) and control (n = 5) groups. The experimental group was tested before and after a 3 weeks simulated hypergravity period, and again 4 weeks after the hypergravity period. The high gravity condition was created by wearing a vest weighing about 13% of the subjects body weight. The vest was worn from morning to evening including the training sessions, and only removed during sleep. The daily training of all subjects consisted of classical weight training and jumping drills. No changes in the ordinary training program were allowed in the experimental group, except for the use of the vest. Vertical jumps, drop jumps and a 15 s continuous jumping test were used to measure the explosive power characteristics of the subjects. After the hypergravity period the experimental subjects demonstrated significant (5-10%, P less than 0.05-0.01) improvements in most of the variables studied: however, 4 weeks after cessation of the high gravity period they tended to return towards the starting values. No changes were observed in the results of the control group. The improvement observed in the experimental subjects was explained as fast adaptation to the simulated high gravity field. It is suggested that adaptation had occurred both in neuromuscular functions and in metabolic processes.

Adult↗
PubMed2002

[Neurogenic spinal deformities. II. Sitting and seating devices: principles and indications].

Sitting is a dynamic process regulated by motor reactions due to endogenic and exogenic influences. Patients with neuromuscular disorders may not continuously adapt their sitting posture but seating devices may improve their quality of life. Prerequisites for the indication of high quality and cost effective seating devices are guidelines for planning and fitting which consider both pathomorphologic mechanisms and the patient's personality. In order to avoid functional problems and pain caused by an insufficient seating device it is necessary to pay attention to the exact indication, time, and combination of technical options. Planning within a seating clinic needs teamwork. First the goal of treatment is defined; it depends on the functional deficit, on the daily living activities of the patient, and on the social environmental factors. Second fitting of the devices follows defined treatment guidelines. By examination of the sensoric and statomotoric system it is possible to classify the patient's sitting or seating ability for simplifying indication: three groups of active sitters who are able to change position of trunk and pelvis actively are differentiated from three groups of passive sitters who have to be seated.

Adult↗
PubMed2006

Effect of augmented plantarflexion power on preferred walking speed and economy in young and older adults.

With age, loss of skeletal muscle mass (sarcopenia) results in decreased muscle strength and power. Decreased strength and power, in turn, are closely linked with declines in physical function. Preferred walking speed, a marker of physical function, is slower in older adults compared to young adults. Research suggests that older adults may walk slower as a consequence of decreased plantarflexor power at push-off. In this study, we hypothesized that providing additional plantarflexion (PF) power during push-off would (1) increase preferred walking speed, and (2) reduce metabolic cost of transport (MCOT), in young and older adults. PF power was augmented using powered ankle-foot orthoses (PAFOs). The PAFOs, which use pneumatic actuators to provide an additional PF moment, were based on a design by Ferris et al. [Ferris DP, Czerniecki JM, Hannaford B. An ankle-foot orthosis powered by artificial pneumatic muscles. J Appl Biomech 2005;21:189-97.]. Nine young (23.3+/-1.6 years) and seven older (74.6+/-6.6 years) adults participated. For the young adults, eight out of nine increased their preferred walking speed when push-off power was augmented (1.18+/-0.16 to 1.25+/-0.16m/s, p=0.03). A similar, but non-significant, trend in preferred walking speed was observed for the older adults. With augmented push-off power, MCOT for young adults decreased from 0.395+/-0.057 to 0.343+/-0.047 (p=0.008); indicating that the neuromuscular system was able to adapt to use external energy to reduce metabolic cost. Only three older adults were tested but MCOT values showed a similar trend. Augmenting PF power increases gait speed and reduces MCOT in young adults. Older adults may need a longer period to take advantage of additional push-off power.

Adult↗
PubMed1998

Adverse changes in fibre type composition of the human masseter versus biceps brachii muscle during aging.

The fibre composition of functionally different regions, the superficial and the deep portions, of the human masseter and the biceps brachii muscles of six elderly subjects (mean age 74 years) was studied by morphological and enzyme-histochemical methods. When compared to previous data for young adults, the masseter muscle from elderly subjects showed a significant decrease in the proportion of type I fibres and an increase of type IM and II fibre types, concomitant with muscle fibre atrophy. In the old biceps, there were no changes in the type I fibre proportion and fibre diameter, but a significant decrease in the type IIB fibre content. The present results of changes in fibre composition, in addition to previous findings of functional deterioration of the old masseter, probably reflect a combination of age related degenerative and adaptive processes within the trigeminal neuromuscular system. When compared with previous findings in young adult masseter, it can be concluded that the human masseter muscle differs from limb muscles both in fibre composition and in structural response of the muscle during aging. These differences between the masseter and the biceps brachii muscle suggest muscle specific alterations during aging probably due to differences in genetical control, functional performance and nerve and hormonal influences.

Adult↗
PubMed1992

Biochemical correlates for behavioral deficits induced by secalonic acid D in developing mice.

Humoral signals (neurotransmitters and hormones) control cell division, migration, and differentiation processes which define the organization of brain pathways. Alterations in maternal, fetal, and neonatal biochemistry during critical periods of neurogenesis may irreparably alter the circuitry and, thus, postnatal behavior of young animals. Secalonic acid D (SAD), an ergochrome mycotoxin, causes behavioral and neurochemical deficits in developing mice following prenatal (transplacental) or early postnatal (transmammary) exposure. SAD-induced functional abnormalities include delays in reflex behaviors, integrated neuromuscular activity and strength, stress adaptation responses, and sensory discrimination. These behavioral changes are associated with reductions of brain monoamine neurotransmitter levels in both fetuses and neonates. SAD also alters concentrations of maternal plasma corticosteroids and fetal cyclic nucleotides during midgestation. SAD thus modulates several chemicals in pregnant mice and their fetuses which contribute to brain development, suggesting that this mycotoxin may pose a neuroteratogenic hazard to other immature mammals, including human infants.

Animals↗
PubMed2002

Sustaining a constant effort by the tongue and hand: effects of acute fatigue.

A constant-effort task was used previously as a potential assessment technique for fatigue. Participants sustained submaximal target effort levels with the tongue and hand against soft air-filled bulbs. For 80% of all trials, pressure decreased exponentially to a positive asymptote. In addition, pressure decreased faster when the muscles were fatigued than when they were rested. This study attempted to replicate the previous findings with new participants and to extend the findings to include surface electromyographic (EMG) data. Pressure and surface EMG signals were collected simultaneously while 10 neurologically normal young adults performed the constant-effort task at 50% of maximum pressure with the tongue and the hand. Eighty-one percent of the pressure data were modeled by a negative exponential equation with a nonzero asymptote. Seventy-three percent of the corresponding EMG data also fit this mathematical model. The pressure signals decayed more slowly than the corresponding EMG signals, particularly for the hand. After participants fatigued the tongue and hand with repeated brief maximal voluntary contractions, the time constants were reduced (rate of decay increased) for the tongue but not the hand. These results corroborate the previous finding that the time constant, determined from an exponential curve-fitting procedure, is a replicable measure. Furthermore, the reduction in the time constant after inducing acute fatigue in the tongue was replicated, although this same relationship was not replicated for the hand. The EMG data suggest that decreases in neuromuscular drive, including increased early adaptation, motor unit derecruitment, and motor unit desynchronization, contributed to the decrease in pressure during the constant-effort task, especially after acute fatigue was induced. These observations support the hypothesis that the task reflects, at least in part, central fatigue processes.

Acute Disease↗
PubMed1991

Mandibular function in children with a lateral forced bite.

Open-close-clench cycles have been studied in 12 children with a lateral forced bite in order to investigate how the neuromuscular system of the mandible adapts itself in the presence of occlusal interferences. The mandibular movements were registered in a frontal plane at the central incisors with an opto-electronic registration technique. Series of 35 cycles were recorded to intercuspal position, against flat occlusal splints constructed in intercuspal raised and retruded positions, and against splints with occlusal stops in a retruded position. Average lateral displacements of the mandible during cycle series against flat occlusal splints were measured relative to cycle series to intercuspal position and relative to series against splints with occlusal stops in the retruded position. The lateral mandibular displacements were registered at maximal tooth-tooth or tooth-splint contact and at 7, 14, and 21 mm mouth-opening. It was found that the mandible in the subjects investigated is displaced to the forced bite side both during cycle series into intercuspal position as well as when occlusal contacts are eliminated by the use of flat occlusal splints.

Child↗
PubMed2005

Designing resistance training programmes to enhance muscular fitness: a review of the acute programme variables.

The popularity of resistance training has grown immensely over the past 25 years, with extensive research demonstrating that not only is resistance training an effective method to improve neuromuscular function, it can also be equally effective in maintaining or improving individual health status. However, designing a resistance training programme is a complex process that incorporates several acute programme variables and key training principles. The effectiveness of a resistance training programme to achieve a specific training outcome (i.e. muscular endurance, hypertrophy, maximal strength, or power) depends on manipulation of the acute programme variables, these include: (i) muscle action; (ii) loading and volume; (iii) exercise selection and order; (iv) rest periods; (v) repetition velocity; and (vi) frequency. Ultimately, it is the acute programme variables, all of which affect the degree of the resistance training stimuli, that determine the magnitude to which the neuromuscular, neuroendocrine and musculoskeletal systems adapt to both acute and chronic resistance exercise. This article reviews the available research that has examined the application of the acute programme variables and their influence on exercise performance and training adaptations. The concepts presented in this article represent an important approach to effective programme design. Therefore, it is essential for those involved with the prescription of resistance exercise (i.e. strength coaches, rehabilitation specialists, exercise physiologists) to acquire a fundamental understanding of the acute programme variables and the importance of their practical application in programme design.

Exercise↗