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INTRODUCTION: Trans-spinal direct current stimulation (tsDCS) is a neuromodulative technique used to improve motor functions in neurological disorders and to facilitate sport performance. However, despite the broad application of spinal cord polarization, the physiological mechanisms behind the observed effects remain unclear. We have recently demonstrated that anodal or cathodal tsDCS can alter motoneuron...
INTRODUCTION: The relationship between the output force and motor command depends on the intrinsic RESULTS: The mathematical decomposition of unfused tetanic contractions of FF and FR MUs into twitch-shape responses to consecutive stimuli was conducted. The decomposition indicated substantial changes predominantly in force and additionally in time parameters of successive twitch‑like components, responsible...
INTRODUCTION: Obesity and diabetes, with associated conditions termed as metabolic syndrome are growing problem worldwide. Consequences of impaired glucose metabolism affect the whole organism including neuromuscular system. Diabetic neuropathy influences predominantly sensory system and to smaller degree motor system. Additionally, skeletal muscles as involved in glucose metabolism are exposed to...
INTRODUCTION: Repeated short-term and high--intensity exercises with a progressive external load are defined as strength or resistance training, which is responsible for an increase in muscle mass and force. AIM(S): The aim of this study was to determine whether strength training induces adaptive changes in firing properties of motoneurons (MNs) innervating the trained muscles. METHOD(S): The study...
Slow motor units (MUs) have no sag in their unfused tetani. This study in anesthetized rats shows that the sag can be observed in slow soleus MUs after prolonged activity. Twitches and unfused tetanic contractions were recorded from male (n=35) and female (n=39) MUs before and after the four minutes of the fatigue test (trains of 13 pulses at 40 Hz repeated every second). After this activity twitch...
BACKGROUND AND AIMS: The aim of this study was to reveal variability of twitch-shape decomposed components of motor unit tetanic contractions of rat soleus muscle, which is almost exclusively composed of slow motor units (MUs). Moreover, sex differences in ranges of the force amplitude or time parameters of these decomposed twitches were analyzed. METHODS: Experiments were performed on adult Wistar...
BACKGROUND AND AIMS: Different forms of chronic physical activity evoke adaptive changes in the neuromuscular system. Long-lasting strength training, with repeated short-term and highintensity exercises, is responsible for an increase of muscle mass and generation of larger forces. However, adaptations in properties of motoneurons innervating muscles subjected to such training have been unknown so...
BACKGROUND AND AIMS: Endurance training is based on a repeated, prolonged activation of a large number of muscles. It causes morphological, biochemical and metabolic changes in the muscles and the nervous system. However, there are no data concerning changes in motor unit (MU) contractile properties following endurance training. METHODS: 61 male rats were assigned to 4 groups, untrained – control...
The study shows that different models of an increased muscular activity may induce measurable effects on electrophysiological properties of motoneurons (MNs). Three types of altered motor activity were compared in rats: chronic compensatory muscle overload, whole-body vibration (WBV), and strength training. Intracellular recordings from spinal motoneurons were made to measure membrane and firing properties...
The study aimed at determining changes in a course of motoneuronal afterhyperpolarization (AHP) and in contractile twitches of motor units (MUs) during activity evoked by increasing number of stimuli (from 1 to 5), at short interspike intervals (5 ms). The stimulation was applied antidromically to spinal motoneurones or to isolated axons of MUs of the medial gastrocnemius muscle within two separate...
Aim of the work was to verify if the sinusoidal modulation of the stimulation rate of individual rat MUs may provide reliable sinusoidal responses of the recorded force with an acceptable harmonic distortion (HD). After MU classification, the isolated axons of the spinal ventral roots were electrically stimulated with rates sinusoidally changing, from a minimum to a maximum value, with different frequencies...
The soleus muscle has unique physiological characteristics, as a typical slow-twitch muscle, composed predominantly of slow motor units (MUs). In this study we examined electrophysiologically functionally isolated MUs of male and female adult Wistar rats. It was revealed that the mean mass of the soleus muscle in males was approximately by 80% bigger than in females, however, a relation of the muscle-to-body...
Plasticity of motor unit (MU) contractile properties observed as a result of various forms of altered physical activity or neurological disorders often leads to difficulties in their division into fast and slow types on a basis of standard physiological criteria (sag disappearance, changes of the contraction time). A method to recognize fast or slow MU types on a basis of a profile of tetanic contraction...
The whole body vibration training was performed on adult male Wistar rats. The experimental group subjected to a whole body vibration consisted of seven rats, while the control group of nine rats. The training program included 5 weeks and was applied by 5 days a week. Each daily session consisted of four 30-s runs of vibration at 50 Hz. Intracellular properties of motoneurones were investigated during...
Compensatory overload of medial gastrocnemius muscle was induced by bilateral tenotomy of synergists (lateral gastrocnemius, plantaris and soleus). Operated muscles were regularly voluntarily activated as after surgery rats were kept in wheel-equipped cages and additionally were exercised on a treadmill. 3 months after the surgery the final electrophysiological experiments were carried out. 106 motor...
In the majority of mammalian skeletal muscles, contractile properties of motor units are variable and three main types of these units can be distinguished. The present review summarizes: results of studies of motor unit properties in the medial gastrocnemius muscle and their variability in two species, cats and rats, and studies on differences of motor unit properties in two genders. Moreover, plasticity...
During natural contractions motor units (MUs) are activated by variable frequency discharge patterns of motoneurones. The aim of this review was (1) to discuss differences between tetanic contractions developed at constant and random frequencies of pulses; (2) to show results of mathematical decomposition of these tetani into series of twitch-shaped responses to individual pulses; (3) to indicate...
Voluntary limb movements are initiated in the brain but the neurones responsible for activating the muscles (motoneurones and interneurones) are located in the spinal cord. The spinal cord also contains neurones that provide the brain, and especially the cerebellum, with continuous information on effects of the descending commands. We show that one population of such neurones provide the cerebellum...
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