Search results for "Motor unit"
showing 10 items of 55 documents
Evidence of resistance training-induced neural adaptation in older adults
2021
The deleterious effects of aging on force production are observable from the age of 40 upwards, depending on the measure. Neural mechanisms contributing to maximum force production and rate of force development have been suggested as descending drive from supraspinal centers, spinal motoneuron excitability, and corticospinal inhibition of descending drive; all of which influence motor unit recruitment and/or firing rate. Resistance-trained Master athletes offer a good source of information regarding the inevitable effects of aging despite the countermeasure of systematic resistance-training. However, most evidence of neural adaptation is derived from longitudinal intervention studies in pre…
Corticoperipheral neuromuscular disconnection in obstructive sleep apnoea.
2020
Abstract The roles of central nervous mechanisms and cortical output in obstructive sleep apnoea remain unclear. We addressed corticomuscular coupling between cortical sensorimotor areas and lower facial motor units as a mechanistic pathway and as a possible surrogate marker of corticoperipheral motor control in obstructive sleep apnoea. In this exploratory cross-sectional retrospective study, we analysed EEG (C3 and C4 leads) and chin EMG from polysomnography recordings in 86 participants (22 females; age range: 26–81 years): 27 with mild (respiratory disturbance index = 5–15 events/h), 21 with moderate (15–30 events/h) and 23 with severe obstructive sleep apnoea (>30 events/h) and 15 cont…
Signal Characteristics of EMG at Different Levels of Muscle Tension
1976
Electromyographic activity of m. rectus femoris at submaximal and maximal voluntary contractions was quantified by conventional integration technique and also be a more "qualitative" procedure of automated motor unit averaging and frequency spectrum analysis. By relating the EMG parameters to produced muscle tension it was observed that the integrated EMG increased in a slightly nonlinear fashion with the increase in muscle force. The other EMG variables also showed clear changes as a function of muscle tension. The averaged motor unit potential (AMUP) and its specific parameters (number of spikes, amplitude, rise time and amplitude-rise time ratio) showed such changes with muscle tension t…
The relative contribution to the plantar-flexor torque of the soleus motor units activated by the H reflex and M response in humans.
2000
Abstract This study proposes a method of quantifying the relative contribution to the plantar-flexor torque of soleus H and M responses evoked by tibial nerve stimulation. For ten subjects, the amplitude of the twitch produced by the H wave was plotted against the corresponding potential, for stimuli producing H without M (i.e. in the ascending portion of the H-recruitment curve). It was then assumed that the contribution of H to twitches produced by M plus H was similar for similar H waves on the curve-descending portion. Hence, the contribution of M was estimated, for the range of M waves including those accompanying H max . The estimated mechanical contributions of H and M wave increase …
Interrelationships between electromyographic, mechanical, muscle structure and reflex time measurements in man.
1981
Reaction time (TRT) with its premotor (PMT) and motor time (MT) components, patellar reflex time (TRfT) with its latency (LAT) and motor time (RfMT) were studied together with isometric force production and relaxation time variables in one leg isometric knee extension. These variables were intercorrelated together with muscle biopsy variables taken from m. vastus lateralis. From these computations MT proved to demonstrate significant correlations to rate of isometric force development (RFD) (P less than 0.001), maximum force (P0) (P less than 0.001) and per cent distribution of ST fibers (P less than 0.001). It is speculated that these relationships are determined by the pattern of the moto…
Force and EMG power spectrum during eccentric and concentric actions
2000
This study was designed to examine the force and activation levels of elbow flexor muscles during preactivated eccentric, concentric and isometric actions.Force, average EMG (aEMG), and the EMG power spectrum were investigated at different constant movement velocities (1 rad x s(-1), 2 rad x s(-1), 3 rad x s(-1), and 4 rad x s(-1)) at different joint angles.Average force at a 110 degree elbow angle was lower and aEMG was higher in concentric actions as compared with eccentric and isometric actions. At a 55 degree elbow angle, there was no difference in aEMG, or it was slightly higher in eccentric actions. MF was higher in the concentric as compared with eccentric actions at the three fastes…
Changes in the probability of firing of motor units following electrical stimulation in human limb muscles
1986
Changes in the probability of motor unit firing was studied in ten different muscles (six muscles in the upper extremity and four muscles in the lower extremity) of eleven healthy human subjects. The responses were elicited by the electrical stimulation of cutaneous or mixed nerves during weak voluntary contraction of the muscle studied, and were recorded by averaging the rectified surface electromyogram. In eight of the ten muscles, well-detectable, short and long latency excitatory phases were observed. The most constant and well-identified excitatory responses were observed in the first interosseus dorsalis muscle in the hand, and in the extensor digitorum brevis muscle in the foot. Thes…
Motor recruitment during action observation: Effect of interindividual differences in action strategy
2020
Abstract Visual processing of other’s actions is supported by sensorimotor brain activations. Access to sensorimotor representations may, in principle, provide the top-down signal required to bias search and selection of critical visual features. For this to happen, it is necessary that a stable one-to-one mapping exists between observed kinematics and underlying motor commands. However, due to the inherent redundancy of the human musculoskeletal system, this is hardly the case for multijoint actions where everyone has his own moving style (individual motor signature—IMS). Here, we investigated the influence of subject’s IMS on subjects’ motor excitability during the observation of an actor…
Neural and mechanical responses of the triceps surae muscle group after 1 h of repeated fast passive stretches
2004
Experiments were carried out to examine interaction between mechanical changes of the muscletendon unit and reduced reflex sensitivity after repeated and prolonged passive muscle stretching (RPS). There is some evidence that this interaction might be relevant also during active stretch-shortening cycle type of fatigue tasks. The results demonstrated a clear deterioration of voluntarily and electrically induced muscle contractions after RPS. Maximal voluntary contraction (MVC), average electromyographic activities of the gastrocnemius and soleus muscles, and maximal twitch contraction decreased on average by 13.8, 10.4, 7.6, and 16.8%, respectively. In addition, there was a 14% lengthening …
Functional properties of motor units in motor neuron diseases and neuropathies.
1997
The relationship between the size of single motor unit (MU) action potentials and their twitch properties was estimated in patients with spinal muscular atrophy (SMA, n = 5) and amyotrophic lateral sclerosis (ALS, n = 10), as well as in patients with peripheral nerve lesions (PNL, n = 9). The data obtained from these groups were compared to normal controls (n = 8). In controls, the single MU twitch force was highly correlated to the corresponding EMG potential size in terms of macro EMG area. An enlargement of MUs, due to collateral sprouting and reflected by increased potential size and twitch force, was found in regenerating PNL and in slowly progressing SMA. Both parameters were highly c…