Search results for "Motor unit"
showing 10 items of 55 documents
Electrophysiology of sensory neuropathies
1995
In sensory neuropathy maximal conduction velocity is a crude measure. Variations up to 10 m/s have to be considered normal. The relation to clinical impairment is poor in either axonal/neuronal lesions or demyelination as indicated by a small normal latency and a delayed broad polyphasic nerve action potential (NAP), respectively. Conduction block evaluated on NAP changes has not yet been established. Mild disorder of impulse conduction may be disclosed by evaluating a) conduction along long nerve segments studying the H-reflex or SSEP, b) late components of the averaged NAP which make > 10% of the main deflection, c) velocities of slow conducting fibers utilizing the collision technique or…
The effect of experimental and clinical musculoskeletal pain on spinal and supraspinal projections to motoneurons and motor unit properties in humans…
2021
Background and Objective Numerous studies have examined the influence of pain on spinal reflex excitability, motor unit behaviour and corticospinal excitability. Nevertheless, there are inconsistencies in the conclusions made. This systematic review sought to understand the effect of pain on spinal and supraspinal projections to motoneurons and motor unit properties by examining the influence of clinical or experimental pain on the following three domains: H-reflex, corticospinal excitability and motor unit properties. Databases and Data Treatment MeSH terms and preselected keywords relating to the H-reflex, motor evoked potentials and motor unit decomposition in chronic and experimental pa…
Differences in cardiorespiratory and neuromuscular responses between voluntary and stimulated contractions of the quadriceps femoris muscle.
2006
The aim of this study was to compare respiratory gas exchange variables and muscle fatigue between equal-intensity (i.e., same force output) electrostimulated and voluntary contractions of the quadriceps muscle (46+/-10% of maximal voluntary force). Twelve healthy men served as volunteers. Oxygen consumption, ventilation and respiratory exchange ratio were recorded during the exercise bouts. Muscle fatigue was quantified as the exercise-induced reduction in maximal voluntary force. The average oxygen consumption (11+/-3 versus 8+/-2 mL min(-1)kg(-1)), ventilation (23+/-4 versus 16+/-2 L min(-1)) and respiratory exchange ratio (0.96+/-0.02 versus 0.85+/-0.01) were significantly higher during…
Decreased motor unit firing rate and force control in older men
2006
Introduction Ageing is related to muscle atrophy that leads to decreases in muscle force. The largest changes are found in fast muscle fibres and fast force production, reducing the capability to recover from sudden balance disturbances. Also ageing-related decrease in force control has been found, as indicated by an increase in force fluctuations and motor unit (MU) firing variability (Galganski et al. 1993). Possibly due to differences in measurement protocols and muscles, the results concerning the effects of ageing on motor unit firing rate are, however, somewhat contradictory (for review, see Roos et al. 1997). The purpose of the present study was to investigate the age-related changes…
Zum Wandel motorischer Einheiten bei Änderung des Aktivitätsmusters durch elektrische Reizung - Elektrostimulation und ihre klinischen Einsatzmöglich…
1989
Motoneuron and muscle fibers interact on the motor unit level, whereby discharge characteristics from the neuron imposed on the muscle seem to play a major role. Within the unit all muscle fibers are biochemically homogeneous and display a high degree of plasticity under different functional demands. To distinguish the existing different units rationals are listed that classify the units by physiological and histochemical parameters. Furthermore the review summarizes the available knowledge on the importance of activity patterns--as a biological principle--involved in the control of phenotypic expression of innervated and denervated muscle. The sequelae are shown of electrical stimulation o…
RECRUITMENT OF BICEPS FEMORIS MUSCLE REGIONS AT DIFFERENT RUNNING SPEEDS
2017
Background The majority of hamstring strain injuries (HSIs) occur in the late swing phase of high-speed running when hamstrings work eccentrically. The proximal region of the biceps femoris (BF) seems to be the most common site of injury. Elongation of the fascicles in eccentric contractions is higher in the proximal region compared to the distal region of BF, but the neural background to this phenomenon is not clear. Objective To examine the region-specificity of BF muscle activity at different running speeds. Design Observational study. Running speeds were randomized. Setting Laboratory, amateur level. Participants Football players without acute injury/illness, and without HSI history wer…
Neural Adaptations to Strength Training
2018
Scientific study of strength training has revealed numerous physiological mechanisms that contribute to: (1) acute fatigue from a single strength training session and (2) chronic adaptation to repetitive and systematic strength training. Therefore, the purpose of this chapter is initially to discuss potential neural mechanisms that influence force production from the perspective of a single repetition. Thereafter, the chapter will highlight scientific evidence for candidate neural mechanisms that acutely limit force production during a single strength training session and long-term adaptations caused by strength training. For some of these potential neural mechanisms, there is strong scient…
Motor unit discharge rate in dynamic movements of the aging soleus
2014
Aging is related to changes at the muscular level, leading to a decline in motor performance increasing the risk of falling and injury. It seems that the age-related changes in motor unit activation are muscle- and intensity dependent. The purpose of this study was to examine possible differences in soleus motor unit discharge rate (MUDR) in both isometric and dynamic contractions between young and elderly adults. 11 young (YOUNG) and 8 elderly (OLD) males participated in the study. The subjects performed isometric and dynamic plantar flexions while seated in an ankle dynamometer. The force levels studied were 10, 20, 40, 60, 80 and 100% of the isometric (ISO) MVC in ISO and 10, 20 and 40% …
Force Control and Motor Unit Firing Behavior Following Mental Fatigue in Young Female and Male Adults
2020
Purpose: The neuromuscular mechanisms leading to impaired motor performance in the presence of mental fatigue remain unclear. It is also unknown if mental fatigue differentially impacts motor performance in males and females. The purpose of this study was to assess the impact of mental fatigue on force production and motor unit (MU) firing behavior in males and females. Methods: Nineteen participants performed 10-s isometric dorsiflexion (DF) contractions at 20 and 50% maximum voluntary contraction (MVC) before, during, and after completing 22 min of the psychomotor vigilance task (PVT), to induce mental fatigue. The DF force and indwelling MU firing behavior of the tibialis anterior (TA) w…
Changes in motor unit characteristics after eccentric elbow flexor exercise
2010
Morphological evidence suggests that fast-twitch fibers are prone to disruption of their membrane structures by eccentric exercise. However, it is unclear how this is reflected in the discharge rate and action potential propagation of individual motor units, especially at high contraction levels. High-density surface electromyograms were recorded from biceps brachii muscle and decomposed to individual motor unit action potentials at isometric contraction levels between 10% and 75% of maximal voluntary contraction (MVC) before intermittent maximal elbow flexor eccentric exercise, and two hours (2H), two days (2D) and four days (4D) post-exercise. Maximal voluntary force decreased by 21.3±5.6…