Motor unit firing frequency of lower limb muscles during an incremental slide board skating test

2017 ◽  
Vol 16 (4) ◽  
pp. 540-551 ◽  
Author(s):  
Tatiane Piucco ◽  
Rodrigo Bini ◽  
Masanori Sakaguchi ◽  
Fernando Diefenthaeler ◽  
Darren Stefanyshyn
Keyword(s):  
Motor Unit ◽  
Lower Limb ◽  
Firing Frequency ◽  
Lower Limb Muscles ◽  
Motor Unit Firing ◽  
Limb Muscles

scholarly journals Contractile function and motor unit firing rates of the human hamstrings

2017 ◽  
Vol 117 (1) ◽  
pp. 243-250 ◽  
Author(s):  
Eric A. Kirk ◽  
Charles L. Rice
Keyword(s):  
Knee Joint ◽  
Motor Unit ◽  
Lower Limb ◽  
Biceps Femoris ◽  
Triceps Surae ◽  
Firing Rates ◽  
Lower Limb Muscles ◽  
Motor Unit Firing ◽  
Limb Muscles ◽  
Length Changes

Neuromuscular properties of the lower limb in health, aging, and disease are well described for major lower limb muscles comprising the quadriceps, triceps surae, and dorsiflexors, with the notable exception of the posterior thigh (hamstrings). The purpose of this study was to further characterize major muscles of the lower limb by comprehensively exploring contractile properties in relation to spinal motor neuron output expressed as motor unit firing rates (MUFRs) in the hamstrings of 11 (26.5 ± 3.8) young men. Maximal isometric voluntary contraction (MVC), voluntary activation, stimulated contractile properties including a force-frequency relationship, and MUFRs from submaximal to maximal voluntary contractile intensities were assessed in the hamstrings. Strength and MUFRs were assessed at two presumably different muscle lengths by varying the knee joint angles (90° and 160°). Knee flexion MVCs were 60–70% greater in the extended position (160°). The frequency required to elicit 50% of maximum tetanic torque was 16–17 Hz. Mean MUFRs at 25–50% MVC were 9–31% less in the biceps femoris compared with the semimembranosus-semitendinosus group. Knee joint angle (muscle length) influenced MUFRs such that mean MUFRs were greater in the shortened (90°) position at 50% and 100% MVC. Compared with previous reports, mean maximal MUFRs in the hamstrings are greater than those in the quadriceps and triceps surae and somewhat less than those in the tibialis anterior. Mean maximal MUFRs in the hamstrings are influenced by changes in knee joint angle, with lower firing rates in the biceps femoris compared with the semimembranosus-semitendinosus muscle group. NEW & NOTEWORTHY We studied motor unit firing rates (MUFRs) at various voluntary contraction intensities in the hamstrings, one of the only major lower limb muscles to have MUFRs affected by muscle length changes. Within the hamstrings muscle-specific differences have greater impact on MUFRs than length changes, with the biceps femoris having reduced neural drive compared with the semimembranosus-semimembranosus. Comparing our results to other lower limb muscles, flexors have inherently higher firing rate compared with extensors.

Cortical Control of Human Motoneuron Firing During Isometric Contraction

1997 ◽  
Vol 77 (6) ◽  
pp. 3401-3405 ◽  
Author(s):  
Stephan Salenius ◽  
Karin Portin ◽  
Matti Kajola ◽  
Riitta Salmelin ◽  
Riitta Hari
Keyword(s):  
Motor Cortex ◽  
Upper Limb ◽  
Isometric Contraction ◽  
Lower Limb ◽  
Biceps Brachii ◽  
Cortical Control ◽  
Lower Limb Muscles ◽  
Cortical Rhythms ◽  
Motor Unit Firing ◽  
Limb Muscles

Salenius, Stephan, Karin Portin, Matti Kajola, Riitta Salmelin, and Riitta Hari. Cortical control of human motoneuron firing during isometric contraction. J. Neurophysiol. 77: 3401–3405, 1997. We recorded whole scalp magnetoencephalographic (MEG) signals simultaneously with the surface electromyogram from upper and lower limb muscles of six healthy right-handed adults during voluntary isometric contraction. The 15- to 33-Hz MEG signals, originating from the anterior bank of the central sulcus, i.e., the primary motor cortex, were coherent with motor unit firing in all subjects and for all muscles. The coherent cortical rhythms originated in the hand motor area for upper limb muscles (1st dorsal interosseus, extensor indicis proprius, and biceps brachii) and close to the foot area for lower limb muscles (flexor hallucis brevis). The sites of origin corresponding to different upper limb muscles did not differ significantly. The cortical signals preceded motor unit firing by 12–53 ms. The lags were shortest for the biceps brachii and increased systematically with increasing corticomuscular distance. We suggest that the motor cortex drives the spinal motoneuronal pool during sustained contractions, with the observed cortical rhythmic activity influencing the timing of efferent commands. The cortical rhythms could be related to motor binding, but the rhythmic output may also serve to optimize motor cortex output during isometric contractions.

Frequency response of vestibular reflexes in neck, back, and lower limb muscles

2013 ◽  
Vol 110 (8) ◽  
pp. 1869-1881 ◽  
Author(s):  
Patrick A. Forbes ◽  
Christopher J. Dakin ◽  
Alistair N. Vardy ◽  
Riender Happee ◽  
Gunter P. Siegmund ◽  
...  
Keyword(s):  
Motor Unit ◽  
Lower Limb ◽  
Dynamic Range ◽  
Erector Spinae ◽  
Medial Gastrocnemius ◽  
Neck Muscle ◽  
Vestibular Reflexes ◽  
Frequency Responses ◽  
Lower Limb Muscles ◽  
Limb Muscles

Vestibular pathways form short-latency disynaptic connections with neck motoneurons, whereas they form longer-latency disynaptic and polysynaptic connections with lower limb motoneurons. We quantified frequency responses of vestibular reflexes in neck, back, and lower limb muscles to explain between-muscle differences. Two hypotheses were evaluated: 1) that muscle-specific motor-unit properties influence the bandwidth of vestibular reflexes; and 2) that frequency responses of vestibular reflexes differ between neck, back, and lower limb muscles because of neural filtering. Subjects were exposed to electrical vestibular stimuli over bandwidths of 0–25 and 0–75 Hz while recording activity in sternocleidomastoid, splenius capitis, erector spinae, soleus, and medial gastrocnemius muscles. Coherence between stimulus and muscle activity revealed markedly larger vestibular reflex bandwidths in neck muscles (0–70 Hz) than back (0–15 Hz) or lower limb muscles (0–20 Hz). In addition, vestibular reflexes in back and lower limb muscles undergo low-pass filtering compared with neck-muscle responses, which span a broader dynamic range. These results suggest that the wider bandwidth of head-neck biomechanics requires a vestibular influence on neck-muscle activation across a larger dynamic range than lower limb muscles. A computational model of vestibular afferents and a motoneuron pool indicates that motor-unit properties are not primary contributors to the bandwidth filtering of vestibular reflexes in different muscles. Instead, our experimental findings suggest that pathway-dependent neural filtering, not captured in our model, contributes to these muscle-specific responses. Furthermore, gain-phase discontinuities in the neck-muscle vestibular reflexes provide evidence of destructive interaction between different reflex components, likely via indirect vestibular-motor pathways.

Electromyographic traces of motor unit synchronization of fatigued lower limb muscles during gait

2021 ◽  
Vol 75 ◽  
pp. 102750
Author(s):  
A. Fidalgo-Herrera ◽  
J.C. Miangolarra-Page ◽  
M. Carratalá-Tejada
Keyword(s):  
Motor Unit ◽  
Lower Limb ◽  
Lower Limb Muscles ◽  
Limb Muscles ◽  
Motor Unit Synchronization

Vestibulospinal influences on lower limb motoneurons

2004 ◽  
Vol 82 (8-9) ◽  
pp. 675-681 ◽  
Author(s):  
Paul M Kennedy ◽  
Andrew G Cresswell ◽  
Romeo Chua ◽  
J Timothy Inglis
Keyword(s):  
Lower Limb ◽  
Human Subjects ◽  
Motor Units ◽  
Vestibular Stimulation ◽  
Firing Frequency ◽  
Galvanic Vestibular Stimulation ◽  
H Reflex ◽  
Free Standing ◽  
Lower Limb Muscles ◽  
Limb Muscles

Galvanic vestibular stimulation (GVS) is a research tool used to activate the vestibular system in human subjects. When a low-intensity stimulus (1–4 mA) is delivered percutaneously to the vestibular nerve, a transient electromyographic response is observed a short time later in lower limb muscles. Typically, galvanically evoked responses are present when the test muscle is actively engaged in controlling standing balance. However, there is evidence to suggest that GVS may be able to modulate the activity of lower limb muscles when subjects are not in a free-standing situation. The purpose of this review is to examine 2 studies from our laboratory that examined the effects of GVS on the lower limb motoneuron pool. For instance, a monopolar monaural galvanic stimulus modified the amplitude of the ipsilateral soleus H-reflex. Furthermore, bipolar binaural GVS significantly altered the onset of activation and the initial firing frequency of gastrocnemius motor units. The following paper examines the effects of GVS on muscles that are not being used to maintain balance. We propose that GVS is modulating motor output by influencing the activity of presynaptic inhibitory mechanisms that act on the motoneuron pool.Key words: galvanic vestibular stimulation, h-reflex, motor unit, vestibulospinal, human.

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