Search results for "h-reflex"

Neurophysiological mechanisms of motor imagery : effects of associated somatosensory stimulation

2018

Mental training, which involves mentally simulating an action without motor output, is an effective stimulus to improve the maximal voluntary contraction. If only the motor pathway is activated, an activation of the somatosensory cortex is observed despite the lack of afferent feedback. Indeed, the motor imagery task efficiency is based in part on an interaction between motor and sensory pathway. Thus, it’s seems reasonable to think that the addition of sensory afferent feedback during motor imagery could potentiate the motor imagery effects and thus improve motor performance. In our first study, we showed that the addition of somatosensory stimulation of Ia-afferents during a motor imagery…

Effect of dynamic maximal voluntary contraction on soleus and gastrocnemii H-reflex and V wave responses

2005

Effects of plyometric and pneumatic explosive strength training on neuromuscular function and dynamic balance control in 60–70year old males

2013

The present study compared neuromuscular adaptations to 12weeks of plyometric (PLY) or pneumatic (PNE) power training and their effects on dynamic balance control. Twenty-two older adults aged 60-70 (PLY n=9, PNE n=11) participated in the study. Measurements were conducted at Pre, 4, 8 and 12weeks. Dynamic balance was assessed as anterior-posterior center of pressure (COP) displacement in response to sudden perturbations. Explosive isometric knee extension and plantar flexion maximal voluntary contractions (MVCs) were performed. Maximal drop jump performance from optimal dropping height was measured in a sledge ergometer. Increases in knee extensor and ankle plantar flexor torque and muscle…

Effects of Propofol on H-reflex in Humans

2001

Background Depression of spinal cord motoneuron excitability has been proposed to contribute to surgical immobility. The H-reflex, which measures alpha-motoneuron excitability, is depressed by volatile anesthetics, whereas the action of propofol is unknown. The objective of this study was to determine the effects of propofol anesthesia on the H-reflex. Methods In 13 patients (group 1), H-reflex was measured before (T0), 3 min after (T1), and 10 min after (T2) a 2-mg/kg bolus dose of propofol, followed by an infusion of 10 mg x kg(-1) x h(-1). Ten patients (group 2) were studied when propofol was given via a programmable pump set to a propofol blood concentration of 6 microg/ml, and 10 pati…

Long-term effects on motor cortical excitability induced by repeated muscle vibration during contraction in healthy subjects

2008

article i nfo Objective: The effects of a novel repeated muscle vibration intervention (rMV; 100 Hz, 90 min over 3 consecutive days) on corticomotor excitability were studied in healthy subjects. Methods: rMV was applied over the flexor carpi radialis (FCR) during voluntary contraction (experiment 1), during relaxation and during contraction without vibration (experiment 2). Focal transcranial magnetic stimulation (TMS) was applied before rMV and one hour, and one, two and three weeks after the last muscle vibration intervention. At each of these time points, we assessed the motor map area and volume in the FCR, extensor digitorum communis (EDC) and abductor digiti minimi (ADM). Short-inter…

Effects of caffeine on neuromuscular function in a non‐fatigued state and during fatiguing exercise

2020

New findings What is the central question of the study? What are the effects of caffeine on neuromuscular function in a non-fatigued state and during fatiguing exercise? What is the main finding and its importance? In a non-fatigued state, caffeine decreased the duration of the silent period evoked by transcranial magnetic stimulation. Caffeine-induced reduction of inhibitory mechanisms in the central nervous system before exercise was associated with an increased performance. Individuals who benefit from caffeine ingestion may experience lower perception of effort during exercise and an accelerated recovery of M-wave amplitude postfatigue. This study elucidates the mechanisms of action of …

Modulation of spinal excitability by a sub-threshold stimulation of M1 area during muscle lengthening

2013

Abstract It is well known that the H-reflex amplitude decreases during passive muscle lengthening in comparison with passive shortening. However, this decrease in spinal synaptic efficacy observed during passive lengthening seems to be lesser during eccentric voluntary contraction. The aim of the present study was to examine whether spinal excitability during lengthening condition could be modulated by magnetic brain stimulation. H reflexes of the triceps surae muscles were elicited on 10 young healthy subjects, and conditioned by a sub-threshold transcranial magnetic stimulation (TMS). The conditioning stimulation was applied over the M1 area of triceps surae muscles at an intensity below …

Effects of short term water immersion on peripheral reflex excitability in hemiplegic and healthy individuals: A preliminary study

2016

Background: Reflex excitability is increased in hemiplegic patients compared to healthy controls. One challenge of stroke rehabilitation is to decrease the effects of hyperreflexia, which may be possible with water immersion. Methods/Aims: The present study examined the effects of acute water immersion on electrically-evoked Hmax:Mmax ratios (a measure of reflex excitability) in 7 hyperreflexive hemiplegic patients and 7 age-matched healthy people. Hmax:Mmax ratios were measured from soleus on dry land (L1), immediately after (W1) and 5 minutes after immersion (W5), and again after five minutes on land (L5). Results: Water immersion led to an acute increase in Hmax:Mmax ratio in both groups…

The Etiology of Muscle Fatigue Differs between Two Electrical Stimulation Protocols

2016

International audience; Purpose: This study aimed at investigating the mechanisms involved in the force reduction induced by two electrical stimulation (ES) protocols that were designed to activate motor units differently. Methods: The triceps surae of 11 healthy subjects (8 men; age, similar to 28 yr) was activated using ES applied over the tibial nerve. Two ES protocols (conventional [CONV]: 20 Hz, 0.05 ms vs wide-pulse high-frequency [WPHF]: 80 Hz, 1 ms) were performed and involved 40 trains (6 s on-6 s off) delivered at an intensity (I-ES) evoking 20% of maximal voluntary contraction. To analyze the mechanical properties of the motor units activated at I-ES, force-frequency relation was…

Plantar flexor activation capacity and H reflex in older adults: adaptations to strength training.

2002

The purpose of this study was to investigate whether the voluntary neural drive and the excitability of the reflex arc could be modulated by training, even in old age. To this aim, the effects of a 16-wk strengthening program on plantar flexor voluntary activation (VA) and on the maximum Hoffman reflex (Hmax)-to-maximum M wave (Mmax) ratio were investigated in 14 elderly men (65–80 yr). After training, isometric maximum voluntary contraction (MVC) increased by 18% ( P < 0.05) and weight-lifting ability by 24% ( P < 0.001). Twitch contraction time decreased by 8% ( P < 0.01), but no changes in half relaxation time and in peak twitch torque were observed. The VA, assessed by twitch …