Search results for "Skeletal"
showing 10 items of 3025 documents
EMG power spectrum and features of the superimposed M-wave during voluntary eccentric and concentric actions at different activation levels.
2001
Muscle fiber conduction velocity (CV) may be affected by the level of voluntary activation and by the diameter of the fiber. Both the frequency component of the electromyography (EMG) power spectrum, such the as median frequency (MF) or mean power frequency, and the duration of muscle compound action potential to single supramaximal electrical impulse (maximal M-wave) may be related to CV. The aim of the present study was to examine how changes in the activation level in lengthening and in shortening conditions would affect the EMG power spectrum during voluntary effort, and compare them to changes in M-wave shape in similar conditions. Ten male subjects performed eccentric and concentric k…
Specific modulation of spinal and cortical excitabilities during lengthening and shortening submaximal and maximal contractions in plantar flexor mus…
2014
This study investigated the influence of the torque produced by plantar flexor muscles on cortical and spinal excitability during lengthening and shortening voluntary contractions. To that purpose, modulations of motor-evoked potential (MEP) and Hoffmann (H) reflex were compared in the soleus (SOL) and medial gastrocnemius (MG) during anisometric submaximal and maximal voluntary contraction (MVC) of the plantar flexor muscles. For the submaximal shortening and lengthening contractions, the target torque was set at 50% of their respective MVC force. The results indicate that the amplitudes of both MEP and H-reflex responses, normalized to the maximal M wave, were significantly ( P < 0.05…
Activation of human plantar flexor muscles increases after electromyostimulation training
2002
Neuromuscular adaptations of the plantar flexor muscles were assessed before and subsequent to short-term electromyostimulation (EMS) training. Eight subjects underwent 16 sessions of isometric EMS training over 4 wk. Surface electromyographic (EMG) activity and torque obtained under maximal voluntary and electrically evoked contractions were analyzed to distinguish neural adaptations from contractile changes. After training, plantar flexor voluntary torque significantly increased under isometric conditions at the training angle (+8.1%, P< 0.05) and at the two eccentric velocities considered (+10.8 and +13.1%, P < 0.05). Torque gains were accompanied by higher normalized soleus EMG a…
Voluntary activation and mechanical performance of human triceps surae muscle after exhaustive stretch-shortening cycle jumping exercise.
2003
The purpose of this study was to examine neuromuscular factors that may contribute to post exercise force loss and subsequent recovery after exhaustive stretch-shortening cycle (SSC) exercise. Six subjects were fatigued on a sledge apparatus by 100 maximal rebound jumps followed by continuous submaximal jumping until complete exhaustion. Exercise-induced changes in neuromuscular performance were followed up to 7 days post exercise. The total number of jumps in the SSC exercise ranged from 336 to 1392. The SSC exercise induced a significant immediate plantarflexion torque decline of 29, 38 and 44% (P<0.05) in maximal voluntary contraction and evoked maximal twitch and low-frequency (LF) stim…
Co-activation and tension-regulating phenomena during isokinetic knee extension in sedentary and highly skilled humans.
1996
The aim of this study was to examine isokinetic torque produced by highly skilled (HS) and sedentary (S) human subjects, during knee extension, during maximal voluntary and superimposed electrical activation. To verify the level of activation of agonist (vastus lateralis, VL, and vastus medialis, VM) and antagonist muscles (semi-tendineous, ST), during maximal voluntary activation, their myo-electrical activities were detected and quantified as root mean square (rms) amplitude. Ten HS and ten S subjects performed voluntary and superimposed isometric actions and isokinetic knee extensions at 14 angular velocities (from -120 to 300 degrees*s(-1)). The rms amplitude of each muscle was normaliz…
Clinical, histological and genetic characterization of reducing body myopathy caused by mutations in FHL1
2008
We recently identified the X-chromosomal four and a half LIM domain gene FHL1 as the causative gene for reducing body myopathy, a disorder characterized by progressive weakness and intracytoplasmic aggregates in muscle that exert reducing activity on menadione nitro-blue-tetrazolium (NBT). The mutations detected in FHL1 affected highly conserved zinc coordinating residues within the second LIM domain and lead to the formation of aggregates when transfected into cells. Our aim was to define the clinical and morphological phenotype of this myopathy and to assess the mutational spectrum of FHL1 mutations in reducing body myopathy in a larger cohort of patients. Patients were ascertained via th…
MRI in DNM2-related centronuclear myopathy: Evidence for highly selective muscle involvement
2006
Dynamin 2 has recently been recognized as a causative gene for the autosomal dominant form of centronuclear myopathy (dominant centronuclear myopathy). Here we report an affected father and daughter with dynamin 2 related AD CNM with predominantly distal onset of weakness. In addition to the diagnostic central location of myonuclei the muscle biopsy also showed core-like structures. Muscle MRI in the lower leg revealed prominent involvement of the soleus, but also of the gastrocnemius and the tibialis anterior whereas in the thigh there was a consistent pattern of selective involvement of adductor longus, semimembranosus, biceps femoris, rectus femoris, and vastus intermedius with relative …
Relationship between velocity and muscular endurance of the upper body
2018
Strength, power and muscular endurance tests have been developed as means of assessing people's physical abilities. However, testing may be expensive or time consuming. A method to reduce the time of physical assessment could be to use predictive algorithms for indirect assessment. The aim of this study will be to determine a relationship between strength, power and muscular endurance in order to identify predictors for an easier and faster assessment. 33 male strength-trained participants (22.8 ± 4.6 years, 172.5 ± 6.7 cm, 68.0 ± 10.6 kg) performed a single pull-up (SPU) and a single push-up (SPH) and a set of pull-ups (EPU) and push-ups (EPH) to exhaustion. The participants were divided i…
The effect of fatigue on store and re-use of elastic energy in slow and fast types of human skeletal muscle
1986
Stretch-shortening exercises are characterized by enhancement of performance when compared to the work output performed in shortening conditions. There is evidence that fast subjects are unable to re-use great amounts of elastic energy during stretch-shortening cycles performed with slow stretching speed and large stretching length. In the present study, 14 subjects possessing different fibre types in m. vastus lateralis performed vertical jumps with and without preliminary countermovement and with large angular displacement and slow stretching speed The jumping tests were executed before and immediately after fatigue induced by short intense exercises (60 s of continuous rebound jumping). …
Mechanism of Free Radical Production in Exhaustive Exercise in Humans and Rats; Role of Xanthine Oxidase and Protection by Allopurinol
2000
Exhaustive exercise generates free radicals, However, the source of this oxidative damage remains controversial. The aim of this paper was to study further the mechanism of exercise-induced production of free radicals, Testing the hypothesis that xanthine oxidase contributes to the production of free radicals during exercise, me found not only that exercise caused an increase in blood xanthine oxidase activity in rats but also that inhibiting xanthine oxidase with allopurinol prevented exercise-induced oxidation of glutathione in both rats and in humans. Furthermore, inhibiting xanthine oxidase prevented the increases in the plasma activity of cytosolic enzymes (lactate dehydrogenase, aspar…