3,676 research outputs found
Delayed onset of vastii muscle activity in response to rapid postural perturbations following eccentric exercise:a mechanism that underpins knee pain after eccentric exercise?
No full textBACKGROUND: Appropriate timing of activity of the vastus medialis obliqus (VMO) and vastus lateralis (VL) muscles is a key factor for proper tracking of the patella in the trochlear groove during knee extension. This study investigates the relative timing of activation of the VMO and VL muscles during unexpected perturbations performed before and after eccentric exercise.METHODS: Surface electromyography signals were recorded from the VMO and VL muscles of the right leg in 11 healthy men during rapid postural perturbations performed at baseline, immediately after eccentric exercise of the quadriceps, and at 24 and 48 h after exercise. Participants stood on a moveable platform during which eight randomised postural perturbations were performed (4 repetitions of 2 perturbation types: 8 cm forward slides, 8 cm backward slides).RESULTS: Before the eccentric exercise, the onset of VMO activity was significantly earlier than the VL muscle (average for both forward and backward perturbations: VMO 39.0±7.1 ms; VL 43.7±7.9 ms). However, the onset of VMO activity was significantly later compared with VL muscle immediately after eccentric exercise and this remained 24 and 48 h after eccentric exercise (average across all postexercise sessions and perturbation directions: VMO 72.3±11.1 ms; VL 56.0±8.2 ms; p<0.05).CONCLUSIONS: The onset of VMO-VL activity in response to rapid destabilising perturbations is altered immediately after eccentric exercise and during eccentric exercise-induced muscle soreness up to 48 h later. These observations may help explain the high prevalence of knee disorders after high intensity eccentric exercise.</p
Non-uniform muscle adaptations to eccentric exercise and the implications for training and sport
No full textDue to the variations in morphological and architectural characteristics of fibers within a skeletal muscle, regions of a muscle may be differently affected by eccentric exercise. Although eccentric exercise may be beneficial for increasing muscle mass and can be beneficial for the treatment of tendinopathies, the non-uniform effect of eccentric exercise results in regional muscle damage and as a consequence, non-uniform changes in muscle activation. This regional muscle weakness can contribute to muscle strength imbalances and may potentially alter the load distribution on joint structures, increasing the risk of injury. In this brief review, the non-uniform effects of eccentric exercise are reviewed and their implications for training and sport are considered.</p
Physiological and Neural Adaptations to Eccentric Exercise:Mechanisms and Considerations for Training
Full text linkEccentric exercise is characterized by initial unfavorable effects such as subcellular muscle damage, pain, reduced fiber excitability, and initial muscle weakness. However, stretch combined with overload, as in eccentric contractions, is an effective stimulus for inducing physiological and neural adaptations to training. Eccentric exercise-induced adaptations include muscle hypertrophy, increased cortical activity, and changes in motor unit behavior, all of which contribute to improved muscle function. In this brief review, neuromuscular adaptations to different forms of exercise are reviewed, the positive training effects of eccentric exercise are presented, and the implications for training are considered.</p
Function and structure of the deep cervical extensor muscles in patients with neck pain
No full textThe deep cervical extensors are anatomically able to control segmental movements of the cervical spine in concert with the deep cervical flexors. Several investigations have confirmed changes in cervical flexor muscle control in patients with neck pain and as a result, effective evidence-based therapeutic exercises have been developed to address such dysfunctions. However, knowledge on how the deep extensor muscles behave in patients with neck pain disorders is scare. Structural changes such as higher concentration of fat within the muscle, variable cross-sectional area and higher proportions of type II fibres have been observed in the deep cervical extensors of patients with neck pain compared to healthy controls. These findings suggest that the behaviour of the deep extensors may be altered in patients with neck pain. Consistent with this hypothesis, a recent series of studies confirm that patients display reduced activation of the deep cervical extensors as well as less defined activation patterns. This article provides an overview of the various different structural and functional changes in the deep neck extensor muscles documented in patients with neck pain. Relevant recommendations for the management of muscle dysfunction in patients with neck pain are presented.</p
Strength training, but not endurance training, reduces motor unit discharge rate variability
No full textThis study evaluates and compares the effects of strength and endurance training on motor unit discharge rate variability and force steadiness of knee extensor muscles. Thirty sedentary healthy men (age, 26.0±3.8yrs) were randomly assigned to strength training, endurance training or a control group. Conventional endurance and strength training was performed 3days per week, over a period of 6weeks. Maximum voluntary contraction (MVC), time to task failure (at 30% MVC), coefficient of variation (CoV) of force and of the discharges rates of motor units from the vastus medialis obliquus and vastus lateralis were determined as subjects performed 20% and 30% MVC knee extension contractions before and after training. CoV of motor unit discharges rates was significantly reduced for both muscles following strength training (P<0.001), but did not change in the endurance (P=0.875) or control group (P=0.995). CoV of force was reduced after the strength training intervention only (P<0.01). Strength training, but not endurance training, reduces motor unit discharge rate variability and enhances force steadiness of the knee extensors. These results provide new insights into the neuromuscular adaptations that occur with different training methods.</p
Motor unit behavior during submaximal contractions following six weeks of either endurance or strength training
Full text linkThe study investigated changes in motor output and motor unit behavior following 6 weeks of either strength or endurance training programs commonly used in conditioning and rehabilitation. Twenty-eight sedentary healthy men (age, mean±SD, 26.1 ± 3.9 yrs) were randomly assigned to strength training (ST) (n = 9), endurance training (ET) (n = 10) or a control group (CT) (n = 8). Maximum voluntary contraction (MVC), time to task failure (isometric contraction at 30% MVC), and rate of force development (RFD) of the quadriceps, were measured before (week 0), during (week 3), and after a training program of 6 weeks. In each experimental session, surface and intramuscular EMG signals were recorded from the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during isometric knee extension at 10% and 30% MVC. After 6 weeks of training, MVC and RFD increased in the ST group (17.5±7.5 % and 33.3±15.9 %, respectively; P < 0.05) whereas time to task failure was prolonged in the ET group (29.7±13.4 %; P < 0.05). Despite surface EMG amplitude during 30% MVC contractions increased following both training programs, there were different changes in motor unit discharge rates between the training groups. After endurance training, the motor unit discharge rate at 30% MVC decreased from 11.3 ±1.3 pulses per second (pps) to 10.1 ± 1.1 pps (P < 0.05) in the vasti muscles, whereas after strength training it increased from 11.4 ± 1.2 pps to 12.7 ± 1.3 pps (P < 0.05). Finally, motor unit conduction velocity during the contractions at 30% MVC increased for both the ST and ET groups, but only after 6 weeks of training (P < 0.05). In conclusion, strength and endurance training programs elicit opposite adjustments in motor unit discharge rates but similar changes in muscle fiber conduction velocity.Fundação para a Ciência e a Tecnologia (FCT) of Portugal (Grant ID - SFRH / BD / 31796 / 2006). Danish Technical Research Counci
Muskeln effektiv kontrollieren
No full textÜber Jahrzehnte beurteilte man die Halsmuskulatur von Patienten mit Nackenbeschwerden anhand von Kraft- und Ausdauertests. Doch neue Forschungsergebnisse belegen, dass diese Patienten eine komplexe Störung der zervikalen neuromotorischen Kontrolle haben. Wie man diese Störung diagnostizieren und behandeln kann, fasst die australische Physiotherapeutin Deborah Falla zusammen.</jats:p
Assessment of the electrophysiological properties of the muscle fibers of a transplanted hand
No full textBACKGROUND: The muscle fibers in a transplanted hand remain denervated for a long period of time after the transplant. This prolonged inactivity may change the electrophysiological membrane properties of muscle fibers, as observed in long-term denervation. We investigated whether electrophysiological properties of the muscle fibers are preserved in a transplanted hand even after several months of denervation. Specifically, we assessed the dependence of muscle fiber conduction velocity (CV) on discharge rate in motor units of the abductor digiti minimi muscle.METHODS: Surface electromyography signals were recorded from the transplanted hand of a patient who was 35 years of age at the time of the transplant. In each of 11 experimental sessions performed over a period of 23 months after the transplant, the subject was asked to linearly increase the activation or to maintain a maximum activation of the abductor digiti minimi muscle for 60 sec. Individual motor unit action potentials were identified from the electromyography recordings and muscle fiber CV was estimated for each action potential as a function of the time interval separating the action potential from the preceding discharge (interspike interval [ISI]).RESULTS: The baseline (ISI >1000 msec) CV was 3.8±0.3 m/sec. CV decreased monotonically with increasing ISI (R=0.95). For ISI in the range 0 to 10 msec, muscle fiber CV was 24.9%±16.3% higher than the baseline value (P<0.05).CONCLUSIONS: The results indicate that in the investigated muscle, the baseline value of CV and its dependency on discharge rate were similar as in able-bodied individuals, despite a period of several months of denervation.</p
Reorganization of muscle synergies during multidirectional reaching in the horizontal plane with experimental muscle pain
Full text linkMuscle pain induces a complex reorganization of the motor strategy which cannot be fully explained by current theories. We tested the hypothesis that the neural control of muscles during reaching in the presence of nociceptive input is determined by a reorganization of muscle synergies with respect to control conditions. Muscle pain was induced by injection of hypertonic saline into the anterior deltoid muscle of eight men. Electromyographic (EMG) signals were recorded from 12 upper limb muscles as subjects performed a reaching task before (baseline) and after the injection of hypertonic (pain) saline, and after the pain sensation vanished. The EMG envelopes were factorized in muscle synergies, and activation signals extracted for each condition. Nociceptive stimulation resulted in a complex muscle reorganization without changes in the kinematic output. The anterior deltoid muscle activity decreased in all subjects while the changes in other muscles were subject specific. Three synergies sufficed to describe the EMG patterns in each condition, suggesting that reaching movements remain modular in the presence of experimental pain. Muscle reorganization in all subjects was accompanied by a change in the activation signals compatible with a change in the central drive to muscles. One, two or three synergies were shared between the baseline and painful conditions, depending on the subject. These results indicate that nociceptive stimulation may induce a reorganization of modular control in reaching. We speculate that such reorganization may be due to the recruitment of synergies specific to the painful condition.</p
Localised resistance selectively activates the semispinalis cervicis muscle in patients with neck pain
No full textThe semispinalis cervicis muscle displays reduced and less defined activation in patients with neck pain which is associated with increased activity of the splenius capitis muscle. Exercises to selectively activate the semispinalis cervicis muscle may be relevant for patients with neck pain however the most appropriate type of exercise has not been determined. The purpose of this study was to investigate whether a specific exercise could selectively activate the semispinalis cervicis muscle relative to the splenius capitis. Ten women with chronic neck pain participated. Intramuscular electrodes were inserted into the semispinalis cervicis and splenius capitis unilaterally on the side of greatest pain. After testing the maximal neck extension force, three isometric exercises were performed in sitting: 1. the investigator placed a hand on the patient's occiput and pushed into flexion asking the patient to resist into extension maximally, 2. the investigator placed the thumb and index finger on the vertebral arch of C2 and pushed into flexion asking the patient to resist maximally, 3. same procedure as for C2 however the resistance was applied at C5. The ratio between the normalized electromyography (EMG) amplitude of the semispinalis cervicis and splenius capitis was computed. The relative activation of the semispinalis cervicis was greater (P < 0.05) than the splenius capitis with resistance at C2 (2.53 ± 2.43) compared to resistance at the occiput (1.39 ± 1.00) or at C5 (1.16 ± 0.85). The results indicate that localized resistance can achieve relative isolation of the semispinalis cervicis muscle. This exercise approach may be relevant for patients with neck pain.</p
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