1,720,993 research outputs found
Muscle echo intensity: reliability and conditioning factors
No full textObjective: To assess the issue of muscle echo intensity reliability and to investigate the relationship between muscle echo intensity and size, shape and location of the region of interest (ROI) used for echo intensity quantification. Methods: Ultrasonographic scans of the following five muscles were acquired in twenty healthy subjects: biceps brachii, rectus femoris, vastus lateralis, tibialis anterior and medial gastrocnemius. Muscle echo intensity was quantified in each scan. Results: We found that the agreement between the different sized ROIs considered in each scan ranged from moderate (ICC: 054) to high (ICC: 086) and that the echo intensity consistency between equal sized ROIs of the three scans ranged from low (ICC: 042) to very high (091). The echo intensity of tibialis anterior and rectus femoris was different between different sized, shaped and located ROIs. The echo intensity of biceps brachii and tibialis anterior was higher than that of all other muscles, and females had higher echo intensity than males. Moreover, the muscle echo intensity was positively correlated with the subcutaneous layer thickness in three of five muscles. Conclusion: The echo intensity reliability was function of the ROI size. Muscle and gender variability in echo intensity was likely due to differences in fibrous and adipose tissue content and distribution. Possible explanations for the observed correlations between muscle echo intensity and subcutaneous layer thickness include the dependence of both variables on total body adiposity or the direct dependence of the extent of intramuscular fat on the amount of subcutaneous fat
Identification of Motor Unit Discharge Patterns from High-Density Surface EMG during High Contraction Levels
No full textOne major limitation in motor unit (MU) studies is the difficulty in assessing the properties of high-threshold units, which are recruited at high force levels. The aim of this study was to validate the decomposition results obtained from high-density surface EMG by the rate of agreement with the decomposition of concurrently recorded intramuscular EMG during high muscle contraction forces. Surface EMG signals were recorded with a grid of 9×10 electrodes from the tibialis anterior muscle of four healthy men (age, range 24-35) during isometric contractions ranging between 50% and 70% of the maximal voluntary contraction. Bipolar intramuscular EMG signals were recorded with three pairs of wire electrodes. Surface and intramuscular EMG were independently decomposed into contributions of individual MUs. For jointly identified MUs, the rate of agreement between both decomposition techniques was calculated as a percentage of jointly identified MU discharges normalized by the number of all MU discharges. On average, 26 ± 8 MUs per contraction were identified from the three channels of intramuscular EMG, but only 6±3 MUs with highly regular discharge pattern and clearly distinguishable action potentials were kept for further analysis. At the same time, surface EMG decomposition allowed to identify 16 ± 6 MUs per contraction. Due to the strict selection of the MUs from the intramuscular EMG recordings, the number of MUs identified by both techniques was relatively low (1 ± 1 MU per contraction). For these MUs, decomposition of surface EMG demonstrated a good match in identified discharges with decomposition of intramuscular EMG (average rate of agreement, 94 ± 3%). These results demonstrate that MU behaviour can be noninvasively investigated reliably during isometric contractions at relatively high forces. © 2011 Springer-Verlag Berlin Heidelber
Architectural changes in superficial and deep compartments of the tibialis anterior during electrical stimulation over different sites
Full text linkElectrical stimulation is widely used in rehabilitation to prevent muscle weakness and to assist the functional recovery of neural deficits. Its application is however limited by the rapid development of muscle fatigue due to the non-physiological motor unit (MU) recruitment. This issue can be mitigated by interleaving muscle belly (mStim) and nerve stimulation (nStim) to distribute the temporal recruitment among different MU groups. To be effective, this approach requires the two stimulation modalities to activate minimally-overlapped groups of MUs. In this manuscript, we investigated spatial differences between mStim and nStim MU recruitment through the study of architectural changes of superficial and deep compartments of tibialis anterior (TA). We used ultrasound imaging to measure variations in muscle thickness, pennation angle, and fiber length during mStim, nStim, and voluntary (Vol) contractions at 15% and 25% of the maximal force. For both contraction levels, architectural changes induced by nStim in the deep and superficial compartments were similar to those observed during Vol. Instead, during mStim superficial fascicles underwent a greater change compared to those observed during nStim and Vol, both in absolute magnitude and in their relative differences between compartments. These observations suggest that nStim results in a distributed MU recruitment over the entire muscle volume, similarly to Vol, whereas mStim preferentially activates the superficial muscle layer. The diversity between spatial recruitment of nStim and mStim suggests the involvement of different MU populations, which justifies strategies based on interleaved nerve/muscle stimulation to reduce muscle fatigue during electrically-induced contractions of TA
Interleukin-6 response to isokinetic exercise in elite athletes: relationships to adrenocortical function and to mechanical and myoelectric fatigue.
No full textExercise stimulates the release of interleukin-6 (IL-6). Aims of the study were to: (a) analyse the IL-6 response to exercise in power (n = 7) and endurance athletes (n = 13); (b) determine the effects of the IL-6 production on mechanical and myoelectric fatigue; (c) evaluate the relationship between IL-6 and adrenocortical responses. EMG variables (conduction velocity, mean power frequency, average rectified value), ACTH, cortisol, DHEA, IL-6, myoglobin, and lactate were analysed before and after an isokinetic exercise. The exercise elicited significant mechanical and myoelectric fatigue as well as significant biochemical responses. Power athletes showed IL-6 and lactate responses higher than endurance athletes. The correlation analyses showed that the greater the mechanical fatigue, the greater the increases in lactate and IL-6. No correlations were found between IL-6 and EMG variables. No relationships were found between IL-6 and cortisol, after correction for ACTH levels. In conclusion, the muscular IL-6 production, as inferred by its circulating levels, had no detectable effects on the myoelectric manifestations of fatigue and the cortisol response to exercise was not related to the amount of circulating IL-6, but only to the activation of ACTH secretion
M-wave properties during progressive motor unit activation by transcutaneous neuromuscular stimulation: effect of the stimulation waveform
Full text linkQuantitative assessment of volumetric muscle loss: Dual-energy X-ray absorptiometry and ultrasonography
No full textThe generalized skeletal muscle disorder that involves (in elderly subjects) the progressive loss of muscle mass and function has been defined sarcopenia, whereas the rapid-onset (traumatic or surgical) and focal (unilateral) loss of skeletal muscle with resultant functional impairment has been defined volumetric muscle loss. Different tools and approaches are commonly used in the clinical settings to quantify the loss of muscle or lean mass and to assess the consequent motor impairment. This review describes the technical principles and provides a summary of the main parameters that can be obtained to assess lean mass (and its distribution) or muscle size (and its structure) through the two imaging techniques most easily accessible and therefore frequently adopted in the clinical practice: dual-energy X-ray absorptiometry and muscle ultrasonography
Characterization of the stimulation output of four devices for focal muscle vibration
Full text linkDifferent devices for mechano-acoustic muscle vibration became available on the market in the last ten years. Although the use of these vibrators is increasing in research and clinical settings, the features of their stimulation output were never described in literature. In this study we aimed to quantify and compare the stimulation output of the four most widespread pneumatic devices for focal muscle vibration available on the market. A piezoelectric pressure sensor was used to measure the pressure profile generated by the four selected devices in the following experimental conditions: i) measurement of the output changes associated with variations of the stimulation amplitude for three stimulation frequencies (100 Hz, 200 Hz, and 300 Hz); ii) measurement of the output changes during a 20-min long stimulation at constant frequency (300 Hz) and amplitude; iii) measurement of the output changes associated with the progressive activation of all stimulation channels at constant frequency (200 Hz) for different amplitudes. The maximum peak-to-peak amplitudes of the pressure waves were in the range 102 mbar - 369 mbar (below the maximum values declared by the different manufacturers). The shape of the pressure waves generated by the four devices was quasi-sinusoidal and asymmetric with respect to the atmospheric pressure. All output features had a remarkable intra- and inter-device variability. Further studies are required to support the technological improvement of the currently available devices and to focus the issues of vibration effectiveness, limitations, proper protocols, modalities of its application and assessment in neuromuscular training and rehabilitation
DXA-Based Detection of Low Muscle Mass Using the Total Body Muscularity Assessment Index (TB-MAXI): A New Index with Cutoff Values from the NHANES 1999–2004
Full text linkThe aims of this study were to investigate age-related changes in total body skeletal muscle mass (TBSMM) and the between-limb asymmetry in lean mass in a large sample of adults. Demographic, anthropometric, and DXA-derived data of National Health and Nutrition Examination Survey participants were considered. The sample included 10,014 participants of two ethnic groups (Caucasians and African Americans). The age-related decline of TBSMM absolute values was between 5% and 6% per decade in males and between 4.5% and 5.0% per decade in females. The adjustment of TBSMM for body surface area (TB-MAXI) showed that muscle mass peaked in the second decade and decreased progressively during the subsequent decades. The following thresholds were identified to distinguish between low and normal TB-MAXI: (i) 10.0 kg/m2 and 11.0 kg/m2 in Caucasian and African American females; and (ii) 12.5 kg/m2 and 14.5 kg/m2 in Caucasian and African American males. The lean asymmetry indices were higher for the lower limbs compared with the upper limbs and were higher for males compared with females. In conclusion, the present study proposes the TB-MAXI and lean asymmetry index, which can be used (and included in DXA reports) as clinically relevant markers for muscle amount and lean distribution
Ultrasound Tissue Characterization of Human Achilles Tendon by Stability Quantification of Echo Patterns
No full textThe assessment of tendon size and structure is commonly included in the clinical management of healthy athletes and different types of patients to personalize their training or rehabilitation. The quantitative analysis of the Achilles tendon structure described here can be performed with a recently introduced system that is noninvasive, relatively inexpensive, portable, radiation-free, and enables the rapid collection of accurate and reproducible data. It uses a standard ultrasound probe that is automatically displaced by a tracker in precise steps of 0.2 mm across the region of interest to collect successive two-dimensional ultrasound images that are then compiled into three-dimensional data-block. The measurement procedure is simple: a subject can be tested in 10-15 min, and a comprehensive report is automatically generated. The quantification of four different echo types enables the evaluation of the tissue integrity: this quantification can be useful for the diagnostic and prognostic assessment of patients with Achilles tendinopathy
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