The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Dario Farina - One of the best experts on this subject based on the ideXlab platform.
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postural activation of the human medial Gastrocnemius Muscle are the Muscle units spatially localised
The Journal of Physiology, 2011Co-Authors: Taian M Vieira, Ian D Loram, Silvia Muceli, Roberto Merletti, Dario FarinaAbstract:Non-technical summary In the medial Gastrocnemius Muscle of cats, the longitudinal size (3–4 cm) of the territory of motor units is large (∼60%) relative to the Muscle length. In the human medial Gastrocnemius, the size of motor unit territories is unknown. By comparing intramuscular and surface electromyograms we show that, when subjects stand at ease, the motor units active in the medial Gastrocnemius have small territories. They extend no longer than 4 cm and no less than 1 cm along the longitudinal axis (∼25 cm long) of the Muscle. Physiologically, the small territories of motor units give the nervous system a mechanism for the independent activation of sub-volumes of the medial Gastrocnemius Muscle.
Robert D. Herbert - One of the best experts on this subject based on the ideXlab platform.
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ultrasound imaging of the human medial Gastrocnemius Muscle how to orient the transducer so that Muscle fascicles lie in the image plane
Journal of Biomechanics, 2016Co-Authors: Bart Bolsterlee, Simon C Gandevia, Robert D. HerbertAbstract:The length and pennation of Muscle fascicles are frequently measured using ultrasonography. Conventional ultrasonography imaging methods only provide two-dimensional images of Muscles, but Muscles have complex three-dimensional arrangements. The most accurate measurements will be obtained when the ultrasound transducer is oriented so that endpoints of a fascicle lie on the ultrasound image plane and the image plane is oriented perpendicular to the aponeurosis, but little is known about how to find this optimal transducer orientation in the frequently-studied medial Gastrocnemius Muscle. In the current study, we determined the optimal transducer orientation at 9 sites in the medial Gastrocnemius Muscle of 8 human subjects by calculating the angle of misalignment between three-dimensional Muscle fascicles, reconstructed from diffusion tensor images, and the plane of a virtual ultrasound image. The misalignment angle was calculated for a range of tilts and rotations of the ultrasound transducer relative to a reference orientation that was perpendicular to the skin and parallel to the tibia. With the transducer in the reference orientation, the misalignment was substantial (mean across sites and subjects of 6.5°, range 1.4 to 20.2°). However for all sites and subjects a near-optimal alignment (on average 2.6°, range 0.5° to 6.0°) could be achieved by maintaining 0° tilt and applying a small rotation (typically less than 10°). On the basis of these data we recommend that ultrasonographic measurements of medial Gastrocnemius Muscle fascicle architecture be obtained, at least for relaxed Muscles under static conditions, with the transducer oriented perpendicular to the skin and nearly parallel to the tibia.
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Passive mechanical properties of human Gastrocnemius Muscle-tendon units
Journal of Foot and Ankle Research, 2012Co-Authors: Robert D. Herbert, Joanna DiongAbstract:Background The passive mechanical properties of skeletal Muscletendon units are important because they determine the amount of motion available at joints. Human Gastrocnemius Muscle-tendon units are of particular interest because this Muscle is prone to develop contractures, may have ar ole in lower limb overuse injuries, and is a common site of Muscle tears. This workshop provides an introduction to what is known of the passive properties of skeletal Muscle-tendon units, focussing on human Gastrocnemius Muscle-tendon units. The workshop will also provide an introduction to the theory and practice of measuring passive mechanical properties of human Gastrocnemius Muscle-tendon units in vivo. Materials and methods The mechanical properties of Muscle-tendon units have been investigated most frequently using in vitro preparations. Testing of elastic properties most often utilises quasi-static protocols. Dynamic protocols have also been used, particularly in studies that seek also to determine viscous properties. Several methods have been developed for testing the mechanical properties (usually elastic or pseudo-elastic properties) of human Muscle-tendon units in vivo. Changes in length of human Gastrocnemius Muscle-tendon units may be estimated from changes in ankle and knee angles if moment arms are known. Fascicle lengths can be measured with ultrasound imaging or MRI. Recently methods have been developed for measuring sarcomere lengths using invasive and minimally invasive techniques. Achilles tendon force can be measured using invasive methods such as fibre optic transducers. The length-tension properties of the Achilles tendon can be estimated using non-invasive methods during isometric contractions. This workshop focuses on a method developed by our research team for non-invasive measurement of the passive length-tension properties of human Gastrocnemius Muscle-tendon units [1], as well as length-tension properties of Muscle fascicles and tendons [2]. The method involves measuring ankle stiffness at a range of knee angles.
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passive mechanical properties of human Gastrocnemius Muscle tendon units Muscle fascicles and tendons in vivo
The Journal of Experimental Biology, 2007Co-Authors: Phu Hoang, Robert D. Herbert, Gabrielle Todd, Robert B Gorman, Simon C GandeviaAbstract:SUMMARY This study provides the first in vivo measures of the passive length–tension properties of relaxed human Muscle fascicles and their tendons. A new method was used to derive passive length–tension properties of human Gastrocnemius Muscle–tendon units from measures of ankle stiffness obtained at a range of knee angles. Passive length–tension curves of the Muscle–tendon unit were then combined with ultrasonographic measures of Muscle fascicle length and pennation to determine passive length–tension curves of the Muscle fascicles and tendons. Mean slack lengths of the fascicles, tendons and whole Muscle–tendon units were 3.3±0.5 cm, 39.5±1.6 cm and 42.3±1.5 cm, respectively (means ± s.d., N =6). On average, the Muscle–tendon units were slack (i.e. their passive tension was zero) over the shortest 2.3±1.2 cm of their range. With combined changes of knee and ankle angles, the maximal increase in length of the Gastrocnemius Muscle–tendon unit above slack length was 6.7±1.9 cm, of which 52.4±11.7% was due to elongation of the tendon. Muscle fascicles and tendons underwent strains of 86.4±26.8% and 9.2±4.1%, respectively, across the physiological range of lengths. We conclude that the relaxed human Gastrocnemius Muscle–tendon unit falls slack over about one-quarter of its in vivo length and that Muscle fascicle strains are much greater than tendon strains. Nonetheless, because the tendons are much longer than the Muscle fascicles, tendons contribute more than half of the total compliance of the Muscle–tendon unit.
Simon C Gandevia - One of the best experts on this subject based on the ideXlab platform.
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ultrasound imaging of the human medial Gastrocnemius Muscle how to orient the transducer so that Muscle fascicles lie in the image plane
Journal of Biomechanics, 2016Co-Authors: Bart Bolsterlee, Simon C Gandevia, Robert D. HerbertAbstract:The length and pennation of Muscle fascicles are frequently measured using ultrasonography. Conventional ultrasonography imaging methods only provide two-dimensional images of Muscles, but Muscles have complex three-dimensional arrangements. The most accurate measurements will be obtained when the ultrasound transducer is oriented so that endpoints of a fascicle lie on the ultrasound image plane and the image plane is oriented perpendicular to the aponeurosis, but little is known about how to find this optimal transducer orientation in the frequently-studied medial Gastrocnemius Muscle. In the current study, we determined the optimal transducer orientation at 9 sites in the medial Gastrocnemius Muscle of 8 human subjects by calculating the angle of misalignment between three-dimensional Muscle fascicles, reconstructed from diffusion tensor images, and the plane of a virtual ultrasound image. The misalignment angle was calculated for a range of tilts and rotations of the ultrasound transducer relative to a reference orientation that was perpendicular to the skin and parallel to the tibia. With the transducer in the reference orientation, the misalignment was substantial (mean across sites and subjects of 6.5°, range 1.4 to 20.2°). However for all sites and subjects a near-optimal alignment (on average 2.6°, range 0.5° to 6.0°) could be achieved by maintaining 0° tilt and applying a small rotation (typically less than 10°). On the basis of these data we recommend that ultrasonographic measurements of medial Gastrocnemius Muscle fascicle architecture be obtained, at least for relaxed Muscles under static conditions, with the transducer oriented perpendicular to the skin and nearly parallel to the tibia.
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passive mechanical properties of human Gastrocnemius Muscle tendon units Muscle fascicles and tendons in vivo
The Journal of Experimental Biology, 2007Co-Authors: Phu Hoang, Robert D. Herbert, Gabrielle Todd, Robert B Gorman, Simon C GandeviaAbstract:SUMMARY This study provides the first in vivo measures of the passive length–tension properties of relaxed human Muscle fascicles and their tendons. A new method was used to derive passive length–tension properties of human Gastrocnemius Muscle–tendon units from measures of ankle stiffness obtained at a range of knee angles. Passive length–tension curves of the Muscle–tendon unit were then combined with ultrasonographic measures of Muscle fascicle length and pennation to determine passive length–tension curves of the Muscle fascicles and tendons. Mean slack lengths of the fascicles, tendons and whole Muscle–tendon units were 3.3±0.5 cm, 39.5±1.6 cm and 42.3±1.5 cm, respectively (means ± s.d., N =6). On average, the Muscle–tendon units were slack (i.e. their passive tension was zero) over the shortest 2.3±1.2 cm of their range. With combined changes of knee and ankle angles, the maximal increase in length of the Gastrocnemius Muscle–tendon unit above slack length was 6.7±1.9 cm, of which 52.4±11.7% was due to elongation of the tendon. Muscle fascicles and tendons underwent strains of 86.4±26.8% and 9.2±4.1%, respectively, across the physiological range of lengths. We conclude that the relaxed human Gastrocnemius Muscle–tendon unit falls slack over about one-quarter of its in vivo length and that Muscle fascicle strains are much greater than tendon strains. Nonetheless, because the tendons are much longer than the Muscle fascicles, tendons contribute more than half of the total compliance of the Muscle–tendon unit.
Taian M Vieira - One of the best experts on this subject based on the ideXlab platform.
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do surface electromyograms provide physiological estimates of conduction velocity from the medial Gastrocnemius Muscle
Journal of Electromyography and Kinesiology, 2013Co-Authors: Alessio Gallina, Taian M Vieira, Roberto Merletti, Cintia Helena RitzelAbstract:Abstract Muscle fiber conduction velocity (CV) is commonly estimated from surface electromyograms (EMGs) collected with electrodes parallel to Muscle fibers. If electrodes and Muscle fibers are not located in parallel planes, CV estimates are biased towards values far over the physiological range. In virtue of their pinnate architecture, the fibers of Muscles such as the Gastrocnemius are hardly aligned in planes parallel to surface electrodes. Therefore, in this study we investigate whether physiological CV estimates can be obtained from the Gastrocnemius Muscle. Specifically, with a large grid of 16×8 electrodes we map CV estimates over the whole Gastrocnemius Muscle while eleven subjects exerted isometric plantar flexions at three different force levels. CV was estimated for couples of single differential EMGs and estimate locations (i.e., channels) were classified as physiological and non-physiological , depending on whether CV estimates were within the physiological range (3–6ms −1 ) or not. Physiological CV values could be estimated from a markedly small Muscle region for eight participants; channels providing physiological CV estimates corresponded to about 5% of the total number of channels. As expected, physiological and non-physiological channels were clustered in distinct regions. CV estimates within the physiological range were obtained for the most distal Gastrocnemius portion (ANOVA, P
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postural activation of the human medial Gastrocnemius Muscle are the Muscle units spatially localised
The Journal of Physiology, 2011Co-Authors: Taian M Vieira, Ian D Loram, Silvia Muceli, Roberto Merletti, Dario FarinaAbstract:Non-technical summary In the medial Gastrocnemius Muscle of cats, the longitudinal size (3–4 cm) of the territory of motor units is large (∼60%) relative to the Muscle length. In the human medial Gastrocnemius, the size of motor unit territories is unknown. By comparing intramuscular and surface electromyograms we show that, when subjects stand at ease, the motor units active in the medial Gastrocnemius have small territories. They extend no longer than 4 cm and no less than 1 cm along the longitudinal axis (∼25 cm long) of the Muscle. Physiologically, the small territories of motor units give the nervous system a mechanism for the independent activation of sub-volumes of the medial Gastrocnemius Muscle.
H Majczynski - One of the best experts on this subject based on the ideXlab platform.
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changes of the force frequency relationship in the rat medial Gastrocnemius Muscle after total transection and hemisection of the spinal cord
Journal of Neurophysiology, 2011Co-Authors: W Mrowczynski, J Celichowski, P Krutki, Anna Cabaj, Urszula Slawinska, H MajczynskiAbstract:The relationships between the stimulation frequency and the force developed by motor units (MUs) of the medial Gastrocnemius Muscle were compared between intact rats and animals after total transec...
