A method for the determination of the force-length relation of selected in-vivo human skeletal muscles

In this paper a method is presented to determine force-length relations of in-vivo human skeletal muscles. The method is experimental and can be used for selected multi-joint muscles. It contains three basic assumptions: (a) the maximal, isometric force a muscle can exert is constant for a given muscle length, (b) antagonistic muscle activity for the experimental contractions is constant, and (c) resultant joint moments obtained during the experiments are produced by muscular forces exclusively. Experimentally determined force-length relations of intact in-vivo human skeletal muscles have not been determined yet. Application of this method will allow the comparison of actual force-length relations of selected human skeletal muscles to force-length relations used previously. Proposed mechanisms responsible for the force-length characteristics of a muscle, such as the cross-bridge theory, may be critically evaluated. Differences of force-length relations obtained under in vivo and in vitro conditions may be quantified.     

Physiological characteristics of two extreme muscle compartments in gastrocnemius medialis of the anaesthetized rat

Rat medial gastrocnemius (GM) muscle is a compartmentalized muscle. The functional properties and fibre type composition of the most proximal and most distal compartment were studied in in situ preparations. The proximal compartment contained predominantly fast twitch oxidative fibres. The distal compartment was mainly composed of fast twitch glycolytic fibres. With the use of two small electrodes placed around the primary nerve branches, both compartments could be separately stimulated within the same muscle. The length-force relationship was less broad and maximal twitch and tetanic forces were obtained at lower muscle lengths for the proximal compartment. The differences (mm) were 0.9 ± 0.2 and 1.2 ± 0.2 for maximal twitch and tetanic force (120 Hz) production, respectively (P < 0.001). The shortening velocity for maximal power production was lower (P < 0.001) for the proximal compartment (proximal: 57.1 ± 2.7 mm s^-1, distal: 73.1 ± 3.0 mm s^-1). During a standard fatigue test the fatiguability was significantly lower for the proximal compared with the distal fibres. Our findings suggest that the proximal compartment is likely to be activated in vivo during activities requiring relatively low power outputs for longer time periods. In contrast the distal compartment is probably recruited only during high power demanding short lasting activities. The presented model makes it possible to study fatigue related changes in power production of the ‘red’ and ‘white’ areas of the GM separately in a way that is probably meaningful with respect to in vivo function.     

Ultrasound of oral and masticatory muscles: Why every neuromuscular swallow team should have an ultrasound machine

Patients with neuromuscular disorders often present with swallowing difficulties due to oral phase problems and pharyngeal residue after swallow. It is important to assess the underlying pathology and cause of the swallowing disturbance in this patient group, such as dystrophic changes in oral and masticatory muscles. This allows for more patient‐tailored recommendations, for example optimal compensation strategies to maintain function for longer. Ultrasound can show structural changes caused by dystrophy or denervation of muscles, detect involuntary movements such as fasciculations, and provide dynamic video images of tongue motion during swallowing attempts. This article, based on the authors' extensive experience with ultrasound in neuromuscular disease, explains the concepts of oral muscle ultrasound and its proven value in assessing neuromuscular mastication and swallowing problems. As a patient‐friendly and portable technique, we advocate its use as a standard tool for analyzing neuromuscular dysphagia. Clin. Anat. 30:183–193, 2017. © 2017 Wiley Periodicals, Inc.     

家兔小腿三头肌亚部化研究

目的：探讨家兔小腿三头肌的亚部划分及该肌的功能。方法：Sihler肌内神经染色法；肌构筑法；肌纤维分型法。结果：从肌内神经的走行进一步证实兔腓肠肌外侧头3个亚部的假设。肌构筑研究显示腓肠肌外侧头慢行时以远端的中间亚部活动为主，快行时有近端的内、外侧亚部更多参与。肌球蛋白ATPase分型研究表明腓肠肌外侧头的3个亚部和腓肠肌内侧头均以ⅡB型纤维居多，比目鱼肌以Ⅰ型纤维占绝对优势。结论：Sihler染色法划分骨骼肌亚部更直观、可靠；腓肠肌外侧头外侧亚部以产生力量，内侧亚部以发挥速度为主；腓肠肌内侧头主要是维持膝在静力和动力状态下的稳定性；比目鱼肌的功能在兔表现不明显。     

Detection of neutrophilic myeloperoxidase in rat skeletal muscles after muscular activity

Department of Sport Biochemistry, Research Institute of Physical Culture, Leningrad. (Presented by Academician of the Academy of Medical Sciences of the USSR S. E. Severin.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 110, No. 11, pp. 489–491, November, 1990.     

An allometric analysis of the number of muscle spindles in mammalian skeletal muscles

An allometric analysis of the number of muscle spindles in relation to muscle mass in mammalian (mouse, rat, guinea-pig, cat, human) skeletal muscles is presented. It is shown that the trend to increasing number as muscle mass increases follows an isometric (length) relationship between species, whereas within a species, at least for the only essentially complete sample (human), the number of spindles scales, on average, with the square root rather than the cube root of muscle mass. An attempt is made to reconcile these apparently discrepant relationships. Use of the widely accepted spindle density (number of spindles g(-1) of muscle) as a measure of relative abundance of spindles in different muscles is shown to be grossly misleading. It is replaced with the residuals of the linear regression of ln spindle number against ln muscle mass. Significant differences in relative spindle abundance as measured by residuals were found between regional groups of muscles: the greatest abundance is in axial muscles, including those concerned with head position, whereas the least is in muscles of the shoulder girdle. No differences were found between large and small muscles operating in parallel, or between antigravity and non-antigravity muscles. For proximal vs. distal muscles, spindles were significantly less abundant in the hand than the arm, but there was no difference between the foot and the leg.     

Decreased water T2 in fatty infiltrated skeletal muscles of patients with neuromuscular diseases

Quantitative imaging techniques are emerging in the field of magnetic resonance imaging of neuromuscular diseases (NMD). T₂ of water (T_2w) is considered an important imaging marker to assess acute and chronic alterations of the muscle fibers, being generally interpreted as an indicator for “disease activity” in the muscle tissue. To validate the accuracy and robustness of quantitative imaging methods, ¹H magnetic resonance spectroscopy (MRS) can be used as a gold standard. The purpose of the present work was to investigate T_2w of remaining muscle tissue in regions of higher proton density fat fraction (PDFF) in 40 patients with defined NMD using multi‐TE single‐voxel ¹H MRS. Patients underwent MR measurements on a 3 T system to perform a multi‐TE single‐voxel stimulated echo acquisition method (STEAM) MRS (TE = 11/15/20/25(/35) ms) in regions of healthy, edematous and fatty thigh muscle tissue. Muscle regions for MRS were selected based on T₂‐weighted water and fat images of a two‐echo 2D Dixon TSE. MRS results were confined to regions with qualitatively defined remaining muscle tissue without edema and high fat content, based on visual grading of the imaging data. The results showed decreased T_2w values with increasing PDFF with R² = 0.45 (p < 10^?3) (linear fit) and with R² = 0.51 (exponential fit). The observed dependence of T_2w on PDFF should be considered when using T_2w as a marker in NMD imaging and when performing single‐voxel MRS for T_2w in regions enclosing edematous, nonedematous and fatty infiltrated muscle tissue.     

Structural manifestations of mitochondrial dysfunction in skeletal muscles of early aging OXYS rats

Changes in the mitochondrial compartment are the central element in the morphogenesis of musculoskeletal abnormalities in early aging OXYS rats. Compensatory hyperplasia and hypertrophy with enlargement of the working surface area are seen in these organelles at the age of 2 months. The mitochondria are characterized by polymorphism, compact packing of cristae. By the age of 9 months destructive changes and sharp reduction of the mitochondrial compartment are observed is many myocytes. Disorders in the mitochondrial structure and function and oxidative stress can be among the causes of degenerative changes in the myofibrillar system and other structures of muscle fibers, including those resultant from activation of apoptosis.Translated from Byulleten Eksperimentalnoi Biologii i Meditsiny, Vol. 138, No. 12, pp. 674–679, December, 2004This revised version was published online in April 2005 with a corrected cover date.