Training-induced changes in muscle architecture and specific tension

Five men underwent unilateral resistance training of elbow extensor (triceps brachii) muscles for 16 weeks. Before and after training, muscle layer thickness and fascicle angles of the long head of the triceps muscle were measured in vivo using B-mode ultrasound, and fascicle lengths were estimated. Series anatomical cross-sectional areas (ACSA) of the triceps brachii muscle were measured by magnetic resonance imaging, from which muscle volume (Vm) was determined and physiological cross-sectional area (PCSA) was calculated. Elbow extension strength (isometric; concentric and eccentric at 30, 90 and 180°·s^–1) was measured using an isokinetic dynamometer to determine specific tension. Muscle volumes, ACSA, PCSA, muscle layer thickness and fascicle angles increased after training and their relative changes were similar, while muscle and fascicle length did not change. Muscle strength increased at all velocities; however, specific tension decreased after training. Increase in fascicle angles, which would be the result of increasedV _m and PCSA, would seem to imply the occurrence of changes in muscle architecture. This might have given a negative effect on the force-generating properties of the muscles.     

The effect of hydrolytic enzymes on the acetylcholine sensitivity of the skeletal muscle cell membrane

Isometric tension developed by rat soleus and extensor digitorum longus (EDL) muscles in response to acetylcholine (Ach) applied in vitro was recorded. Tension of contractures elicited in response to Ach increased after muscles had been incubated with phospholipase C, pepsin, or soluble fractions prepared from muscle homogenate.Using intracellular microelectrodes, resting membrane potential (RMP) and depolarisation in response to Ach added to the bathing medium were recorded in endplate-free regions of the muscle fibres. No significant change in RMP was observed in muscles incubated with soluble muscle fraction or phospholipase C, but depolarisation in response to Ach or carbachol was significantly increased. The time course for the increase in depolarisation and the contracture response to Ach was similar.When all available receptors were blocked with -bungarotoxin prior to incubation so that no response to Ach could be elicited, with subsequent incubation in muscle soluble fraction or phospholipase C, both contractures and depolarisation in response to Ach returned. These results support the hypothesis that receptors, not previously available to interact with Ach or -bungarotoxin were revealed following incubation.     

Experimental induction of ring fibers in regenerating skeletal muscle

Light microscopy and electron microscopy were used to study the formation of ring fibers induced experimentally in regenerating muscle subjected to tenotomy-induced tension deficiency. Anterior tibial rat muscles were injured by intramuscular injection of mepivacain, tenotomized at varying stages of the regenerative process, and analyzed 30 days after sectioning the tendon. The combination of regeneration and tenotomy led to the appearance of ring fibers at different developmental stages. Ring fibers were not observed in regenerating control muscles and were scarce in tenotomized controls. Our results showed that the regenerative phase in which tension deficiency was established had a significant influence on the number of developing ring fibers; the number increased when tenotomy was performed during subsarcolemmic myofibrillogenesis in regenerating fibers. As a consequence, one might hypothesize that tension deficiency during muscle fiber repair plays a critical role in ring fiber formation.     

生长因子对骨骼肌损伤与修复的作用

BACKGROUND: Growth factors involved in the regulation of cellular processes play an important role in the wound healing and tissue regeneration. OBJECTIVE:To elaborate the role of a variety of cellular processes involving growth factors in the repair of skeletal muscle injury, and to provide the references for the treatment and rehabilitation strategies, and the synthesis of biomaterials with growth factor for the skeletal muscle after injury. METHODS: A computer-based online search was conducted in PubMed, Mendeley, Google Scholar, and CNKI databases from 1995 to November 2015 to screen the relevant literatures using the keywords “skeletal muscle, damage repair, insulin-like growth factor, epidermal growth factor, growth factor”. Data screening, processing, and summary were performed. RESULTS AND CONCLUSION: Fifty-one eligible literatures were included. Exercise training promotes the repair and regeneration of the injured skeletal muscle cells and the recovery of the function by activating satellite cells in the sarcolemma and basement membrane to produce the numerous myoblasts. The repair involves the complex biological process regulated by growth factors. Exogenous growth factors up-regulate the mRNA expression of endogenous growth factors, stimulate the proliferation of the myoblasts, accelerate the fusion between myotubes and muscle fibers, promote the repair of skeletal muscle injury, inhibit the formation of scars, thereby enhancing the healing quality. 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Regeneration pattern of cardiac and skeletal muscle after transplantation into a skeletal muscle bed in rats

Background: The ability of skeletal muscle to regenerate after injury is well established. In contrast, cardiac muscle is incapable of regeneration and recovery after injury. The aim of the present study was to evaluate and compare the regeneration pattern of cardiac and skeletal muscle after transplantation into a skeletal muscle bed in rats. Methods: The following group of transplants were performed at the site prepared by removing the host extensor digitorum longus (EDL) muscle. The first group consisted of cardiac muscle transplanted as one piece or after mincing into 1-mm pieces. The second group included cotransplants of cardiac and skeletal muscle minces that were intermixed. Entire EDL muscle or minced EDL muscle were also transplanted for comparison. Rats were sacrificed 3–30 days after transplantation for morphological analysis. Results: The results demonstrated that skeletal muscle transplants underwent rapid regeneration, and by 30 days the entire muscle was filled with regenerated myofibers. In transplants of cardiac muscle significant inflammation, myocardial degeneration and necrosis were observed. In spite of the necrosis and fibrosis, the presence of a few regenerated myotubes in the outer region was observed. In cardiac and skeletal muscle cotransplants, the inflammation was restricted to cardiac tissue; however, by 30 days the entire contransplant was filled with regenerated myotubes and myofibers. Conclusions: These results show that skeletal muscle is capable of growth, regeneration, and integration with the cardiac muscle after cotransplantation. Combination of skeletal and cardiac muscle may prove useful in defining the cellular processes necessary for enhancing cardiac repair after injury. © 1995 Wiley-Liss, Inc.     

The possible role of acetate in exercise hyperemia in dog skeletal muscle

The possible role of acetate in the genesis of exercise hyperemia was studied in five series of dogs. Intraarterial infusion of an isomotic solution of sodium acetate at 0.76 ml/min in the dog forelimb decreased the resistance to flow through skeletal muscle by 48%, primarily by decreasing resistance to flow through small vessels. Skin lymph flow and lymph protein concentration were unaffected. The hindlimb of the conscious dog took up acetate at rest (A-V difference, _58.3±19.6 nmoles/ml) and put out acetate during treadmill exercise (A-V difference, –105.6±20.12 nmoles/ml); femoral venous blood acetate concentration increased by 145 nmoles/ml (control 195 nmoles/ml). In the gracilis muscle of the anesthetized dog, simulated exercise at 0.5, 1.0 or 2.0 Hz increased acetate tissue content (72, 248 and 442 nmoles/g, respectively), output (18,899, and 1,830 nmoles/100 g/min, respectively) and venous cencentration (82, 49 and 39 nmoles/ml, respectively) and changes in tissue acetate content correlated with changes in vascular resistancer=0.75,P<0.001. Intraarterial infusion of an isosmotic solution of sodium acetate in the quiescent gracilis muscle perfused at constant flow produced a significant (6%) decrease in resistance when arterial blood acetate was increased by a calculated 96 nmoles/ml. These studies suggest that acetate might be included among those metabolites that contribute to exercise hyperemia.Supported by grants CO7610 and CO7635 from the Uniformed Services University. Preliminary communications included Physiologist 21:115, 1978, Federation Procedings 39:270, 1980 and Physiologist 23:156, 1980     

Transmission phenomena and early tension recovery in skinned muscle fibres of the frog

Tension responses due to small rapid length changes completed in 50 s were obtained from segments with different length of single fibres of the ileofibularis muscle of the frog. The very early parts of the responses varied with segment length. A simulation of the early parts of the response was carried out by means of a linear model in which the fibre is regarded as a rod of infinitesimally small segments containing undamped elasticity, damped elasticity and mass in series. In the simulation corrections were included for the effects caused by the viscosity and density of the surrounding fluid and for the force transducer characteristics. The results indicate the presence of a very rapid component in the fast recovery with a time constant of 5–15 s. The undamped elasticity of the activated fibres corrected for their passive properties was such that a sudden shortening corresponding to 2.6 nm/half sarcomere would reduce active tension to zero.     

Assessment of skeletal muscle damage in successive biopsies from strength-trained and untrained men and women

Summary The effects of repeated biopsy sampling on muscle morphology was qualitatively and quantitatively assessed in strength-trained and untrained men and women. College-age men (13) and women (8) resistance trained twice a week for 8 weeks. A progressive resistance-training program was performed consisting of squats, leg presses, and leg extensions. Nontraining men (7) and women (5) served as controls. Muscle biopsy specimens and fasting bloods were obtained at the beginning and every 2 weeks and histochemical, biochemical, and ultrastructural methods were employed to assess the type and amount of damage. Except for a few scattered atrophic fibers in 2 of the 33 biopsy samples, all initial specimens were normal. In contrast, many of the subsequent biopsy samples from both untrained and resistance-trained men and women contained evidence of damage. Ultrastructural analysis confirmed that degenerative-regenerative processes were occurring in both groups. However, training subjects had a four-fold greater number of damaged fibers than nontraining subjects (8.53% vs 2.08%). In addition, only biopsy samples from training individuals contained fibers with internal disorganization (e.g., Z-line streaming, myofibrillar disruption). Calpain II levels in the biopsy samples and serum creatine kinase activity were not significantly affected supporting the light and electron microscopic observations that most of the damaged fibers were normal in appearance except for their small diameter. In summary, focal damage induced by the biopsy procedure is not completely repaired after 2 weeks and could affect the results, particularly cross-sectional area measurements. Moreover, resistance training appears to cause additional damage to the muscle and may delay repair of the biopsied region.     

A general, computer-based method for study of the spatial distribution of muscle fiber types in skeletal muscle

Summary The present method provides detailed quantitative information on the spatial distribution of the muscle fiber types in skeletal muscle. This is accomplished by comparing the measured spatial distribution of the fiber types with a computer-simulated random pattern. The method is based on a registration of the absolute frequency for six principal categories of fiber contacts (I-I, I-IIA, I-IIB, IIA-IIA, IIA-IIB, IIB-IIB). A computer program was designed tosimulate a random pattern of fibers. The simulations were performed with high accuracy with regard to fiber type proportion and the number of neighbouring fibers. The computer then calculated the frequency for each of the different categories of fiber contacts in the simulated random pattern. The measured distribution of fiber contacts could thus be compared to the simulated random pattern. In three bovine muscles studied, the spatial distribution of the muscle fiber types showed a similar pattern. The muscle fibers had a distinct tendency to be surrounded by fibers of a different type. In all three muscles the difference between the measured and the simulated random pattern was statistically significant (p<10^-3).     

Post-exercise leg and forearm flexor muscle cooling in humans attenuates endurance and resistance training effects on muscle performance and on circulatory adaptation

The influence of regular post-exercise cold application to exercised muscles trained by ergometer cycling (leg muscles) or handgrip exercise using a weight-loaded handgrip ergometer (forearm flexor muscles) was studied in human volunteers. Muscle loads were applied during exercise programs three to four times a week for 4–6 weeks. Besides measuring parameters characterizing muscle performance, femoral and brachial artery diameters were determined ultrasonographically. Training effects were identified by comparing pre- and post-training parameters in matched groups separately for the trained limbs cooled after exercise by cold-water immersion and the corresponding trained limbs kept at room temperature. Significant training effects were three times more frequent in the control than in the cold group, including increases in artery diameters in the control but not in the cold group. It is concluded that training-induced molecular and humoral adjustments, including muscle hyperthermia, are physiological, transient and essential for training effects (myofiber regeneration, muscle hypertrophy and improved blood supply). Cooling generally attenuates these temperature-dependent processes and, in particular, hyperthermia-induced HSP formation. This seems disadvantageous for training, in contrast to the beneficial combination of rest, ice, compression and elevation in the treatment of macroscopic musculo-tendinous damage. Part of the results were presented at the Congress on Physiology and Pharmacology of Temperature Regulation held in Rhodes (Greece) in October 14, 2004 [Ohnishi N, Yamane M, Uchiyama N, Shirasawa S, Kosaka M, Shiono H, Okada T (2004) Adaptive changes in muscular performance and circulation by resistance training with regular cold adaptation. J Therm Biol 29: 839–843].     

骨骼肌生长因子、肌球蛋白及骨骼肌胶原与骨骼肌的损伤与修复

BACKGROUND: Regeneration and repair of injured skeletal muscle are influenced by a variety of factors. Skeletal muscle myosin heavy chain and skeletal muscle collagen content are known to be involved in the repair of injured skeletal muscle. OBJECTIVE: To summarize the changes and roles of skeletal muscle growth factors, myosin, and collagen in the repair of injured skeletal muscle. METHODS: A computer-based online search was conducted in PubMed and Wanfang databases from 2002 to 2015 to screen the relevant literatures. Roles of skeletal muscle growth factors, myosin, and collagen in the repair of injured skeletal muscle was summarized by collecting the data regarding the factors influencing exercise and the repair of injured skeletal muscle, and growth factors involved in the regeneration and repair of injured skeletal muscle. RESULTS AND CONCLUSION: Insulin-like growth factor, fibroblast growth factor and hepatocyte growth factor regulate inflammation after skeletal muscle injury extensively. Myosin heavy chain is considered as a specific marker for skeletal muscle regeneration. Types I and III collagen and fibronectin functioning as a skeleton for skeletal muscle fiber play critical roles in the regeneration and repair of injured skeletal muscle. 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Carbonic anhydrase isoform expression and functional role in rodent extraocular muscle

Carbonic anhydrase (CA) accelerates contractile function, particularly in fast-twitch skeletal muscles. Since the extraocular muscles are considered to be amongst the fastest skeletal muscles in mammals, this study tested two hypotheses: (1) CA is expressed at higher levels in rat extraocular muscles than in extensor digitorum longus (EDL, a fast limb muscle), and (2) inhibition of CA activity increases twitch duration and force in the extraocular muscles to a greater extent than in EDL. By real-time quantitative PCR we determined that the expression of CA3 isoform, typically high in skeletal muscles, is significantly depressed in extraocular muscles. Message levels for the CA2 and CA4 isoforms were higher in the extraocular muscles, while CA5 expression was equivalent in both muscles. Strong CA activity was demonstrated by histochemistry in frozen EDL muscle sections, in particular along the sarcolemma and in capillaries. By contrast, extraocular muscle had very low sarcolemmal or cytosolic CA activity. CA inhibition with 6-ethoxyzolamide (ETZ) reversibly increased twitch duration and force in EDL muscle bundles. In the extraocular muscles, ETZ did not alter twitch kinetics. Based on these results, we reject our initial hypotheses and conclude that CA does not influence the fast contractile kinetics characteristic of the extraocular muscles.     

Functional significance of collateral blood flow in working skeletal muscle of the dog

Summary The semitendinosus muscle of the dog is supplied by two separate arteries and drained by two corresponding veins. In the muscles used in this study no blood entering via the distal artery was found to leave via the proximal vein during perfusion through both arteries (orthograde perfusion). Therefore, collateral flow (CF) could be determined as proximal venous outflow during occlusion of the proximal artery. During orthograde perfusion total blood flow averaged 12 ml × min⁻¹ × 100 g⁻¹ at rest and 58.4 ml × min⁻¹ × 100 g⁻¹ during exercise. CF was found to average 6.2 ml × min⁻¹ × 100 g⁻¹ at rest and increased to 9.2 ml × min⁻¹ × 100 g⁻¹ during exercise. CF was sufficient to cover the metabolic demand of resting muscle. During exercise the O₂-uptake ( ) of the distal muscle portion was increased 13.4 fold in comparison to a 3.1 fold increase in the proximal muscle portion. The average contractile power decreased by 46%. Additional infusion of adenosine into the distal artery resulted in an increase of CF to 11.4 ml × min⁻¹ × 100 g⁻¹ and of orthograde flow to 71 ml × min⁻¹ × 100 g⁻¹. The average contractile power of the muscle increased by 13%. Both orthograde flow and CF were found to decrease with increasing muscle load. But this decrease was significantly more pronounced in the case of CF especially at a. lower range of loads. It is concluded that after acute occlusion of orthograde flow, CF is limited by the number, the size and the dilatory capacity of precapillary network vessels. Furthermore, CF is influenced considerably by changes of extravascular support. Presented in part at the 43rd Meeting of the Deutsche Physiologische Gesellschaft [9] and at the XXVI International Congress of Physiological Sciences, New Delhi [6] Supported by the Deutsche Forschungsgemeinschaft (Hi 137/6)     

Acoustic phenomena in the latent period of skeletal muscle: a simple method for in-vivo measurement of the electro-mechanic latency (EML)

An in-vivo method for the assessment of the latency of muscular contraction is presented. It is based on acoustic registration of musclar thickening by a microphone. It was found that the recorded sound wave is often preceded by a small wave of opposite polarity (flattening of the muscle belly) which is an acoustic correlate of the latency relaxation. Strong direct stimulation produced another small sound wave at the beginning of the latent period. The physiological significance of these findings is discussed.This work was supported by the Deutsche Forschungsgemeinschaft (SFB 70)     

微小RNA调节骨骼肌发育与损伤修复的作用及其机制

microRNAs是一类非编码小RNAs分子,新近发现其具有重要的调节基因表达的功能,它能通过抑制翻译和降解靶mRNA来负性调控转录后水平的基因表达,miRNAs已经被证实在肌肉发育和肌细胞增殖和分化的调节中具有重要作用。最近研究发现,肌肉特异性转录因子控制一些microRNAs的表达,通过多种机制调节肌肉发育和功能。结合信息学、生物化学和遗传基因学方法,不仅将阐明骨骼肌microRNAs调控网络,更好地理解肌肉组织的调节,还将通过鉴定候选microRNAs的潜在临床应用靶点,增加肌肉营养不良的治疗干预的新机会。     

The consequences of eccentric contractions and their relationship to delayed onset muscle pain

Summary Exercise can cause muscle pain for a number of reasons. Usually the pain is experienced during the exercise and recovers rapidly afterwards. There is one type of muscle pain that has a very different and characteristic time course. In this situation the exercise itself, and the immediate post-exercise period are painfree. The pain is not felt for about eight hours and is maximal 1 or 2 days later. Delayed onset muscle pain occurs after unaccustomed, high force contractions and is particularly associated with eccentric contractions. The concensus of opinion is that the pain is caused by some form of damage, but the mechanism for the pain is not known. This review summarises the literature on the consequences of eccentric contractions and relates them to delayed onset muscle pain. There is clear evidence of damage to the muscle fibres themselves, their membranes and, at a later stage, mononuclear cell infiltration, but all these have very different time courses and none are the same as the pain. Intramuscular pressures are raised in some, but not all, painful compartments and even when raised follow a different time course to the pain. Anti-inflammatory agents do not affect the pain, but due to the incomplete understanding of the action of these drugs, the role of inflammation in delayed onset muscle pain is uncertain.Despite the considerable evidence of damage after eccentric contractions, the cause of delayed onset muscle pain is still unknown.     

The effect of polycythemia on blood flow in working and non-working skeletal muscle

The effect of acutely induced polycythemia on blood flow and viscosity in the vasodilated vascular bed of working and non-working skeletal muscle was studied. In 12 mongrel dogs anesthetized with thiopental sodium the calf muscle of one hind limb was isolated. Vasodilation was induced either by sciatic stimulation setting the muscle at maximal work or by i.a. infusion of papaverine. Blood flow was measured at different perfusion pressures before and after infusion of 300 ml packed homologous red cells. Blood viscosity in vitro was determined in a coneplate viscometer. Apparent viscosity in vivo was analyzed by comparing pressure-flow relationships for blood and a reference solution. Polycythemia decreased blood flow by 35% in the non-working muscle but less than 10% in the working muscle at comparable perfusion pressures. Blood viscosity in vitro increased by 35% at low shear rates. Apparent viscosity in vivo increased by 35% in the non-working muscle but less than 10% in the working muscle. The flow impairment induced by polycythemia was far more pronounced in the non-working skeletal muscle indicating a flow facilitation by the rhythmic muscle contractions. Erythrocyte flow in fact increased in the working muscle after induced polycythemia while decreased in the non-working muscle.     

Effects of eccentric overload training on patellar tendon and vastus lateralis in three days of consecutive running

Background

The analysis of structural changes in patellar tendon and muscle of healthy subjects in response to mechanical loads provides useful insight into the mechanism underlying overuse injuries.

On the mechanism of an increase of muscle performance and of vasodilation during emotional stress in man

The mechanism of the increase of muscle performance and of vasodilation during emotional stress was studied. The emotional increment of voluntary performance does not depend on the level of blood supply to the working muscles, and the effect is maintained under conditions of cessation of arterial inflow. Augmentation of muscle performance is also observed during emotional stress when isometric contraction is evoked by electrical tetanic stimulation of the nerve, when the number of muscle fibres participating in the evoked response does not increase during emotional stress. The emotional vasodilation is greatly reduced in patients suffering from McArdle's syndrome, in whom the normal course of glycolysis in muscles is disrupted. It is suggested that acetylcholine liberated from sympathetic fibres causes the activation of glycolysis in muscles, which in its turn induces vasodilation in resting skeletal muscles and increase of muscle performance during emotional stress.