Sarcomere number regulation maintained after immobilization in desmin-null mouse skeletal muscle

Structured respiratory physiotherapy protocol for resolution of atelectasis in pediatric intensive care

Children are at higher risk of atelectasis due to their anatomical and physiological particularities. Several physiotherapy techniques are used to treat atelectasis, but only four studies cite methods in pediatric patients undergoing Invasive Mechanical Ventilation (IMV). The objective of this study was to evaluate the Structured Respiratory Physiotherapy Protocol (SRPP) for airway clearance and lung reexpansion for infants on IMV with atelectasis. This is a prospective study including 30 infants (mean ± standard deviation age 8.9 ± 8.0 months; weight 7.5 ± 3.0 kg; BMI 15.8 ± 1.6 kg/cm2 and IMV duration 7.7 ± 4.3 days). The sample was randomized into a Control Group (CG), which received routine physiotherapy, and an Intervention Group (IG), submitted to SRPP (postural drainage, mechanical thoracic vibration, manual hyperinflation, stretching of the accessory respiratory muscles, and functional positioning). Both groups were evaluated before and after physiotherapy for respiratory effort using the Wood Downes Score (WD) and pulmonary aeration using lung ultrasonography (Lung Ultrasound Score ‒ LUS). The outcome of the intervention was evaluated by the magnitude of the effect by the Hedges' g test [(small (0.2 < Hedges' g < 0.5), moderate (0.5 < Hedges' g < 0.8) and large (Hedges' g > 0.8) effects]. There were large within-group effects on the reduction of WD in the CG after intervention in both the CG (Hedges' g = -1.53) and IG (Hedges' g = -2.2). There was a moderate effect on LUS reduction in the CG (Hedges' g = -0.64) and a large effect on IG (Hedges' g = -1.88). This study has shown that the SRPP appears to be safe and may be effective in improving airway clearance and lung reexpansion in children on IMV with atelectasis.

The Structural Adaptations That Mediate Disuse-Induced Atrophy of Skeletal Muscle

The maintenance of skeletal muscle mass plays a fundamental role in health and issues associated with quality of life. Mechanical signals are one of the most potent regulators of muscle mass, with a decrease in mechanical loading leading to a decrease in muscle mass. This concept has been supported by a plethora of human- and animal-based studies over the past 100 years and has resulted in the commonly used term of 'disuse atrophy'. These same studies have also provided a great deal of insight into the structural adaptations that mediate disuse-induced atrophy. For instance, disuse results in radial atrophy of fascicles, and this is driven, at least in part, by radial atrophy of the muscle fibers. However, the ultrastructural adaptations that mediate these changes remain far from defined. Indeed, even the most basic questions, such as whether the radial atrophy of muscle fibers is driven by the radial atrophy of myofibrils and/or myofibril hypoplasia, have yet to be answered. In this review, we thoroughly summarize what is known about the macroscopic, microscopic, and ultrastructural adaptations that mediated disuse-induced atrophy and highlight some of the major gaps in knowledge that need to be filled.

Ultrasonographic measurements of fascicle length overestimate adaptations in serial sarcomere number

Ultrasound-derived measurements of muscle fascicle length (FL) are often used to infer increases (chronic stretch or training) or decreases (muscle disuse or aging) in serial sarcomere number (SSN). Whether FL adaptations measured via ultrasound can truly approximate SSN adaptations has not been investigated. We casted the right hindlimb of 15 male Sprague-Dawley rats in a dorsiflexed position (i.e., stretched the plantar flexors) for 2 weeks, with the left hindlimb serving as a control. Ultrasound images of the soleus, lateral gastrocnemius (LG), and medial gastrocnemius (MG) were obtained with the ankle at 90° and full dorsiflexion for both hindlimbs pre and post-cast. Following post-cast ultrasound measurements, legs were fixed in formalin with the ankle at 90°, then muscles were dissected and fascicles were teased out for measurement of sarcomere lengths via laser diffraction and calculation of SSN. Ultrasound detected an 11% increase in soleus FL, a 12% decrease in LG FL, and an 8-11% increase in MG FL for proximal fascicles and at full dorsiflexion. These adaptations were partly reflected by SSN adaptations, with a 6% greater soleus SSN in the casted leg than the un-casted leg, but no SSN differences for the gastrocnemii. Weak relationships were observed between ultrasonographic measurements of FL and measurements of FL and SSN from dissected fascicles. Our results showed that ultrasound-derived FL measurements can overestimate an increase in SSN by ∼5%. Future studies should be cautious when concluding a large magnitude of sarcomerogenesis from ultrasound-derived FL measurements, and may consider applying a correction factor. NEW FINDINGS: What is the central question of this study? Measurements of muscle fascicle length via ultrasound are often used to infer changes in serial sarcomere number, such as increases following chronic stretch or resistance training, and decreases with ageing: does ultrasound-derived fascicle length accurately depict adaptations in serial sarcomere number? What is the main finding and its importance? Ultrasound detected an ∼11% increase in soleus fascicle length, but measurements on dissected fascicles showed the actual serial sarcomere number increase was only ∼6%; therefore, measurements of ultrasound-derived fascicle length can overestimate serial sarcomere number adaptations by as much as 5%.

What does desmin do: A bibliometric assessment of the functions of the muscle intermediate filament

Intermediate filaments were first described in muscle in 1968, and desmin was biochemically identified about 10 years afterwards. Its importance grew after the identification of desminopathies and desmin mutations that cause mostly cardiopathies. Since its characterization until recently, different functions have been attributed to desmin. Here, we use bibliometric tools to evaluate the articles published about desmin and to assess its several putative functions. We identified the most productive authors and the relationships between research groups. We studied the more frequent words among 9734 articles (September 2021) containing "desmin" on the title and abstract, to identify the major research focus. We generated an interactive spreadsheet with the 934 papers that contain "desmin" only on the title that can be used to search and quantify terms in the abstract. We further selected the articles that contained the terms "function" or "role" from the spreadsheet, which we then classified according to type of function, organelle, or tissue involved. Based on the bibliographic analysis, we assess comparatively the putative functions, and we propose an alternative explanation for the desmin function.

Biomechanical Properties of the Sarcolemma and Costameres of Skeletal Muscle Lacking Desmin

Intermediate filaments (IFs), composed primarily by desmin and keratins, link the myofibrils to each other, to intracellular organelles, and to the sarcolemma. There they may play an important role in transfer of contractile force from the Z-disks and M-lines of neighboring myofibrils to costameres at the membrane, across the membrane to the extracellular matrix, and ultimately to the tendon (“lateral force transmission”). We measured the elasticity of the sarcolemma and the connections it makes at costameres with the underlying contractile apparatus of individual fast twitch muscle fibers of desmin-null mice. By positioning a suction pipet to the surface of the sarcolemma and applying increasing pressure, we determined the pressure at which the sarcolemma separated from nearby sarcomeres, P_separation, and the pressure at which the isolated sarcolemma burst, P_bursting. We also examined the time required for the intact sarcolemma-costamere-sarcomere complex to reach equilibrium at lower pressures. All measurements showed the desmin-null fibers to have slower equilibrium times and lower P_separation and P_bursting than controls, suggesting that the sarcolemma and its costameric links to nearby contractile structures were weaker in the absence of desmin. Comparisons to earlier values determined for muscles lacking dystrophin or synemin suggest that the desmin-null phenotype is more stable than the former and less stable than the latter. Our results are consistent with the moderate myopathy seen in desmin-null muscles and support the idea that desmin contributes significantly to sarcolemmal stability and lateral force transmission.

Skeletal Muscle in Cerebral Palsy: From Belly to Myofibril

This review will provide a comprehensive, up-to-date review of the current knowledge regarding the pathophysiology of muscle contractures in cerebral palsy. Although much has been known about the clinical manifestations of both dynamic and static muscle contractures, until recently, little was known about the underlying mechanisms for the development of such contractures. In particular, recent basic science and imaging studies have reported an upregulation of collagen content associated with muscle stiffness. Paradoxically, contractile elements such as myofibrils have been found to be highly elastic, possibly an adaptation to a muscle that is under significant in vivo tension. Sarcomeres have also been reported to be excessively long, likely responsible for the poor force generating capacity and underlying weakness seen in children with cerebral palsy (CP). Overall muscle volume and length have been found to be decreased in CP, likely secondary to abnormalities in sarcomerogenesis. Recent animal and clinical work has suggested that the use of botulinum toxin for spasticity management has been shown to increase muscle atrophy and fibrofatty content in the CP muscle. Given that the CP muscle is short and small already, this calls into question the use of such agents for spasticity management given the functional and histological cost of such interventions. Recent theories involving muscle homeostasis, epigenetic mechanisms, and inflammatory mediators of regulation have added to our emerging understanding of this complicated area.

Therapeutic Effect of Microcurrent Therapy in Children With In-toeing Gait Caused by Increased Femoral Anteversion: A Pilot Study

Objective

To investigate the efficacy of portable microcurrent therapy device (PMTD) of the hip internal rotators in the treatment of in-toeing gait caused by increased femoral anteversion in children over 8 years of age.

Methods

Eleven children (22 legs; 4 boys and 7 girls; mean age, 10.4±1.6 years) with in-toeing gait caused by increased femoral anteversion were included in the present study. All children received 60 minutes of PMTD (intensity, 25 µA; frequency, 8 Hz) applied to the hip internal rotators daily for 4 weeks. Hip internal rotation (IR) angle, external rotation (ER) angle, and midmalleolar-second toe angle (MSTA) measurement during stance phase at transverse plane and Family Satisfaction Questionnaire, frequency of tripping and fatigue like pains about the PMTD were performed before treatment and at 4 weeks after initial PMTD treatment. Paired t-test and Fisher exact test were used for statistical analysis.

Results

Hip IR/ER/MSTA was 70.3°±5.4°/20.1°±5.5°/–11.4°±2.7°, and 55.7°±7.8°/33.6°±8.2°/–2.6°±3.8° before treatment and at 4 weeks after initial PMTD treatment, respectively (p<0.01). Ten of 11 (91%) children's family stated that they were generally satisfied with the PMTD treatment. The frequency of tripping and fatigue like pains was significantly lower at 4 weeks after PMTD treatment (p<0.05). Excellent inter-rater and intra-rater reliability was observed for repeated MSTA measurements between the examiners (k=0.91–0.96 and k=0.93–0.99), respectively.

Conclusion

PMTD of the hip internal rotators can be effective in improving the gait pattern of children with in-toeing gait caused by increased femoral anteversion.

Reduced skeletal muscle satellite cell number alters muscle morphology after chronic stretch but allows limited serial sarcomere addition

INTRODUCTION

Muscles add sarcomeres in response to stretch, presumably to maintain optimal sarcomere length. Clinical evidence from patients with cerebral palsy, who have both decreased serial sarcomere number and reduced satellite cells (SCs), suggests a hypothesis that SCs may be involved in sarcomere addition.

METHODS

A transgenic Pax7-DTA mouse model underwent conditional SC depletion, and their soleii were then stretch-immobilized to assess the capacity for sarcomere addition. Muscle architecture, morphology, and extracellular matrix (ECM) changes were also evaluated.

RESULTS

Mice in the SC-reduced group achieved normal serial sarcomere addition in response to stretch. However, muscle fiber cross-sectional area was significantly smaller and was associated with hypertrophic ECM changes, consistent with fibrosis.

CONCLUSIONS

While a reduced SC population does not hinder serial sarcomere addition, SCs play a role in muscle adaptation to chronic stretch that involves maintenance of both fiber cross-sectional area and ECM structure. Muscle Nerve 55: 384-392, 2017.

Avaliação de sóleos de ratas Wistar ooforectomizadas e remobilizadas em meio aquático

INTRODUÇÃO: as incertezas sobre a forma mais eficaz de remobilização para músculos após períodos de imobilização.OBJETIVO: avaliar o comportamento da remobilização com natação sobre parâmetros histomorfométricos do músculo sóleo de ratas ooforectomizadas e pseudo-ooforectomizadas.MÉTODOS: foram utilizadas 24 ratas Wistar subdivididas em quatro grupos: G1: submetidos à ooforectomia, imobilização por 15 dias e remobilizados livremente; G2: ooforectomia, imobilização e remobilizados com natação por 10 dias; G3: pseudo-ooforectomia, imobilização e remobilizados livremente; G4: pseudo-ooforectomia, imobilização e remobilizados com natação. Os músculos sóleos direitos e esquerdos foram dissecados para as análises histomorfométricas longitudinal e transversal. A contagem de sarcômeros se deu em 300 µm e o comprimento da fibra muscular foi medida por paquímetro analógico. O peso muscular foi obtido em balança analítica e o diâmetro foi realizado em 100 fibras por músculo.RESULTADOS: houve redução significativa, tanto na análise longitudinal quanto transversal, quando comparados os músculos sóleos direitos e esquerdos de ambos os grupos.CONCLUSÃO: a imobilização do músculo sóleo de ratas ooforectomizadas e pseudo-ooforectomizadas acarreta efeitos deletérios à morfometria muscular e a remobilização por meio da natação não foi capaz de promover o retorno dos padrões estruturais do músculo sóleo.

Efeitos do ultrassom terapêutico associados ao alongamento estático sobre parâmetros histomorfométricos longitudinais de sóleos imobilizados de ratos

O músculo é um tecido dotado de plasticidade que se adapta a diferentes estímulos. A imobilização causa danos ao sistema muscular incluindo atrofia, perda da extensibilidade e resistência muscular. O alongamento muscular e o ultrassom terapêutico são modalidades utilizadas para acelerar o processo de reparo muscular, provendo aumento da síntese proteica e melhora da extensibilidade. OBJETIVO: Comparar o uso do ultrassom terapêutico, associado ao alongamento, na remobilização de músculo sóleo, de ratos, submetido ao encurtamento muscular, sobre os aspectos histomorfométricos longitudinais. MATERIAIS E MÉTODOS: Vinte e oito ratos Wistar foram imobilizados por 15 dias e, após liberados do aparato de imobilização, distribuídos em quatro grupos: grupo (GA) apenas remobilizado por alongamento durante 10 dias; e os demais foram submetidos a 10 dias de intervenção terapêutica do ultrassom de 1MHz a 1,0W/cm² (GAUS 1,0); 0,5W/cm² (GAUS 0,5); e 0,2W/cm² (GAUS 0,2), e posterior alongamento dos músculos sóleos. Ao final do tratamento, os animais foram eutanasiados e tiveram seus músculos removidos para posterior análise histológica dos parâmetros longitudinais (contagem de sarcômeros). RESULTADOS: Na análise intragrupo, quanto ao comprimento muscular, apenas o grupo GAUS 0,5 não teve diferença significativa. Quanto à contagem de sarcômeros, os grupos GA e GAUS 0,2 tiveram diferença significativa. Quanto ao tamanho dos sarcômeros, nenhum grupo teve diferença significativa. Na análise intergrupos, nenhum grupo apresentou diferença significativa. CONCLUSÃO: O alongamento foi insuficiente para reverter os efeitos da imobilização. Quando associado ao ultrassom terapêutico, a dose 0,5W/cm² recuperou o comprimento muscular, e as doses 1,0 e 0,5W/cm² contribuíram para o aumento da quantidade dos sarcômeros em série.

Adaptações neuromusculares de flexores dorsais e plantares a duas semanas de imobilização após entorse de tornozelo

INTRODUÇÃO: A entorse de tornozelo é uma lesão de alta incidência comumente tratada com períodos de imobilização, levando a adaptações estruturais e funcionais dos músculos atuantes nesta articulação. OBJETIVO: Identificar as adaptações dos músculos flexores dorsais e flexores plantares após duas semanas de imobilização em sujeitos que sofreram entorse de tornozelo. MÉTODOS: Onze indivíduos (seis mulheres e cinco homens) acometidos por entorse de tornozelo grau II foram submetidos a 14 dias de imobilização por tala gessada. Após a retirada da imobilização, foram realizadas avaliações bilaterais de (1) perimetria da perna, (2) amplitude de movimento (ADM) do tornozelo, (3) torque isométrico máximo de flexores dorsais e flexores plantares em sete ângulos do tornozelo e (4) ativação eletromiográfica dos músculos tibial anterior (TA), sóleo (SO) e gastrocnêmio medial (GM). Os resultados obtidos no segmento imobilizado foram comparados com os do segmento saudável contralateral através de um teste t de Student pareado (p < 0,05). RESULTADOS: O segmento imobilizado apresentou redução (1) da circunferência nas regiões proximais da perna, (2) da ADM de flexão dorsal e plantar, (3) do torque isométrico máximo de flexores dorsais e plantares e (4) do sinal eletromiográfico do TA em todos os ângulos articulares e do SO nos maiores comprimentos musculares. Não houve diferença no sinal eletromiográfico do músculo GM. CONCLUSÃO: Um período relativamente curto de imobilização (duas semanas) prejudica a funcionalidade dos músculos flexores dorsais e flexores plantares do tornozelo.

Vitamin E and C supplementation does not ameliorate muscle dysfunction after anterior cruciate ligament surgery

Muscle atrophy and weakness are predominant impairments after anterior cruciate ligament (ACL) surgical repair. We tested the hypothesis that vitamin E and C supplementation will improve recovery from ACL injury. Men undergoing elective ACL surgery were randomly assigned to twice-daily supplements of either antioxidants (AO; vitamins E and C, n=10) or matching placebos (n=10) from 2 weeks before until 3 months after surgery. Each subject provided several fasting blood draws, two muscle biopsies from the thigh muscle of the injured limb, and strength and thigh circumference measurements of the lower limbs. Muscle atrophy was apparent in both groups before and several days after surgery. Compared with baseline measurements, peak isometric force of the injured limb increased significantly (P<0.05) by 3 months postsurgery in both treatment groups; however, AO supplementation did not augment these strength gains. By contrast, baseline plasma ascorbic acid concentrations correlated (r=0.59, P=0.006) with subsequent improvement in the strength of the injured limb. In summary, vitamin E and C supplementation was ineffective in potentiating the improvement in force production by the injured limb; however, baseline vitamin C status was associated with beneficial outcomes in strength, suggesting that long-term dietary habits are more effective than short-term supplements.

Adaptações do sistema respiratório referentes à função pulmonar em resposta a um programa de alongamento muscular pelo método de Reeducação Postural Global

A proposta deste estudo foi analisar as adaptações do sistema respiratório referentes à função pulmonar em resposta ao alongamento da cadeia muscular respiratória pelo método de Reeducação Postural Global (RPG). Foram estudados 20 homens, sedentários, de antropometria semelhante, sem antecedentes de doenças musculoesqueléticas ou cardiorrespiratórias. Os voluntários foram divididos aleatoriamente em dois grupos de dez, sendo um grupo controle (GC), que não participou do protocolo de alongamento, e o outro submetido à intervenção pelo método de RPG, denominado grupo tratado (GT). O alongamento foi realizado duas vezes por semana, durante oito semanas, totalizando 16 sessões. Os dois grupos foram submetidos à prova de função pulmonar, medindo-se a capacidade vital lenta, capacidade vital forçada e ventilação voluntária máxima, antes e após o período de intervenção. Os valores obtidos em todas as variáveis dos voluntários do GC na avaliação inicial não apresentaram diferença estatisticamente significante quando comparados aos obtidos na avaliação final (p>0,05). No GT os valores finais apresentaram-se significativamente maiores que os iniciais (p<0,05). O protocolo de alongamento da cadeia muscular respiratória proposto pelo método de RPG mostrou pois ser eficiente para promover aumento das variáveis espirométricas, sugerindo que pode ser utilizado como um recurso fisioterapêutico coadjuvante às condutas de fisioterapia respiratória.

Efeitos da corrida em esteira em músculos sóleos de ratos encurtados por imobilização

O objetivo deste trabalho foi verificar as adaptações de peso e comprimento do músculo sóleo de ratos Wistar machos, além da estimativa do total de sarcômeros em série e comprimento médio dos sarcômeros, quando submetidos a um processo de remobilização em esteira. Foram utilizados 18 ratos (Wistar), divididos em três grupos: GC - músculo sóleo esquerdo (MSE) imobilizado e remobilizado solto; G10 - MSE imobilizado e remobilizado em velocidade de 10m/min; e G12 (n = 6) - MSE imobilizado e remobilizado em velocidade de 12m/min. Os resultados mostraram as seguintes variações, peso muscular: GC -22,35% (p = 0,0089), G10 -12,52% (p = 0,0623), G12 -12,07%, (p = 0,0004); comprimento muscular: GC -5,47% (p = 0,0120), G10 -3,31% (p = 0,2868), G12 0,41% (p = 0,8987); estimativa de sarcômeros em série: GC -15,42% (p = 0,0047), G10 -10,87% (p = 0,0193), G12 -4,97 (p = 0,2409); comprimento de sarcômeros GC 11,16% (p = 0,0142), G10 9,31% (p = 0,1270), G12 5,58% (p = 0,1327). Conclui-se que G12 obteve maior eficácia após o período de imobilização, pois apresentou maior semelhança com o membro não imobilizado.

Altered contractile properties of the gastrocnemius muscle poststroke

Spasticity, contracture and muscle weakness often occur together poststroke and cause considerable motor impairments to stroke survivors. The underlying changes in contractile properties of muscle fascicles are still not clear. The purpose of this study was to investigate the contractile property changes of the medial gastrocnemius muscle fascicles poststroke. Ten stroke survivors and ten healthy subjects participated in the study. The medial gastrocnemius fascicular length was measured at various combinations of ankle and knee positions using ultrasonography, with the muscle activated selectively using electrical stimulation. The stimulation intensity was kept constant across different ankle and knee positions to establish the active force-length relationship of the muscle fascicles. It was found that stroke survivors showed a shift of the force-length curve with a significantly shorter optimal fascicle length (33.2 +/- 3.2 mm) compared with that of healthy controls (47.4 +/- 2.7 mm) with P < 0.001. Furthermore, the width span of the fascicular force-length curve of stroke survivors was significantly narrower with steeper slopes than that of controls (P <or= 0.001), suggesting reduced number of sarcomeres along the fascicles and/or reduced sarcomere length poststroke. Regression analysis showed that the medial gastrocnemius fascicular length of stroke survivors varied significantly less with ankle and knee flexions (P <or= 0.001) than that of controls, suggesting shorter and stiffer muscle fascicles poststroke, which might be attributed to muscle architectural adaptation. This study showed that there are considerable changes in the contractile properties of muscle fascicles poststroke, which may contribute directly to the joint-level changes of decreased range of motion, increased stiffness, muscle weakness, and impaired motor functions in stroke survivors.

Measurement of muscle disease by quantitative second-harmonic generation imaging

Determining the health of muscle cells by in vivo imaging could impact the diagnosis and monitoring of a large number of congenital and acquired muscular or cardiac disorders. However, currently used technologies are hampered by insufficient resolution, lack of specificity, or invasiveness. We have combined intrinsic optical second-harmonic generation from sarcomeric myosin with a novel mathematical treatment of striation pattern analysis, to obtain measures of muscle contractile integrity that correlate strongly with the neuromuscular health of mice suffering from genetic, acquired, and age-related decline in skeletal muscle function. Analysis of biopsies from a pilot group of human volunteers suggests a similar power in quantifying sarcopenic changes in muscle integrity. These results provide the first strong evidence that quantitative image analysis of sarcomere pattern can be correlated with physiological function, and they invite the application of SHG imaging in clinical practice, either in biopsy samples or via microendoscopy.

Remobilização por alongamento estático cíclico em músculo sóleo de ratos imobilizados em encurtamento

A fibra muscular tem grandes propriedades plásticas, respondendo a diferentes estímulos com o aumento ou diminuição de sua massa, comprimento e número de sarcômeros em série. O objetivo deste estudo foi analisar os efeitos do alongamento passivo estático em 3 séries diárias de 30 s e da remobilização livre, por um período de duas semanas, no músculo sóleo de ratos imobilizado em posição de encurtamento. Para isso, foram utilizados 12 ratos (Wistar) divididos em 2 grupos: G1 (n=6) - músculo sóleo esquerdo (MSE) imobilizado e solto na gaiola (GIS); G2 (n=6) - MSE imobilizado e alongado diariamente (GIA). Foram comparadas as variações encontradas entre o MSE e o MSD (direito) de cada grupo. As variáveis foram: peso muscular, comprimento muscular, número de sarcômeros em série e comprimento de sarcômeros. Os resultados das variáveis analisadas, comparando o MSE com o MSD foram: peso muscular: GIS=-23,16%, (p=0,0007), GIA-32,43% (p=0,0008); comprimento muscular: GIS=-5,47% (p=0,0120); GIA=-9,99% (p=0,0034); número de sarcômeros em série: GIS=-15,42% (p=0,0047); GIA=-8,08% (p=0,0008); comprimento do sarcômero: GIS=11,16% (p=0,0142); GIA=-1,92% (p=0,3783). Através desses resultados, pode-se concluir que nem o alongamento, nem a remobilização livre promovem a restauração na estrutura dos músculos esqueléticos submetidos à imobilização prolongada.

Efeito de um programa de alongamento muscular pelo método de Reeducação Postural Global sobre a força muscular respiratória e a mobilidade toracoabdominal de homens jovens sedentários

OBJETIVO: Avaliar o efeito do alongamento da cadeia muscular respiratória, pelo método de Reeducação Postural Global (RPG), sobre a força muscular respiratória e a mobilidade toracoabdominal de homens jovens sedentários. MÉTODOS: Estudo randomizado, realizado com 20 voluntários sedentários, idade 22,65 ± 2,5 anos, divididos em dois grupos de 10: grupo controle, que não participou do alongamento, e grupo submetido à intervenção pelo método de RPG. O protocolo foi constituído por um programa de alongamento da cadeia muscular respiratória na postura 'rã no chão com os braços abertos' realizado com a regularidade de duas vezes por semana, durante 8 semanas, totalizando 16 sessões. Os dois grupos foram submetidos à avaliação da medida da pressão inspiratória máxima, pressão expiratória máxima e cirtometria toracoabdominal, antes e após o período de intervenção. RESULTADOS: Os valores das pressões respiratórias máximas e da cirtometria do grupo controle antes e após o período de intervenção não apresentaram alterações significativas (p > 0,05). No grupo RPG, os valores de todas as variáveis apresentaram diferenças estatisticamente significativas após o protocolo de intervenção (p < 0,05). CONCLUSÕES: O protocolo de alongamento da cadeia muscular respiratória proposto pelo método de RPG mostrou ser eficiente para promover o aumento das pressões respiratórias máximas e das medidas da cirtometria toracoabdominal, sugerindo que pode ser utilizado como um recurso fisioterapêutico para o desenvolvimento da força muscular respiratória e da mobilidade toracoabdominal.

Plasticity of the muscle-tendon complex with disuse and aging

Muscles and tendons are highly adaptive tissues in response to chronic changes in loading and to aging. A remarkable reorganization in muscle architecture occurs in both conditions together with significant alterations in tendon mechanical properties. This review discusses the possible mechanisms underlying these myotendinous changes and the influence thereof on the behavior of the muscle-tendon complex as a whole.

Lack of human muscle architectural adaptation after short-term strength training

The mechanisms governing the increases in force production in response to short periods of strength training have yet to be fully elucidated. We examined whether muscle architectural adaptation was a contributing factor. Ultrasound imaging techniques were used to measure quadriceps muscle architecture at 17 sites in vivo in trained and untrained legs of men and women after 2.5 and 5 weeks of unilateral knee extension training, as well as in a nontraining control group. Despite increases in knee extensor strength of the trained and untrained (women only) legs, there were no changes in muscle thickness, fascicle angle, or fascicle length in any of the muscles tested. The moderate correlation between vastus lateralis thickness (middle site) and eccentric (r = 0.55; P < 0.05) and concentric (r = 0.46; P < 0.1) torque after, but not before, training is suggestive of neural rather than architectural adaptations predominating in the early phase of training.

Understanding Muscle Architectural Adaptation: Macro- and Micro-Level Research

Recent research using muscle-imaging techniques has revealed a remarkable plasticity of human muscle architecture where significant changes in fascicle lengths and angles have resulted from the chronic performance, or cessation, of strong muscle contractions. However, there is a paucity of data describing architectural adaptations to chronic stretching, disuse and immobilization, illness, and aging, and those data that are available are equivocal. Understanding their impact is important in order that effective interventions for illness/injury management and rehabilitation, and programs to improve the physical capacity of workers, the aged and athletes can be determined. Nonetheless, recent advances in myocellular research could provide a framework allowing the prediction of architectural changes in these understudied areas. Examination of the site-specific response to mechanical stress of calpain-dependent ubiquitin-proteasome proteolysis, or of the cellular response to stress after the knockout (or incapacitation) of sarcomeric and cytoskeletal proteins involved in cellular signal transduction, provides an exciting paradigm by which myocellular adaptation can be described. Such research might contribute to the understanding of macro-level changes in muscle architecture.

Acetylcholine and calcium signalling regulates muscle fibre formation in the zebrafish embryo

Nerve activity is known to be an important regulator of muscle phenotype in the adult, but its contribution to muscle development during embryogenesis remains unresolved. We used the zebrafish embryo and in vivo imaging approaches to address the role of activity-generated signals, acetylcholine and intracellular calcium, in vertebrate slow muscle development. We show that acetylcholine drives initial muscle contraction and embryonic movement via release of intracellular calcium from ryanodine receptors. Inhibition of this activity-dependent pathway at the level of the acetylcholine receptor or ryanodine receptor did not disrupt slow fibre number, elongation or migration but affected myofibril organisation. In mutants lacking functional acetylcholine receptors myofibre length increased and sarcomere length decreased significantly. We propose that calcium is acting via the cytoskeleton to regulate myofibril organisation. Within a myofibre, sarcomere length and number are the key parameters regulating force generation; hence our findings imply a critical role for nerve-mediated calcium signals in the formation of physiologically functional muscle units during development.

Essential role of obscurin in cardiac myofibrillogenesis and hypertrophic response: evidence from small interfering RNA-mediated gene silencing

Obscurin is a recently identified giant multidomain muscle protein (approximately 800 kDa) whose structural and regulatory functions remain to be defined. The goal of this study was to examine the effect of obscurin gene silencing induced by RNA interference on the dynamics of myofibrillogenesis and hypertrophic response to phenylephrine in cultured rat cardiomyocytes. We found that that the adenoviral transfection of short interfering RNA (siRNA) constructs targeting the first coding exon of obscurin sequence resulted in progressive depletion of cellular obscurin. Confocal microscopy demonstrated that downregulation of obscurin expression led to the impaired assembly of new myofibrillar clusters and considerable aberrations of the normal structure of the contractile apparatus. While the establishment of the initial periodic pattern of alpha-actinin localization remained mainly unaffected in siRNA-transfected cells, obscurin depletion did cause the defective lateral alignment of myofibrillar bundles, leading to their abnormal bifurcation, dispersal and multiple branching. Bending of immature myofibrils, apparently associated with the loss of their rigidity, a modified titin pattern, the absence of well-formed A-bands in newly formed contractile structures as documented by a diffuse localization of sarcomeric myosin labeling, and an occasional irregular periodicity of sarcomere spacing were typical of obscurin siRNA-treated cells. These results suggest that obscurin is indispensable for spatial positioning of contractile proteins and for the structural integration and stabilization of myofibrils, especially at the stage of myosin filament incorporation and A-band assembly. This demonstrates a vital role for obscurin in myofibrillogenesis and hypertrophic growth.

Differential serial sarcomere number adaptations in knee extensor muscles of rats is contraction type dependent

Sarcomerogenesis, or the addition of sarcomeres in series within a fiber, has a profound impact on the performance of a muscle by increasing its contractile velocity and power. Sarcomerogenesis may provide a beneficial adaptation to prevent injury when a muscle consistently works at long lengths, accounting for the repeated-bout effect. The association between eccentric exercise, sarcomerogenesis and the repeated-bout effect has been proposed to depend on damage, where regeneration allows sarcomeres to work at shorter lengths for a given muscle-tendon unit length. To gain additional insight into this phenomenon, we measured fiber dynamics directly in the vastus lateralis (VL) muscle of rats during uphill and downhill walking, and we measured serial sarcomere number in the VL and vastus intermedius (VI) after chronic training on either a decline or incline grade. We found that the knee extensor muscles of uphill walking rats undergo repeated active concentric contractions, and therefore they suffer no contraction-induced injury. Conversely, the knee extensor muscles during downhill walking undergo repeated active eccentric contractions. Serial sarcomere numbers change differently for the uphill and downhill exercise groups, and for the VL and VI muscles. Short muscle lengths for uphill concentric-biased contractions result in a loss of serial sarcomeres, and long muscle lengths for downhill eccentric-biased contractions result in a gain of serial sarcomeres.

Does microcurrent stimulation increase the range of movement of ankle dorsiflexion in children with cerebral palsy?

AIM

To determine whether microcurrent stimulation (MENS) increases the range of motion (ROM) of the ankle joint in children with cerebral palsy.

DESIGN

Twelve children with spastic hemiplegia (age range 4.5 to 16 years) with moderate myocontracture of the triceps surae, received MENS for 1 h five times a week for 4 weeks. An equally long baseline period was preceded. The assessments were: active and passive ROM of ankle dorsiflexion, popliteal flexion and ankle dorsiflexion in maximal flexion of knees in standing position while maintaining the heels in contact with the floor, one foot standing and hopping on one foot.

RESULTS

After the treatment with MENS, the passive ROM of ankle dorsiflexion with both knees flexed and extended (p<0.001) increased significantly. Increases were also observed in popliteal flexion (p<0.001) and ankle dorsiflexion (p=0.0012) during maximal flexion of the knees in a standing position. The ROM of active dorsiflexion with the knee flexed (p<0.05) and one foot standing (p<0.05) also improved. Children and parents found this treatment easy to carry out.

CONCLUSIONS

MENS relieves myocontracture and can enhance conventional rehabilitation programmes for children with cerebral palsy.

Tension- and afferent input-associated responses of neuromuscular system of rats to hindlimb unloading and/or tenotomy

Responses of electromyogram (EMG) in soleus muscle and both afferent and efferent neurograms at the fifth lumbar (L5) segmental level of spinal cord were investigated during acute and chronic unloading induced by hindlimb suspension and/or tenotomy in adult rats. The soleus EMG and afferent neurogram decreased 88 and 37%, respectively, relative to those at quadrupedal posture on the floor after acute hindlimb suspension that causes passive shortening of soleus due to ankle plantarflexion. However, the afferent neurogram ( P < 0.05) and soleus EMG ( P > 0.05) recorded on the floor increased after tenotomy of synergists. Furthermore, the afferent input was inhibited when the soleus EMG disappeared after tenotomy of soleus. The afferent neurogram and EMG of the soleus showed correlated responses to a variety of treatments, suggesting that the afferent neurogram recorded at the L5segmental level reflects the neural input associated with the activity level of the soleus predominantly. The level of efferent neurogram decreased after acute hindlimb suspension but was not influenced significantly by tenotomy of synergists and/or soleus itself. The EMG and afferent neurograms remained low up to the 4th day but recovered to the preexperimental levels within 14 days, due to reorganization of sarcomere number and length, as well as the shortening of muscle fiber length and recovery of tension development. It is suggested that the levels of EMG and afferent neurogram associated with antigravity muscle are closely related to the tension development of the muscle.