Free mobilization and low- to high-intensity exercise in immobilization-induced muscle atrophy

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.

Prior swimming exercise favors muscle recovery in adult female rats after joint immobilization

[Purpose] To evaluate the efficacy of pre-exercise on immobilization and subsequent recovery of white gastrocnemius (WG) and soleus (SOL) muscles of female rats. [Subjects and Methods] Thirty, 8-month-old, female Wistar rats were randomly and evenly allocated to six groups: sedentary (S); immobilized sedentary (IS); immobilized/rehabilitated sedentary (IRS); trained (T); immobilized trained (IT); and immobilized/rehabilitated trained (IRT). For four months, T, IT and IRT group animals performed swimming exercise (three sessions per week, 60 minutes per session), while S, IS and IRS groups animals remained housed in cages. After this period, the left hindlimb of the animals from the IS, IRS, IT and IRT groups was immobilized for five days, with the ankle at 90°. After removal of the orthosis, animals from the IRS and IRT groups followed a rehabilitation program based on swimming (five sessions per week, 60 minutes per session) for two weeks. [Results] Immobilization significantly reduced the cross-sectional area of the white gastrocnemius muscle; no changes were observed in the soleus muscles of the trained animals. Transforming growth factor-β1 protein levels were similar among the trained groups. [Conclusion] Prior swimming prevents hypotrophy of the soleus muscle after immobilization, and protein levels reflected the adaptive capacity of the skeletal muscle.

Exercício excêntrico e alongamento para músculos flexores plantares aplicados durante 21 dias após imobilização não modificam o tecido não contrátil

RESUMO As adaptações da matriz extracelular, que está intimamente ligada à manutenção da integridade e do desempenho do sistema musculoesquelético, não estão consensualmente descritas na literatura após recarga por desuso. O objetivo deste estudo foi analisar a área de tecido conjuntivo perimisial e de secção transversa das fibras musculares nos músculos sóleo e plantar de ratas imobilizadas e posteriormente reabilitadas por protocolos de alongamento e exercício excêntrico. A expressão do tecido conjuntivo perimisial de ambos os músculos estudados não apresentou diferença significativa após o procedimento de imobilização e treinamento. O treino excêntrico aplicado por 10 dias foi suficiente para recuperar a área das fibras para o músculo plantar, enquanto a recuperação do músculo sóleo aconteceu somente após o protocolo de 21 dias.

Three days of intermittent stretching after muscle disuse alters the proteins involved in force transmission in muscle fibers in weanling rats

The aim of this study was to determine the effects of intermittent passive manual stretching on various proteins involved in force transmission in skeletal muscle. Female Wistar weanling rats were randomly assigned to 5 groups: 2 control groups containing 21- and 30-day-old rats that received neither immobilization nor stretching, and 3 test groups that received 1) passive stretching over 3 days, 2) immobilization for 7 days and then passive stretching over 3 days, or 3) immobilization for 7 days. Maximal plantar flexion in the right hind limb was imposed, and the stretching protocol of 10 repetitions of 30 s stretches was applied. The soleus muscles were harvested and processed for HE and picrosirius staining; immunohistochemical analysis of collagen types I, III, IV, desmin, and vimentin; and immunofluorescence labeling of dystrophin and CD68. The numbers of desmin- and vimentin-positive cells were significantly decreased compared with those in the control following immobilization, regardless of whether stretching was applied (P<0.05). In addition, the semi-quantitative analysis showed that collagen type I was increased and type IV was decreased in the immobilized animals, regardless of whether the stretching protocol was applied. In conclusion, the largest changes in response to stretching were observed in muscles that had been previously immobilized, and the stretching protocol applied here did not mitigate the immobilization-induced muscle changes. Muscle disuse adversely affected several proteins involved in the transmission of forces between the intracellular and extracellular compartments. Thus, the 3-day rehabilitation period tested here did not provide sufficient time for the muscles to recover from the disuse maladaptations in animals undergoing postnatal development.

Activity attenuates skeletal muscle fiber damage after ischemia and reperfusion

INTRODUCTION

In this investigation we aimed to determine whether: (1) physical activity protects rat skeletal muscle from ischemia/reperfusion (I/R) injury; and (2) continued activity after I/R improves the rate of healing.

METHODS

Rats were divided into sedentary or active (voluntary wheel running) groups. Active rats ran for 4 weeks before I/R or 4 weeks before plus 4 weeks after I/R.

RESULTS

Activity before I/R resulted in 73.2% less muscle damage (Evans blue dye inclusion). Sedentary and active rats had a similar decline in neural-evoked (∼ 99%) and directly stimulated (∼ 70%) in vivo muscle torque, and a similar reduction in junctophilin 1. Active rats produced 19% and 15% greater neural-evoked torque compared with sedentary rats at 14 and 28 days postinjury, respectively, although the rate of recovery appeared similar.

CONCLUSIONS

Activity protects against long-term muscle damage, but not short-term neural injury or excitation-contraction uncoupling. Continued activity neither accelerates nor hinders the rate of functional recovery.

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.

Effects of eccentric exercise in rehabilitation of phasic and tonic muscles after leg immobilization in rats

Eccentric exercise is an essential resource for skeletal muscle rehabilitation following muscle disuse however, abnormalities linked to the tissue recuperation require further research. Our aim was analyze the adaptation ability of rehabilitated muscular tissue in rats during different periods of eccentric training after 10 days of limb immobilization. Twenty-seven Wistar rats were divided into six groups: immobilized 10 days, immobilized and eccentric trained for 10 days, immobilized and eccentric trained for 21 days, and three age-matched control groups. After sacrifice, soleus and plantaris muscles were frozen, cut and stained for general histology using hematoxylin and eosin and Gomori trichrome methods and immunohistochemical methods for fiber typing (mATPase, NADH2-TR), for capillaries (CD31) and intermediate filaments (desmin, vimentin) and high resolution microscopy of resin embedded material. Immobilization resulted in more intense morphological alterations in soleus muscles such as formation of target fibers, nuclear centralization, a reduction in the number of type I fibers, diameter of type I, IIA, IIAD fibers, and capillaries. After 10 days of eccentric training, increases in the nuclear centralization and the number of lobulated fibers were observed. This period was insufficient to reestablish the capillary/fiber (C/F) ratio and distribution of fiber types as that observed in the control group. However, 21 days of rehabilitation allowed the reversal of all morphological and quantitative abnormalities. For the plantaris muscles, 10-days of training restored their basic characteristics. Despite the fact that immobilization affected soleus and plantaris muscles, 10 days of eccentric training was insufficient to restore the morphological characteristics of soleus muscles, which was not the case observed in plantaris muscle.

Remobilization through stretching improves gait recovery in the rat

Remobilization of a previously immobilized rat right hindlimb in the ankle plantar-flexion-shortened position by free movement alone or associated with intermittent passive stretching was assessed by analysis of gait variables and dorsiflexion range of motion. The variables were related with the expression of extracellular matrix proteins and the addition of serial sarcomeres. Sixty-four female Wistar rats were divided into 8 groups: immobilized, free for 10 days, immobilized/stretched/free for 1, 3 or 10 days, immobilized/free for 1, 3 or 10 days. Gait variables, range of motion, serial sarcomeres number, localization and staining intensity of fibronectin, and expressions of types I and III collagen were analyzed. The hypokinesia changed the functional variables of gait, reduced the dorsiflexion range of motion (ROM), increased the number of fibers with intracellular fibronectin/total number of fibers (FIF/TNF), and decreased the expression of the type I collagen. After three days, morphological changes were exacerbated and the number of serial sarcomeres was increased in both groups, immobilized/stretched/free and immobilized/free. Functional impairment, ROM restriction and increased FIF/TNF were also observed. Despite the above described alterations, 10 days of stretching program increased the effectiveness of remobilization leading to recovery of the abnormalities observed in the muscle.

Evaluation of mechanical allodynia in an animal immobilization model using the von frey method

OBJECTIVE

The purpose of this study was to evaluate the mechanical allodynia in animals after immobilization and chiropractic manipulation using the Activator instrument (Activator Methods International, Phoenix, Ariz) through the Von Frey test in an animal model that had its hind limb immobilized as a form to induce mechanical allodynia.

METHOD

Eighteen adult male Wistar rats were used and divided into 3 groups: control group (C) (n = 6) that was not immobilized; immobilized group (I) (n = 6) that had its right hind limb immobilized; immobilized and adjusted group (IAA) (n = 6) that had its right hind limb immobilized and received chiropractic manipulation after. The mechanical allodynia was induced through the right hind limb immobilization. At the end of the immobilization period, the first Von Frey test was performed, and after that, 6 chiropractic manipulations on the tibial tubercle were made using the Activator instrument. After the manipulation period, Von Frey test was performed again.

RESULTS

It was observed that after the immobilization period, groups I and IAA had an exacerbation of mechanical allodynia when compared with group C (P < .001) and that after the manipulation, group IAA had a reversion of these values (P < .001), whereas group I kept a low pain threshold when compared with group C (P < .001).

CONCLUSION

This study demonstrates that immobilization during 4 weeks was sufficient to promote mechanical allodynia. Considering the chiropractic manipulation using the Activator instrument, it was observed that group IAA had decreased levels of mechanical allodynia, obtaining similar values to group C.

Effects of alfacalcidol on muscle strength, muscle fatigue, and bone mineral density in normal and ovariectomized rats

Vitamin D affects not only bone but also muscle to prevent falls and osteoporotic fractures. However, these effects on muscle and the mechanisms of fall prevention are still unclear. The purpose of this study was to investigate the effects of alfacalcidol [1α(OH)D(3)] on muscle strength, muscle fatigue, and bone mineral density (BMD) in ovariectomized rats. Seven-month-old female Wistar rats were orally administered 1α(OH)D(3) or its vehicle everyday for 4 weeks after ovariectomy (OVX) or sham operation. Calf muscle strength and fatigue were evaluated by electrical stimulation of the sciatic nerve under general anesthesia. 1α(OH)D(3) administration significantly increased the maximum muscle strength in the sham-operated (P < 0.01) and the OVX (P < 0.01) groups compared to their respective control groups. However, 1α(OH)D(3) administration did not significantly affect muscle fatigue in these groups. The BMD of the femur in the 1α(OH)D(3)-treated OVX group was significantly higher than that in the vehicle-treated OVX group (P = 0.04). These results suggested that 1α(OH)D(3) increases muscle strength but does not affect muscle fatigue in this rat model. The effectiveness of activated vitamin D in preventing bone fractures may be partly owing to its effect on muscle strength in addition to its known effect on bone metabolism.

IGF-1 minimiza os efeitos deletérios do desuso no músculo sóleo de ratos

OBJETIVO: Avaliar o efeito do tratamento com IGF-1 sobre o perfil metabólico e morfológico do músculo sóleo submetido à imobilização articular de tornozelo. MÉTODOS: Ratos Wistar foram divididos em 3 grupos (n=6): controle (C), imobilizado (I) e imobilizado tratado com IGF (I+IGF; 40mg/Kg) durante 7 dias. RESULTADOS: A imobilização reduziu o peso (34%), o conteúdo de glicogênio (31,6%) a área das fibras musculares (44%), e elevou na densidade do tecido conjuntivo (216%). Por outro lado, o IGF-1 aumentou o glicogênio em 234,6% quando comparado ao I, minimizou a redução de 33,7% na área das fibras musculares e aumentou de 76% no tecido conjuntivo comparado ao C (p<0,05). CONCLUSÕES: O tratamento com IGF demonstrou uma ação anti-catabólica, fato esse que pode favorecer uma recuperação mais rápida na fase pós-imobilização. Nivel de evidência: Nível II: estudo prospectivo comparativo.

The effect of a low dose of clenbuterol on rat soleus muscle submitted to joint immobilization

The aim of the present study was to evaluate the effect of joint immobilization on morphometric parameters and glycogen content of soleus muscle treated with clenbuterol. Male Wistar (3-4 months old) rats were divided into 4 groups (N = 6 for each group): control, clenbuterol, immobilized, and immobilized treated with clenbuterol. Immobilization was performed with acrylic resin orthoses and 10 microg/kg body weight clenbuterol was administered subcutaneously for 7 days. The following parameters were measured the next day on soleus muscle: weight, glycogen content, cross-sectional area, and connective tissue content. The clenbuterol group showed an increase in glycogen (81.6%, 0.38 +/- 0.09 vs 0.69 +/- 0.06 mg/100 g; P < 0.05) without alteration in weight, cross-sectional area or connective tissue compared with the control group. The immobilized group showed a reduction in muscle weight (34.2%, 123.5 +/- 5.3 vs 81.3 +/- 4.6 mg; P < 0.05), glycogen content (31.6%, 0.38 +/- 0.09 vs 0.26 +/- 0.05 mg/100 mg; P < 0.05) and cross-sectional area (44.1%, 2574.9 +/- 560.2 vs 1438.1 +/- 352.2 microm(2); P < 0.05) and an increase in connective tissue (216.5%, 8.82 +/- 3.55 vs 27.92 +/- 5.36%; P < 0.05). However, the immobilized + clenbuterol group showed an increase in weight (15.9%; 81.3 +/- 4.6 vs 94.2 +/- 4.3 mg; P < 0.05), glycogen content (92.3%, 0.26 +/- 0.05 vs 0.50 +/- 0.17 mg/100 mg; P < 0.05), and cross-sectional area (19.9%, 1438.1 +/- 352.2 vs 1724.8 +/- 365.5 microm(2); P < 0.05) and a reduction in connective tissue (52.2%, 27.92 +/- 5.36 vs 13.34 +/- 6.86%; P < 0.05). Statistical analysis was performed using Kolmogorov-Smirnov and homoscedasticity tests. For the muscle weight and muscle glycogen content, two-way ANOVA and the Tukey test were used. For the cross-sectional area and connective tissue content, Kruskal-Wallis and Tukey tests were used. This study emphasizes the importance of anabolic pharmacological protection during immobilization to minimize skeletal muscle alterations resulting from disuse.

Changes in postnatal skeletal muscle development induced by alternative immobilization model in female rat

The objective of this study was to adapt a model of hind limb immobilization to newly weaned female rats and to determine the morphology of shortened soleus and plantaris muscles. Female Wistar rats were divided into three groups: control zero (n = 3) and control and free (n = 8), animals aged 21 and 31 days, respectively, submitted to no intervention, and immobilized (n = 25), animals aged 21 days submitted to immobilization for 10 days and sacrificed at 31 days of age. The device used for immobilization had advantages such as easy connection, good fit, and low cost. The immobilized rats showed a reduction in muscle fiber area and in connective tissue. The adaptation of this immobilization model originally used for adult rats was an excellent alternative for newly weaned rats and was also efficient in inducing significant hind limb disuse.

Effect of foot and ankle immobilization on leg and thigh muscles' volume and morphology: a case study using magnetic resonance imaging

Our aim was to determine the time course of any changes in muscle volume and shape in the lower limbs following immobilization. A healthy young woman (29 years) had suffered a fracture of the fifth metatarsal of the right foot. MRI scanning of her right thigh and calf muscles had been performed 1 month before the injury (Pre) during a scan initially planned as a teaching tool, 2 days following a 4-week immobilization period (Post), and after a 2-month recovery period (Post+2). The results show muscle volume decrements in the triceps surae (TS), quadriceps (Quad), and hamstring (Ham) of 21.9%, 24.1%, and 6.5%, respectively, between the Pre and Post measurements. At Post+2, the Quad and TS muscle volumes were still 5.2% and 9.5% lower, compared with the Pre data. The Ham muscle volume, however, was 2.7% greater than at the Pre phase. Following recovery, the increase in individual TS muscles volume was limited to both proximal and medial (with respect to the knee joint) segments of the muscles. These results indicate very substantial and rapid losses in muscle volumes, both proximally and distally to the immobilization site. The results also show that recovery is far from complete up to 2 months post cast removal. The results have implications for the requirements for rehabilitation for orthopedic patients.

Propriedades mecânicas do gastrocnêmio eletroestimulado pós-imobilização

INTRODUÇÃO: As propriedades mecânicas (PM) consistem num instrumento de aplicabilidade clínica para profissionais de saúde que atuam no sistema músculo-esquelético. OBJETIVOS: Avaliar dois protocolos de estimulação elétrica neuromuscular (NMES) na potencialização do restabelecimento das PM no complexo músculo-tendíneo após imobilização segmentar de ratas. MATERIAIS E MÉTODOS: Foram utilizados 50 animais distribuídos em: Controle (GC, n=10); Imobilizado (GI, n=10); Imobilizado e remobilizado livre (GIL, n=10), Imobilizado e NMES uma vez ao dia (GIE1, n=10) e Imobilizado e NMES duas vezes ao dia (GIE2, n=10). A imobilização foi realizada por 14 dias. O GIL foi liberado posteriormente por 10 dias. A NMES foi aplicada pós-imobilização por 10 dias, GIE1 aplicado pela manhã (10 minutos) e, GIE2 aplicado pela manhã e à tarde (totalizando 20 minutos). Posteriormente, o músculo gastrocnêmio foi submetido ao ensaio mecânico de tração sendo as PM de rigidez, resiliência, carga e o alongamento no limite máximo avaliadas. RESULTADOS: A imobilização reduziu os valores das propriedades de carga e rigidez (p<0,05). A NMES utilizada duas vezes ao dia determinou resultados menos satisfatórios das PM avaliadas que àqueles obtidos uma vez ao dia e no grupo remobilizado (p>0,05). CONCLUSÃO: O músculo gastrocnênio tornou-se estruturalmente mais organizado frente à aplicação unitária da NMES e na remobilização.

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.

Avaliação do volume de fluxo venoso da bomba sural por ultra-sonografia Doppler durante cinesioterapia ativa e passiva: um estudo piloto

CONTEXTO: O fisioterapeuta na unidade hospitalar atua sobre os efeitos da hipoatividade ou inatividade do paciente acamado. Na prática diária, a contração do músculo da panturrilha é difundida entre os profissionais de saúde no ambiente hospitalar, principalmente nos períodos de pré e pós-operatório, como forma de diminuir a estase venosa e os riscos de trombose venosa profunda nos membros inferiores. OBJETIVO: Avaliar o volume de fluxo venoso na bomba sural, através de ultra-sonografia doppler, durante cinesioterapia ativa e passiva (flexão plantar do tornozelo). MÉTODOS: A amostra foi constituída por 30 indivíduos escolhidos aleatoriamente e submetidos a ultra-sonografia doppler da veia poplítea direita, visando mensurar o volume de fluxo sanguíneo em quatro momentos: repouso, compressão manual da panturrilha, movimentação passiva e ativa do tornozelo em flexão plantar. Na análise dos resultados, utilizou-se o teste t, sendo utilizado um valor de p < 0,05 como índice de significância estatística. RESULTADOS: Na amostra constituída, 16 eram do sexo feminino e 14 do sexo masculino, apresentando as seguintes médias: idade (31,57 anos), altura (1,68 m), peso (68,25 kg) e índice de massa corporal (24,16). Na análise estatística, a flexão plantar do tornozelo realizada de forma passiva, quando comparada ao valor basal, é significante (p < 0,000056) em relação à ativação da bomba sural, embora não tanto quanto o exercício ativo (p < 0,0000016). Também mostrou significância a compressão manual do músculo tríceps sural em relação ao exercício passivo (p < 0,000000081). CONCLUSÃO: Neste estudo, a flexão plantar do tornozelo de forma ativa mostrou-se estatisticamente mais eficaz do que a passiva na ativação da bomba sural, aumentando o volume do fluxo de sangue na veia poplítea e diminuindo a estase venosa nos membros inferiores.

Metformina minimiza as alterações morfométricas no músculo sóleo de ratos submetidos à imobilização articular

A proposta deste trabalho foi avaliar o músculo sóleo (S) de ratos submetidos à imobilização articular por sete dias, associado ou não ao tratamento com metformina (MET, 1,4mg.ml-1) por meio de análises morfométricas. Ratos adultos Wistar (n = 5) foram divididos nos grupos: controle (C), imobilizado em posição neutra do tornozelo (I), tratado com metformina (M), imobilizado tratado com metformina (I + MET). Foram avaliadas a área das fibras, a densidade de área do tecido conjuntivo intramuscular e a massa muscular do S. A análise estatística foi realizada pelo teste de normalidade, ANOVA e de Tukey (p < 0,05). A imobilização reduziu o peso muscular (mg) do S (34%). No grupo M não houve alteração significativa do peso muscular quando comparado com o grupo C. Já no grupo I + MET foi observado aumento do peso muscular em 29,6% quando comparado com o grupo I. O tratamento com metformina não alterou a área da fibra muscular quando comparado com grupo C. Já no grupo I, houve redução de 44% na área da fibra. Com relação ao grupo I + MET, houve aumento de 22% quando comparado com o grupo I. Por outro lado, ao compararmos o grupo C com o grupo I + MET, houve redução de 31%. Ao avaliar a densidade de área do tecido conjuntivo, observou-se que o grupo I apresentou elevação de 216% quando comparado com o grupo C. No grupo I + MET, houve redução de 67% comparado com o grupo I. O tratamento com metformina em músculos submetidos à imobilização minimizou a redução da área das fibras do S, bem como o aumento do tecido conjuntivo. Esses resultados sugerem que a metformina pode favorecer recuperação mais rápida na fase pós-imobilização.

Biomechanical effects of immobilization and rehabilitation on the skeletal muscle of trained and sedentary rats

Because of the scarcity of information about the comparison of training to sedentarism beforehand immobilization and rehabilitation through muscle mechanical properties, the present work investigates this theme. Seventy rats were divided into 7 groups: 1-control (C); 2-trained (T); 3-sedentary (S); 4-trained and immobilized (TI); 5-sedentary and immobilized (SI); 6-trained, immobilized and rehabilitated (TIR); 7-sedentary, immobilized and rehabilitated (SIR).

INTERVENTIONS

Swimming training; Sedentarism (reduced size cages); Cast immobilization (pelvic limb) and water rehabilitation. Load at the limit of proportionality (LLP), maximum limit load (MLL) and stiffness (St) were the mechanical properties determined after a mechanical test of traction of the gastrocnemius. The training improved all mechanical properties when compared to sedentarism. After immobilization, LLP and MLL were reduced in TI and SI. However, there was no difference in St between C and TI. Additionally, TI showed improved MLL when compared to SI. The comparison of TI and TIR showed significant melioration in all properties after remobilization. SIR showed an improvement only in MLL when compared to SI. Significant melioration in LLP and St was observed in TIR compared to SIR. We demonstrated that the training before immobilization and rehabilitation had a positive effect on the muscle mechanical behavior compared to sedentarism. This analysis is of fundamental importance because it helps characterize the muscle tissue under different functional demands.

Efeitos da remobilização em duas semanas com natação sobre o músculo sóleo de ratos submetidos à imobilização

Uma importante questão para a reabilitação é como proteger o músculo esquelético dos efeitos da imobilização, pois, o músculo é o mais mutável dentre os tecidos biológicos e responde às demandas normais ou alteradas com adaptações morfológicas e funcionais. O objetivo deste artigo foi verificar o efeito de duas diferentes intensidades de carga de natação sobre a morfologia do músculo sóleo, e se são eficazes para reverter o processo de atrofia causado pela imobilização durante o período de 15 dias. Foram utilizados 10 ratos, com idade de 10±2 semanas, divididos em 2 grupos: G1 (imobilização/natação sem peso) e G2 (imobilização/natação com sobrecarga de 10% do peso corporal). Dentro das variáveis analisadas ao comparar o membro esquerdo (submetido à imobilização) com o direito (não submetido) foram observados: para peso muscular em G1=-20,55% (p=0,0344) e G2= -17,02% (p=0,0053); comprimento muscular em G1= -10,66% (p=0,0011) e G2= -6,55% (p=0,1016); estimativa de sarcômeros em série no músculo para G1= -14,18% (p=0,0101) e G2= -10,99% (p=0,0043); e para comprimento de sarcômeros em G1= 3,51% (p=0,3989) e G2= 5,28% (p=0,1771). Conclui-se que duas semanas de remobilização através da natação, com diferentes tipos de sobrecarga não foram suficientes para reverter totalmente o processo de atrofia causado pela imobilização.

Morphological comparison of different protocols of skeletal muscle remobilization in rats after hindlimb suspension

The aim of this study was to evaluate and compare the efficacy of different remobilization protocols in different skeletal muscles considering the changes induced by hindlimb suspension of the tail. Thirty-six female Wistar rats were divided into six groups: control I, control II, suspended, suspended free, suspended trained on a declined treadmill and suspended trained on a flat treadmill. Fragments of soleus and tibialis anterior (TA) muscle were frozen and processed by different histochemical methods. The suspended soleus showed a significant increase in the proportional number of intermediate/hybrid fibers and a decrease in the number of type I fibers. Some of these changes proved to be reversible after remobilization. The three remobilization programs led to the recovery of both the proportional number of fibers and their size. The TA muscle presented a significant increase in the number and size of type I fibers and a cell size reduction of type IIB fibers, which were recovered after training on a declined treadmill and free movement. Especially regarding the soleus, the present findings indicate that, among the protocols, training on a declined treadmill was found to induce changes of a more regenerative nature, seemingly indicating a better tissue restructuring after the suspension procedure.

Influência do alongamento passivo em três repetições de 30 segundos a cada 48 horas em músculo sóleo imobilizado de ratos

O músculo esquelético tem a propriedade de adaptar-se a diferentes estímulos, alterando o número de sarcômeros em série, de acordo com o comprimento a que está submetido. Este trabalho tem como objetivo comparar as adaptações de peso e comprimento do músculo sóleo de ratos, além de estimativa do total de sarcômeros em série, quando submetidos a alongamento intermitente durante imobilização em plantiflexão. Foram utilizados 24 ratos (Wistar) machos de 14 ± 2 semanas de idade, divididos em 4 grupos: C (n = 6) - controle; A (n = 6) - músculo sóleo esquerdo (MSE) alongado; I - (n = 6) MSE imobilizado; IA (n = 6) MSE imobilizado e alongado. O protocolo utilizado foi 3 séries de alongamento com duração de 30s a cada 48h; e período total de imobilização de 21 dias. Foram comparadas as variações observadas entre os músculos sóleus direito (MSD) e o MSE com relação a peso muscular, comprimento muscular e estimativa do número de sarcômeros em série (ENSS), através da contagem em 300mm. Nas variáveis analisadas ao comparar o MSD (controle) e o MSE (submetido a alongamento e/ou imobilização) foram observados: peso muscular: C = -1,59%, (p = 0,67); A = +5,41% (p = 0,05); I = -41,48% (p = 0,01); IA = -32,46% (p = 0,01); comprimento muscular: C = -2,63% (p = 0,43); A = +7,54% (p = 0,07); I = -12,74% (p = 0,01); IA = -10,42% (p = 0,11); ENSS: C = -3,81% (p = 0,09); A = + 2,73% (p = 0,56); I = -12,20% (p = 0,01); IA = -12,21% (p = 0,21). Conclui-se que o alongamento durante a imobilização preservou o comprimento muscular e a quantidade de sarcômeros em série, mas não evitou a perda do peso muscular.

Morphological effects of two protocols of passive stretch over the immobilized rat soleus muscle

This study evaluated two different stretching protocols employed during a period of hind-limb immobilization in terms of their effects on muscle morphology. Quantitative data regarding the soleus muscle were obtained based on the clinical hypothesis that a high frequency of this exercise would improve the recovery of muscle structure. Twenty-four male Wistar rats were divided into four groups (n = 6 each): the control group (C); the immobilized group, in which the left hind limb was immobilized in order to maintain the soleus muscle in a fully shortened position for 3 weeks (I); the 'immobilized and stretched every 3 days' group, in which the left hind limb was immobilized as in the immobilized group, but with the soleus muscle stretched every 3 days for 40 min (Ist3); and the 'immobilized (as in the immobilized group) and stretched every 7 days' group (ISt7). All soleus muscles were excised 21 days after the beginning of the experiment, and were processed for (1) haematoxylin and eosin and myosin ATPase to evaluate muscle morphology and cross-sectional area and the proportions of the different fibre types, and (2) ultrastructural analysis. The cross-sectional area was found to have decreased in all fibre types (I, II and C), mainly in ISt7, when compared with the C group and ISt3 group. The proportion of the different fibre types did not show statistical difference between groups. Light and electron microscopy examination revealed signs of cell degeneration that was more intense in the group immobilized and stretched three times a week. In conclusion, sessions of passive stretching applied to the soleus during immobilization induce muscle fibre injury, suggesting that this therapeutic tool should be applied carefully to disused muscles.

Effect of swimming on myostatin expression in white and red gastrocnemius muscle and in cardiac muscle of rats

The aim of this study was to test the hypothesis that swimming training might impact differentially myostatin expression in skeletal muscles, depending on fibre type composition, and in cardiac muscle of rats. Myostatin expression was analysed by real time reverse transcriptase-polymerase chain reaction, Western blot and immunohistochemistry of the red deep portion (mainly composed of slow and type II A fibres) and in the superficial, white portion (composed of fast type II X and II B fibres) of the gastrocnemius muscle in adult male Wistar rats: (i) subjected to two consecutive swimming bouts for 3 h; (ii) subjected to intensive swimming training for 4 weeks; and (iii) sedentary control rats. Myostatin mRNA content was in all cases higher in white than in red muscles. Two bouts of swimming did not alter myostatin expression, whereas swimming training for 4 weeks resulted in a significant reduction of myostatin mRNA contents, significant both in white and red muscles but more pronounced in white muscles. Western blot did not detect any change in the amount of myostatin protein. Immunohistochemistry showed that, in control rats, myostatin was localized in presumptive satellite cells of a few muscle fibres. After training, the number of myostatin-positive spots decreased significantly. Myostatin mRNA content in cardiac muscle was lower than in skeletal muscle and was significantly increased by swimming training. In conclusion, the results obtained showed that intense training caused a decreased expression of myostatin mRNA in white and red skeletal muscles but an increase in cardiac muscle.

Denervation does not change the ratio of collagen I and collagen III mRNA in the extracellular matrix of muscle

Denervation or inactivity is known to decrease the mass and alter the phenotype of muscle and the mechanics of tendon. It has been proposed that a shift in the collagen of the extracellular matrix (ECM) of the muscle, increasing type III and decreasing type I collagen, may be partially responsible for the observed changes. We directly investigated this hypothesis using quantitative real-time PCR on muscles and tendons that had been denervated for 5 wk. Five weeks of denervation resulted in a 2.91-fold increase in collagen concentration but no change in the content of collagen in the muscle, whereas in the tendon there was no change in either the concentration or content of collagen. The expression of collagen I, collagen III, and lysyl oxidase mRNA in the ECM of muscle decreased (76 +/- 1.6%, 73 +/- 2.3%, and 83 +/- 3.2%, respectively) after 5 wk of denervation. Staining with picrosirius red confirmed the earlier observation of a change in staining color from red to green. Taken with the observed equivalent decreases in collagen I and III mRNA, this suggests that there was a change in orientation of the ECM of muscle becoming more aligned with the axis of the muscle fibers and no change in collagen type. The change in collagen orientation may serve to protect the smaller muscle fibers from damage by increasing the stiffness of the ECM and may partly explain why the region of the tendon closest to the muscle becomes stiffer after inactivity.

Rat hindlimb joint immobilization with acrylic resin orthoses

The objective of the present study was to propose an orthosis of light material that would be functional for the animal and that would maintain only the ankle joint immobilized. Male Wistar rats (3 to 4 months old, 250-300 g) were divided into 2 groups (N = 6): control and immobilized for 7 days. Rats were anesthetized with sodium pentobarbital (40 mg/kg weight) and the left hindlimb was immobilized with the orthoses composed of acrylic resin model, abdominal belt and lateral supports. The following analyses were performed: glycogen content of the soleus, extensor digitorum longus, white gastrocnemius, red gastrocnemius, and tibialis anterior muscles by the phenol sulfuric method, and the weight, fiber area and intramuscular connective tissue of the soleus by the planimetric system. Data were analyzed statistically by the Kolmogorov-Smirnov, Student t and Wilcoxon tests. Immobilization decreased glycogen in all muscles (P < 0.05; soleus: 31.6%, white gastrocnemius: 56.6%, red gastrocnemius: 39%, extensor digitorum longus: 41.7%, tibialis anterior: 45.2%) in addition to reducing soleus weight by 34% (P < 0.05). Furthermore, immobilization promoted reduction of the fiber area (43%, P < 0.05) and increased the connective tissue (200%, P < 0.05). The orthosis model was efficient comparing with another alternative immobilization model, like plaster casts, in promoting skeletal muscle alterations, indicating that it could be used as a new model in other studies related to muscle disuse.

Texture analysis of magnetic resonance images of rat muscles during atrophy and regeneration

OBJECTIVES

The goals of the current study were (i) to introduce texture analysis on magnetic resonance imaging (MRI-TA) as a noninvasive method of muscle investigation that can discriminate three muscle conditions in rats; these are normal, atrophy and regeneration; and (ii) to show consistency between MRI-TA results and histological results of muscle type 2 fibers' cross-sectional area.

METHOD

Twenty-three adult female Wistar rats were randomized into (i) control (C), (ii) immobilized (I) and (iii) recovering (R) groups. For the last two groups, the right hind limb calf muscles were immobilized against the abdomen for 14 days; then, the hind limb was remobilized only for the R group for 40 days. At the end of each experimental period, MRI was performed using 7-T magnet Bruker Avance DRX 300 (Bruker, Wissembourg); T1-weighted MRI acquisition parameters were applied to show predominantly muscle fibers. Rats were sacrificed, and the gastrocnemius muscle (GM) was excised immediately after imaging. (A) Histology: GM type 2 fibers (fast twitch) were selectively stained using the adenosine triphosphatase (ATPase) technique. The mean cross-sectional areas were compared between the three groups. (B) Image analysis: regions of interest (ROIs) were selected on GM MR images where statistical methods of texture analysis were applied followed by linear discriminant analysis (LDA) and classification.

RESULTS

Histological analysis showed that the fibers' mean cross-sectional areas on GM transversal sections represented a significant statistical difference between I and C rats (ANOVA, P<.001) as well as between R and I rats (ANOVA, P<.01), but not between C and R rats. Similarly, MRI-TA on GM transversal images detected different texture for each group with the highest discrimination values (Fisher F coefficient) between the C and I groups, as well as between I and R groups. The lowest discrimination values were found between C and R groups. LDA showed three texture classes schematically separated.

CONCLUSION

Quantitative results of MRI-TA were statistically consistent with histology. MRI-TA can be considered as a potentially interesting, reproducible and nondestructive method for muscle examination during atrophy and regeneration.

Bouts of passive stretching after immobilization of the rat soleus muscle increase collagen macromolecular organization and muscle fiber area

This study evaluated the effect of short bouts of stretching on the soleus muscle after immobilization, by measuring the birefringence of the intramuscular connective tissue (ICT) and the muscle fiber area. Thirty rats were divided into five groups: the left soleus was immobilized in the shortened position; after immobilization the animals remained free; after immobilization, the soleus was stretched daily (10 stretches of 60 sec followed by 30 sec rest); after immobilization, the soleus was stretched 3 times a week; control. Immobilization caused a loss of birefringence of the ICT and of muscle fiber area and only daily stretching increased both compared with the control (p< 0.01). In conclusion, short daily bouts of stretching after immobilization induced molecular reorganization of the collagen bundles and muscle fiber hypertrophy in the rat soleus.

Effects of immobilizing a single muscle on the morphology and the activation of its muscle fibers

A single muscle of Wistar female rats, either soleus or peroneus longus, was immobilized by fixing its cut distal tendon to the bone during 8 weeks. We observed a transitory weight loss in both muscles; the mean fiber cross-sectional area (CSA) showed a reduction at day 30, followed by an increase at day 60. The time course of the activation of the immobilized muscle was evaluated by recording the chronic electromyographic (EMG) activity during short periods (1 min every other day) of treadmill locomotion. During immobilization, the integrated EMG amplitude of the soleus increased, reaching a maximum at 4 weeks, but remained close to control values during 8 weeks for the peroneus. The median frequency (MF) of the power density spectrum of the soleus EMG was not statistically different between immobilized and control muscles, while MF of the immobilized peroneus EMG was permanently higher than that of control muscles. This suggests two different modes of adaptation in motor unit command, depending on the muscle profile, which could be concomitant with the restoration of muscle fibers CSA after 8 weeks.

Oxidative stress after muscle damage from immobilization and remobilization occurs locally and systemically

Higher oxidative stress reportedly plays a key role in muscle damage caused by immobilization and subsequent remobilization. However, we have no clear understanding regarding oxidative stress during immobilization and remobilization. The purpose of this study was to clarify the characteristics of oxidative stress by measuring oxidative stress locally and systemically. Twenty-three New Zealand White rabbits were used in this study. Blood samples were collected on Days 1, 3, 7, 14, and 21 of immobilization, and Days 1, 2, 3, and 4 of remobilization. The soleus muscles in immobilized and nonimmobilized limbs were harvested on Day 21 of immobilization and Day 7 or Day 14 of remobilization. Muscle wet weight was determined as the indicator of muscle atrophy. The levels of lipid peroxidation and glutathione in plasma and soleus muscles were measured. Immobilization and remobilization induced an increase in the lipid peroxidation levels and a decrease in glutathione levels in muscle and blood. These findings suggest that oxidative stress occurs locally and systemically, lasts throughout the immobilization period, but peaks at the early phase of remobilization.

Effect of passive stretching on the immobilized soleus muscle fiber morphology

The aim of the present study was to determine the effect of stretching applied every 3 days to the soleus muscle immobilized in the shortened position on muscle fiber morphology. Eighteen 16-week-old Wistar rats were used and divided into three groups of 6 animals each: a) the left soleus muscle was immobilized in the shortened position for 3 weeks; b) during immobilization, the soleus was stretched for 40 min every 3 days; c) the non-immobilized soleus was only stretched. Left and right soleus muscles were examined. One portion of the soleus was frozen for histology and muscle fiber area evaluation, while the other portion was used to identify the number and length of serial sarcomeres. Immobilized muscles (group A) showed a significant decrease in weight (44 +/- 6%), length (19 +/- 7%), serial sarcomere number (23 +/- 15%), and fiber area (37 +/- 31%) compared to the contralateral muscles (P < 0.05, paired Student t-test). The immobilized and stretched soleus (group B) showed a similar reduction but milder muscle fiber atrophy compared to the only immobilized group (22 +/- 40 vs 37 +/- 31%, respectively; P < 0.001, ANOVA test). Muscles submitted only to stretching (group C) significantly increased the length (5 +/- 2%), serial sarcomere number (4 +/- 4%), and fiber area (16 +/- 44%) compared to the contralateral muscles (P < 0.05, paired Student t-test). In conclusion, stretching applied every 3 days to immobilized muscles did not prevent the muscle shortening, but reduced muscle atrophy. Stretching sessions induced hypertrophic effects in the control muscles. These results support the use of muscle stretching in sports and rehabilitation.

The Effects of Aging and Treadmill Running on Soleus and Gastrocnemius Muscle Morphology in the Senescence-Accelerated Mouse (SAMP1)

We investigated the effects of aging on the soleus and gastrocnemius muscles in male SAMP1 (senescence-accelerated mouse prone 1). Body mass, muscle wet weight, fiber size, and the percent of type II fibers declined from 50 weeks of age. Voluntary motor behavior also significantly declined with age. Furthermore, we examined the effects of high (twice daily) and low (once daily) frequency treadmill running, for 6 weeks at 5 days per week, beginning when the mice were 50 weeks old. Muscle fiber size for the high frequency running significantly increased. Pathological fiber alterations in these mice were increased by running, especially by high frequency running. This suggests that age-related muscle morphological changes in SAMP1 occurs from 50 weeks of age, and that the decline in voluntary motor behavior is an important factor in aging muscle atrophy. In addition, high frequency running is more beneficial for aged muscle hypertrophy. This model is useful for studying the acceleration of the aging process in skeletal muscle of the SAM.

Effect of one stretch a week applied to the immobilized soleus muscle on rat muscle fiber morphology

We determined the effect of stretching applied once a week to the soleus muscle immobilized in the shortened position on muscle fiber morphology. Twenty-six male Wistar rats weighing 269 +/- 26 g were divided into three groups. Group I, the left soleus was immobilized in the shortened position for 3 weeks; group II, the soleus was immobilized in the shortened position and stretched once a week for 3 weeks; group III, the soleus was submitted only to stretching once a week for 3 weeks. The medial part of the soleus muscle was frozen for histology and muscle fiber area evaluation and the lateral part was used for the determination of number and length of serial sarcomeres. Soleus muscle submitted only to immobilization showed a reduction in weight (44 +/- 6%, P = 0.002), in serial sarcomere number (23 +/- 15%) and in cross-sectional area of the fibers (37 +/- 31%, P < 0.001) compared to the contralateral muscles. The muscle that was immobilized and stretched showed less muscle fiber atrophy than the muscles only immobilized (P < 0.05). Surprisingly, in the muscles submitted only to stretching, fiber area was decreased compared to the contralateral muscle (2548 +/- 659 vs 2961 +/- 806 microm(2), respectively, P < 0.05). In conclusion, stretching applied once a week for 40 min to the soleus muscle immobilized in the shortened position was not sufficient to prevent the reduction of muscle weight and of serial sarcomere number, but provided significant protection against muscle fiber atrophy. In contrast, stretching normal muscles once a week caused a reduction in muscle fiber area.

Recovery from immobilisation: responses of fast-twitch muscle fibres to spontaneous and intensive exercise in rat calf muscles

Four weeks of immobilisation with two types of re-mobilisation programmes (intensive concentric treadmill exercising during 6 days, and free exercising, and immobilisation without any re-mobilisation period were studied to clarify possible exercise-induced calf muscle damage especially in fast-twitch fibres used in running compared to non-immobilised rats housing freely in their cages. As markers of muscle injury, conventional histology, beta-glucuronidase (beta-GU) activity and fetal myosin heavy chain expression (MHC-d) were assessed on Days 0, 1, 3, 6 and 14 after the cast removal. Only minor focal hypercontraction, ruptures and necrosis of myofibrils, and weak inflammatory cell reactions were found in all samples examined, except in the controls. No MHC-d positive cells were found indicating absence of active regeneration after immobilisation or re-mobilisation. Minor increase in beta-GU activity was observed in all three muscles studied, but statistically significant increase was observed only in the samples of the free exercising group on Day 14 after the cast removal. To conclude, intensive concentric treadmill exercise for 6 days did not cause significantly more muscle damage than did free exercising re-mobilisation.

Different frequency treadmill running in immobilization-induced muscle atrophy and ankle joint contracture of rats

We investigated the effects of different frequencies of treadmill running on immobilization-induced soleus and gastrocnemius muscle atrophy and ankle joint contracture in rats using morphology and histochemistry. The right ankle joint of rat was immobilized for 2 weeks. Thereafter, the rats were randomly assigned to four groups for 6 weeks of exercise under different conditions: free cage activity and free remobilization (FR), once-a-week treadmill running (low-frequency running program (LFR)), three-time-a-week running (middle-frequency running program (MFR)), and six-time-a-week running (high-frequency running program (HFR)) groups. Two weeks of immobilization significantly reduced the cross-sectional area of soleus type I (62%, P<0.05) and type II muscle fibers (66%, P<0.05), gastrocnemius type I (78%, P<0.05) and type II muscle fibers (68%, P<0.05), and the range of ankle joint movement (46%, P<0.05). Immobilization also increased the ratio of type II to total fiber numbers in the soleus (P<0.05), and gastrocnemius (P<0.05), and induced pathological changes in muscle fibers. Some of these changes could not be corrected by free remobilization; however, the LFR, MFR, and HFR groups clearly recovered toward normal levels with exercise frequency, the effect on muscle recovery being more beneficial in the MFR and HFR groups. In addition, the range of ankle joint contracture was improved in LFR, MFR, and HFR groups in comparison with that in the FR group. These findings indicate that treadmill running exercise improved the immobilization-induced muscle fiber histochemical alterations and the range of the ankle motion in rats. Running three times and six times a week was more beneficial for recovery of immobilization-induced muscle atrophy and joint contracture compared with no running or once-a-week running.

Contraction-induced injury run amok: an introduction

Skeletal muscle has an amazing capacity to adapt to increased levels of physical activity. Adaptation is often preceded by contraction-induced injury. In most cases, the damage is repaired quickly, the muscle adapts, and becomes stronger and less fatigable. Diseased or deconditioned muscle is an exception; the response to increased functional demand, and the associated injury can be incomplete or even maladaptive. When and why is an adaptive response limited? This question will be addressed in the symposium papers following this brief introduction. The papers will discuss cellular, molecular, and immunological mechanisms that may be involved in impaired muscle adaptation.

Basic science and clinical studies coincide: active treatment approach is needed after a sports injury

The basic response to injury at the tissue level is well known and consists of acute inflammatory phase, proliferative phase, and maturation and remodeling phase. Knowing these phases, the treatment and rehabilitation program of athletes' acute musculoskeletal injuries should use a short period of immobilization followed by controlled and progressive mobilization. Both experimental and clinical trials have given systematic and convincing evidence that this program is superior to immobilization - a good example where basic science and clinical studies do coincide - and therefore active approach is needed in the treatment of these injuries.

Organization and distribution of intramuscular connective tissue in normal and immobilized skeletal muscles. An immunohistochemical, polarization and scanning electron microscopic study

Collagen fiber network is a major contributor to the coherence and tensile strength of normal skeletal muscle. Despite the well-recognized importance of the intramuscular connective tissue to the normal integrity and function of the skeletal muscle, the specific architecture including the location and three-dimensional orientation of the intramuscular connective tissue within the muscle tissue is poorly described. The structure of the intramuscular connective tissue was studied by immunohistochemistry, polarization microscopy (the crimp length and angle of the collagen fibers) and scanning electron microscope (SEM) in rat skeletal muscles (gastrocnemius, soleus and tibialis anterior) in normal situation and after 3 weeks of disuse (immobilization). Three separate networks of collagen fibers were distinguished by SEM in the normal endomysium; fibers running longitudinally on the surface of the muscle fibers (the main collagen orientation), fibers running perpendicularly to the long axis of the muscle fibers and having contacts with adjacent muscle fibers, and fibers attached to the intramuscular nerves and arteries. Similarly, the SEM analysis also disclosed three distinct collagen fiber networks running in different directions in the perimysium, but, contrary to the endomysium, the main fiber orientation could not be established. Immobilization resulted in a marked increase in the endo- and perimysial connective tissue, the majority of the increased endomysial collagen being deposited directly on the sarcolemma of the muscle cells. Immobilization also resulted in substantial increase in the number of perpendicularly oriented collagen fibers with contacts to two adjacent muscle fibers in the endomysium. Further, immobilization clearly disturbed the normal structure of the endomysium making it impossible to distinguish the various networks of fibers from each other. In the perimysium, immobilization-induced changes were similar, the number of longitudinally oriented collagen fibers was increased, the connective tissue was very dense, the number of irregularly oriented collagen fibers was markedly increased, and consequently, the different networks of collagen fibers could not be distinguished from each other. Of the three studied intact muscles, the crimp angle of the collagen fibers was lowest in the soleus and highest in the gastrocnemius muscle, and the crimp angle decreased over 10% in all muscles after the immobilization-period. Altogether, the above described quantitative and qualitative changes in the intramuscular connective tissue are likely to contribute to the deteriorated function and biomechanical properties of the immobilized skeletal muscle.

Mechanical loading regulates the expression of tenascin-C in the myotendinous junction and tendon but does not induce de novo synthesis in the skeletal muscle

Tenascin-C is a hexabrachion-shaped matricellular protein with a very restricted expression in normal musculoskeletal tissues, but it is expressed abundantly during regenerative processes of these tissues and embryogenesis. To examine the importance of mechanical stress for the regulation of tenascin-C expression in the muscle-tendon unit, the effects of various states of mechanical loading (inactivity by cast-immobilization and three-varying intensities of subsequent re-activity by treadmill running) on the expression of tenascin-C were studied using immunohistochemistry and mRNA in situ hybridization at the different locations of the muscle-tendon unit of the rat gastrocnemius muscle, the Achilles tendon complex. This muscle-tendon unit was selected as the study site, because the contracting activity of the gastrocnemius-soleus muscle complex, and thus the mechanical loading-induced stimulation, is easy to block by cast immobilization. Tenascin-C was expressed abundantly in the normal myotendinous and myofascial junctions, as well as around the cells and the collagen fibers of the Achilles tendon. Tenascin-C expression was not found in the normal skeletal muscle, although it was found in blood vessels within the muscle tissue. Following the removal of the mechanical loading-induced stimulation on the muscle-tendon unit by cast immobilization for 3 weeks, the immonoreactivity of tenascin-C substantially decreased or was completely absent in the regions expressing tenascin-C normally. Restitution of the mechanical loading by removing the cast and allowing free cage activity for 8 weeks resulted in an increase in tenascin-C expression, but it could not restore the expression of tenascin-C to the normal level (in healthy contralateral leg). In response to the application of a more strenuous mechanical loading stimulus after the removal of the cast (after 8 weeks of low- and high-intensity treadmill running), the expression of tenascin-C was markedly increased and reached the level seen in the healthy contralateral limb. Tenascin-C was abundantly expressed in myotendinous and myofascial junctions and in the Achilles tendon, but even the most strenuous mechanical loading (high-intensity treadmill running) could not induce the expression of tenascin-C in the skeletal muscle. This was in spite of the marked immobilization-induced atrophy of the previously immobilized skeletal muscle, which had been subjected to intensive stress during remobilization. mRNA in situ hybridization analysis confirmed the immunohistochemical results for the expression of tenascin-C in the study groups. In summary, this study shows that mechanical loading regulates the expression of tenascin-C in an apparently dose-dependent fashion at sites of the muscle-tendon unit normally expressing tenascin-C but can not induce de novo synthesis of tenascin-C in the skeletal muscle without accompanying injury to the tissue. Our results suggest that tenascin-C provides elasticity in mesenchymal tissues subjected to heavy tensile loading.

GLUT4 expression at the plasma membrane is related to fibre volume in human skeletal muscle fibres

In this study we examined the relationship between GLUT4 expression at the plasma membrane and muscle fibre size in fibre-typed human muscle fibres by immunocytochemistry and morphometry in order to gain further insight into the regulation of GLUT4 expression. At the site of the plasma membrane, GLUT4 was more abundantly expressed in slow as compared to fast fibres at the same fibre diameter (p < 0.01) and the GLUT4 expression increased with increasing fibre radius independently of fibre type (p < 0.01). The GLUT4 density at the surface of slow fibres of both diabetic and obese was reduced compared to control subjects at the same diameter (p < 0.001). Fast fibres in obese and type 2 diabetic subjects expressed a fibre-volume-dependent GLUT4 expression (p < 0.001), while this did not reach significance in slow fibres (obese p = 0.18 and diabetic p = 0.06). Our results show that increasing fibre volume is associated with increasing GLUT4 expression in both slow and fast fibres. Based on the possible dependency of GLUT4 expression on volume, we hypothesize that the reduced GLUT4 expression in obesity and type 2 diabetes may partly be compensated for by physical activity.

Muscular mass assessed by ultrasonography after administration of low-dose corticosteroids and muscle relaxants in critically ill hemiplegic patients

BACKGROUND AIMS

The present study investigates the influence of low-dose and short- term administration of corticosteroids and muscle relaxants on the muscular mass (MM) in hemiplegic ICU patients, with the aid of ultrasonography (U/S).

METHODS

Thirty-seven patients hospitalised in the ICU for 18.6+/-3.6 days, were included in the study. Sixteen patients did not receive either drug (group A), five patients received dexamethasone (24 mg/day) for 4 days (group B), eight patients received dexamethasone (24 mg/day) for 4 days and atracurium (0.3-0.6 mg/kg/h) for 2.8+/-0.4 days (group C), whereas eight other non-hemiplegic ICU patients comprised the control group. MM was measured in cm by U/S and serum Albumin (ALB, g/l) at the first and the tenth ICU hospitalisation day. The corresponding differences (DeltaMM, DeltaALB) were compared between the four groups of patients.

RESULTS

MM and ALB decreased significantly in all groups. DeltaMM was significantly higher in group C in comparison to all other groups, while DeltaMM was also higher in group B, when compared to the control and A groups. DeltaALB did not show significant inter-group differences. DeltaMM was significantly related to patients' age (r=0.41,P =0.001).

CONCLUSIONS

Muscular atrophy of the ICU hemiplegic patients is significantly influenced by the synchronous treatment with muscle relaxants and corticosteroids at low doses and for short term. This myopathy should be taken into account for the better prognosis and the safer outcome of the patient and U/S is suitable for accurate and non-invasive monitoring of MM.

Skeletal muscle damage and recovery

Muscular strength is essential for recovery after an acute illness. Disuse atrophy of muscle begins within 4 hours of the start of bed rest resulting in decreases in muscle mass, muscle cell diameter, and the number of muscle fibers. Strenuous exercise of atrophic muscle can lead to muscle damage including sarcolemmal disruption, distortion of the myofibrils' contractile components, and cytoskeletal damage. Assessment of skeletal muscle for disuse atrophy is done clinically at the bedside through strength assessment. Examination of the muscle itself can be conducted through the use of nuclear magnetic resonance imaging, whereas muscle strength can be quantified with a computerized dynamometer. Biochemical markers, including creatine kinase and troponin, also are available for the assessment of skeletal muscle damage. Activity management in the critical care environment focuses on an individualized plan, developed in cooperation with the recovering patient, with the goal of preserving and improving atrophic skeletal muscle.

Range of motion training in brace vs. plaster immobilization after anterior cruciate ligament reconstruction: a prospective randomized comparison with a 2-year follow-up

The purpose of this prospective and randomized study was to compare rehabilitation with early range of motion (ROM) training vs immobilization following anterior cruciate ligament (ACL) reconstruction. Fifty patients, undergoing an ACL reconstruction with a bone-patellar tendon-bone graft, were postoperatively allocated randomly to either a plaster cast or a brace for 5 weeks. The brace group had ROM exercises from postoperative day 7. The commencement of ROM exercises was postponed 4 weeks for the plaster group compared to the brace group, but progressed subsequently with equal speed. There was no difference between the groups in the ROM of flexion or extension 20 weeks after the ACL reconstruction and later. Twenty-four months after surgery, the muscle strength deficit in the hamstring muscles (isokinetic measurements; percent difference, injured vs uninjured) was significantly larger in the brace group (mean +/- SD: 5.9 +/- 7.8%, P < 0.01) than in the plaster group (- 0.9 +/- 11.8%, NS) (brace vs plaster group, P < 0.05). Furthermore, there was also a tendency in the brace group to a larger strength deficit in the quadriceps muscle (brace: 11.1 +/- 13.2%, P < 0.001; plaster: 3.8 +/- 12.9%, NS) (brace vs plaster group, P= 0.07). There was no difference between the groups in the total sagittal knee laxity, as measured with an arthrometer, or in the subjective knee function or activity level (Lysholm score together with the Tegner activity level) between the groups. It is concluded that the postoperative treatment with early range of motion training after ACL reconstruction gave as good ROM, knee stability, subjective knee function and activity level as the treatment with immobilization. It is hypothesized that the larger strength deficit observed after rehabilitation with early range of motion training is secondary to the more intensive training and physical therapist involvement that was demanded in order to achieve full ROM following immobilization.

Exercise-enhanced satellite cell proliferation and new myonuclear accretion in rat skeletal muscle

The effects of increased functional loading on early cellular regenerative events after exercise-induced injury in adult skeletal muscle were examined with the use of in vivo labeling of replicating myofiber nuclei and immunocyto- and histochemical techniques. Satellite cell proliferation in the soleus (Sol) of nonexercised rats (0.4 +/- 0.2% of fibers) was unchanged after an initial bout of declined treadmill exercise but was elevated after two (1.0 +/- 0.2%, P < or = 0.01), but not four or seven, daily bouts of the same task. Myonuclei produced over the 7-day period comprised 0.9-1.9% of myonuclei in isolated fibers of Sol, tibialis anterior, and vastus intermedius of nonexercised rats. The accretion of new myonuclei was enhanced (P < or = 0.05) in Sol and vastus intermedius by the initial exercise followed by normal activity (to 3.1-3.4% of myonuclei) and more so by continued daily exercise (4.2-5.3%). Observed coincident with a lower incidence of histological fiber injury and unchanged fiber diameter and myonuclei per millimeter, the greater new myonuclear accretion induced by continued muscle loading may contribute to an enhanced fiber repair and regeneration after exercise-induced injury.

Effect of high-intensity running in rectus femoris muscle fiber in rats

The effect of a 12-week high-intensity intermittent exercise program on fiber type composition and the oxidative capacity of rectus femoris skeletal muscle from 20 male Wistar rats (Trained, n = 10; Sedentary, n = 10) was histochemically determined. The training exercise program was developed in a motorized treadmill. It consisted of four running bouts of 2 min duration at 48 m/min, alternated with recovery intervals of 4 min. Training increased relative cross-sectional area of oxidative fibers (I, IIA, IIX) and decreased the same parameter in type IIB non-oxidative fibers (P < 0.001). Our results suggest that this type of strength exercise program is enough to induce changes in muscle fiber composition. This opens a possibility to use this kind of exercise in preventing and treating muscle atrophy.

Parvalbumin Expression Is Downregulated in Rat Fast-Twitch Skeletal Muscles during Aging

In this study, the protein expression profile of extensor digitorum longous (EDL) and Soleus (SOL) muscles, representing fast- and slow-twitch skeletal muscles, respectively, was established using high resolution two-dimensional electrophoresis (2-DE). One protein spot was found uniquely expressed in EDL muscle. N-terminal sequence analysis identified the protein as parvalbumin. Parvalbumin is a high affinity calcium binding protein that regulates muscle contraction and relaxation. Our experiments revealed that parvalbumin expression in EDL muscle was down-regulated during aging. In addition, high-intensity exercise could reverse this age-related change. Soleus muscles do not normally express parvalbumin, but high-intensity exercise could ectopically induce its expression in both young and old SOL muscles. We have also confirmed our 2-DE findings by immunohistochemistry on muscle sections. Our results suggest that high-intensity training could be used to improve muscle functions during aging because parvalbumin play an important role in regulating skeletal muscle contraction and relaxation.

Recovery from 6 weeks of repeated strain injury to rat soleus muscles

Recovery from chronic strain injury (50 strains daily, five times weekly for 6 weeks to hyperactive soleus muscles) was followed for 3 months in female rats after cessation of chronic hyperactivity induced by pretreatment of the plantar flexor muscles with tetanus toxin. After 6 weeks of repeated strains, muscle mass decreased by 62%, myofiber areas were reduced by 87%, and noncontractile tissue expanded dramatically by 222%. Collagen content increased by almost ninefold (control 40 +/- 3 microg/mg, chronic injury 392 +/- 53 microg/mg), whereas the molar ratio of collagen (pyridinoline) crosslinks to collagen remained the same (control 0.20 +/- 0.01, chronic injury 0.16 +/- 0.01). After 3 months of ambulation, muscle mass returned to normal but myofiber areas remained smaller by 21%, noncontractile tissue was still markedly elevated by 18% with increased collagen content (107 +/- 15 microg/mg), and the molar ratio of crosslinks to collagen increased by 75% during recovery. Thus, rat soleus muscles recovered very slowly and incompletely from chronic strain injuries that produced muscle fibrosis, highlighting the necessity of devising preventative strategies for repeated strain injuries.

Impact of mechanical load on functional recovery after muscle reloading

The purposes of this study included: 1) to determine the impact of reloading after hindlimb suspension on the in vitro isometric contractile properties of the rat soleus muscle (experiment 1), and 2) to determine the impact of altered mechanical load on the recovery of muscle contractile properties after reloading-induced injury (experiment 2). Male Sprague-Dawley rats (240-270 g) were used for both experiments. In experiment 1, all rats were hindlimb suspended for a period of 7 d and studied either immediately afterward (no reloading, 0D-RL), after 1 d (24 h) of reloading (1D-RL), or after 2 d (48 h) reloading (2D-RL). In experiment 2, all rats underwent hindlimb suspension for 7 d followed by reloading for 2 d. Rats were then randomly assigned to one of three groups: 1) cage-bound, 2) treadmill walking (12m x min(-1) x 20 min daily), or 3) resuspended. Rats were then studied 7 or 14 d later. In experiment 1, maximal isometric specific force (force/cross-sectional area, Po) was significantly decreased by approximately 32% and approximately 50% in the ID-RL and 2D-RL groups (P < 0.05) compared with 0D-RL group. During the recovery phase (experiment 2), Po was significantly higher in the cage-bound and treadmill walking groups compared with the resuspended group both at 7 and 14 d. However, there was no significant difference in Po between the cage-bound and treadmill walking groups at either time point. Results from this study indicate that skeletal muscle reloading (after a period of unloading) results in a significant force decrement. Additionally, removal of the load during the recovery phase significantly impairs functional recovery, whereas mild exercise offers no advantage over cage-bound activity.