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O presente estudo avaliou a influência de diferentes doses de decanoato de nandrolona (DN) associado ao Treinamento de Força (TF) sobre o fenótipo de fibras e área de secção transversa (AST) do músculo extensor longo dos dedos (EDL) em ratos "Wistar". Os animais foram divididos em sete grupos: controle (GC) e grupos de acordo com a concentração de DN (0,1, 1, 2, 5, 10 e 20 mg/kg) administrada intramuscular 3 vezes/semana. O TF consistiu de saltos em meio líquido (carga 50-70% do peso corporal) 3x/semana, durante cinco semanas. A associação do TF e DN promoveu ação modulatória sobre os tipos de fibras. Houve hipertrofia das fibras de contração rápida (tipo II) em comparação com as fibras de contração lenta (tipo I). Em conclusão, apesar da associação do TF com DN aumentar a AST muscular e alterar o fenótipo das fibras, não houve efeito gradual das doses mais altas.

The aim of the present study was to evaluate the influence of different doses of nandrolone decanoate (ND) associated with Strength Training (ST) on the phenotype of fibers and cross-sectional area (CSA) of the extensor digitorum longus (EDL) in Wistar rats. The animals were divided into seven groups: control (CG) and the groups according to the dose of ND administered (0,1, 1, 2, 5, 10 e 20 mg/kg). The ST consisted of water jumping with loads of 50-70% of their body mass, three times per week during five weeks. The association of ST with ND promoted a modulatory role on the muscle fiber types. There was a hypertrophy of fast twitch fibers (type II) as compared with slow twitch (type I). In conclusion, although the association of ST with ND increased muscle CSA and modified fiber phenotype, there was no additional effect of higher doses.

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The aim of this study was to test whether high-intensity resistance training with insufficient recovery time between bouts, could result in a decrease of muscle fiber cross-sectional area (CSA), alter fiber-type frequencies and myosin heavy chain (MHC) isoform content in rat skeletal muscle. Wistar rats were divided into two groups: trained (Tr) and control (Co). Tr group were subjected to a high-intensity resistance training program (5 days/week) for 12 weeks, involving jump bouts into water, carrying progressive overloads based on percentage body weight. At the end of experiment, animals were sacrificed, superficial white (SW) and deep red (DR) portions of the plantaris muscle were removed and submitted to mATPase histochemical reaction and SDS-PAGE analysis. Throughout the experiment, both groups increased body weight, but Tr was lower than Co. There was a significant reduction in IIA and IID muscle fiber CSA in the DR portion of Tr compared to Co. Muscle fiber-type frequencies showed a reduction in Types I and IIA in the DR portion and IID in the SW portion of Tr compared to Co; there was an increase in Types IIBD frequency in the DR portion. Change in muscle fiber-type frequency was supported by a significant decrease in MHCI and MHCIIa isoforms accompanied by a significant increase in MHCIIb isoform content. MHCIId showed no significant differences between groups. These data show that high-intensity resistance training with insufficient recovery time between bouts promoted muscle atrophy and a transition from slow-to-fast contractile activity in rat plantaris muscle.

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The muscle fiber phenotype is mainly determined by motoneuron innervation and changes in neuromuscular interaction alter the muscle fiber type. In dystrophin-deficient mdx mice, changes in the molecular assembly of the neuromuscular junction and in nerve terminal sprouting occur in the sternomastoid (STN) muscle during early stages of the disease. In this study, we were interested to see whether early changes in neuromuscular assembly are correlated with alterations in fiber type in dystrophic STN at 2 months of age. A predominance of hybrid fast myofibers (about 52% type IIDB) was observed in control (C57Bl/10) STN. In mdx muscle, the lack of dystrophin did not change this profile (about 54% hybrid type IIDB). Pure fast type IID fibers predominated in normal and dystrophic diaphragm (DIA; about 39% in control and 30% in mdx muscle) and a population of slow Type I fibers was also present (about 10% in control and 13% in mdx muscle). In conclusion, early changes in neuromuscular assembly do not affect the fiber type composition of dystrophic STN. In contrast to the pure fast fibers of the more affected DIA, the hybrid phenotype of the STN may permit dynamic adaptations during progression of the disease.

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Diaphragm myopathy has been described in patients with heart failure (HF), with alterations in myosin heavy chains (MHC) expression. The pathways that regulate MHC expression during HF have not been described, and myogenic regulatory factors (MRFs) may be involved. The purpose of this investigation was to determine MRF mRNA expression levels in the diaphragm. Diaphragm muscle from both HF and control Wistar rats was studied when overt HF had developed, 22 days after monocrotaline administration. MyoD, myogenin and MRF4 gene expression were determined by RT-PCR and MHC isoforms by polyacrylamide gel electrophoresis. Heart failure animals presented decreased MHC IIa/IIx protein isoform and MyoD gene expression, without altering MHC I, IIb, myogenin and MRF4. Our results show that in HF, MyoD is selectively down-regulated, which might be associated with alterations in MHC IIa/IIx content. These changes are likely to contribute to the diaphragm myopathy caused by HF.

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Skeletal muscles respond to several stimuli changing their phenotype. Muscular fibers adaptation capability is related to the presence of several myosin heavy chains (MHC). These express four types of pure fibers: I, IIA, IID and IIB containing MHCI, IIa, IId and IIb, respectively. Among pure fibers, there are hybrid fibers, which can express two or more types of myosins. In this study, types of fibers constituting male Wistar rats semitendinous and their myosin heavy chains, as well as influence of intermittent training on hypertrophy of these fibers have been checked through MATPase histochemical technique and electrophoretic proteins separation. All types of pure and hybrid muscular fiber have been found, however the fibers of the types IIA, IID and IIB were predominant, featuring muscle as a fast-contracting one. Training has promoted muscular fibers transition with a significant increase of fibers of IC, IIAD and IIDB type. A cross-section increase of fibers of IIDB and IIB type has also been noticed. In summary, semitendinous muscle is essentially constituted by fast-contracting fibers and training could promote transition and hypertrophy of these fast fibers.

Los músculos esqueléticos responden a diversos estímulos cambiando su fenotipo. La capacidad de adaptación de las fibras musculares está relacionada con la presencia de diversas miosinas de cadena pesada (MHC). Estas miosinas expresan cuatro tipos de fibras puras: I, IIA, IID, IIB, que contienen MHCI IIa IId IIb, respectivamente. Entre las fibras puras hay fibras híbridas, las cuales pueden expresar dos o más tipos de miosinas. En este trabajo, se observaron los tipos de fibras y las cadenas pesadas de miosinas del músculo semitendinoso en ratas Wistar macho, así como también, la influencia del entrenamiento intermitente en la hipertrofia de aquellas fibras, a través de la técnica histoquímica de mATPasa y separación eletroforética de proteínas. Todos los tipos de fibras musculares puras e híbridas fueron encontradas, siendo las fibras de tipo IIA IID y IIB predominantes, por ser un músculo de contracción rápida. El entrenamiento promovió la transición de las fibras musculares con un aumento significativo de las fibras del tipo IC, IIAD y IIDB. En una sección transversal, un incremento de fibras del tipo IIDB y IIB también fue reportada. En resumen, el músculo semitendinoso está compuesto esencialmente por fibras de contracción rápida y el entrenamiento puede promover la transición e hipertrofia de las fibras musculares rápidas.

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O objetivo do presente estudo foi investigar as alterações no desempenho de força máxima e as adaptaçõesmorfológicas decorrentes do treinamento de força máxima e de potência muscular. Quarentasujeitos foram randomicamente divididos nos grupos treino de força (TF; 178,7 ± 4,3 cm; 75,2 ± 7,3 kg;22,5 ± 3,8 anos), treino de potência (TP; 177,0 ± 5,9 cm; 76,0 ± 8,9 kg; 24,2 ± 4,1 anos), e controle (C;178,9 ± 11,0 cm; 74,1 ± 9,6 kg; 24,1 ± 2,7 anos). Os sujeitos dos grupos TF e TP foram submetidos a oitosemanas de treinamento, com três sessões semanais. O grupo TF realizou agachamento com cargasentre 60 e 95% de 1 RM, enquanto o grupo TP realizou agachamento com cargas entre 30 e 60% de 1RM, com a maior velocidade possível. Foi avaliado o ganho de força máxima no teste de 1 RM noagachamento e a área de secção transversa das fibras tipo I, tipo IIa e tipo IIb pré- e pós-treinamento.Os grupos TF e TP aumentaram a força máxima após o período de treinamento (p < 0,001), de maneirasimilar (p > 0,05). Houve um efeito principal de tempo para o aumento da área de secção transversapara todos os tipos de fibras (p < 0,05). Concluindo, o TF e o TP produziram ganhos de força e dehipertrofia muscular semelhantes, após oito semanas de treinamento.

The aim of this study was to investigate the changes in maximum strength and morphological adaptationsafter a strength and a power training programs. Forty subjects were randomly divided into a strength traininggroup (TF; 178.7 ± 4.3 cm; 75.2 ± 7.3 kg; 22.5 ± 3.8 years), a power training group (TP; 177.0 ± 5.9 cm; 76.0± 8.9 kg; 24.2 ± 4.1 years), and a control group (C; 178.9 ± 11.0 cm; 74.1 ± 9.6 kg; 24.1 ± 2.7 years). Subjectsin the TF and TP underwent an 8-week, three sessions per week, training program. The TF performed the squatexercise with loads from 60 to 95% of the squat 1 RM, while the TP used loads from 30 to 60% of 1 RM, asfast as possible. Maximum strength and type I, type IIa, and type IIb cross sectional area were evaluatedbefore and after the training programs. TF and TP increased maximum strength from pre- to post-training (p< 0.001), but there were no difference between them (p > 0.05). There was a main time effect for muscle crosssectional area for all fiber types (p < 0.05). In conclusion, the TF and the TP produced similar strength gainsand muscle fiber hypertrophy after an 8-week training period.

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The effects of testosterone on skeletal muscle were assessed in adult male Wistar rats aged 80 days and 1 year. The animals were divided into 4 groups: young testosterone (YT), old testosterone (OT), young control (YC), and old control (OC) groups. The YT and OT groups received 15 applications of testosterone cypionate (5 mg/kg) on alternate days and the controls received injections containing sterile oil alone. After 30 days the animals were sacrificed and the soleus (SOL) and extensor digitorum longus (EDL) muscles were analyzed using mATPase histochemistry. After treatment, YT group gained less body weight than YC group and OT group decreased body weight, differently from the body weight gain observed in the OC group. Testosterone treatment did not show significant changes in both relative muscle weight and muscle fiber composition profile. However, in the YT group we observed an increase in the cross-sectional area of type I fibers in the SOL muscle, and type I and IIAD fibers in the EDL muscle. In the OT group, the cross sectional area of type I was decreased in the EDL muscle. These results reveal that testosterone did not cause a shift in muscle fiber type, but the cross-sectional area had fiber type-specific changes.

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Heart failure (HF) is characterized by a skeletal muscle myopathy with increased expression of fast myosin heavy chains (MHCs). The skeletal muscle-specific molecular regulatory mechanisms controlling MHC expression during HF have not been described. Myogenic regulatory factors (MRFs), a family of transcriptional factors that control the expression of several skeletal muscle-specific genes, may be related to these alterations. This investigation was undertaken in order to examine potential relationships between MRF mRNA expression and MHC protein isoforms in Wistar rat skeletal muscle with monocrotaline-induced HF. We studied soleus (Sol) and extensor digitorum longus (EDL) muscles from both HF and control Wistar rats. MyoD, myogenin and MRF4 contents were determined using reverse transcription-polymerase chain reaction while MHC isoforms were separated using polyacrylamide gel electrophoresis. Despite no change in MHC composition of Wistar rat skeletal muscles with HF, the mRNA relative expression of MyoD in Sol and EDL muscles and that of MRF4 in Sol muscle were significantly reduced, whereas myogenin was not changed in both muscles. This down-regulation in the mRNA relative expression of MRF4 in Sol was associated with atrophy in response to HF while these alterations were not present in EDL muscle. Taken together, our results show a potential role for MRFs in skeletal muscle myopathy during HF.

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O objetivo deste estudo foi o de verificar os aspectos fisiológicos envolvidos na interação entre o treinamento de endurance e hipertrofia muscular e se estas modalidades devem ou não ser realizadas na mesma sessão de treinamento. O treinamento de hipertrofia e endurance realizado na mesma sessão parece inibir o desenvolvimento muscular comparado ao treinamento de hipertrofia realizado isoladamente. Algumas hipóteses foram propostas para explicar tal fenômeno, tais como a incapacidade do músculo esquelético de se adaptar metabólica e morfologicamente às duas modalidades de treinamento realizadas numa única sessão, alteração do padrão de recrutamento de unidades motoras pela depleção de glicogênio e cálcio, e ativação do sistema proteolítico cálcio-dependente de calpaínas. Concluímos que as modalidades de treinamento de hipertrofia e endurance apresentam diferentes aspectos de adaptação muscular. Assim, a hipertrofia muscular é mais pronunciada quando a sessão de treino é restrita a apenas uma modalidade de treinamento.

The purpose of this study was to verify the physiological aspects involved in the interaction between endurance training and muscular hypertrophy and if those modalities should or should not be performed in the same training session. The hypertrophy and endurance training performed in the same training session seems to inhibit the muscular development compared with hypertrophy training alone. Some hypotheses have been proposed to explain such phenomenon, such as the incapacity of skeletal muscle to adapt metabolically and morphologically to both training modalities, alteration in the motor unit recruitment pattern due to glycogen and calcium depletion, and activation of the proteolytic calcium-dependent calpain system. In conclusion, the training modalities of hypertrophy and endurance presents different muscular adaptation. Thus, muscular hypertrophy is more pronounced when the training session is restricted to a single modality of training.

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Rat skeletal muscle contains up to four myosin isoforms. Analysis of single muscle fibers has identified type I, IIA, IID and IIB fibers containing type I, IIa, IId and IIb myosin isoforms, respectively. Hybrid fibers have at least two myosin isoforms, such as myosin heavy chain (MHC) I+MHCIIa, MHCIIa+ MHCIId or MHCIId+ MHCIIb. These fiber types are identified as IC, IIC, IIAD, IIDA, IIDB or IIBD. The muscles of C57BL6J mice have not been extensively characterized, especially with regard to the presence and composition of hybrid fibers. The aim of this study was to examine the fiber composition of the soleus (SOL), extensor digitorum longus (EDL), tibialis anterior (TA) and gastrocnemius (GAS) muscle of C57BL6J mice using histochemical and biochemical methods. The SOL muscle contained type I fiber poncentage, median +- semi amplitude, (37, 42 +- 8, 20 per cent), IIa (38, 62 +- 6, 81 per cent), IIAD (18, 74 +- 6, 95 per cent) and IIAD (5, 69 +- 3, 09 per cent) fibers. The EDL had type I (0, 44 +- 1, 27 per cent), IC/IIC (3, 05 +- 3, 49 per cent), IIA (0, 46 +- 0, 68 per cent), IIAD (7, 56 +- 4, 51 per cent), IID (0, 46 +- 1, 34 per cent), IIDB (21, 48 +- 7, 33 per cent) and IIB (66, 01 +- 8, 51 per cent) fibers. The Ta muscle also showed a predominance of type IIB (59 ,68 +- 9, 95 per cent) and IIDB (33, 83 +- 15, 85 per cent) fibers followed by type IIAD (3, 42 +- 4, 87 per cent), IID (2, 25 +- 1, 64 per cent), IIA (1, 12 +- 2, 17 per cent), I (0, 17 +- 1, 25 per cent) and IC/IIC (0, 008 +- 1, 04 per cent) fibers. The GAS muscle had type IIB (54, 42 +- 8, 11 per cent), IIDB (19, 37 +- 2, 98 per cent), IID (2, 26 +- 2, 24 per cent), IIAD (12, 40 +- 2 ,34 per cent), IIA (5, 73 +- 3, 24 per cent) and I (5, 74 +- 2, 55 per cent) fibers. Thus, the SOL muscles of C57BL6J mice had predominantly type IIA fibers, unlike rats in which almost all of the fibers are type I. The EDL, TA and GAS muscles had prenominantly IIB and IIDB fibers as in rats.

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The purpose of this investigation was to determine whether changes in myosin heavy chain (MHC) expression and atrophy in rat skeletal muscle are observed during transition from cardiac hypertrophy to chronic heart failure (CHF) induced by aortic stenosis (AS). AS and control animals were studied 12 and 18 weeks after surgery and when overt CHF had developed in AS animals, 28 weeks after the surgery. The following parameters were studied in the soleus muscle: muscle atrophy index (soleus weight/body weight), muscle fibre diameter and frequency and MHC expression. AS animals presented decreases in both MHC1 and type I fibres and increases in both MHC2a and type IIa fibres during late cardiac hypertrophy and CHF. Type IIa fibre atrophy occurred during CHF. In conclusion, our data demonstrate that skeletal muscle phenotype changes occur in both late cardiac hypertrophy and heart failure; this suggests that attention should be given to the fact that skeletal muscle phenotype changes occur prior to overt heart failure symptoms.

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