Intense resistance training induces pronounced metabolic stress and impairs hypertrophic response in hind-limb muscles of rats

Skeletal muscle hypertrophy is an exercise-induced adaptation, particularly in resistance training (RT) programs that use large volumes and low loads. However, evidence regarding the role of rest intervals on metabolic stress and muscular adaptations is inconclusive. Thus, we aimed to investigate the effects of a strenuous RT model (jump-training) on skeletal muscle adaptations and metabolic stress, considering the scarce information about RT models for rats. We hypothesized that jump-training induces metabolic stress and influences negatively the growth of soleus (SOL) and extensor digitorum longus (EDL) muscles of rats. Male Wistar rats (aged 60 days) were randomly assigned to non-trained or trained groups (n = 8/group). Trained rats performed jump-training during 5 days a week for 1, 3, or 5 weeks with 30 s of inter-set rest intervals. Forty-eight hours after the experimental period, rats were euthanized and blood samples immediately drawn to measure creatine kinase activity, lactate and corticosterone concentrations. Muscle weight-to-body weight ratio (MW/BW), cross-sectional area (CSA) and myosin heavy chain (MHC) isoform expression were determined. Higher lactate levels occurred after 20 min of training in weeks 1 and 3. Corticosterone levels were higher after 5 weeks of training. Jump-training had negative effects on hypertrophy of types-I and II muscle fibers after 5 weeks of training, as evidenced by decreased CSA and reduced muscle weight. Our results demonstrated that pronounced metabolic stress and impairment of muscle growth might take place when variables of exercise training are not appropriately manipulated. Lay summary Resistance training (RT) has been used to increase muscle mass. In this regard, training variables (intensity, volume, and frequency) must be strictly controlled in order to evoke substantial muscular fitness. This study shows that rats submitted to 5 weeks of intensive resistance jump-training - high intensity, large volume, and short rest intervals - present high levels of blood corticosterone associated with negative effects on hypertrophy of types-I and II muscle fibers223377386FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2005/60284-

EFFECTS of CREATINE SUPPLEMENTATION DURING RESISTANCE TRAINING on MYOSIN HEAVY CHAIN (MHC) EXPRESSION IN RAT SKELETAL MUSCLE FIBERS

Aguiar, AF, Aguiar, DH, Felisberto, ADS, Carani, FR, Milanezi, RC, Padovani, CR, and Dal-Pai-Silva, M. Effects of creatine supplementation during resistance training on mysoin heavy chain (MHC) expression in rat skeletal muscle fibers. J Strength Cond Res 24(1): 88-96, 2010-The purpose of this study was to utilize a rodent model to test the hypothesis that creatine (Cr) supplementation during resistance training would influence the pattern of slow-twitch muscle myosin heavy chain (MHC) isoforms expression. Male Wistar rats (2-3 months old, 250300 g) were divided into 4 groups: Nontrained without creatine supplementation (CO), nontrained with creatine supplementation (CR), trained without creatine supplementation (TR), and trained with creatine supplementation (TRCR). TR and TRCR groups were submitted to a resistance training program for 5 weeks (5 days/week) for morphological and biochemical analysis of the soleus muscle. Weightlifting exercise involved jump sessions into water, carrying progressive overload equivalent to percentage of body weight. CR and TRCR groups were given creatine at 0.5 g/kg(-1)/d(-1). Both Cr supplementation and resistance training alone or associated did not result in significant alterations (p > 0.05) in body weight gain, food intake, and muscle weight in the CR, TR and TRCR groups compared to the CO group. Also compared to the CO group, the CR group showed a significant (p 0.05) changes in MHC content of the TRCR group compared to the CO group. The data show that Cr supplementation provides a potential action to abolish the exercise-induced MHC isoform transitions from slow to fast in slow-twitch muscle. Thus, Cr supplementation might be a suitable strategy to maintaining a slow phenotype in slow muscle during resistance training, which may be favorable to maintenance of muscle oxidative capacity of endurance athletes.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Tipos de miosinas de linhagens de frangos de corte criados em sistemas de confinamento e semiconfinamento Types of myosin of chickens of different strains reared in confinement and semi-confinement systems

O objetivo neste trabalho foi avaliar o peso vivo, o peso de pernas, os aspectos morfológicos das fibras musculares do músculo flexor longo do hálux e o perfil eletroforético das miosinas de cadeia pesada de quatro linhagens de frangos de corte criados nos sistemas de confinamento e semiconfinamento. Foram utilizados 1.440 pintos distribuídos em delineamento inteiramente casualisado em esquema fatorial 4 &#215; 2, composto de quatro linhagens (Ross 305, Máster Gris, Label Rouge e Vermelhão Pesado) e dois sistemas de criação (confinamento e semiconfinamento), cada combinação avaliada com quatro repetições. Aos 28 e 84 dias de idade, foram abatidas quatro aves por tratamento, totalizando 64 aves. A eletroforese identificou a presença das três isoformas de miosinas, tipo MyHC-I, MyHC-IIa e MyHC-IIb, no músculo flexor longo do hálux dos frangos de corte. Com aumento da idade, a isoforma de miosina MyHC-II aumenta, enquanto a MyHC-I diminui. Somente aos 84 dias de idade, a expressão das isoformas de miosina do tipo MyHC-II foram influenciadas pela linhagem, confirmando o reflexo da seleção na linhagem Ross no músculo mais glicolítico.A linhagem Ross apresenta maior peso vivo, peso de perna, peso e área do músculo flexor longo do hálux em comparação às linhagens tipo caipira.<br>The objective was to evaluate body weight, leg weight and morphologic aspects of the muscle fibers of the flexor hallucis longus muscle and electrophoretic profile of myosin heavy chain of four strains of broilers, reared in confinement and semi-confinement systems. 1440 chicks were randomly assigned in a 4 &#215; 2 factorial arrangement: four strains (Ross 305, Master Gris, Label Rouge and Vermelhao Pesado), two production systems (confinement and semi-confinement), with four replicates for each treatment. Four birds were sacrificed for each treatment, at 28 and 84 d, totaling 64 animals. Electrophoresis technique identified the presence of three myosin heavy chain types: MyHC-I, MyHC-IIa and MyHC-IIb, in the flexor hallucis longus muscle of the broilers. There was increase in MyHC-II and decrease in MyHC-I, as age passed. Only at 84 days-old was the MyHC-II expression influenced by strain, confirming a response of selection in Ross lineage on a more glycolytic muscle. The Ross lineage has higher live weight, leg weight, weight and area of the flexor hallucis longus, compared to different chicken strains