Effect of different rest intervals, between sets, on muscle performance during leg press exercise, in trained older women

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Efeito de diferentes intervalos de recuperação entre as séries sobre o desempenho muscular no exercício leg-press em idosas não treinadas

OBJETIVO: Verificar a influência de dois diferentes intervalos de recuperação (IR) entre as séries no exercício leg-press sobre o número e sustentabilidade das repetições e no volume total, em idosas não treinadas. MÉTODOS: Onze idosas (66,5 ± 5,0 anos; 59,2 ± 9,1kg; 146,4 ± 34,9cm) foram submetidas a duas sessões experimentais de exercícios com pesos com intensidade de 15 repetições máximas. Cada sessão experimental foi composta por três séries realizadas até a fadiga muscular utilizando IR de um (IR-1) ou três minutos (IR-3). As sessões experimentais foram separadas por, no mínimo, 48 horas. Todas as participantes realizaram ambos os protocolos e um delineamento cross-over balanceado foi utilizado para determinar a ordem das sessões experimentais. RESULTADOS: Para ambos os IR entre as séries, reduções significativas (P < 0,05) no número e na sustentabilidade das repetições foram observadas da primeira para a segunda e terceira séries e da segunda para a terceira séries. Diferenças significativas (P < 0,05) entre os IR foram observadas nas duas séries finais. O volume total da sessão realizada com IR-3 foi estatisticamente superior (20,4%; P < 0,05) quando comparada a sessão IR-1. CONCLUSÃO: O número e a sustentabilidade das repetições e o volume total de treino de idosas não treinadas são influenciados pelo IR empregado entre as séries. Maiores IR devem ser utilizados quando a finalidade for otimizar o volume de treino por meio da sustentabilidade das repetições. Em contrapartida, menores IR devem ser utilizados quando a meta for obter maiores níveis de fadiga muscular.

Análise dos receptores de acetilcolina (nAChRs) na musculatura esquelética de ratos com insuficiência cardíaca submetidos ao treinamento aeróbico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Alongamento estático, envelhecimento e desempenho neuromuscular

Pós-graduação em Ciências da Motricidade - IBRC

Discriminant analysis of neuromuscular variables in chronic low back pain

Background: Investigation and discrimination of neuromuscular variables related to the complex aetiology of low back pain could contribute to clarifying the factors associated with symptoms. Objective: Analysing the discriminative power of neuromuscular variables in low back pain. Methods: This study compared muscle endurance, proprioception and isometric trunk assessments between women with low back pain (LBP, n=14) and a control group (CG, n=14). Multivariate analysis of variance and discriminant analysis of the data were performed. Results: The muscle endurance time (s) was shorter in the LBP group than in the CG (p=0.004) with values of 85.81 (37.79) and 134.25 (43.88), respectively. The peak torque (Nm/kg) for trunk extension was 2.48 (0.69) in the LBP group and 3.56 (0.88) in the GG (p=0.001); for trunk flexion, the mean torque was 1.49 (0.40) in the LBP group and 1.85 (0.39) in the CG (p=0.023). The repositioning error (degrees) before the endurance test was 2.66 (1.36) in the LBP group and 2.41 (1.46) in the CG (p=0.664), and after the endurance test, it was 2.95 (1.94) in the LBP group and 2.00 (1.16) in the CG (p=0.06). Furthermore, the variables showed discrimination between the groups (p=0.007), with 78.6% of the individuals with low back pain correctly classified in the LBP group. In turn, variables related to muscle activation showed no difference in discrimination between the groups (p=0.369). Conclusion: Based on these findings, the clinical management of low back pain should consist of both resistance and strength training, particularly in the extensor muscles.

Avaliação de parâmetros de desempenho muscular em jovens sedentárias com dor lombar

Pós-graduação em Desenvolvimento Humano e Tecnologias - IBRC

Electromyographic fatigue threshold of erector spinae muscle induced by a muscular endurance test in health men

Purpose: To identify the electromyographic fatigue threshold in the erector spinae muscle. Methods: Eight 19 to 24-year-old male volunteers participated in this study, in which surface electrodes were used, as well as a biological signals acquisition module (Lynx) with a sampling frequency of 1000Hz, a 1000 times gain, a 20Hz high pass filter and a 500Hz low pass filter. The test consisted of repeated isometric contractions of the erector spinae muscle in a 45° hip flexion posture, with 30%, 40%, 50% and 60% of the maximum voluntary isometric contraction. Results: A positive correlation of the RMS (root mean square) value as a function of time was found for most of the subjects with 40% (N = 6), 50% (N = 7) and 60% (N = 8) loads of the maximum voluntary isometric contraction. Conclusions: It was concluded, from this study, that the proposed protocol provides evidence, through the electromyographic signal, of the development of fatigue in the erector spinae muscle with loads of 40%, 50% and 60% of the maximum voluntary isometric contraction. The protocol also allows the electromyographic fatigue threshold and its probable applicability in the diagnosis of this phenomenon during repetitive activities to be determined.

Effects of elbow flexor muscle resistance training on strength, endurance and perceived exertion

Purpose. To verify the effects of resistance training at the electromyographic fatigue threshold (EMGFT) based on one-repetition maximum strength (1RM), heart rate (HR), rate of perceived exertion (PE) and endurance time (EndT). Methods. Nineteen subjects (training group [TG]: n = 10; control group [CG]: n = 9), performed 1-min bicep curl exercises sets at 25%, 30%, 35% and 40% 1RM. Electromyography (biceps brachii and brachiorradialis), HR and PE were registered. Biceps brachii EMGFT was used to create a load index for an eight-week resistance training programme (three sets until exhaustion/session, two sessions/week) for the TG. The CG only attended one session in the first week and another session in the last week of the eight-week training period for EndT measurement. EndT was determined from the number of repetitions of each of the three sets performed in the first and last training sessions. After training, 1RM, EMGFT, EndT, HR and PE at the different bicep curl load intensities were again measured for both groups. Results. Increases in 1RM (5.9%, p < 0.05) and EndT (> 60%, p < 0.001) after training were found. In addition, PE was reduced at all load intensities (p < 0.05), while no changes were found for HR and EMGFT after training. Conclusions. Strength-endurance training based on the EMGFT improved muscular endurance and also, to a lesser extent, muscular strength. Moreover, the reduced levels of physical exertion after training at the same intensity suggest that endurance training exercises may improve comfort while performing strength exercises.

Alterations in muscular enzymes of horses competing long-distance endurance rides under tropical climate

Estudaram-se as alterações de atividade das enzimas musculares creatino quinase (CK), lactato desidrogenase (LDH) e aspartato aminotransferase (AST) em um grupo de cavalos que utilizados em provas de enduro de 70 e 100km de distância, em cinco competições. Os valores (U/l) basais (antes da largada) foram 245,13±9,84 para CK, 496,61±14,76 para LDH e 328,95±8,65 para AST. Todas as atividades das enzimas decresceram no primeiro momento das provas (~30km). Valores de pico, significativamente diferentes, foram alcançados para CK (413,59±50,75) imediatamente após 70km de distância; 24 horas após para LDH (628,61±33,30); e 48 horas após as provas para AST (389,89±16,96). A monitoração do período de recuperação revelou diferente comportamento entre as concentrações enzimáticas com CK retornando aos valores basais 24 horas pós-provas (279,61 ± 23,05). LDH e AST retornaram aos valores basais, 72 horas pós-provas (505,25±33,78 e 359,35±24,90, respectivamente). Os dados obtidos revelaram diferentes alterações na concentração de enzimas musculares de cavalos de enduro, diretamente relacionadas com a duração do esforço.

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

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Endurance training improves responsiveness to insulin and modulates insulin signal transduction through the phosphatidylinositol 3-kinase/Akt-1 pathway

Background: Endurance training increases insulin-stimulated muscle glucose transport and leads to improved metabolic control in diabetic patients.Objective: To analyze the effects of endurance training on the early steps of insulin action in muscle of rats. Design: Male rats submitted to daily swimming for 6 weeks were compared with sedentary controls. At the end of the training period, anesthetized animals received an intravenous (i.v.) injection of insulin and had a fragment of their gastrocnemius muscle excised for the experiments.Methods: Associations between insulin receptor, insulin receptor substrates (IRS)-1 and -2 and phosphatidylinositol 3-kinase (PI3-kinase) were analyzed by immunoprecipitation and immunoblotting. Akt-1 serine phosphorylation and specific protein quantification were detected by immunoblotting of total extracts, and IRS-1/IRS-2-associated PI3-kinase activity were determined by thin-layer chromatography.Results: Insulin-induced phosphorylation of IRS-1 and IRS-2 increased respectively by 1.8-fold (P < 0.05) and 1.5-fold (P < 0.05), whereas their association with PI3-kinase increased by 2.3-fold (P < 0.05) and 1.9-fold (P < 0.05) in trained rats as compared with sedentary controls, respectively. The activity of PI3-kinase associated with IRS-1 and IRS-2 increased by 1.8-fold (P < 0.05) and 1.7-fold (P < 0.05) respectively, in trained rats as compared with their untrained counterparts. Serine phosphorylation of Akt-1/PKB increased 1.7-fold (P < 0.05) in trained rats in response to insulin. These findings were accompanied by increased responsiveness to insulin as demonstrated by a reduced area under the curve for insulin during an i.v. glucose tolerance test, by increased glucose disappearance rate during an insulin tolerance test, and by increased expression of glucose transporter-4.Conclusions: the increased responsiveness to insulin induced by chronic exercise in rat skeletal muscle may result, at least in part, from the modulation of the insulin signaling pathway at different molecular levels.

Back extensor muscle fatigue at submaximal workloads assessed using frequency banding of the electromyographic signal

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Relação da potência aeróbica máxima e da força muscular com a economia de corrida em atletas de endurance

The objective of this study was to analyze the relationship of maximal aerobic power and the muscular strength (maximal isotonic strength and vertical jump explosive power) with the running economy (RE) in endurance athletes. Twenty-six male runners (27.9 ± 6.4 years; 62.7 ± 4.3 kg; 168.6 ± 6.1 cm; 6.6 ± 3.1% of body fat) performed in different days the following tests: a) incremental test to determine the maximal oxygen uptake (V̇O2max) and the intensity corresponding to the V̇O2max (IV̇O2max); b) constant-velocity treadmill run to determine RE; c) 1-RM test in the leg press and; d) maximal vertical jump test (VJ). V̇O2max (63.8 ± 8.3 ml/kg/min) was significantly correlated (r = 0.63; p < 0.05) with RE (48.0 ± 6.6 ml/kg/min). However, the IV̇O2max (18.7 ± 1.1 km/h), the maximal isotonic strength (230.3 ± 41.2 kg) and the VJ (30.8 ± 3.8 cm) were not significantly correlated with RE. One concludes that the maximal aerobic power can explain in part the inter-individual RE variability in endurance athletes. However, maximal isotonic strength and explosive strength seem not to be associated with RE values observed in this group of athletes.

Electromyographic fatigue threshold of the biceps brachii: The effect of endurance time

Muscle fatigue can be a limiting factor to determine index as the electromyographic fatigue threshold (EMGFT) due the alterations in motivation and disconfots. This way, the purpose of this study was to identify the right biceps brachii and left biceps brachii obtained from repetitive elbow flexions at each 10% of total time. Nine healthy subjects performed the exercise named biceps curl until exhaustion with 25%, 35%, and 45% of one repetition maximum, in three different days. EMG amplitude (root mean square - RMS) was obtained for concentric contractions during these load levels and correlated with time to determine the slope values for each load and them detemine the EMGFT. The EMGFT was obtained within of each 10% of total time and they were compared by analysis of variance. The results showed a progressive increase in RMS with time, for both muscles in all loads, characterizing the muscle fatigue process, and for the EMGFT values ware not found predominantly significant differences between the execution time, as well as between muscles (right biceps × left biceps). This protocol allowed to identify the EMGFT to both muscles during the biceps curl, which was similar at different percentage of total time, indicating the possibility to reduce the length of the contraction test without the need to maintain the contraction until exhaustion. Further studies are needed to evaluate the applicability of this method to determining the effects on performance.

Glycogen storage and muscle glucose transporters (GLUT-4) of mice selectively bred for high voluntary wheel running

To examine the evolution of endurance-exercise behaviour, we have selectively bred four replicate lines of laboratory mice (Mus domesticus) for high voluntary wheel running ('high runner' or HR lines), while also maintaining four non-selected control (C) lines. By generation 16, HR mice ran ∼2.7-fold more than C mice, mainly by running faster (especially in females), a differential maintained through subsequent generations, suggesting an evolutionary limit of unknown origin. We hypothesized that HR mice would have higher glycogen levels before nightly running, show greater depletion of those depots during their more intense wheel running, and have increased glycogen synthase activity and GLUT-4 protein in skeletal muscle. We sampled females from generation 35 at three times (photophase 07:00 h-19:00 h) during days 5-6 of wheel access, as in the routine selection protocol: Group 1, day 5, 16:00 h-17:30 h, wheels blocked from 13:00 h; Group 2, day 6, 02:00 h-03:30 h (immediately after peak running); and Group 3, day 6, 07:00 h-08:30 h. An additional Group 4, sampled 16:00 h-17:30 h, never had wheels. HR individuals with the mini-muscle phenotype (50% reduced hindlimb muscle mass) were distinguished for statistical analyses comparing C, HR normal, and HR mini. HR mini ran more than HR normal, and at higher speeds, which might explain why they have been favored by the selective-breeding protocol. Plasma glucose was higher in Group 1 than in Group 4, indicating a training effect (phenotypic plasticity). Without wheels, no differences in gastrocnemius GLUT-4 were observed. After 5 days with wheels, all mice showed elevated GLUT-4, but HR normal and mini were 2.5-fold higher than C. At all times and irrespective of wheel access, HR mini showed approximately three-fold higher [glycogen] in gastrocnemius and altered glycogen synthase activity. HR mini also showed elevated glycogen in soleus when sampled during peak running. All mice showed some glycogen depletion during nightly wheel running, in muscles and/or liver, but the magnitude of this depletion was not large and hence does not seem to be limiting to the evolution of even-higher wheel running.