Neuromuscular electrical stimulation improves skeletal muscle regeneration through satellite cell fusion with myofibers in healthy elderly subjects.

The aim of this study was to determine whether neuromuscular electrical stimulation (NMES) affects skeletal muscle regeneration through a reduction of oxidative status in satellite cells of healthy elderly subjects. Satellite cells from the vastus lateralis skeletal muscle of 12 healthy elderly subjects before and after 8 wk of NMES were allowed to proliferate to provide myogenic populations of adult stem cells [myogenic precursor cells (MPCs)]. These MPCs were then investigated in terms of their proliferation, their basal cytoplasmic free Ca2+ concentrations, and their expression of myogenic regulatory factors (PAX3, PAX7, MYF5, MYOD, and MYOG) and micro-RNAs (miR-1, miR-133a/b, and miR-206). The oxidative status of these MPCs was evaluated through superoxide anion production and superoxide dismutase and glutathione peroxidase activities. On dissected single skeletal myofibers, the nuclei were counted to determine the myonuclear density, the fiber phenotype, cross-sectional area, and tension developed. The MPCs obtained after NMES showed increased proliferation rates along with increased cytoplasmic free Ca2+ concentrations and gene expression of MYOD and MYOG on MPCs. Muscle-specific miR-1, miR-133a/b, and miR-206 were upregulated. This NMES significantly reduced superoxide anion production, along with a trend to reduction of superoxide dismutase activity. The NMES-dependent stimulation of muscle regeneration enhanced satellite cell fusion with mature skeletal fibers. NMES improved the regenerative capacity of skeletal muscle in elderly subjects. Accordingly, the skeletal muscle strength and mobility of NMES-stimulated elderly subjects significantly improved. NMES may thus be further considered for clinical or ageing populations.NEW & NOTEWORTHY The neuromuscular electrical stimulation (NMES) effect on skeletal muscle regeneration was assessed in healthy elderly subjects for the first time. NMES improved the regenerative capacity of skeletal muscle through increased myogenic precursor cell proliferation and fusion with mature myofibers. The increased cytoplasmic free Ca2+ concentration along with MYOD, MYOG, and micro-RNA upregulation could be related to reduced O2·- production, which, in turn, favors myogenic regeneration. Accordingly, the skeletal muscle strength of NMES-stimulated lower limbs of healthy elderly subjects improved along with their mobility.

Five-Kilometers Time Trial: Preliminary Validation of a Short Test for Cycling Performance Evaluation.

BACKGROUND: The five-kilometer time trial (TT5km) has been used to assess aerobic endurance performance without further investigation of its validity. OBJECTIVES: This study aimed to perform a preliminary validation of the TT5km to rank well-trained cyclists based on aerobic endurance fitness and assess changes of the aerobic endurance performance. MATERIALS AND METHODS: After the incremental test, 20 cyclists (age = 31.3 ± 7.9 years; body mass index = 22.7 ± 1.5 kg/m(2); maximal aerobic power = 360.5 ± 49.5 W) performed the TT5km twice, collecting performance (time to complete, absolute and relative power output, average speed) and physiological responses (heart rate and electromyography activity). The validation criteria were pacing strategy, absolute and relative reliability, validity, and sensitivity. Sensitivity index was obtained from the ratio between the smallest worthwhile change and typical error. RESULTS: The TT5km showed high absolute (coefficient of variation < 3%) and relative (intraclass coefficient correlation > 0.95) reliability of performance variables, whereas it presented low reliability of physiological responses. The TT5km performance variables were highly correlated with the aerobic endurance indices obtained from incremental test (r > 0.70). These variables showed adequate sensitivity index (> 1). CONCLUSIONS: TT5km is a valid test to rank the aerobic endurance fitness of well-trained cyclists and to differentiate changes on aerobic endurance performance. Coaches can detect performance changes through either absolute (± 17.7 W) or relative power output (± 0.3 W.kg(-1)), the time to complete the test (± 13.4 s) and the average speed (± 1.0 km.h(-1)). Furthermore, TT5km performance can also be used to rank the athletes according to their aerobic endurance fitness.

Detection of the Lactate Threshold in Runners: What is the Ideal Speed to Start an Incremental Test?

Incremental tests on a treadmill are used to evaluate endurance athletes; however, no criterion exists to determine the intensity at which to start the test, potentially causing the loss of the first lactate threshold. This study aimed to determine the ideal speed for runners to start incremental treadmill tests. The study consisted of 94 runners who self-reported the average speed from their last competitive race (10-42.195 km) and performed an incremental test on a treadmill. The speeds used during the first three test stages were normalised in percentages of average competition speed and blood lactate concentration was analysed at the end of each stage. The relationship between speed in each stage and blood lactate concentration was analysed. In the first stage, at an intensity corresponding to 70% of the reported average race speed, only one volunteer had blood lactate concentration equal to 2 mmol·L(-1), and in the third stage (90% of the average race speed) the majority of the volunteers had blood lactate concentration ≥2 mmol·L(-1). Our results demonstrated that 70% of the average speed from the subject's last competitive race - from 10 to 42.195 km - was the best option for obtaining blood lactate concentration <2 mmol·L(-1) in the first stage, however, 80% of the average speed in marathons may be a possibility. Evaluators can use 70% of the average speed in competitive races as a strategy to ensure that the aerobic threshold intensity is not achieved during the first stage of incremental treadmill tests.

The psychobiological model: a new explanation to intensity regulation and (in)tolerance in endurance exercise

The mechanisms underpinning fatigue and exhaustion, and the specific sources of exercise-endurance intensity regulation and (in)tolerance have been investigated for over a century. Although several scientific theories are currently available, over the past five years a new framework called Psychobiological model has been proposed. This model gives greater attention to perceptual and motivational factors than its antecedents, and their respective influence on the conscious process of decision-making and behavioral regulation. In this review we present experimental evidences and summarize the key points of the Psychobiological model to explain intensity regulation and (in)tolerance in endurance exercise. Still, we discuss how the Psychobiological model explains training-induced adaptations related to improvements in performance, experimental manipulations, its predictions, and propose future directions for this investigative area. The Psychobiological model may give a new perspective to the results already published in the literature, helping scientists to better guide their research problems, as well as to analyze and interpret new findings more accurately...

Os mecanismos que explicam fadiga e exaustão, controle da intensidade e (in)tolerância ao exercício de resistência cardiorrespiratória têm sido estudados há mais de um século. Apesar de diversas teorias científicas atualmente disponíveis, nos últimos cinco anos um novo modelo chamado de Psicobiológico tem sido proposto. Este modelo dá maior importância aos fatores perceptuais e motivacionais em relação aos seus antecessores, bem como a respectiva influência destes fatores no processo consciente de tomada de decisão e controle comportamental. Nesta revisão, nós apresentamos evidências experimentais e sintetizamos os pontos chaves do modelo Psicobiológico que explicam o controle da intensidade e (in)tolerância ao exercício de resistência cardiorrespiratória. Adicionalmente, nós discutimos como o modelo explica as adaptações ao treinamento relacionadas à melhora no desempenho, as manipulações experimentais e suas predições. Ao final, propomos futuras direções para esta área investigativa. O modelo Psicobiológico pode proporcionar uma nova perspectiva aos resultados anteriormente publicados na literatura, ajudando os cientistas a entenderem melhor seus problemas de pesquisa, assim como analisar e interpretar novas evidências mais precisamente...

Respostas neuromusculares dos membros inferiores durante protocolo intermitente de saltos verticais em voleibolistas / Neuromuscular responses of the lower limb muscles during vertical jumping in volleyball athletes

O objetivo deste estudo foi analisar o desempenho e as respostas eletromiográficas dos músculos Reto Femoral, Bíceps Femoral e Gastrocnêmio Medial durante protocolo de saltos verticais. Participaram 13 voleibolistas do sexo feminino (15,6 ± 0,9 anos). Inicialmente foi realizado um protocolo de potência máxima (três saltos máximos), seguido do protocolo de resistência de saltos (ciclos de três saltos máximos em aproximadamente 10 segundos (s) – um salto a cada três s, com recuperação de 15 s). O tempo de duração do protocolo de resistência foi de 20 minutos. Foi usada a técnica do salto com contramovimento sem ajuda dos braços, sobre tapete de contato. Para tratamento dos dados os saltos foram divididos em quatro períodos com 12 ciclos cada um. Os resultados mostraram queda na altura dos saltos de aproximadamente 1,3cm entre os períodos de 1 a 4, sendo que, essa queda foi mais significativa nos 3º e 4º períodos em comparação ao 1º e 2º. Entretanto, com relação às variáveis RMS e FM, não ocorreu alteração nas respostas eletromiográficas entre músculos e períodos. Concluiu-se, assim, que a fadiga pode depender de variáveis psicofisiológicas, ao nível do SNC, que também influem no desempenho.

The purpose of this study was to analyze the performance and the electromyographic responses of the muscles Rectus Femoris, Biceps Femoris and Gastrocnemius Medialis during vertical jumping protocol. Participated 13 female volleyball players (15,6 ± 0,9 years). Initially was performed a protocol of maximum power (three maximum jumps), followed by resistance jumps protocol (cycles of three maximum jumps in about 10 seconds (s) – one jump every three s, with recovery of 15s. The duration of resistance protocol was 20 minutes. Technique used was countermovement jump without the aid of arms on a mat of contact. The data collected during the jumps were divided into four periods containing 12 cycles each. The results showed a decrease in the height of the jumps of about 1,3cm between the periods from 1 to 4, and this decrease was more significant in the 3rd and 4th periods compared with the 1st and 2nd. However, with respect to the variables RMS and FM, a change did not occur in the electromyographic responses between muscles and periods. It was concluded that fatigue may depend of the psychophysiological variables, the level of the CNS, which also influence the performance.

Resposta da frequência cardíaca durante sessão de treinamento de karatê / Heart rate response during a karate training session

A prática do karatê pode promover adaptações benéficas sobre os componentes da aptidão física relacionada com a saúde. Dentre esses componentes, o consumo máximo de oxigênio (VO2max) é um importante indicador de aptidão cardiorrespiratória, como também forte preditor de risco de morte por doença cardiovascular. Estudos anteriores avaliaram as respostas da Frequência Cardíaca na modalidade de karatê durante protocolos elaborados pelos pesquisadores que simularam o treinamento. No entanto, esses resultados devem ser interpretados com cautela, uma vez que protocolos podem comprometer a validade ecológica do comportamento da FC. Dessa forma, o objetivo deste estudo foi, através do monitoramento da FC, investigar a distribuição da intensidade durante uma sessão de treinamento de karatê (ST) com a validade ecológica preservada. Nove atletas (M (DP) = 22 (5,2) anos; 60,3 (12,9) kg; 170,0 (0,10) cm; 11,6 (5,7) % gordura) realizaram teste incremental máximo (T I) e uma ST, com monitoramento contínuo da FC, distribuída posteriormente conforme método proposto por Edwards. O tempo médio de duração da ST foi de 91,3 (11,9) minutos (IC95% = 82,0 - 100,5). Os valores de FC média e máxima da ST foram equivalentes a 72% (IC95% = 66-78%) e 94% (IC95% = 89-99%) da FC máxima alcançada durante T I (FCmax), respectivamente. Durante 79,9% (IC95% = 65,7-94,1%) do tempo total da ST, os karatecas permaneceram em uma intensidade superior a 60% da FCmax. Deste modo, conclui-se que a intensidade da ST de karatê atende às recomendações do ACSM com relação à intensidade, duração e frequência semanal, apresentando-se como uma interessante alternativa de exercícios físicos para promoção da aptidão cardiorrespiratória.

Karate practice can promote beneficial adaptations on the health-related components of physical fitness. Among the components, the maximum oxygen uptake (VO2max) is an important indicator of cardiorespiratory fitness, as it is also a strong and independent predictor of the risk of death from cardiovascular disease and all other causes. Previous studies have evaluated the heart rate (HR) responses in the karate modality during protocols elaborated by researchers who simulated training. However, the results should be carefully interpreted, since elaborated protocols can compromise the ecological validity of the HR behavior. Thus, the aim of the study was to monitor the HR to investigate the distribution of intensity during a karate training session (TS) with ecological validity preserved. Nine athletes (M (SD) = 22 (5.2) years; 60.3 (12.9) weight; 170.0 (0.10) height; 170.0 (0.10) cm; 11.6 (5.7) % fat) performed a maximal incremental test (IT) and one TS with continuous HR monitoring, subsequently distributed by Edward´s method. The mean TS duration was 91.3 (11.9) min (IC95% = 82.0 - 100.5). The values of average and maximum HR of the TS were equivalent to 72 % (IC95% = 66 - 78 %) and 94 % (IC95% = 89 - 99 %) respectively, of maximum HR reached in the incremental test (HRmax). During 79.9 % (IC95% = 65.7 - 94.1 %) of the total time of TS the athletes remained at intensity above 60% of HRmax. Thus, it was concluded that the TS lies within the ACSM recommendations concerning intensity, duration and weekly frequency, presenting itself as an interesting alternative of exercise to promote cardiorespiratory fitness.

O nível de treinamento não influencia a percepção subjetiva de esforço durante um teste incremental / Training level does not influence the rating of perceived exertion during an incremental test

Níveis de treinamento distintos, associados à experiência em realizar esforços exaustivos podem produzir diferentes sensações frente à fadiga. O objetivo deste estudo foi comparar a percepção subjetiva de esforço (PSE) entre ciclistas e não-ciclistas durante teste incremental máximo (TIMAX). Participaram do estudo 23 indivíduos que foram divididos em grupo ciclistas (GC) (n = 12; idade 26,5 ± 4,7 anos; massa corporal 68,2 ± 11kg; estatura 176 ± 8,6cm) e grupo não-ciclistas (GNC) (n=11; idade 25,2 ± 4,0 anos; massa corporal 72,9 ± 9kg; estatura 175,1 ± 6,3cm). Todos realizaram um TIMAX, até a exaustão, do tipo rampa em ciclossimulador, com início a 0 W e incrementos de 20 W.min-1. Durante TIMAX a PSE foi aferida e anotada a cada 30 segundos de teste e, ao final, a potência máxima (PMAX) atingida pelos indivíduos. O tempo total de cada teste foi normalizado em porcentagens (de 10% a 100%, intervalos de 10%), e foi anotada a respectiva PSE para cada intervalo. Os valores de PMAX para GC e GNC foram 368 ± 12,7W e 256 ± 11,2W, respectivamente (P < 0,01). Os valores das medianas das PSE para GC e GNC não apresentaram diferença significativa para nenhuma porcentagem de tempo. Conclui-se que as respostas de PSE não sofreram alterações entre GC e GNC durante TIMAX, sugerindo que o nível de treinamento não influencia a PSE.

Different training levels, combined with experience in performing exhaustive exercise, may produce different sensations of fatigue. The objective of this study was to compare the rating of perceived exertion (RPE) between cyclists and non-cyclists during a maximal incremental test (ITMAX). Twenty-three subjects were recruited and divided into a cyclist group (CG) (n = 12; age: 26.5 ± 4.7 years, body weight: 68.2 ± 11kg, height: 176 ± 8.6 cm) and a non-cyclist group (NCG) (n = 11; 25.2 ± 4.0 years, body weight: 72.9 ± 9 kg, height: 175.1 ± 6.3 cm). All subjects performed an ITMAX until exhaustion on a cycling simulator, starting at 0 W and with increments of 20 W.min-1. RPE was measured at 30-second intervals during ITMAX and the maximal power output (PMAX) of each subject was also recorded. The total time of each test was normalized to the percentage of completed trial (10% to 100%, intervals of 10%), and the corresponding RPE was recorded. PMAX was 368 ± 12.7 W and 256 ± 11.2 W for CG and NCG, respectively (P < 0.01). No significant difference in median RPE was observed between groups at any time point. In conclusion, RPE responses did not differ between CG and NCG during ITMAX, suggesting that training level does not influence RPE.