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OBJECTIVES: To determine the residual acute vibration-stretching effect on preactivation levels, short-latency stretch reflex, and performance during execution of drop jumps. DESIGN: Repeated measures. METHODS: Eleven male recreational athletes performed a set of three 45cm drop jumps before and immediately after a 30s static stretching exercise with and without simultaneously imposed muscle vibration (45Hz, 5mm). Drop jump height, ground reaction forces and electromyographic data including Vastus Lateralis onset/levels of preactivation and short-latency stretch reflex were recorded. RESULTS: No changes were induced on drop jump height. However, stretching-induced decrements on ground reaction force peak and time to peak as well as an increment in contact time followed a delay in short-latency stretch reflex onset and a reduced preactivation level of Vastus Lateralis. Otherwise, when vibration was simultaneously imposed, there was no evidence of changes in high-speed force production variables or electromyographic recordings. CONCLUSIONS: Mechanical vibration, when applied simultaneously to static-stretching routines, appeared to be effective to counteract decreased musculotendinous unit stiffness-induced high-speed force production deficit during jumping performance.
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Contração Muscular , Adulto , Humanos , Masculino , Exercícios de Alongamento Muscular , Vibração , Adulto JovemRESUMO
OBJECTIVES: It remains unclear whether an increased intrafusal mechanical sensitivity is related to the vibration-induced performance improvement. This investigation aimed to determine the residual acute effect of whole-body vibration and its duration on pre-activation levels, short-latency stretch reflex and performance during drop jumps. DESIGN: Repeated measures. METHODS: Eleven amateur athletes performed a set of three 45cm-drop jumps before and during a 20min-interval following three randomized conditions: No, Low (30Hz, 5mm) and High vibration (45Hz, 5mm). Ground reaction force peak, Soleus and Vastus Lateralis short latency stretch reflex onset and amplitude were assessed during drop jumps. RESULTS: A significant effect for time revealed an immediate drop jump height increase after High vibration. A longer contact time also followed High vibration while no changes were detected after Low vibration. Vibration did not affect ground reaction force peak and short latency stretch reflex component. CONCLUSIONS: High vibration constituted an intervention for improving performance although there was no evidence of increased stretch reflex responses.
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Desempenho Atlético/fisiologia , Tempo de Reação/fisiologia , Reflexo de Estiramento/fisiologia , Vibração , Adulto , Eletromiografia , Voluntários Saudáveis , Humanos , Adulto JovemRESUMO
A hypoxic model was used to investigate changes in localized cerebral and muscle haemodynamics during knee extension (KE) in healthy individuals. Thirty-one young healthy volunteers performed one set of KE until failure under hypoxia (14 % O(2)) or normoxia (21 % O(2)) at 50, 75 or 100 % of 1 repetition maximum, in random order, on three occasions. Prefrontal cerebral and vastus lateralis muscle oxygenation and blood volume (Cox, Mox, Cbv and Mbv, respectively) were recorded simultaneously by near-infrared spectroscopy. Hypoxia induced significant declines in Cox [-0.017 ± 0.016 optical density (OD) units] and Mox (-0.014 ± 0.026 OD units) and increases in Cbv (0.017 ± 0.027 OD units) and Mbv (0.016 ± 0.023 OD units) at rest. Hypoxia significantly reduced total work (TW) performed during KE at each exercise intensity. Cox, Cbv, Mox, and Mbv changes during KE did not differ between normoxia and hypoxia. Correlations between TW done and Cox changes under normoxia (r = 0.04, p = 0.182) and hypoxia (r = 0.05, p = 0.122) were not significant. However, TW was significantly correlated with Mox under both normoxia (R (2) = 0.24, p = 0.000) and hypoxia (R (2) = 0.15, p = 0.004). Since changes in Cox and Mox reflect alterations in the balance between oxygen delivery and extraction in these tissues, which, in the brain, is an index of neuronal activation, we conclude that: (1) limitation of KE performance was mediated peripherally under both normoxia and hypoxia, with no additional effect of hypoxia, and (2) because of the low common variance with Mox additional intramuscular factors likely play a role in limiting KE performance.
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Hipóxia/fisiopatologia , Articulação do Joelho/fisiopatologia , Contração Muscular , Fadiga Muscular , Músculo Esquelético/fisiopatologia , Consumo de Oxigênio , Resistência Física , Adulto , Velocidade do Fluxo Sanguíneo , Circulação Cerebrovascular , Feminino , Humanos , Masculino , Amplitude de Movimento ArticularRESUMO
l-Arginine (L-arg) is an amino acid precursor to nitric oxide (NO). Dietary supplements containing L-arg have been marketed with the purpose of increasing vasodilation, thereby elevating blood flow to the exercising muscle and enhancing the metabolic response to exercise. Our goal was to identify the acute effect of L-arg supplementation on biceps strength performance, indicators of NO production (nitrite and nitrate - NOx), and muscle blood volume (Mbv) and oxygenation (Mox) during recovery from 3 sets of resistance exercise. Fifteen males participated in a randomized, double-blind, placebo-controlled study. After withdrawing resting blood samples, the subjects were supplemented with 6 g of L-arg (ARG) or placebo (PLA). Monitoring of Mbv and Mox with near-infrared spectroscopy began 30 min after supplementation and lasted for 60 min. The exercise protocol (3 sets of 10 maximal voluntary contractions of isokinetic concentric elbow extension at 60°·s(-1), 2-min rest between sets) was initiated 80 min after supplementation. Blood samples were drawn at 30, 60, 90, and 120 min after supplementation. Repeated measures ANOVA showed that Mbv significantly (p ≤ 0.05) increased in ARG compared with the PLA during the recovery period of each set of resistance exercise. NOx, Mox, peak torque, total work, and set total work were not significantly different between groups. We found that acute L-arg supplementation increases Mbv during recovery from sets of resistance exercise with no increase in strength performance. It is still premature to recommend nutritional supplements containing L-arg as an ergogenic aid to increase muscle strength during resistance training in healthy subjects.
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Arginina/administração & dosagem , Volume Sanguíneo/efeitos dos fármacos , Suplementos Nutricionais , Contração Muscular , Força Muscular/efeitos dos fármacos , Músculo Esquelético/irrigação sanguínea , Músculo Esquelético/efeitos dos fármacos , Treinamento Resistido , Adulto , Análise de Variância , Arginina/sangue , Biomarcadores/sangue , Fenômenos Biomecânicos , Brasil , Método Duplo-Cego , Humanos , Masculino , Músculo Esquelético/metabolismo , Nitratos/sangue , Óxido Nítrico/metabolismo , Nitritos/sangue , Consumo de Oxigênio/efeitos dos fármacos , Recuperação de Função Fisiológica , Fluxo Sanguíneo Regional/efeitos dos fármacos , Espectroscopia de Luz Próxima ao Infravermelho , Fatores de Tempo , Torque , Extremidade Superior , Vasodilatação/efeitos dos fármacos , Adulto JovemRESUMO
Dietary supplements containing L-arginine, a semi-essential amino acid, are one of the latest ergogenic aids intended to enhance strength, power and muscle recovery associated with both aerobic and resistance exercise. L-arginine is claimed to promote vasodilation by increasing nitric oxide (NO) production in the active muscle during exercise, improving strength, power and muscular recovery through increased substrate utilization and metabolite removal, such as lactate and ammonia. Research on L-arginine has recently tested this hypothesis, under the assumption that it may be the active compound associated with the vasodilator effects of NO. There were only five acute studies retrieved from the literature that evaluated exercise performance after L-arginine supplementation, three of which reported significant improvements. Regarding studies on chronic effects, eight studies were encountered: four reported enhancements in exercise performance, whilst four reports showed no changes. Whether these improvements in exercise performance - regardless of the aerobic or anaerobic nature of the exercise - can be associated with increases in NO production, has yet to be demonstrated in future studies. Low oral doses (≤20 g) are well tolerated and clinical side effects are rare in healthy subjects. In summary, it is still premature to recommend dietary supplements containing L-arginine as an ergogenic aid for healthy physically active subjects.
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Arginina/farmacologia , Desempenho Atlético/fisiologia , Suplementos Nutricionais , Metabolismo Energético/efeitos dos fármacos , Força Muscular/efeitos dos fármacos , Resistência Física/efeitos dos fármacos , Arginina/efeitos adversos , Exercício Físico/fisiologia , Humanos , Óxido Nítrico/metabolismo , Aptidão Física/fisiologia , Treinamento Resistido , Vasodilatação/fisiologiaRESUMO
The aim of the study was to examine the changes in cerebral and muscle blood volume (Cbv, Mbv) and oxygenation (Cox, Mox) during static and dynamic knee extensions to fatigue in men (N=10; 29±9 years) and women (N=14; 27±8 years). After assessment of 1 repetition maximum (1RM) during unilateral knee extensions with the dominant limb, each subject exercised at 50%, 75% and 100% of 1 RM in random order on separate occasions. Simultaneous changes in Cbv, Cox, Mbv and Mox from the contralateral prefrontal lobe and the dominant limb were measured by near infrared spectroscopy. During all three contractions, Cbv and Cox increased while Mbv and Mox decreased until fatigue in both genders. There were no signs of levelling off or decline in Cbv and Cox during any of these contractions, implying that there was no reduction in cerebral neuronal activation. Conversely, there was a rapid decline in Mbv and Mox during the early stages of the contractions, with a plateau or slight increase towards the end. The respective delta values at 50%, 75% and 100% of 1RM for Cbv (0·088 versus 0·062 versus 0·070), Cox (0·042 versus 0·033 versus 0·038), Mbv (-0·225 versus -0·198 versus -0·196), and Mox (-0·169 versus -0·146 versus -0·158) were not significantly different in the total group (N=24). These findings suggest that fatigue during resistance exercise lasting up to 60 s is mediated peripherally because of reduced blood volume and oxygen availability and is independent of the type and intensity of muscle contraction and gender.
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Encéfalo/metabolismo , Contração Muscular , Fadiga Muscular , Músculo Esquelético/metabolismo , Consumo de Oxigênio , Oxigênio/metabolismo , Treinamento Resistido , Espectroscopia de Luz Próxima ao Infravermelho , Adulto , Análise de Variância , Encéfalo/irrigação sanguínea , Circulação Cerebrovascular , Feminino , Humanos , Joelho , Ácido Láctico/sangue , Masculino , Músculo Esquelético/irrigação sanguínea , Oxigênio/sangue , Fluxo Sanguíneo Regional , Fatores Sexuais , Fatores de Tempo , Adulto JovemRESUMO
Cerebral contra-lateral frontal lobe and the dominant vastus lateralis muscle oxygenation (Cox, Mox) and blood volume (Cbv, Mbv) were recorded simultaneously using near infrared spectroscopy (NIRS) in 12 healthy volunteers (37.4 +/- 9.9 years; 72.3 +/- 16.1 kg; 171.0 +/- 9.6 cm) during 2 min resting baseline, an isometric knee extension with the 1 RM load sustained to the point of fatigue, and 3 min recovery. The mean exercise duration was 19.1 +/- 2.6 s. During the contraction, Cox and Cbv increased systematically with no sign of levelling off until the point of fatigue. In contrast, Mox and Mbv declined continuously until the termination of exercise. Qualitative analysis of these NIRS profiles suggested that maximal isometric performance under normoxic conditions was most likely not limited by central neuronal activation, but rather, was due to factors within the exercising muscle. It is likely that depletion of intramuscular stores of high energy phosphates and oxymyoglobin, as well as the accumulation of metabolites from anaerobic pathways, were implicated in fatigue during this sustained high intensity isometric contraction.
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Encéfalo/fisiologia , Contração Isométrica/fisiologia , Articulação do Joelho/fisiologia , Músculo Esquelético/fisiologia , Consumo de Oxigênio/fisiologia , Resistência Física/fisiologia , Esforço Físico/fisiologia , Adulto , Feminino , Humanos , MasculinoRESUMO
INTRODUÇÃO: Pouco se sabe sobre o efeito da velocidade de execução e do intervalo entre séries sobre o desempenho no exercício contra-resistência. OBJETIVO: Comparar o número máximo de repetições até a fadiga voluntária (REPS) na cadeira extensora com o joelho dominante para diferentes cargas, velocidades e intervalos entre séries. MÉTODOS: Nove voluntários (35,8 ± 10,8 anos; 74,2 ± 16,7kg; 171,0 ± 10,0cm) reportaram ao laboratório para determinação de 1RM e REPS em seis situações, determinadas aleatoriamente e separadas por no mínimo 48h: uma série com 60 por cento 1RM a 80°s¹ e 25°s-1; uma série com 80 por cento 1RM a 25°s¹; três séries com 80 por cento 1RM a 80°s-1 e intervalos de 3 min, 1 min e naquele que permitisse a estabilização da oxigenação muscular (RMox), medida por espectroscopia no infravermelho próximo. RESULTADOS: O teste t dependente mostrou que REPS foi significativamente (p < 0,05) maior na carga leve que na pesada, nas velocidades lenta (leve = 8,8 ± 1,3; pesada = 5,9 ± 0,9) e rápida (leve = 16,3 ± 3,9; pesada = 9,4 ± 1,9), e significativamente maior na velocidade rápida que na lenta, para ambas as cargas. A ANOVA 3x3 não mostrou diferença entre os intervalos na série 1 (3 min = 9,4 ± 1,9; 1 min = 10,8 ± 3,2; RMox = 10,1 ± 3,0), porém, houve diferenças significativas nas séries 2 e 3 entre 3 min (série 2 = 7,0 ± 1,7; série 3 = 6,4 ± 1,3) e 1 min (série 2 = 5,6 ± 1,1; série 3 = 4,8 ± 1,2), mas não entre RMox (série 2 = 6,4 ± 1,7; série 3 = 6,1 ± 1,5) e os demais intervalos. Nos três intervalos, REPS na série 1 foi significativamente maior que nas demais. CONCLUSÕES: O desempenho no exercício contra-resistência é afetado pela carga, velocidade e intervalo entre séries e é independente da recuperação em oxigenação muscular. A prescrição do exercício e a avaliação do desempenho devem levar...
INTRODUCTION: Very little is known about the effects of movement velocity and rest intervals between sets of resistance exercise. PURPOSE: To compare the maximum number of repetitions to volitional fatigue (REPS) on a knee extension machine with the dominant leg for different loads, velocities and rest intervals between sets. METHODS: Nine volunteers (35.8 ± 10.8 years; 74.2 ± 16.7 kg; 171.0 ± 10.0 cm) reported to the laboratory to determine 1RM and REPS under six conditions, randomly determined and separated by at least 48 h: 1 set with 60 percent 1RM at 80°s-1 and 25°s-1; 1 set with 80 percent 1RM at 25°s-1; 3 sets with 80 percent 1RM at 80°s-1 and rest intervals of 3 min, 1 min and one that allowed recovery or stabilization of muscle oxygenation (RMox), measured by near infrared spectroscopy (NIRS). RESULTS: Dependent samples t-test showed that REPS was significantly (p < 0.05) larger for the lighter than the heavier load, for slow (light = 8.8 ± 1.3; heavy = 5.9 ± 0.9) and fast velocities (light = 16.3 ± 3.9; heavy = 9.4 ± 1.9), and significantly larger for the fast than the slow velocity, for both loads. The 3x3 ANOVA did not show differences among intervals on set 1 (3 min = 9.4 ± 1.9; 1 min = 10.8 ± 3.2; RMox = 10.1 ± 3.0), however, there were significant differences on sets 2 and 3 between 3 min (set 2 = 7.0 ± 1.7; set 3 = 6.4 ± 1.3) and 1 min (set 2 = 5.6 ± 1.1; set 3 = 4.8 ± 1.2), but not between RMox (set 2 = 6.4 ± 1.7; set 3 = 6.1 ± 1.5) and the other intervals. For all three intervals, REPS on set 1 was significantly larger than on the other sets. CONCLUSIONS: Performance in resistance exercise is affected by load, velocity and rest interval between sets and is independent of muscle oxygenation recovery. Exercise prescription and assessment of performance should take these variables into consideration...
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There is growing interest in resistance training, but many aspects related to this type of exercise are still not fully understood. Performance varies substantially depending on how resistance training variables are manipulated. Fatigue is a complex phenomenon usually attributed to central (neuronal) and/or peripheral (muscular) origin. Cerebral oxygenation may be associated with the decision to stop exercise, and muscle oxygenation may be related to resistance training responses. Near infrared spectroscopy (NIRS) is a non-invasive optical technique used to monitor cerebral and muscle oxygenation levels. The purpose of this review is to briefly describe the NIRS technique, validation and reliability, and its application in resistance exercise. NIRS-measured oxygenation in cerebral tissue has been validated against magnetic resonance imaging during motor tasks. In muscle tissue, NIRS-measured oxygenation was shown to be highly related to venous oxygen saturation and muscle oxidative rate was closely related to phosphocreatine resynthesis, measured by (31)P-magnetic resonance spectroscopy after exercise. The test-retest reliability of cerebral and muscle NIRS measurements have been established under a variety of experimental conditions, including static and dynamic exercise. Although NIRS has been used extensively to evaluate muscle oxygenation levels during aerobic exercise, only four studies have used this technique to examine these changes during typical resistance training exercises. Muscle oxygenation was influenced by different resistance exercise protocols depending on the load or duration of exercise, the number of sets and the muscle being monitored. NIRS is a promising, non-invasive technique that can be used to evaluate cerebral and muscle oxygenation levels simultaneously during exercise, thereby improving our understanding of the mechanisms influencing performance and fatigue.