Strength and flexibility are common components of exercise programmes; however, it is not clear how best to include both of these elements in a single training programme. It is common practice among athletes, coaches and recreational exercisers to perform a stretching routine before a strength training session. Stretching exercises are regularly recommended, even in many textbooks, with the claimed purpose of preventing injury and muscle soreness, or even enhancing performance. However, as highlighted in recent review articles, this recommendation lacks scientific evidence. Thus, the purpose of the present review is to determine the acute and chronic effects of stretching on strength performance, together with the underlying mechanisms. Although most studies have found acute decreases in strength following stretching, and that such decreases seem to be more prominent the longer the stretching protocol, the number of exercises and sets, and the duration of each set have, in general, exceeded the ranges normally recommended in the literature. Consequently, the duration of the stimuli were excessively long compared with common practice, thus making evident the need for further studies. In addition, when recommending flexibility exercises, one should consider other underlying issues, such as the safety of the participants, possible increases in injury risks and the unnecessary time expenditure. Many mechanisms underlying stretching exercises still demand investigation so that links between the observed effects, their causes and the consequences may be constructed.

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.

The purpose of this meta-analytic review was to examine the extent and quality of research on the post-activation potentiation acute effect of rest interval manipulation on jumping performance. This manuscript adopted the recommendations from the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement. Criteria eligibility included crossover, randomised, non-randomised and counterbalanced studies that observed the voluntary muscle action-induced post-activation potentiation on jumping performance. Fourteen studies selected by two independent raters were included in the analysis. The rest intervals involved ranges including 0-3, 4-7, 8-12 and ≥16 min. The results demonstrated medium effect sizes for rest intervals 0-3 and 8-12 min (-0.25, confidence interval (CI): -0.51 to 0.01 for 0-3 min; 0.24, CI: -0.02 to 0.49 for 8-12 min) and a small effect for other ranges (0.15, CI: -0.08 to 0.38 for 4-7 min; 0.07, CI: -0.21 to 0.24 for ≥16 min). There was no evidence of heterogeneity for sub-groups (I2 = 0%; P < 0.001) and no indication of publication bias (Egger's test, P = 0.179). While a rest interval of 0-3 min induced a detrimental effect on jump performance, the range including 8-12 min had a beneficial impact on jump height. Findings suggest that the rest interval manipulation seems to affect post-activation potentiation magnitude and jump height.

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.

A confiabilidade intra-avaliadores é fundamental na determinação da qualidade dos dados coletados em uma pesquisa. Poucos estudos controlados têm reportado valores de confiabilidade de testes de força e, apesar de esta ser considerada boa na maioria dos estudos publicados (0,79 a 0,99), as diferenças entre teste e reteste têm sido observadas como estatisticamente significativas. Dessa forma, sugere-se a utilização dos valores de um segundo teste, pelo menos, em estudos de pesquisa, de modo que eventuais modificações nos valores de força possam ser atribuídas ao efeito dos tratamentos realizados e não à simples adaptação ao protocolo de teste. As relações entre testes de força máxima e testes submáximos ou variáveis antropométricas têm sido investigadas com o intuito de predizer a força máxima sem que o indivíduo tenha que ser submetido a um teste de carga máxima, evitando possíveis riscos de lesão. Valores de carga máxima, ou percentuais desta, são comumente utilizados para melhor prescrever o treinamento. A predição de uma repetição máxima (1RM) através de testes submáximos parece boa (em geral, correlações > 0,90); entretanto, na maioria dos estudos revisados, as equações preditivas desenvolvidas quase sempre não são aprovadas no escrutínio de uma validação cruzada. Assim sendo, especial atenção deve ser dispensada à especificidade da população, do exercício e da técnica de execução, quando do desenvolvimento e aplicação dessas equações. Variáveis antropométricas não foram confirmadas como boas preditoras de 1RM. O número de repetições para dado % de 1RM é diferente para diferentes exercícios, como também o é a carga para determinado número de repetições máximas (nRM), quando executadas em diferentes velocidades. A prescrição do exercício baseada, indiferentemente, em número de repetições ou % de 1RM deve ser considerada com cautela.