RESUMO O objetivo desta revisão foi examinar na literatura atual os avanços feitos com relação aos efeitos da suplementação de cafeína sobre a força máxima e seus mecanismos associados a partir de 2010, ano em foram publicados dois importantes artigos. As buscas foram realizadas nas bases de dados PubMed, Medline, Scielo e Web of Science procurando-se artigos publicados após 2010. Dezesseis estudos foram incluídos com base nos critérios de inclusão e exclusão. Cinco estudos não relataram alterações da força voluntária máxima (31,3%). Quatro deles usaram contrações musculares isométricas, embora isso possa não ser um fator chave, porque outros cinco estudos também usaram contrações isométricas e relataram efeitos ergogênicos. Além disso, esses quatro estudos avaliaram pequenos grupos musculares e os voluntários não eram habituados à cafeína. A cafeína produziu efeitos ergogênicos em 11 dos 16 estudos analisados (68,8%). Nenhuma dose foi claramente relacionada com efeitos ergogênicos; contudo, há indícios da necessidade de uma dose de pelo menos 3 mg/kg de cafeína. A ergogenicidade da cafeína foi afetada por vários fatores. Havia uma falta de protocolos padronizados e controle de fatores intervenientes (por exemplo, ciclo circadiano e estado nutricional) que poderiam afetar os resultados. Ainda é preciso definir um protocolo ideal de suplementação de cafeína que seja útil para futuras pesquisas, atletas e praticantes de atividade física. Um pequeno avanço feito desde 2010 envolveu a possível falta de diferença de gênero - parece que a suplementação de cafeína afeta homens e mulheres igualmente. Nível de Evidência I; Revisão Sistemática de Estudos de Nível I.

ABSTRACT The purpose of this review was to examine in the current literature the advances made in terms of the effects of caffeine supplementation on maximum strength and its associated mechanisms since the publication of two important papers in 2010. Searches were carried out in the PubMed, Medline, Scielo and Web of Science databases for articles published after 2010. Sixteen studies were included based on inclusion and exclusion criteria. Five studies did not report changes in maximal voluntary strength (31.3%). Four of them used isometric muscle contractions, although this may not be a key factor because five other studies also used isometric contractions and reported ergogenic effects. Furthermore, these four studies evaluated small muscle groups and volunteers were not accustomed to consuming caffeine. Caffeine produced ergogenic effects in eleven of the sixteen studies analyzed (68.8%). None of the doses were clearly related to ergogenic effects; however, a dose of at least 3 mg/kg of caffeine is probably necessary. Caffeine ergogenicity was affected by various factors. There was a lack of standardized protocols and controls for intervening factors (e.g., circadian cycles and nutritional states), which could affect results. An ideal caffeine supplementation protocol that is useful for future research, athletes, and physical activity practitioners, has yet to be defined. A small advance made since 2010 involved a possible lack of gender difference; it would appear that caffeine supplementation affects men and women equally. Level of Evidence I; Systematic Review of Level I Studies.

RESUMEN El objetivo de esta revisión fue examinar en la literatura actuallos avances hechos con respecto a los efectos del suplemento de cafeína sobre la fuerza máxima y sus mecanismos asociados desde 2010, año en que se publicaron dos artículos importantes. Las búsquedas se realizaron en las bases de datos PubMed, Medline, Scielo y Web of Science, por artículos publicados después de 2010. Se incluyeron 16 estudios basados en los criterios de inclusión y exclusión. Cinco estudios no reportaron cambios de la fuerza voluntaria máxima (31,3%). Cuatro de ellos usaron contracciones musculares isométricas, aunque esto puede no ser un factor clave, porque otros cinco estudios también utilizaron contracciones isométricas y reportaron efectos ergogénicos. Además, estos cuatro estudios evaluaron grupos musculares pequeños y los voluntarios no tenían el hábito de consumo de cafeína. La cafeína produjo efectos ergogénicos en 11 de los 16 estudios analizados (68,8%). Ninguna dosis fue claramente relacionada con efectos ergogénicos, sin embargo, hay indicios de la necesidad de una dosis de al menos 3 mg/kg de cafeína. La ergogenicidad de la cafeína se vio afectada por varios factores. Hubo una falta de protocolos y controles estandarizados de factores intervinientes (por ejemplo, ciclo circadiano y estado nutricional) que podrían afectar los resultados. Todavía es necesario definir un protocolo ideal de suplemento de cafeína que sea útil para futuras investigaciones, atletas y practicantes de actividad física. Un pequeño avance hecho desde 2010 involucró la posible falta de diferencia de género - parece que el suplemento de cafeína afecta a hombres y mujeres igualmente. Nivel de Evidencia I; Revisión sistemática de estudios de Nivel I.

OBJECTIVE: The reliability of heart rate variability (HRV) analysis is not yet fully understood, especially considering different body positions and the mathematical influence of heart rate. The aim of this study was to evaluate the reliability of HRV in supine and standing positions, with and without mathematical adjustment of HRV by the average R-R interval (iRR). METHODS: We evaluated 37 young males (23.1±4 years; 25.1±3 kg/m2). A 5-min segment of the iRR was collected in the supine and standing positions on three occasions separated by 48-hour intervals. Absolute and relative reliability of temporal and spectral indices were assessed by the coefficient of variation (CV) and the intraclass correlation coefficient (ICC), respectively. RESULTS: We did not observe differences in HRV indices in the three occasions in the supine or standing position (p>0.05). Moderate to good reproducibility was observed for temporal and spectral indices of HRV in the supine position (ICC: 0.65-0.89; CV: 0.9-19.8). In the orthostatic position, low to good reproducibility was observed (ICC: 0.35-0.89; CV: 1.1-34.8), with higher ICCs for temporal indices. After mathematical adjustment, only a small modification in HRV reliability was observed in both positions. CONCLUSIONS: In young adult males, the mathematical adjustment of HRV by the average iRR led to a nonsignificant effect on HRV reliability. Additionally, HRV reliability is dependent on body position and the index analyzed. Promising measures in both supine and standing positions include r-MSSD and the HF band (parasympathetic indices).

Abstract Aim: Heart rate variability threshold (HRVT) is a valid method to determine parasympathetic depression during an incremental exercise test (IET). However, HRVT is usually assessed using the last 60s of each 180s stage of an IET, resulting in longer and demotivating tests. This study aimed to evaluate the agreement of HRVT analysis adopting the first and second minute of R-R interval (iRR) segment comparatively to a standard third-minute segment obtained at each 3-min stage on IET. Methods: Seventeen young male subjects (22.2 ± 3.1 years; 23.4 ± 2.3 kg/m2) underwent IET on a cycle ergometer. HRVT was considered the load corresponding to the point of stabilization of the SD1 index (HRVTV), or the first load with SD1 value < 3ms (HRVT<3), both assessed by the 1st (HRVT1V, HRVT1<3), 2nd (HRVT2V, HRVT2<3) and standard 3rd (HRVT3V, HRVT3<3) 60s iRR segment analyzed at each stage of IET. Agreement and reliability were assessed by the Bland-Altman analysis and the intraclass correlation coefficient (ICC), respectively. Results: High reliability and non-significant bias were observed considering HRVT1V vs HRVT3V (ICC = 0.92; p = 0.18) or HRVT2V vs HRVT3V (ICC = 0.94; p = 0.99). However, lower reliability was observed for HRVT1<3 vs HRVT3<3 (ICC = 0.79; p = 0.75) and for HRVT2<3 vs HRVT3<3 (ICC = 0.91; p = 0.33). Conclusion: HRVT can be similarly assessed by the 1st, 2nd or 3rd 60 seconds iRR segment, mainly when assessed by a visual method.

Abstract The objective of this study was to evaluate reproducibility of heart rate variability threshold (HRVT) and parasympathetic reactivation in physically active men (n= 16, 24.3 ± 5.1 years). During the test, HRVT was assessed by SD1 and r-MSSD dynamics. Immediately after exercise, r-MSSD was analyzed in segments of 60 seconds for a period of five minutes. High absolute and relatively reproducible analysis of HRVT were observed, as assessed by SD1 and r-MSSD dynamics (ICC = 0.92, CV = 10.8, SEM = 5.8). During the recovery phase, a moderate to high reproducibility was observed for r-MSSD from the first to the fifth minute (ICC = 0.69-0.95, CV = 7.5-14.2, SEM = 0.07-1.35). We conclude that HRVT and r-MSSD analysis after a submaximal stress test are highly reproducible measures that might be used to assess the acute and chronic effects of exercise training on cardiac autonomic modulation during and/or after a submaximal stress test.

RESUMO Introdução: A avaliação da função autonômica cardíaca (FAC) após o teste de esforço (TE) é considerada um preditor poderoso e independente de risco cardiovascular. É escasso o conhecimento da influência de diferentes protocolos de recuperação sobre a FAC após TE em esteira rolante com os voluntários na posição ortostática. Objetivo: Comparar a reativação vagal e o grau de modulação global da FAC em dois diferentes protocolos de recuperação, passiva (RP) e ativa (RA), imediatamente após TE submáximo em esteira rolante. Métodos: Foram avaliados 24 homens fisicamente ativos com idade (média ± DP) de 27,2 ± 4,4 anos e IMC 24,8 ± 1,8 kg/m2. A ordem dos protocolos de recuperação foi definida de forma aleatória. Os testes foram realizados com intervalo de sete dias. Ambas as recuperações foram realizadas na posição ortostática durante cinco minutos, imediatamente após TE. Os índices temporais da variabilidade da frequência cardíaca foram utilizados para avaliar a reativação vagal e o grau de modulação global de FAC, rMSSD e SDNN, respectivamente, na RP e RA. Após análise da distribuição dos dados, utilizaram-se os testes de Mann-Whitney e de Friedman com post-hoc de Dum, no nível de significância de p ≤ 0,05. Resultados: Verificou-se maior reativação vagal no primeiro minuto de recuperação na RP comparativamente a RA [4,1 (4,9-3,4) ms vs. 3,4 (4,0-2,9) ms, p = 0,03] e maior grau de modulação global da FAC do terceiro ao quinto minuto e tendência a diferença significativa no segundo minuto de RP comparativamente a RA (p = 0,09-0,005). Conclusão: Os achados demonstram que o mínimo esforço físico, como caminhar lentamente sobre a esteira rolante, diminuiu a reativação vagal e o grau de modulação global da FAC após o TE submáximo em homens fisicamente ativos.

ABSTRACT Introduction: The evaluation of cardiac autonomic function (CAF) after stress test (ST) is considered a powerful and independent predictor of cardiovascular risk. The knowledge about the influence of different recovery protocols on CAF after ST on treadmill with volunteers in standing position is scarce. Objective: To compare the vagal reactivation and the degree of global CAF modulation in two different recovery protocols, passive (PR) vs. active (AR) immediately after submaximal ST in treadmill. Methods: We evaluated 24 physically active males, aged (mean ± SD) 27.2 ± 4.4 years and BMI 24.8 ± 1.8 kg/m2. The order of the recovery protocol was set at random. The tests were performed in 7-day intervals. Both recovery protocols were performed in standing position for 5 minutes, immediately after ST. The time indices of heart rate variability were used to assess the vagal reactivation and the overall degree of CAF, rMSSD, and SDNN, respectively, in PR and AR. After analysis of the data distribution, the Mann-Whitney and Friedman tests with Dum post-hoc were used at a significance level of p ≤ 0.05. Results: We observed a higher vagal reactivation at first minute of the PR compared to AR [4.1 (4.9-3.4) ms vs. 3.4 (4.0-2.9) ms, p = 0.03], and a higher degree of global CAF modulation from the third to the fifth minute and a tendency to significant difference in the second minute of PR compared to AR (p = 0.09−0.005). Conclusion: The findings demonstrate that minimum physical effort, such as walking slowly on a treadmill, decreased the vagal reactivation and the overall modulation degree of CAF after a submaximal ST in physically active men.

RESUMEN Introducción: La evaluación de la función autonómica cardíaca (FAC) después de la prueba de esfuerzo (PE) se considera un predictor potente e independiente del riesgo cardiovascular. Es escaso el conocimiento de la influencia de los diferentes protocolos de recuperación sobre la FAC después de la PE en la cinta rodante con voluntarios en la posición de pie. Objetivo: Comparar la reactivación vagal y el grado de la modulación general de la FAC en dos diferentes protocolos de recuperación, pasiva (RP) vs. activa (RA) inmediatamente después de la PE submáxima en la cinta rodante. Métodos: Se evaluaron 24 hombres físicamente activos con edades (promedio ± DE) de 27,2 ± 4,4 años y IMC de 24,8 ± 1,8 kg/m2. El orden de los protocolos de recuperación se definió al azar. Las pruebas se realizaron en un intervalo de siete días. Ambas recuperaciones se realizaron en la posición de pie durante cinco minutos inmediatamente después de la PE. Los índices temporales de la variabilidad de la frecuencia cardiaca fueron utilizados para evaluar la reactivación vagal y el grado de modulación general de la FAC, rMSSD y SDNN, respectivamente, en RP y RA. Después del análisis de la distribución de los datos, se utilizaron la prueba de Mann-Whitney y la de Friedman con post-hoc de Dum, a un nivel de significación de p ≤ 0,05. Resultados: Se observó una mayor reactivación vagal en el primer minuto de la PR comparada a la RA [4,1 (4,9-3,4) ms vs. 3,4 (4,0-2,9) ms, p = 0,03] y un mayor grado de modulación general de la FAC del tercer al quinto minuto y una tendencia a la diferencia estadística en el segundo minuto de RP comparada a RA (p = 0,09-0,005). Conclusión: Los resultados muestran que el esfuerzo físico mínimo, como caminar lentamente sobre la cinta rodante, disminuyó la reactivación vagal y el grado de modulación general de la FAC después de la PE submáxima en hombres físicamente activos.