Impact of Caffeine Intake Strategies on Heart Rate Variability during Post-Exercise Recovery: A Systematic Review and Meta-Analysis.

OBJECTIVES: The objective of this systematic review and meta-analysis is to evaluate the influence of caffeine (CAF) intake strategies, taking into account their form, timing, and dosage, on heart rate variability (HRV) indices in the post-exercise recovery period. METHODS: The meta-analysis adhered to the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines and is registered in the PROSPERO database (CRD42023425885). A comprehensive literature search was carried out across MEDLINE, Web of Science, LILACS, and SCOPUS, concluding in May 2023. We concentrated on randomized clinical trials comparing CAF supplementation effects to placebo on HRV indices post-exercise in active adults aged 18 and above. The primary endpoint was the assessment of HRV indices, measured both prior to and following exercise. RESULTS: Of the 10 studies included, 7 were used for the meta-analysis, and all contributed to the systematic review. The research explored a variety of CAF strategies, spanning different forms (capsule, drink, gum), times (10, 45, 60 min) and doses (2.1 to 6.0 mg/kg). The outcomes revealed no substantial variations between the placebo and CAF conditions in terms of both the square root of the average of successive squared differences between adjacent RR intervals (RMSSD) (standardized mean difference (SMD) -0.03, 95% CI -0.265 to 0.197, p=0.77) and high frequency (HF) index (SMD -0.061, 95% CI -0.272 to 0.150, p=0.57). Furthermore, metaregression analysis, employing a fixed-effects model and accounting for the administered CAF doses, revealed no significant correlation between caffeine doses and HRV indices (p>0.05). CONCLUSION: In conclusion, there is moderate-certainty evidence suggesting that different CAF intake strategies, encompassing aspects such as form, time, and dose, do not have a significant impact on HRV indices recovery post-exercise (i.e., vagal modulation).

Caffeine increases performance and leads to a cardioprotective effect during intense exercise in cyclists.

The present study was designed to investigate the effects of different caffeine dietary strategies to compare the impact on athletic performance and cardiac autonomic response. The order of the supplementation was randomly assigned: placebo(4-day)-placebo(acute)/PP, placebo(4-day)-caffeine(acute)/PC and caffeine(4-day)-caffeine(acute)/CC. Fourteen male recreationally-trained cyclists ingested capsules containing either placebo or caffeine (6 mg kg-1) for 4 days. On day 5 (acute), capsules containing placebo or caffeine (6 mg kg-1) were ingested 60 min before completing a 16 km time-trial (simulated cycling). CC and PC showed improvements in time (CC vs PP, Δ - 39.3 s and PC vs PP, Δ - 43.4 s; P = 0.00; ƞ2 = 0.33) and in output power (CC vs PP, Δ 5.55 w and PC vs PP, Δ 6.17 w; P = 0.00; ƞ2 = 0.30). At the final of the time-trial, CC and PC exhibited greater parasympathetic modulation (vagal tone) when compared to the PP condition (P < 0.00; ƞ2 = 0.92). Our study provided evidence that acute caffeine intake (6 mg∙kg-1) increased performance (time-trial) and demonstrated a relevant cardioprotective effect, through increased vagal tone.

Caffeine Supplementation for 4 Days Does Not Induce Tolerance to the Ergogenic Effects Promoted by Acute Intake on Physiological, Metabolic, and Performance Parameters of Cyclists: A Randomized, Double-Blind, Crossover, Placebo-Controlled Study.

The present study investigated whether the caffeine supplementation for four days would induce tolerance to the ergogenic effects promoted by acute intake on physiological, metabolic, and performance parameters of cyclists. A double-blind placebo-controlled cross-over design was employed, involving four experimental trials; placebo (4-day)-placebo (acute)/PP, placebo (4-day)-caffeine (acute)/PC, caffeine (4-day)-caffeine (acute)/CC and caffeine (4-day)-placebo (acute)/CP. Fourteen male recreationally-trained cyclists ingested capsules containing either placebo or caffeine (6 mg∙kg-1) for 4 days. On day 5 (acute), capsules containing placebo or caffeine (6 mg∙kg-1) were ingested 60 min before completing a 16 km time-trial (TT). CC and PC showed improvements in time (3.54%, ES = 0.72; 2.53%, ES = 0.51) and in output power (2.85%, ES = 0.25; 2.53%, ES = 0.20) (p < 0.05) compared to CP and PP conditions, respectively. These effects were accompanied by increased heart rate (2.63%, ES = 0.47; 1.99%, ES = 0.34), minute volume (13.11%, ES = 0.61; 16.32%, ES = 0.75), expired O2 fraction (3.29%, ES = 0.96; 2.87, ES = 0.72), lactate blood concentration (immediately after, 29.51% ES = 0.78; 28.21% ES = 0.73 recovery (10 min), 36.01% ES = 0.84; 31.22% ES = 0.81), and reduction in expired CO2 fraction (7.64%, ES = 0.64; 7.75%, ES = 0.56). In conclusion, these results indicate that caffeine, when ingested by cyclists in a dose of 6 mg∙kg-1 for 4 days, does not induce tolerance to the ergogenic effects promoted by acute intake on physiological, metabolic, and performance parameters.

Cardiopulmonary Performance During Maximal Exercise in Soccer Players with Alterations in Renal Function.

The aim of this study was to evaluate the curves of cardiorespiratory variables during cardiopulmonary exercise testing (CPET) in soccer players who had acute alterations in the glomerular filtration rate (GFR) after performing the pre-season training protocol. Sixteen male professional soccer players (25 ± 3 years; 179 ± 2 cm; and 77 ± 6 kg) were evaluated for oxygen uptake (VO2), heart rate (HR) and pulse relative oxygen (relative O2 Pulse) curves with intervals corresponding to 10% of the total duration of CPET. Athletes were grouped according to the GFR and classified as decreased GFR (dGFR; n = 8) and normal GFR (nGFR; n = 8). Athletes from the dGFR group exhibited lower VO2 values (p < 0.05) when 90% (dGFR 49.8 ± 4.0 vs. nGFR 54.4 ± 6.1 ml·kg-1·min-1) and 100% (dGFR 52.6 ± 4.1 vs. nGFR 57.4 ± 5.9 ml·kg-1·min-1) of the test was complete; HR high values (p < 0.05) when 90% (dGFR 183.7 ± 5.1 vs. nGFR 176.6 ± 4.8 bpm-1) and 100% (dGFR 188.1 ± 5.0 vs. nGFR 180.8 ± 4.8 bpm-1) of the test was complete; and lower relative O2 Pulse values (p < 0.05) when 70% (dGFR 25.6 ± 8.4 vs. nGFR 27.9 ± 9.7 ml·beat-1·kg-1), 80% (dGFR 26.6 ± 8.8 vs. nGFR 29.1 ± 10.0 ml·beat-1·kg-1), 90% (dGFR 27.1 ± 9.0 vs. nGFR 30.8 ± 10.6 ml·beat-1·kg-1) and 100% (dGFR 28 ± 9.2 vs. nGFR 31.8 ± 10.9 ml·beat-1·kg-1) of the test was complete. A correlation was found (r = -0.66, R2 = 0.44, p = 0.00) between lower VO2 peak and elevated levels of urinary protein excretion. In conclusion, soccer players with reduced kidney function after performing the pre-season training protocol also presented alterations in cardiopulmonary variables. We suggest that monitoring of renal function may be used to identify less conditioned soccer players.

Acute effects of caffeine intake on athletic performance: A systematic review and meta-analysis / Efectos agudos de la ingesta de cafeína en el rendimiento atlético: Una revisión sistemática y meta-análisis

ABSTRACT Objective: Our objective was to perform a systematic review and meta-analysis of the research literature assessing the effect of caffeine on athletic performance. Methods: A total of 13 studies published between 2010 and 2015 were included in the meta-analysis of the effects of caffeine on maximum running distance (2 studies), time trial performance (7 studies), and muscle power (4 studies). The effect sizes were calculated as standardized differences in means (std in means). Meta-analysis was completed using a random effects model. Results: Caffeine supplementation did not increase maximum running distance (effect size= 0.37, p= 0.14) and muscle power (effect size= 0.17, p= 0.36). However, improvements were observed in the time trial performance (effect size= −0.40, p< 0.01). Subgroup analyses revealed that the improvement in time trial results may be related to the use of the 6 mg/kg of body weight of caffeine dose (effect size= −0.45, p= 0.01). Conclusion: Our meta-analysis showed that caffeine intake does not improve performance in maximum running distance and muscle power, but it seems to improve time trial performance. The effect of caffeine on time trial performance related to dose.

RESUMEN Objetivo: Realizar una revisión sistemática y meta-análisis de la literatura de investigación que evalúa el efecto de la cafeína en el rendimiento atlético. Método: Un total de 13 estudios publicados entre 2010 y 2015 fueron incluidos en el meta-análisis de los efectos de la cafeína sobre la distancia máxima de carrera (2 estudios), el tiempo de prueba (7 estudios) y la potencia muscular (4 estudios). Los tamaños del efecto se calcularon como diferencias estandarizadas en las medias (std en los medias), y el meta-análisis se completó utilizando un modelo de efectos aleatorios. Resultados: La suplementación con cafeína no aumentó la distancia máxima de funcionamiento (tamaño del efecto= 0.37, p= 0.14) ni la potencia muscular (tamaño del efecto= 0.17, p= 0.36). Sin embargo, se observaron mejoras en el rendimiento del ensayo con tiempo (tamaño del efecto= −0.40, p< 0,01). Los análisis de subgrupos revelaron que la mejora en los resultados de los ensayos a tiempo podía estar relacionada con el uso de la dosis de 6 mg/kg de peso corporal de cafeína (tamaño del efecto= −0.45, p = 0.01). Conclusiones: El meta-análisis demostró que la ingesta de cafeína no mejora el rendimiento en la distancia máxima de carrera ni la potencia muscular, pero parece mejorar el rendimiento de la prueba de tiempo. Este efecto potencial de la cafeína en el rendimiento de la prueba de tiempo estuvo relacionado con la dosis.

Caffeine Attenuates Decreases in Leg Power Without Increased Muscle Damage.

Ribeiro, BG, Morales, AP, Sampaio-Jorge, F, Barth, T, de Oliveira, MBC, Coelho, GMdO, and Leite, TC. Caffeine attenuates decreases in leg power without increased muscle damage. J Strength Cond Res 30(8): 2354-2360, 2016-Caffeine ingestion has been shown to be an effective ergogenic aid in several sports. Caffeine administration may increase exercise capacity, which could lead to a greater degree of muscle damage after exercise. This was a randomized, double-blind, placebo-controlled crossover study. Six male handball athletes ingested placebo (PLA) or caffeine (CAF) (6 mg·kg body mass) capsules on 2 different occasions. Sixty minutes after ingestion of the capsules, serum CAF levels were evaluated. Thereafter, all participants performed a protocol of vertical jumps (VJs). The protocol consisted of 4 sets of 30 seconds of continuous VJs with 60 seconds of recovery between sets. Blood lactate (LAC) and creatine kinase (CK) levels were determined before and after the protocol. We found significant differences in serum CAF levels between PLA (0.09 ± 0.18 µg·ml) vs. CAF (6.59 ± 4.44 µg·ml) (p < 0.001). Caffeine elicited a 5.23% (p ≤ 0.05) improvement in the leg power compared with PLA. The CAF trial displayed higher LAC (p ≤ 0.05) compared with PLA (6.26 ± 2.01 vs. 4.39 ± 2.42 mmol·L, respectively) after protocol of VJs, whereas no difference in CK was observed between trials (p > 0.05). These results indicate that immediate ingestion of CAF (6 mg·kg body weight) can reduce the level of muscle fatigue and preserve leg power during the test, possibly resulting in increase in LAC. There was no increase in muscle damage, which indicates that immediate administration of (6 mg·kg body weight) CAF is safe. Thus, nutritional interventions with CAF could help athletes withstand a greater physiological overload during high-intensity training sessions. The results of this study would be applicable to sports and activities that require repetitive leg power.

Resistance exercise inter-set cooling strategy: effect on performance and muscle damage.

PURPOSE: To compare the effect of inter-set cooling and no cooling during resistance exercise (RE) on the total repetitions and select muscle damage biomarker responses. METHODS: Sixteen healthy men volunteered to participate in this study and were randomly assigned to Cooling (n = 8) or Control (n = 8) groups. They performed a RE protocol consisting of four sets of biceps curl at 80% of 1RM. The cooling group received the application of wet bags of ice during each interest rest interval (Cooling), while the Control realized the same protocol without ice application. Exercise was performed to voluntary fatigue and the numbers of repetitions per set were recorded. Subjects provided blood samples before and at 24, 48, and 72 h following RE to evaluate serum CK activity and myoglobin concentration. RESULTS: The Cooling group produced a greater number of repetitions (approx. 21%) than did the Control, but there were no differences in serum CK activity and myoglobin responses between the groups. CONCLUSION: Incorporating inter-set external cooling augments the number of repetitions per set during RE without inducing an additional muscle damage biomarker response.

Análise eletromiográfica dos músculos masseter, temporal e trapézio em diferentes condições da lordose cervical / Electromyographic analysis of masseter, temporalis and trapezius muscles in different conditions of the cervical lordosis

Desequilíbrios osteomioarticulares da região cervical e craniomandibular têm sido referenciados como fontes potenciais de disfunções da articulação temporomandibular. O presente estudo objetivou analisar a atividade eletromiográfica (EMG) dos músculos masseter, temporal anterior e trapézio, bilateralmente, com a coluna cervical em posição lordose fisiológica (LF) e em posição de hiperlordose ( HL), induzida através da colocação de um rolo de espuma com raio de 5 cm, nas condições de repouso e durante oclusão dentária com força máxima. 10 indivíduos saudáveis (5 homens e 5 mulheres), sem acometimento da articulação temporomandibular ou da coluna cervical foram voluntários no estudo, sendo observado que em condição de repouso o músculo masseter direito apresentou maior atividade EMG na postura de LF (7.0+-1.uV) em relação à postura de HL ( 6.1+-1.ouV) (p<0.05), já o músculo trapézio esquerdo apresentou maior atividade EMG na postura de HL (9.2+-1.O uV) se comparada à postura de LF (7.0+-O.6uV)(p<0.05), durante o ato de oclusão dentária com força máxima houve maior ativação do músculo trapézio direito na postura de HL (9.6+-1.8uV) se comparada à postura de LF (6.6+-1.3.uV) (p<0.05). Os dados deste estudo apontam para uma potencial influência do input sensorial da região cervical na ativação do músculo masseter e trapézio, sendo recomendada a realização de estudos que reproduzam a metodologia aqui aplicada a amostras de indivíduos portadores de disfunção da articulação temporomandibular.

Unbalance in the skeletal system of the cervical and craniomandibular regions have benn indicated as potentials sources of temporomandibular dysfunctions. This study aims to analysis the electromyographical activity(EMG) of masseter, anterior temporal and upper trapezius muscles, bilaterally, with the cervical spine in physiological lordosis (PL) and in hiperlordosis (HL) positions, induced by roll placement with 5 cm of ray. In both positions the EMG was recorded during rest and dental occlusion with maximal effort. 10 health subjects (5 men and 5 women) without history of temnporomandibular or cervical spine disease participated in the estudy. In rest condition the EMG activity of right masseter muscle in PL posture ((7.0+-1.uV) was greater than HL ( 6.1+-1.ouV) (p<0.05), the left trapezius muscle showed greater EMG activity in the HL (9.2+-1.O uV) in relation to the PL posture (7.0+-O.6uV)(p<0.05), the EMG activity of the right trapezius muscle in the posture (9.6+-1.8uV) was greater than the PL (6.6+-1.3.uV) (p<0.05) during the occlusion acts. The results obtained indicate the potential influence of the sensorial input of the cervical region in the masseter and trapezius muscle activities. We recommend that more studies are made reproducing this methodology, applying to the subjects with temporomandibular disorders.

Influências da barra infracapital sobre alterações posturais proprioceptivas ascendentes / Influences of the infracaptal bar on ascending proprioceptives postural alterations

A postura deve ser harmônica, equilibrada, com gasto energético mínimo necessário, para que não ocorra adaptações e lesões futuras. O pé é um dos principais captores, recebendo influências propriceptivas ascendentes para o ajuste postural. A utilização de palmilhas proprioceptivas com apoios previne e trata alterações posturais, sendo essencial para uma melhor qualidade de vida. O objetivo deste estudo foi analisar as influências da barra infracapital sobre a postura de indivíduos com alterações posturais proprioceptivas ascendentes, analisando o alinhamento de algumas estruturas ósseas previamente marcadas e relacionar o comprimento da mão com a lateralidade. A amostra foi constituída por 10 voluntários de ambos os sexos, com idade entre 20 e 30 anos. O estudo foi um ensaio clínico controlado. O experimento foi mensurado pela biofotometria e analisado pelo software Sapo, sendo assim analisado o alinhamento de estruturas ósseas previamente marcadas. Os dados foram exportados para o Excel e transformados em variação percentual, analisados pela estatística descritiva e aplicado o teste t de Student com nível de significância de (p<0,05). A partir dos resultados obtidos pode-se concluir que a barra infracapital influencia nas alterações posturais proprioceptivas ascendentes, melhorando o alinhamento das estruturas corporais, possivelmente através do reequilíbrio do tônus postural e das cadeias musculares, quando utilizadas no local indicado. A lateralidade não mostrou relação com o comprimento do membro superior. Porém sugere-se um novo estudo com um número maior de voluntários para comparação dos resultados.

The attitude should be harmonious, balanced, with minimum energy expenditure necessary for that does not occurtions and injuries in the future. The foot is a major captors, receiving influences proprioceptives upside to the postural adjustment. The use of insoles proprioceptives, with support prevents and treats the postural alterations being essencial for a better quality of life. The objective of this study was to analyze the influence of the bar infracapital about the posture of individuals with postura alterations proprioceptives upside, analyzing the alignment of some bony structures previously marked and linking the length of the hand with dominant side. The sample was composed of 10 volunteers of both sexes, aged 20 and 30 years. The study was a controlled clinical try. The experiment was measured by biofotometria and analyzed by the software "Sapo" and therefore considered the alignment of bony structures previously marked. The data were exported to Excel and transformed into percent variation, analyzed by descriptive statistics and applied the Student t the with significance level of (p<0.05). From the results it can be concluded that the bar infracapital influences in postural alteration proprioceptives upside, improving the alignment of body structures through the rebalancing of postural tone and muscle of the chains, when used in the place indicated. The dominant side didn't show relation with the length of the upper limb. But it is suggested a new study with a larger number of volunteers.