The Effects of Caffeine on Heart Rate and Heart Rate Variability at Rest and During Submaximal Cycling Exercise

The aim of this study was to investigate the effects of caffeine on heart rate and heart rate variability (HRV) at rest and during submaximal exercise. Using a balanced, double-blind, randomized, crossover design, 16 male cyclists (age: 37 ± 9 years; V ˙ O2max: 4.44 ± 0.67 L·min-1) completed three trials in an air-conditioned laboratory. In Trial 1, cyclists completed two incremental cycling tests to establish the V ˙ O2-power output relationship and V ˙ O2max. In trials 2 and 3, cyclists were evaluated for heart rate and HRV at rest, after which they ingested a capsule containing 5 mg·kg-1 of caffeine or placebo. Thirty-five minutes post-supplementation, additional resting heart rate and HRV readings were taken after which cyclists completed a submaximal incremental cycling test (6 min stages) at 40-80% of V ˙ O2max; with HR and HRV measurements taken in the last 5 min of each increment. HRV was determined from the root mean square of successive differences between R-R intervals. There were significant supplement × exercise intensity interactions on heart rate (p = .019) and HRV (p = .023), with post hoc tests on the latter showing that caffeine increased HRV at 40%, 50%, and 60% of V ˙ O2max by 3.6 ± 4.9, 2.6 ± 2.8, and 0.6 ± 1.7 ms, respectively. There was a supplement × time interaction effect on resting HRV (p < .001), but not on heart rate (p = .351). The results of this study support the suggestion that caffeine increases the parasympathetic modulation of heart rate.Clinical trial registration number: NCT05521386.

Comparative effects of caffeine, beta-alanine, and their combination on mechanical, physiological, and perceptual responses to upper-body superset resistance training

Caffeine and beta-alanine are widely used in multi-ingredient pre-workout supplements believed to enhance resistance training, but their specific role in driving this effect remains unclear. The current study employed a randomized, triple-blinded, placebo-controlled and crossover experimental design to explore the acute effects of caffeine (200 mg), beta-alanine (3 g), or their combination (200 mg caffeine and 3 g beta-alanine; C+B-A) administered 30 min prior to resistance training (RT) on mechanical, physiological, and perceptual variables. Twenty-one young resistance-trained males (age = 23.5 ± 4.5 years, body mass = 82.1 ± 10.2 kg) visited the laboratory on six occasions: one familiarization session, one preliminary testing session for load determination, and four experimental sessions which differed only in supplementation condition and involved four supersets of bench press and bench pull exercises. The supplement condition did not significantly affect any mechanical variables (p ≥ 0.335), except for the velocity of the last repetition of the set, where beta-alanine produced lower values (0.383 m/s) compared to placebo (0.407 m/s; p < 0.05), with no differences observed for C+B-A (0.397 m/s) and caffeine (0.392 m/s). Heart rate was consistent across the different supplement conditions with the exception of the higher values observed immediately before the start of the RT session for placebo compared to caffeine (p = 0.010) and C+B-A (p = 0.019). Post-RT blood lactate concentration (p = 0.384), general and local ratings of perceived exertion (p = 0.177 and 0.160, respectively), and readiness (p = 0.281-0.925), did not differ significantly between supplement conditions. Selected supplements have minimal effects on performance and physiological responses in agonist-antagonist upper-body superset RT not leading to failure.

Habitual Caffeine Consumption and Training Status Affect the Ergogenicity of Acute Caffeine Intake on Exercise Performance

BACKGROUND

Acute caffeine ingestion can improve exercise performance. Interplay between caffeine habituation and training status on the performance-enhancing effect of caffeine is unknown.

HYPOTHESIS

Habitual caffeine consumption and training status affect the ergogenicity of pre-exercise caffeine intake on exercise performance.

STUDY DESIGN

Double-blind, placebo-controlled, counterbalanced experimental design.

LEVEL OF EVIDENCE

Level 3.

METHODS

Eighty physically inactive men were randomized into 1 of 4 groups: caffeine supplementation (CAF), caffeine supplementation + exercise training (CAFEXE), placebo (PLA), and placebo + exercise training (PLAEXE); high-intensity interval training and caffeine were administered for 9 and 8 weeks, respectively. Data were collected pre-test, mid-test, post-test, and delayed post-test, each including 2 experiment sessions (3 mg/kg caffeine or placebo), with an additional experiment session post-test (6 mg/kg caffeine). In each experiment session, 45-min after consuming a placebo or caffeine, a 3-km running test and a Wingate power test were performed.

RESULTS

Pre-exercise ingestion of 3 mg/kg caffeine improved 3-km running time and mean power output (MPO) in all groups at all stages (P < 0.05); this effect was higher in trained than in untrained volunteers (P < 0.05). Habitual caffeine consumption reduced the ergogenic effect of caffeine in both aerobic and anaerobic trials (P < 0.05); 6 mg/kg caffeine enhanced this decrease only in CAFEXE (P < 0.05). Short-term caffeine withdrawal augmented the reduced ergogenic effect of caffeine on 3-km running performance and MPO in CAF and CAFEXE (P < 0.05).

CONCLUSION

Habituation to caffeine and training status could partially influence the ergogenic effects of caffeine on exercise performance.

CLINICAL RELEVANCE

Regular caffeine consumption leads to some degree of tolerance and decreases its ergogenicity. A pre-exercise increase in caffeine dosage in trained people and short-term caffeine withdrawal in both trained and untrained people could compensate for the reduced caffeine ergogenicity in young men.

Does caffeine supplementation affect sleep in athletes? A systematic review of nine randomized controlled trials

OBJECTIVE

This systematic review aimed to assess the effects of caffeine supplements on sleep parameters among professional athletes.

METHODS

A systematic search of randomized controlled trials (PROSPERO: CRD42024505377) was performed from 1980 to December 2023 through Web of Science (ISI), Cinahl, Embase, CENTRAL, PubMed/MEDLINE, Scopus, and Scienceopen. The effect of caffeine supplement on all sleep parameters (e.g. duration, quality, insomnia), assessed through objective and subjective methods, was investigated among the athletic community.

RESULTS

Of 1469 records, nine trials were eligible for the current review. The studies showed varying results concerning sleep quality, quantity, efficiency, number of awakenings, sleep onset latency, and other sleep-related variables. These differences in findings may be attributable to factors such as the timing of caffeine consumption in relation to sleep time and the time of exercise, habitual caffeine use, and the dose of caffeine prescribed. Given the nature of caffeine, insomnia following ingestion is likely to occur.

CONCLUSIONS

This review explores the mechanisms by which caffeine influences sleep in athletes. While caffeine supplementation may enhance athletic performance, it could have a detrimental effect on sleep and therefore recovery. It is important that supplementation considers individual responses to caffeine so that it does not adversely affect sleep in this population.

PROSPERO REGISTRATION NUMBER

CRD42024505377.

Habitual preexercise caffeine supplementation prevents exercise training-induced attenuation of exercising systolic blood pressure and double product

We examined the effect of habitual preexercise caffeine supplementation on training-induced adaptations to exercising systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP), heart rate (HR), and double product (DP). Young women (means ± SD; 24 ± 7 yr) were randomized to a caffeine (120 mg) supplement (CAF; n = 17) or placebo (PLA; n = 16) group, completed 6 wk of high-intensity exercise training on three nonconsecutive days per week, and supplemented with CAF or PLA 30-60 min before exercise or else upon waking. Before (PRE) and after (POST) the intervention, SBP, DBP, and HR were measured and PP and DP were calculated, at rest and during fixed-power exercise at 50 and 75 W. Statistical analyses included three-way mixed-factorial ANOVAs with post hoc comparisons as necessary. Group × intensity × time interactions were observed for SBP (P = 0.0105) and DP (P = 0.003). SBP and DP increased with increasing exercise intensity at PRE and POST in both groups. However, although SBP and DP decreased PRE to POST at 50 and 75 W in PLA, SBP and DP did not change at any intensity from PRE to POST in CAF. An intensity × time interaction was observed for DBP (P = 0.006) indicating no change in resting DBP, but reductions from PRE to POST at 50 and 75 W that were independent of group. Main effects of intensity (P < 0.0001) and time (P = 0.03) were observed for HR, and a main effect of intensity was observed for PP (P < 0.0001). Habitual caffeine supplementation blunted training-induced reductions in exercising SBP and DP. Individuals may wish to avoid preexercise supplementation if seeking to maximize the BP-lowering benefits of exercise.NEW & NOTEWORTHY Habitual preexercise caffeine consumption prevented reductions in exercising systolic blood pressure and double product induced by 6 wk of high-intensity exercise in women. Therefore, our findings indicate that habitual preexercise caffeine supplementation may impede beneficial hemodynamic adaptations of exercise training in healthy, young women.

Effects of Caffeine Intake Combined with Self-Selected Music During Warm-Up on Anaerobic Performance: A Randomized, Double-Blind, Crossover Study

BACKGROUND

Both listening to music during warm-up and consuming caffeine before exercise have been independently shown to enhance athletic performance. However, the potential synergistic effects of combining these strategies remain largely unexplored. To date, only two studies have reported additional benefits to combining music during warm-up with a caffeine dose of 3 mg/kg on taekwondo-specific performance tasks. However, these studies did not evaluate whether this combination produces additive or synergistic effects on other types of sports performance. The present study aimed to assess the effects of listening to music alone or combined with caffeine intake on performance in the Wingate anaerobic test (WAnT) in physically active subjects.

METHODS

Twenty-four physically active male participants took part in this randomized, double-blind, crossover experiment. Participants underwent WAnT performance evaluations under three conditions: (i) no intervention (control; CON); (ii) music plus placebo (Mus + PLA), involving the intake of a placebo (maltodextrin) 60 min prior and self-selected high-tempo music during warm-up; and (iii) music plus caffeine (Mus + CAF), involving the intake of 3 mg/kg of caffeine 60 min prior and self-selected high-tempo music during warm-up. Under all conditions, participants wore the same Bluetooth headphones (with or without music), performed a 10 min standardized warm-up, and completed the 30 s WAnT with a load of 7.5% of their body weight on a calibrated ergometer. Power output was recorded at a frequency of 1 Hz throughout the exercise. The Feeling Scale was assessed both before and after the exercise test, while heart rate (HR) and the rating of perceived exertion (RPE) were measured immediately following the exercise.

RESULTS

Mus + PLA and Mus + CAF significantly improved peak power, mean power, and total work compared with CON (p < 0.05). Furthermore, peak power was higher in Mus + CAF than in Mus + PLA (p = 0.01). Post-exercise HR and RPE showed no significant differences across conditions (p > 0.05). Regarding the Feeling Scale (FS) before exercise, the Mus + PLA and Mus + CAF conditions showed significantly higher scores than CON (p < 0.05), while no differences were found after exercise. The perceived fitness metrics displayed no significant differences among conditions (p > 0.05), except for self-perceived power, which was higher in Mus + CAF than in CON (p = 0.03).

CONCLUSIONS

Self-selected music during warm-up, either alone or combined with caffeine, significantly enhanced several WAnT performance metrics, including peak power, mean power, and total work. Remarkably, combining music with caffeine further improved peak power and increased self-perceived power compared with music alone. While listening to self-selected music during warm-up provided measurable benefits on anaerobic exercise performance, the combination of music and caffeine demonstrated additive effects, making it the optimal strategy for maximizing anaerobic performance.

Efficacy of caffeine as an ergogenic aid in multiple cycling time trials

INTRODUCTION

Evidence that caffeine supplementation is effective to improve performance in cycling time trials has been obtained in single rather than multiple time trials. We investigated whether 5 mg.kg-1 of caffeine enhanced performance in multiple 4 km cycling time trials (TT4km) conducted within the same day and across different days.

METHODS

After selection of eligible cyclists and familiarization with the TT4km, thirteen well-trained cyclists participated in a balanced placebo-controlled designed with two caffeine sessions (CAF-1 and CAF-2) and a placebo session. In each session, cyclists performed a baseline TT4km before caffeine, and two supplemented TT4km (50 min and 80 min after supplementation). Relative and absolute reliability were obtained through intraclass coefficient correlation and standard error of the measurement (SEM), respectively. The cyclists' performance responses to caffeine were classified as beneficial, unchanged, and adverse by calculating the change between caffeine and placebo relative to SEM.

RESULTS

Caffeine enhanced performance in the first supplemented TT4km in CAF-1 and CAF-2 (0.5% and 1.8%, respectively), although only CAF-2 was significantly different from placebo (p < 0.001). Analysis with grouped data showed good absolute and relative reliability of caffeine effects within and across days. However, analysis of individual data showed that 38% and 31% of the cyclists changed their classification of responsiveness to caffeine between the supplemented trials across days.

CONCLUSIONS

Despite the good reliability of caffeine to enhance performance in a single TT4km performed within and across days, individual analysis challenged the use of caffeine supplementation protocols based on grouped data.

Caffeine, but not paracetamol (acetaminophen), enhances muscular endurance, strength, and power

BACKGROUND

Caffeine is one of the most popular ergogenic aids consumed by athletes. Caffeine's ergogenic effect has been generally explained by its ability to bind to adenosine receptors, thus modulating pain and reducing perceived exertion. Another pharmacological agent that may improve performance due to its analgesic proprieties is paracetamol. This study aimed to explore the effects of caffeine, paracetamol, and caffeine + paracetamol consumption on muscular endurance, strength, power, anaerobic endurance, and jumping performance.

METHODS

In this randomized, crossover, double-blind study, 29 resistance-trained participants (11 men and 18 women) ingested either a placebo, caffeine (3 mg/kg), paracetamol (1500 mg) or caffeine + paracetamol 45 min before the testing sessions. The testing sessions included performing the bench press exercise with 75% of one-repetition maximum to momentary muscular failure, isokinetic knee extension and flexion at angular velocities of 60°/sec and 180°/sec, Wingate, and countermovement jump (CMJ) tests.

RESULTS

Compared to placebo, isolated caffeine ingestion increased the number of repetitions performed in the bench press (p = 0.005; d = 0.42). Compared to placebo, isolated caffeine ingestion and/or caffeine + paracetamol consumption was ergogenic for strength (torque), muscular endurance (total work), or power in the isokinetic assessment, particularly at slower angular velocities (p = 0.027 to 0.002; d = 0.16 to 0.26). No significant differences between the conditions were observed for outcomes related to the Wingate and CMJ tests.

CONCLUSION

This study provided novel evidence into the effectiveness of caffeine, paracetamol, and their combination on exercise performance. We found improvements in muscular endurance, strength, or power only when caffeine was consumed in isolation, or in combination with paracetamol. Isolated paracetamol consumption did not improve performance for any of the analyzed outcomes, thus calling into question its ergogenic potential.

Effects of different doses of caffeine on cognitive performance in healthy physically active individuals

PURPOSE

Caffeine is a potent central nervous system stimulant that increases the activity of the prefrontal cortex and can improve various cognitive skills. An improvement in these cognitive skills can lead to further benefits in athletic performance. Therefore, it is necessary to clarify the dose-response of caffeine on cognitive performance. This study aimed to determine the effects of different doses of caffeine on sport-related cognitive aspects.

METHODS

Twenty-nine healthy physically active young adults were recruited. All participants completed three trials under the following conditions: (a) placebo, (b) 3 mg/kg, or (c) 6 mg/kg body mass of caffeine. In each trial, different cognitive abilities were evaluated with the following battery of tests: reaction time (Dynavision™ D2), anticipation (Bassin Anticipation Timer), sustained attention (Go/No-Go and Eriksen Flanker Test) and memory tests. Moreover, the side effects and the perceived sensation index were recorded 24 h after each test.

RESULTS

Reaction time only improved following 6 mg/kg of caffeine intake (Physical reaction time: -0.04 s, 95% CI -0.08 to -0.01 s, P = 0.036, d = 0.5; Motor reaction time: -0.04 s, 95% CI -0.07 to -0.01 s, P = 0.008, d = 0.6) compared to the placebo condition. Anticipation, sustained attention, and memory were not affected after either caffeine dose intake (all P > 0.05). In addition, the 6 mg/kg dose of caffeine augmented the occurrence of the side effects of increased activeness (P = 0.046) and nervousness (P = 0.001).

CONCLUSION

Acute intake of 6 mg/kg caffeine is effective in improving reaction time despite increasing the occurrence of side effects in healthy physically active young adults.

STUDY REGISTRATION

This study has been registered in ClinicalTrials whose ID is: NCT05995314 (2023-08-08).

Effects of Caffeinated Chewing Gum on Exercise Performance and Physiological Responses: A Systematic Review

BACKGROUND

Caffeine intake in the form of chewing gum is characterized by rapid absorption and utilization.

OBJECTIVES

The purpose of this study was to investigate the effects of caffeinated chewing gum on exercise performance and physiological responses in a systematic review.

METHODS

All articles were searched using the PubMed and Scopus databases to include articles published up to June 2024, following the Preferred Reporting Items for Systematic Evaluation and Meta-Analysis (PRISMA) protocol.

RESULTS

Thirty-two studies were finally included. Most studies have found that pre-exercise caffeinated chewing gum supplementation is effective in improving endurance, repetitive sprinting, lower limb strength, and sport-specific performance, as well as lowering rating of perceived exertion (RPE) or fatigue index even with lower dosages of caffeine. Sympathetic activation may be one of the mechanisms by which caffeinated chewing gum affects athletic performance. No significant effect on energy metabolism indicators (blood glucose, blood lactate, free fatty acids) was found. In addition, two studies found that caffeinated chewing gum reduced or maintained cortisol levels and increased testosterone levels. However, caffeinated chewing gum intake does not have an impact on catecholamines and β-endorphins. There have been inconsistent results for explosive performance, agility performance, and pain perception. Only a few studies have examined balance performance. In conclusion, a low dose of caffeine (100-300 mg or 2-4 mg/kg) in the form of chewing gum is rapidly absorbed and utilized, positively impacting most exercise and physiological performance.

CONCLUSIONS

Future studies should also consider the performance variables of agility, pain perception, and explosive performance to gain a more comprehensive understanding of the effects of caffeinated chewing gum on sympathetic activation and exercise performance.

Determining the Levels of Cortisol, Testosterone, Lactic Acid and Anaerobic Performance in Athletes Using Various Forms of Coffee

BACKGROUND

Coffee is considered one of the most preferred and consumed beverage types in the world, and caffeine is known to increase physical performance due to its ergogenic properties. The aim of this study is to examine the effects of coffee consumption in different forms on cortisol, testosterone, lactic acid and anaerobic performance levels.

METHODS

A total of 15 licensed male football players participated in the research voluntarily. The research was implemented in a single-blind, counterbalanced, randomized and crossover study design. Participants were given caffeinated coffee (CK), decaffeinated coffee (placebo) (DK), powdered caffeine (in a gelatin capsule) (PC) and powdered placebo (maltodextrin in a capsule) (PM) on different days, and the Wingate test protocol was performed after the warm-up protocol. Blood samples were collected post-test. Cortisol, testosterone and lactic acid levels in the serum samples taken were determined by the ELISA method.

RESULTS

As a result, it was revealed that caffeinated coffee given to participants who exercise increased anaerobic power. However, it was observed that lactic acid levels were higher in placebo and decaffeinated coffee. The highest level of cortisol was found in caffeinated coffee and powdered caffeine compared to the placebo. Testosterone values were observed to be highest in caffeinated coffee and decaffeinated coffee compared to a placebo.

CONCLUSIONS

The study suggests that the type of caffeine is a factor that affects absorption rate, which impacts performance and hormone levels.

The effect of caffeine supplementation on muscular strength and endurance: A meta-analysis of meta-analyses

Background

Caffeine is commonly used as an ergogenic aid to increase strength and endurance in athletes. The results of meta-analyses in this regard are still conflicting. Therefore, the current umbrella meta -analysis was conducted to determine the effects of caffeine supplementation on muscle strength and endurance as a clear and final conclusion.

Methods

Relevant studies were searched in international databases including PubMed, Scopus, and Web of Science until August 15, 2022. Meta-analysis studies examining the effects of caffeine supplementation on muscle strength and endurance were included in this study. Random effects model was used to perform meta-analysis. Additional analyses including subgroup and sensitivity analyzes were performed.

Findings

In general, 9 meta-analyses were included in the study. The results showed that caffeine supplementation led to a significant increase in muscle strength (SMD = 0.18, 95 % CI: 0.14, 0.21; p < 0.001) and muscle endurance (SMD = 0.30, 95 % CI 0.21, 0.38; p < 0.001).

Conclusion

Meta -analysis showed the significant effects of caffeine consumption on muscle strength and muscle endurance. Due to the lack of evidence, further studies are needed in the women's population.

Pre-Exercise Caffeine and Sodium Bicarbonate: Their Effects on Isometric Mid-Thigh Pull Performance in a Crossover, Double-Blind, Placebo-Controlled Study

Caffeine and sodium bicarbonate are extensively researched ergogenic aids known for their potential to enhance exercise performance. The stimulant properties of caffeine on the central nervous system, coupled with the buffering capacity of sodium bicarbonate, have been associated with improved athletic performance. This has led to investigations of their combined effects on strength. The aim of the present study is to investigate the effect of isolated and combined caffeine and sodium bicarbonate consumption on strength using the isometric mid-thigh pull test (IMTP). Nineteen male college students (age 23.6 ± 1.6 years) participated in this crossover, double-blind, placebo-controlled study. They were exposed to the following conditions: control (no supplement), placebo (20 g maltodextrin), caffeine (6 mg/kg), sodium bicarbonate (0.3 g/kg), and a combination of caffeine and sodium bicarbonate. Supplements and placebo were diluted in water and consumed 60 min prior to the IMTP tests. Two 5 s IMTP trials were performed at 40-60% and 60-80% of One Repetition of Maximum (1RM) with a 60 s rest between. Consumption of caffeine or Caf + NaHCO3 did not significantly change peak IMTP strength values at any intensity (p = 0.110). The peak IMTP values did not show significant differences between conditions or from control condition values (1091 ± 100 N) to Caf (1224 ± 92 N), NaHCO3 (1222 ± 74 N), and Caf ± NaHCO3 (1152 ± 109 N). However, the test of the results of the ANOVA analysis of repeated measures of effect within the caffeine condition was significant for the increase in IMTP relative strength compared to control (p < 0.05). Thus, the IMTP force values increased significantly from control to Caf (p = 0.016) and from Pla to Caf (p = 0.008), but not for other comparisons (p > 0.05). In summary, caffeine supplementation alone, taken 60 min before exercise, positively affects submaximal strength performance. In contrast, sodium bicarbonate, whether taken alone or in combination with caffeine, does not enhance submaximal strength in the IMTP tests.

Moderate-dose caffeine enhances anaerobic performance without altering hydration status

The effects of direct nutritional supplements on athletic performance are still being investigated and arouse curiosity. Only one study in the literature was found that investigated the kicking speed performance of futsal players following low-dose caffeine supplementation (3 mg/kg); thus, the question of whether caffeine supplementation improves kicking speed as well as essential physical parameters in soccer players is still controversial. Therefore, the aim of this study was to determine the effect of caffeine supplementation on vertical jump (VJ), sprint, reaction time, balance, change of direction (COD), and ball-kicking speed in soccer players. In a double-blind, cross-over design, nine moderately trained male soccer players (21.11 ± 2.02 years, 171.22 ± 6.14 cm, 71.78 ± 10.02 kg) consumed caffeine (6 mg/kg) or a placebo 60 min before completing balance, reaction time, vertical jump, agility, 30 m sprint, and ball-kicking speed tests. Greater VJ height (p = 0.01) and power (p = 0.08), and faster completion time according to the Illinois Agility Test (p = 0.08) were found following caffeine supplementation compared to placebo. Elapsed time (p = 0.01), average (p = 0.01) time, and the slowest reaction times (p = 0.016) were significantly reduced after caffeine consumption compared to placebo supplementation. Caffeine intake significantly improved VJ, agility, and reaction time (p < 0.05) but did not affect 30 m sprint, ball-kicking speed, balance, and RPE values in soccer players (p > 0.05). Although non-significant, caffeine intake also improved sprint (0.67%) and ball kicking (2.7%) performance percentages. Also, caffeine consumption did not induce dehydration, and the athletes' body hydration levels were normal. These findings support the use of caffeine supplementation as an effective nutritional ergogenic aid to enhance anaerobic performance, at least for vertical jumps, COD speed, and reaction time, in trained male soccer players.

Caffeine Supplementation Effects on Concurrent Training Performance in Resistance-Trained Men: A Double-Blind Placebo-Controlled Crossover Study

Purpose: The aim of the present study was to investigate the effects of acute caffeine supplementation on the performance during a session of resistance training alone (RT) or in combination with aerobic training (i.e. concurrent training; CT). Method: Fourteen resistance-trained men (23.1 ± 4.2 years) were recruited and performed both RT and CT under three different conditions: control (CONT), placebo (PLA), and caffeine (CAF; 6 mg.kg-1) for a total of six experimental conditions. Results: Both total and per set number of repetitions, and total volume load were lower during CT as compared to RT, irrespective of the supplementation condition (all p < .001), whereas a supplementation main effect was observed for the total number of repetitions (p = .001), the number of repetitions in the first (p = .002) and second sets (p = .001), and total volume load (p = .001). RPE values were higher after the CT sessions than after the RT sessions (p < .001), whereas no differences were observed between supplementation conditions (p = .865). Conclusions: Caffeine supplementation was not sufficient to minimize the acute interference effect on strength performance in a CT session when compared to RT alone. In contrast, caffeine improved strength performance during the first set of both CT and RT, while maintaining a similar RPE between the supplementation conditions. However, the overall effect was small.

Timing Matters: Time of Day Impacts the Ergogenic Effects of Caffeine-A Narrative Review

Caffeine has attracted significant attention from researchers in the sports field due to its well-documented ergogenic effects across various athletic disciplines. As research on caffeine continues to progress, there has been a growing emphasis on evaluating caffeine dosage and administration methods. However, investigations into the optimal timing of caffeine intake remain limited. Therefore, this narrative review aimed to assess the ergogenic effects of caffeine administration at different times during the morning (06:00 to 10:00) and evening (16:00 to 21:00). The review findings suggest that circadian rhythms play a substantial role in influencing sports performance, potentially contributing to a decline in morning performance. Caffeine administration has demonstrated effectiveness in mitigating this phenomenon, resulting in ergogenic effects and performance enhancement, even comparable to nighttime levels. While the specific mechanisms by which caffeine regulates circadian rhythms and influences sports performance remain unclear, this review also explores the mechanisms underlying caffeine's ergogenic effects, including the adenosine receptor blockade, increased muscle calcium release, and modulation of catecholamines. Additionally, the narrative review underscores caffeine's indirect impact on circadian rhythms by enhancing responsiveness to light-induced phase shifts. Although the precise mechanisms through which caffeine improves morning performance declines via circadian rhythm regulation necessitate further investigations, it is noteworthy that the timing of caffeine administration significantly affects its ergogenic effects during exercise. This emphasizes the importance of considering caffeine intake timing in future research endeavors to optimize its ergogenic potential and elucidate its mechanisms.

Effects of Acute Ingestion of Caffeine Capsules on Muscle Strength and Muscle Endurance: A Systematic Review and Meta-Analysis

This study aimed to explore the effects of acute ingestion of caffeine capsules on muscle strength and muscle endurance. We searched the PubMed, Web of Science, Cochrane, Scopus, and EBSCO databases. Data were pooled using the weighted mean difference (WMD) and 95% confidence interval. Fourteen studies fulfilled the inclusion criteria. The acute ingestion of caffeine capsules significantly improved muscle strength (WMD, 7.09, p < 0.00001) and muscle endurance (WMD, 1.37; p < 0.00001), especially in males (muscle strength, WMD, 7.59, p < 0.00001; muscle endurance, WMD, 1.40, p < 0.00001). Subgroup analyses showed that ≥ 6 mg/kg body weight of caffeine (WMD, 6.35, p < 0.00001) and ingesting caffeine 45 min pre-exercise (WMD, 8.61, p < 0.00001) were more effective in improving muscle strength, with the acute ingestion of caffeine capsules having a greater effect on lower body muscle strength (WMD, 10.19, p < 0.00001). In addition, the acute ingestion of caffeine capsules had a greater effect in moderate-intensity muscle endurance tests (WMD, 1.76, p < 0.00001). An acute ingestion of caffeine capsules significantly improved muscle strength and muscle endurance in the upper body and lower body of males.

Effects of Various Caffeine Doses on Cognitive Abilities in Female Athletes with Low Caffeine Consumption

Caffeine (CAF), a prevalent psychoactive stimulant, is believed to potentially enhance cognitive ability. However, studies on the effects of various doses are limited and yield inconsistent results, particularly in female athletes. Therefore, we aimed to assess the association between three different dosages of CAF intake (low, moderate, and high) and cognitive skills in female athletes with low CAF consumption. This study had a randomized, crossover, double-blind design in which each athlete performed four experimental sessions after ingesting either a placebo (PLAC), 3 mg·kg-1 of CAF (3 mg of CAF), 6 mg·kg-1 of CAF (6 mg of CAF), or 9 mg·kg-1 of CAF (9 mg of CAF) with an in-between washout period of at least 72 h. Following a 60 min window post-capsule consumption, fourteen female athletes (age: 17.4 ± 0.8 years) were assessed through various cognitive tests, namely, simple reaction time (SRT), choice reaction time (CRT), and attentional task (AT) tests, along with the mental rotation test (MRT). Additionally, they were required to complete a questionnaire about the undesirable side effects of CAF. Our results indicated that, compared to those of PLAC, the SRT, CRT, and AT performance were significantly improved following the administration of both 3 mg of CAF and 6 mg of CAF. While the greatest enhancement was observed after consuming 3 mg of CAF, no significant differences were found between the effects of 3 mg and 6 mg of CAF. Interestingly, MRT performance did not improve with any of the CAF dosages. Moreover, the ingestion of 9 mg of CAF did not enhance cognitive skills and was linked to the highest occurrence of CAF-related side effects. In conclusion, our results highlight the recommendation for a low CAF dosage of 3 mg·kg-1, in contrast to a higher dose of 6 mg·kg-1 or 9 mg·kg-1 of CAF, to enhance various aspects of cognitive performance in female athletes with low CAF consumption without adverse side effects.

Optimizing Short-Term Maximal Exercise Performance: The Superior Efficacy of a 6 mg/kg Caffeine Dose over 3 or 9 mg/kg in Young Female Team-Sports Athletes

Caffeine (CAF) is among the most extensively researched dietary supplements worldwide. However, little is known about the relationship between dosage and performance enhancement, particularly in female athletes. This study aimed to explore the effects of three different CAF dosages (3 mg·kg-1, 6 mg·kg-1, and 9 mg·kg-1) on high-intensity exercise and the prevalence of undesirable side effects related to these doses among female team-sports athletes. All participants (n = 16; age: 16.9 ± 0.6 y; height: 1.64 ± 0.1 m; BMI: 21.6 ± 1.5 kg·m-2) were mild CAF consumers. This study had a randomized, crossover, double-blind design in which each athlete performed four experimental sessions after ingesting either a placebo (PLAC), 3 mg·kg-1 CAF (CAF-3), 6 mg·kg-1 CAF (CAF-6), or 9 mg·kg-1 of CAF (CAF-9), with an in-between washout period of at least 72 h. In each experimental session, 60 min after ingesting the capsules, participants underwent a countermovement jumps test (CMJ), modified agility t-test (MATT), repeated sprint ability (RSA) test, and a rating of perceived exertion (RPE) and completed the CAF side effects questionnaire. Our findings revealed that in comparison to the PLAC condition, the MATT, RSAmean, and RSAbest performances were significantly greater only under the CAF-6 and CAF-9 conditions. Although the RPE scores remained unchanged, CMJ performance improved under all CAF conditions. All the performance outcomes were better for the CAF-6 and CAF-9 conditions than for the CAF-3 condition. Notably, no significant difference between the CAF-6 and CAF-9 conditions was observed for any of these parameters despite the highest incidence of side effects being noted for the CAF-9 condition. In summary, our findings highlight the recommendation for a moderate CAF dosage of 6 mg·kg-1 rather than 3 or 9 mg·kg-1 to enhance various aspects of short-term maximal performance in mild-CAF-consumer female team-sports athletes while mitigating the occurrence of adverse CAF side effects.

Caffeine intake enhances peak oxygen uptake and performance during high-intensity cycling exercise in moderate hypoxia

PURPOSE

We investigated whether caffeine consumption can enhance peak oxygen uptake ([Formula: see text]) by increasing peak ventilation during an incremental cycling test, and subsequently enhance time to exhaustion (TTE) during high-intensity cycling exercise in moderate normobaric hypoxia.

METHODS

We conducted a double-blind, placebo cross-over design study. Sixteen recreational male endurance athletes (age: 20 ± 2 years, [Formula: see text]: 55.6 ± 3.6 ml/kg/min, peak power output: 318 ± 40 W) underwent an incremental cycling test and a TTE test at 80% [Formula: see text] (derived from the placebo trial) in moderate normobaric hypoxia (fraction of inspired O2: 15.3 ± 0.2% corresponding to a simulated altitude of ~ 2500 m) after consuming either a moderate dose of caffeine (6 mg/kg) or a placebo.

RESULTS

Caffeine consumption resulted in a higher peak ventilation [159 ± 21 vs. 150 ± 26 L/min; P < 0.05; effect size (ES) = 0.31]. [Formula: see text] (3.58 ± 0.44 vs. 3.47 ± 0.47 L/min; P < 0.01; ES = 0.44) and peak power output (308 ± 44 vs. 302 ± 44 W; P = 0.02, ES = 0.14) were higher following caffeine consumption than during the placebo trial. During the TTE test, caffeine consumption enhanced minute ventilation (P = 0.02; ES = 0.28) and extended the TTE (426 ± 74 vs. 358 ± 75 s; P < 0.01, ES = 0.91) compared to the placebo trial. There was a positive correlation between the percent increase of [Formula: see text] following caffeine consumption and the percent increase in TTE (r = 0.49, P < 0.05).

CONCLUSION

Moderate caffeine consumption stimulates breathing and aerobic metabolism, resulting in improved performance during incremental and high-intensity endurance exercises in moderate normobaric hypoxia.

Effects of caffeine supplementation on anaerobic power and muscle activity in youth athletes

This study aimed to investigate the effects of caffeine ingestion on anaerobic performance and muscle activity in young athletes. In this randomized, double-blind, and placebo-controlled study, ten highly trained male post-puberal futsal players aged 15.9 ± 1.2 years conducted two laboratory sessions. Athletes performed the Wingate test 60 min after ingestion of caffeine (CAF, 6 mg/kg body mass) or placebo (PL, dextrose) (blinded administration). Peak power, mean power, and the fatigue index were assessed. During the performance of the Wingate test, electromyographic (EMG) data were recorded from selected lower limbs muscles to determine the root mean square (RMS), mean power frequency (MPF), and median power frequency (MDPF) as frequency domain parameters and wavelet (WT) as time-frequency domain parameters. Caffeine ingestion increased peak (0.80 ± 0.29 W/Kg; p = 0.01; d = 0.42) and mean power (0.39 ± 0.02 W/Kg; p = 0.01; d = 0.26) but did not significantly affect the fatigue index (52.51 ± 9.48%, PL: 49.27 ± 10.39%; p = 0.34). EMG data showed that the MPF and MDPF parameters decreased and the WT increased, but caffeine did not have a significant effect on these changes (p > 0.05). Moreover, caffeine ingestion did not significantly affect RMS changes in the selected muscles (p > 0.05). Here we showed that acute caffeine ingestion improved anaerobic performance without affecting EMG parameters in young male futsal athletes.

Isolated but not combined ergogenic effects of caffeine and L-arginine during an isokinetic knee extension

Introduction

The use of single supplements as ergogenic aids to enhance performance in strength-oriented sports is widespread among athletes (74%). The aim of this study was to increase knowledge about the combined effects of caffeine and L-arginine dietary supplements on performance.

Methods

In this double-blind, randomized and counterbalanced crossover study, 29 participants (age: 23.2 ± 3.6 yr.; height: 181.0 ± 7.6 cm; weight: 77.0 ± 8.8 kg) each underwent six trials. In each trial performance tests were conducted to examine the effects of the supplement combinations on maximum (NmMax) and averaged torque (NmM), maximum (JMax) and averaged work (JM), the blockwise mean values of torque and work, and rate of perceived exertion (RPE) during an isokinetic leg extension task (90°·s-1) with the right leg for two sets of 40 repetitions and a set rest of 3 min on a dynamometer. The first and second trials were used to familiarize the participants with the movements in the dynamometer and no supplements were taken. After this 2-week pre-test trial, the supplement combinations of placebo/placebo, caffeine/placebo (5 mg·kg-1), L-arginine/placebo (0.15 g·kg-1), and caffeine/L-arginine (5 mg·kg-1 + 0.15 g·kg-1) were ingested.

Results

The main finding of this study is the absence of an ergogenic effect of the combined supplements caffeine and L-arginine during voluntary maximal isokinetic leg extensions, although an increase of 3.5% was noted for Nmmax compared to the placebo trial. However, the administration of caffeine was able to increase the NmMax of the quadriceps femoris muscle about 5.1% (p = 0.043). In addition, caffeine (4.2%, p = 0.026) and also L-arginine (4.2%, p = 0.040) significantly increased NmM over a complete set. No single or combined supplement had an effect on muscle fatigue looking at the blockwise mean values of torque and work or RPE (all p > 0.05).

Conclusion

The combination of caffeine and L-arginine was not superior to the isolated intake of both supplements in a strength-based exercise and a synergistic effect was absent.

Multi-omics reveals changed energy metabolism of liver and muscle by caffeine after mice swimming

In recent years, numerous studies have investigated the effects of caffeine on exercise, and provide convincing evidence for its ergogenic effects on exercise performance. However, the precise mechanisms underlying these ergogenic effects remain unclear. In this study, an exercise swimming model was conducted to investigate the effects of orally administered with caffeine before swimming on the alterations of proteome and energy metabolome of liver and muscle after swimming. We found proteins in liver, such as S100a8, S100a9, Gabpa, Igfbp1 and Sdc4, were significantly up-regulated, while Rbp4 and Tf decreased after swimming were further down-regulated in caffeine group. The glycolysis and pentose phosphate pathways in liver and muscle were both significantly down-regulated in caffeine group. The pyruvate carboxylase and amino acid levels in liver, including cysteine, serine and tyrosine, were markedly up-regulated in caffeine group, exhibiting a strong correlation with the increased pyruvic acid and oxaloacetate levels in muscle. Moreover, caffeine significantly decreased the lactate levels in both liver and muscle after swimming, potentially benefiting exercise performance.

Moderators of Caffeine's Effects on Jumping Performance in Females: A Systematic Review and Meta-Analysis

We aimed to perform a systematic review and meta-analysis of caffeine's effects on vertical jumping performance in females, with subgroup analyses for potential moderators, including phase of the menstrual cycle, testing time of day, caffeine dose, and test type. Fifteen studies were included in the review (n = 197). Their data were pooled in a random-effects meta-analysis of effect sizes (Hedges' g). In the main meta-analysis, we found an ergogenic effect of caffeine on jumping performance (g: 0.28). An ergogenic effect of caffeine on jumping performance was found when the testing was carried out in the luteal phase (g: 0.24), follicular phase (g: 0.52), luteal or follicular phase (g: 0.31), and when the phase was not specified (g: 0.21). The test for subgroup differences indicated that the ergogenic effects of caffeine were significantly greater in the follicular phase compared to all other conditions. An ergogenic effect of caffeine on jumping performance was found when the testing was carried out in the morning (g: 0.38), evening (g: 0.19), mixed morning or evening (g: 0.38), and when time was not specified (g: 0.32), with no subgroup differences. An ergogenic effect of caffeine on jumping performance was found when the dose was ≤3 mg/kg (g: 0.21), or >3 mg/kg (g: 0.37), with no subgroup differences. An ergogenic effect of caffeine on jumping performance was found in the countermovement jump test (g: 0.26) and squat jump test (g: 0.35), with no subgroup differences. In summary, caffeine ingestion is ergogenic for vertical jumping performance in females, and it seems that the magnitude of these effects is the largest in the follicular phase of the menstrual cycle.

The Effect of Caffeine Supplementation on Female Volleyball Players' Performance and Wellness during a Regular Training Week

BACKGROUND

caffeine is an ergogenic aid that still needs to be investigated in women's sports performance.

METHODS

Eight semi-professional women's volleyball players (height = 1.63 ± 0.08 m; weight = 66.67 ± 4.74 kg) voluntarily participated in this study. A randomized crossover design was implemented where players underwent caffeine and placebo conditions. In the caffeine condition, participants consumed 5 mg/kg of caffeine based on their body weight before acute training. The evaluations were performed over two weeks of training. In both conditions, the countermovement jump, repeated jumps for 15 s, and handgrip tests were performed. The change of direction was assessed using the 505 test. Well-being was also assessed with a wellness questionnaire. A repeated measures ANOVA and correlation analysis were performed.

RESULTS

The repeated measures ANOVA revealed a main effect of supplementation (F (1.7) = 8.41, p = 0.02, η2 = 0.54) across the training week on physical performance. Additionally, there was a positive effect on perceived fatigue (F (1.7) = 7.29, p = 0.03, η2 = 0.51).

CONCLUSIONS

Caffeine improved performance and fatigue parameters over one week of training. Further research is needed on women, focusing on physical performance and wellbeing, especially during intense periods.

The striatum drives the ergogenic effects of caffeine

Caffeine is one of the main ergogenic resources used in exercise and sports. Previously, we reported the ergogenic mechanism of caffeine through neuronal A2AR antagonism in the central nervous system [1]. We now demonstrate that the striatum rules the ergogenic effects of caffeine through neuroplasticity changes. Thirty-four Swiss (8-10 weeks, 47 ± 1.5 g) and twenty-four C57BL/6J (8-10 weeks, 23.9 ± 0.4 g) adult male mice were studied behaviorly and electrophysiologically using caffeine and energy metabolism was studied in SH-SY5Y cells. Systemic (15 mg/kg, i.p.) or striatal (bilateral, 15 μg) caffeine was psychostimulant in the open field (p < 0.05) and increased grip efficiency (p < 0.05). Caffeine also shifted long-term depression (LTD) to potentiation (LTP) in striatal slices and increased the mitochondrial mass (p < 0.05) and membrane potential (p < 0.05) in SH-SY5Y dopaminergic cells. Our results demonstrate the role of the striatum in the ergogenic effects of caffeine, with changes in neuroplasticity and mitochondrial metabolism.

Athlete Sleep Behavior Questionnaire in Japanese (ASBQ-J): An Adaptation and Validation Study

Purpose

The Athlete Sleep Behavior Questionnaire (ASBQ) is an 18-item self-reported questionnaire that can be used to screen for sleep disorders in athletes and assess environmental, behavioral, and sports-related factors along with sleep disorders. This study aimed to analyze the reliability and validity of the ASBQ translated into Japanese (ASBQ-J).

Patients and Methods

111 female collegiate athletes completed both the initial test and retest. Independent variables were what kind of sports they perform, level as an athlete, grade (freshman, sophomore, junior, senior), and age. The reliability of the survey was assessed using Cronbach's alpha and intraclass correlation, and Pearson's correlation coefficient was calculated to determine the correlation between the total ASBQ scores and three components which were routine/environmental, behavioral, and sports factors.

Results

A total of 37.8% of athletes had ASBQ scores equal or less than 36 indicating good sleep. However, 19.8% of athletes scored more than 42, indicating poor sleep. Cronbach alpha was 0.62 and 0.65 for test and retest, respectively. Intraclass correlation was 0.78 (P < 0.01), indicating sufficient internal consistency and test-retest validity. Mean ASBQ scores were 38.5 ± 5.0 and 37.0 ± 6.5 for test and retest, respectively, and it was not significantly different between the two groups (P = 0.37). The correlation coefficients between the ASBQ-J and component scores were all statistically significant (all P < 0.01).

Conclusion

ASBQ-J is a reliable questionnaire for assessing sleep disorders in athletes whose primary language is Japanese.

The Effect of Acute Caffeine Intake on Resistance Training Volume, Prooxidant-Antioxidant Balance and Muscle Damage Markers Following a Session of Full-Body Resistance Exercise in Resistance-Trained Men Habituated to Caffeine

No previous study has analyzed the impact of caffeine intake on prooxidant-antioxidant balance and muscle damage following resistance exercise. The aim of this study was to determine the effect of 3 mg/kg of caffeine on the number of repetitions and the prooxidant-antioxidant balance and muscle damage after a session of full-body resistance exercise. Ten resistance-trained men habituated to caffeine participated in a randomized, crossover and double-blind experiment. Each participant performed two identical resistance training sessions after the intake of 3 mg/kg of caffeine or a placebo. Blood was collected before and 60 min after substance intake, just after exercise, 60 minutes after exercise, and 24 hours after testing to evaluate the activity of antioxidant enzymes (superoxide dismutase, glutathione peroxidase, catalase), non-enzymatic antioxidants (reduced glutathione, uric acid) levels of oxidative stress markers (plasma malondialdehyde) and muscle damage markers (creatine kinase, lactate dehydrogenase). There were no significant differences between placebo and caffeine conditions in the total number of repetitions (180 ± 15 vs 185 ± 14 repetitions, respectively; p = 0.276; Effect size [ES] = 0.34), the total time under tension (757 ± 71 vs 766 ± 56 s, respectively; p = 0.709; ES = 0.14) or the rating of perceived exertion (13.8 ± 2.7 vs 14.7 ± 2.7 a.u., respectively; p = 0.212; ES = 0.32). Reduced glutathione concentration obtained 1 hour after exercise was higher with caffeine than with placebo (p = 0.047), without significant difference between conditions for any other prooxidant-oxidant or muscle damage marker at any time point (p > 0.050 for all). The oral intake of 3 mg/kg of caffeine by resistance-trained men habituated to caffeine did not enhance the number of repetitions during a medium load full-body resistance training session to failure and had a minimal impact on the prooxidant-antioxidant balance and muscle damage. The study was registered prospectively at ClinicalTrials.gov with the following ID: NCT05230303.

Caffeine Enhances 10-km Cycling Performance in Habitual Users Only When Preceded by Caffeine Abstinence

PURPOSE

The primary objective was to assess the performance benefits of caffeine (CAF) supplementation in habitual users. Importantly, this investigation was designed to account for the potential confounding effects of CAF withdrawal (CAFW), which are inherent and common in previous work.

METHODS

Ten CAF-consuming (394 [146] mg·d-1) recreational cyclists (age 39.1 [14.9] y; maximum oxygen consumption 54.2 [6.2] mL·kg-1·min-1) completed four 10-km time trials (TTs) on a cycle ergometer. On each trial day, 8 hours before reporting to the laboratory, subjects consumed 1.5 mg·kg-1 CAF to prevent withdrawal (no withdrawal [N]) or a placebo (PLA; withdrawal [W]). Then, 1 hour prior to exercise, they received either 6 mg·kg-1 CAF or PLA. These protocols were repeated 4 times, employing all combinations of N/W and CAF/PLA.

RESULTS

CAFW did not impair TT power output (PLAW vs PLAN P = .13). However, preexercise CAF only improved TT performance when compared to PLA in the W condition (CAFN vs PLAW P = .008, CAFW vs PLAW P = .04), not when W was mitigated (PLAN vs CAFN P = .33).

CONCLUSIONS

These data indicate that preexercise CAF only improves recreational cycling performance when compared to bouts preceded by CAF abstinence, suggesting that habitual users may not benefit from 6 mg·kg-1 of CAF and that previous work may have overstated the value of CAF supplementation for habitual users. Future work should examine higher doses of CAF for habitual users.

Tracking sleep in the field: sleep quality and sleep behaviours of elite track and field athletes during preparation and competition

Elite athletes are susceptible to inadequate sleep, which may peak during competition and be exacerbated by poor sleep behaviours. This study sought to characterise and compare the sleep quality and sleep behaviours of elite track and field athletes during preparation and major competitions. Forty elite international track and field athletes (50% female, aged 25.1 ± 3.9 years) completed the Athlete Sleep Screening Questionnaire and the Athlete Sleep Behaviour Questionnaire on three separate occasions: during habitual training, during a pre-meet training camp and during a major international competition. Overall, 62.5% of athletes reported at least mild sleep difficulty during competition. Athletes reported higher sleep difficulty and poorer sleep behaviour during major competitions and the pre-meet training camp compared to habitual training (P = .001-.025). No significant differences were observed between the training camp and major competition. Global sleep behaviour scores were underpinned by unique characteristics at each timepoint. Sleep behaviour (R² = .330, P = .017), injury status (R² = .253, P = .003) and major championship experience (R² = .113, P = .034) were associated with sleep difficulty during competition. Sleep quality and behaviours vary according to stage of the track and field season, providing a foundation for targeted intervention.

The Long Way to Establish the Ergogenic Effect of Caffeine on Strength Performance: An Overview Review

This overview review aimed to describe the evolution of the characteristics of the research on caffeine effects on strength. A total of 189 experimental studies with 3459 participants were included. The median sample size was 15 participants, with an over-representation of men vs. women (79.4 vs. 20.6%). Studies on young participants and elders were scarce (4.2%). Most studies tested a single dose of caffeine (87.3%), while 72.0% used doses adjusted to body mass. Single-dose studies ranged from 1.7 to 7 mg/kg (4.8 ± 1.4 mg/kg), while dose-response studies ranged from 1 to 12 mg/kg. Caffeine was mixed with other substances in 27.0% of studies, although only 10.1% of studies analyzed the caffeine interaction with these substances. Capsules (51.9%) and beverages (41.3%) were the most common forms of caffeine administration. Similar proportions of studies focused on upper (24.9%) or lower body strength 37.6% (37.6% both). Participants' daily intake of caffeine was reported in 68.3% of studies. Overall, the pattern in the study of caffeine's effects on strength performance has been carried out with experiments including 11-15 adults, using a single and moderate dose of caffeine adjusted to participants' body mass in the form of a capsule.

Anti-Inflammatory Effect of Caffeine on Muscle under Lipopolysaccharide-Induced Inflammation

Evidence has shown that caffeine administration reduces pro-inflammatory biomarkers, delaying fatigue and improving endurance performance. This study examined the effects of caffeine administration on the expression of inflammatory-, adenosine receptor- (the targets of caffeine), epigenetic-, and oxidative metabolism-linked genes in the vastus lateralis muscle of mice submitted to lipopolysaccharide (LPS)-induced inflammation. We showed that caffeine pre-treatment before LPS administration reduced the expression of Il1b, Il6, and Tnfa, and increased Il10 and Il13. The negative modulation of the inflammatory response induced by caffeine involved the reduction of inflammasome components, Asc and Casp1, promoting an anti-inflammatory scenario. Caffeine treatment per se promoted the upregulation of adenosinergic receptors, Adora1 and Adora2A, an effect that was counterbalanced by LPS. Moreover, there was observed a marked Adora2A promoter hypermethylation, which could represent a compensatory response towards the increased Adora2A expression. Though caffeine administration did not alter DNA methylation patterns, the expression of DNA demethylating enzymes, Tet1 and Tet2, was increased in mice receiving Caffeine+LPS, when compared with the basal condition. Finally, caffeine administration attenuated the LPS-induced catabolic state, by rescuing basal levels of Ampk expression. Altogether, the anti-inflammatory effects of caffeine in the muscle can be mediated by modifications on the epigenetic landscape.

Evaluation of Caffeine Ingested Timing on Endurance Performance based on CYP1A2 rs762551 Profiling in Healthy Sedentary Young Adults

Background

Caffeine is generally suggested to increase VO2max in endurance performance. Nevertheless, the response to caffeine ingestion does not seem to be uniform across individuals. Therefore, caffeine ingested timing on endurance performance based on the type of CYP1A2 single nucleotide polymorphism rs762551, that were classified as fast and slow metabolizers, need to be evaluated.

Methods

Thirty participants participated in this study. DNA was obtained from saliva samples and genotyped using polymerase chain reaction-restriction fragment length polymorphism. Each respondent completed beep tests under three treatments blindly: placebo, 4 mg/kg body mass of caffeine one hour, and two hours before test.

Results

Caffeine increased estimated VO2max in fast metabolizers (caffeine=29.39±4.79, placebo=27.33±4.02, p<0.05) and slow metabolizers (caffeine=31.25±6.19, placebo=29.17±5.32, p<0.05) in one hour before test. Caffeine also increased estimated VO2max in fast metabolizers (caffeine=28.91±4.65, placebo=27.33±4.02, p<0.05) and slow metabolizers (caffeine=32.53±6.68, placebo=29.17±5.32, p<0.05) in two hour before test. However, for slow metabolizers, the increasing was greater when caffeine was administered two hours before test (slow=3.37±2.07, fast=1.57±1.62, p<0.05).

Conclusion

Genetic variance may affect the optimal caffeine ingestion timing, sedentary individuals who want to enhance their endurance performance may ingest caffeine 1 hour before exercise for fast metabolizers and 2 hours before exercise for slow metabolizers.

Cardiorespiratory, Metabolic, and Performance Changes from the Effects of Creatine and Caffeine Supplementations in Glucose-Electrolyte-Based Sports Drinks: A Double-Blind, Placebo-Controlled Study

The purpose of this study is to investigate the additive effects of creatine and caffeine on changes in the cardiorespiratory system, metabolism, and performance of soccer players. Seventeen male soccer players randomly ingested three sports drinks comprising the following: glucose−electrolyte-based (Drink 1, control; D1), glucose−electrolyte-based drink + 5 g creatine (Drink 2; D2), and glucose−electrolyte-based drink + 5 g creatine + 35 mg caffeine (Drink 3; D3) during a 15 min recovery period after the modified Loughborough Intermittent Shuttle Test (LIST) on a standard outdoor soccer field. Then, a 20-m repeated intermittent sprinting activity was performed. The results showed no significant differences in cardiorespiratory and gas exchange variables. The non-significant levels of blood glucose concentrations among drinks with higher blood lactate concentrations were detected in parallel with increased heart rate during intermittent sprinting as a result of exercise intensities. Significantly longer sprinting time was found in D3 than D1 (p < 0.05), with no significant differences between D2 and D3. From this study, we conclude that the additive effect of caffeine−creatine supplements in a glucose−electrolyte drink during the 15 min recovery period enhances repeated 20-m high-intensity running in soccer players with no negative effect on cardiorespiratory functions.

Association of urinary caffeine and caffeine metabolites with bone mineral density in children and adolescents

In epidemiological research, the link between coffee consumption and bone mineral density (BMD) is still debated. Moreover, there hasn't been any research on the relationship between urine caffeine and caffeine metabolites and BMD. This study aimed to investigate if there was a connection between urine caffeine and its metabolites and BMD in people between the ages of 8 and 19. Using data from the National Health and Nutrition Examination Survey 2009 to 2014, multivariate logistic regression models were utilized to investigate the association between urinary caffeine and caffeine metabolites and total BMD. Fitted smoothing curves and generalized additive models were also used. A total of 1235 adolescents were included in this analysis, after controlling for various variables, we found that the association between urinary theophylline and total BMD was negative, whereas the association between urinary paraxanthine, theobromine and caffeine and total BMD was positive. In our study, an inverted U-shaped association between urinary paraxanthine and urinary caffeine was found with BMD in women. In this cross-sectional study, the correlation between urinary caffeine and its metabolites and total BMD differed by sex and race. More studies are needed to confirm the results of this study and to investigate the underlying causes.

Mental Performance and Sport: Caffeine and Co-consumed Bioactive Ingredients

The plant defence compound caffeine is widely consumed as a performance enhancer in a sporting context, with potential benefits expected in both physiological and psychological terms. However, although caffeine modestly but consistently improves alertness and fatigue, its effects on mental performance are largely restricted to improved attention or concentration. It has no consistent effect within other cognitive domains that are important to sporting performance, including working memory, executive function and long-term memory. Although caffeine's central nervous system effects are often attributed to blockade of the receptors for the inhibitory neuromodulator adenosine, it also inhibits a number of enzymes involved both in neurotransmission and in cellular homeostasis and signal propagation. Furthermore, it modulates the pharmacokinetics of other endogenous and exogenous bioactive molecules, in part via interactions with shared cytochrome P450 enzymes. Caffeine therefore enjoys interactive relationships with a wide range of bioactive medicinal and dietary compounds, potentially broadening, increasing, decreasing, or modulating the time course of their functional effects, or vice versa. This narrative review explores the mechanisms of action and efficacy of caffeine and the potential for combinations of caffeine and other dietary compounds to exert psychological effects in excess of those expected following caffeine alone. The review focusses on, and indeed restricted its untargeted search to, the most commonly consumed sources of caffeine: products derived from caffeine-synthesising plants that give us tea (Camellia sinensis), coffee (Coffea genus), cocoa (Theabroma cacao) and guaraná (Paullinia cupana), plus multi-component energy drinks and shots. This literature suggests relevant benefits to mental performance that exceed those associated with caffeine for multi-ingredient energy drinks/shots and several low-caffeine extracts, including high-flavanol cocoa and guarana. However, there is a general lack of research conducted in such a way as to disentangle the relative contributions of the component parts of these products.

Risk or benefit? Side effects of caffeine supplementation in sport: a systematic review

PURPOSE

The aim of this study was to systematically review evidence on the prevalence and magnitude of side effects associated with caffeine supplementation in athletes.

METHODS

Systematic searches through the PubMed, VHL, Scopus, and Web of Science databases were conducted according to the PRISMA guidelines. Peer-reviewed articles written in English that reported the prevalence/percentage or magnitude/effect size of side effects after caffeine supplementation in athletes in a sports context were included. Studies were grouped by the dose of caffeine administered as follows: low =  ≤ 3.0 mg/kg; moderate = from 3.1 to 6.0 mg/kg; high =  ≥ 6.1 mg/kg. The magnitude of the side effects was calculated with effect sizes.

RESULTS

The search retrieved 25 studies that met the inclusion/exclusion criteria with a pooled sample of 421 participants. The supplementation with caffeine produced a higher prevalence or magnitude of all side effects under investigation when compared to placebo/control situations. The prevalence (magnitude) was between 6 and 34% (ES between 0.13 and 1.11) for low doses of caffeine, between 0 and 34% (ES between -0.13 and 1.20) for moderate doses of caffeine, and between 8 and 83% (ES between 0.04 and 1.52) with high doses of caffeine. The presence of tachycardia/heart palpitations and the negative effects on sleep onset had the highest prevalence and magnitude, in athletes using supplementation with caffeine.

CONCLUSION

In summary, caffeine supplementation in the doses habitually used to enhance physical performance produces several side effects, both after exercise and at least 24 h after the ingestion. However, the prevalence and magnitude of side effects with high doses of caffeine were habitually higher than with low doses of caffeine. From a practical perspective, using ~3.0 mg/kg of caffeine may be the dose of choice to obtain the ergogenic benefits of caffeine with the lowest prevalence and magnitude of side effects.

Caffeine consumption within British fencing athletes

The ergogenic effects of caffeine are well documented, yet despite the potential benefits of supplementation, there is a lack of understanding of caffeine habits and supplementation within fencing. British fencers (n = 136) completed a Web-based questionnaire, exploring self-reported caffeine consumption, reasons for use and education. Fencers (94.1%) habitually consumed caffeine, primarily due to the taste of the products (93.8%). Respondents ingested 183.4 ± 137.5 mg of caffeine daily, with a significant difference between age groups (p &lt; 0.05). Many respondents (30.1%) consumed caffeine 60 mins prior/during fencing training and/or competition with the main reason highlighted as cognitive performance enhancement. Respondents ingested 140.8 ± 104.6 mg of caffeine during training/competition, mainly as energy drinks, bars, and powders. Education on caffeine supplementation was low (25.7%), with significant associations between age groups (p &lt; 0.05). Evidence implies caffeine toxicity has been experienced by 35% of fencers, highlighting the need for education on caffeine consumption. To conclude there is evidence of caffeine supplementation in fencing, primarily to magnify cognitive performance. However, there is a requirement for targeted education on caffeine supplementation to fencers, so that negative side effects and potential anti-doping infringements can be avoided.

Examining the Effects of Caffeine on Isokinetic Strength, Power, and Endurance

This study examined caffeine's effects on isokinetic strength, power, and endurance. The sample included 25 young, resistance-trained males. The participants were tested on three occasions, in a control trial (no substance ingestion) and following the ingestion of 6 mg·kg^-1 of caffeine or placebo. Exercise tests involved isokinetic knee extension and flexion using angular velocities of 60° s^-1 and 180° s^-1. Analyzed outcomes included peak torque, average power, and total work. For knee extension at an angular velocity of 60° s^-1, there were significant differences for: (1) peak torque when comparing caffeine vs. control (Hedges' g = 0.22) and caffeine vs. placebo (g = 0.30) and (2) average power when comparing caffeine vs. control (g = 0.21) and caffeine vs. placebo (g = 0.29). For knee extension at an angular velocity of 180° s^-1, there were significant differences for: (1) peak torque when comparing caffeine vs. placebo (g = 0.26), (2) average power when comparing caffeine vs. control (g = 0.36) and caffeine vs. placebo (g = 0.43), and (3) total work when comparing caffeine vs. control (g = 0.33) and caffeine vs. placebo (g = 0.36). Caffeine was not ergogenic for knee flexors in any of the analyzed outcomes. Additionally, there was no significant difference between control and placebo. In summary, caffeine enhances the mechanical output of the knee extensors at lower and higher angular velocities, and these effects are present when compared to placebo ingestion or no substance ingestion (control).

Acute Effects of Caffeine Supplementation on Physical Performance, Physiological Responses, Perceived Exertion, and Technical-Tactical Skills in Combat Sports: A Systematic Review and Meta-Analysis

Although the effects of caffeine supplementation on combat sports performance have been extensively investigated, there is currently no consensus regarding its ergogenic benefits.This systematic review with meta-analysis aimed to summarize the studies investigating the effects of caffeine supplementation on different aspects of performance in combat sports and to quantitatively analyze the results of these studies to better understand the ergogenic effect of caffeine on combat sports outcomes. A systematic search for randomized placebo-controlled studies investigating the effects of caffeine supplementation on combat sports' performance was performed through Scopus, Pubmed, Web of Science and Cochrane Library databases up to 18 April 2022. Random-effects meta-analyses of standardized mean differences (Hedge's g) were performed to analyze the data. Twenty-six studies of good and excellent methodological quality (based on the Pedro scale) fulfilled the inclusion criteria. The meta-analysis results revealed caffeine has a small but evident effect size (ES) on handgrip strength (ES = 0.28; 95% CI: 0.04 to 0.52; p = 0.02), and total number of throws during the special judo fitness test (SJFT) (ES = 0.42; 95% CI: 0.06 to 0.78; p = 0.02). Regarding the physiological responses, caffeine increased blood lactate concentration ([La]) in anaerobic exercise (ES = 1.23; 95% CI: 0.29 to 2.18; p = 0.01) and simulated combat (ES = 0.91; 95% CI: 0.34 to 1.47; p = 0.002). For Heart Rate (HR), caffeine increased HR final (ES = 0.31; 95% CI: 0.11 to 0.52; p = 0.003), and HR 1min (ES = 0.20; 95% CI 0.004 to 0.40; p = 0.045). However, caffeine had no impact on the countermovement jump height, the SJFT index, the judogi strength-endurance test, the number and duration of offensive actions, HR at the end of the fight, and the rating of perceived exertion. Caffeine supplementation may be ergogenic for a range of combat sports aspects involving isometric strength, anaerobic power, reaction time, and anaerobic metabolism. However, supplementation effects might be ineffective under certain circumstances, indicating supplementation needs to take into account the performance metric in question prior to creating a dosing protocol.

Effects of Sodium Bicarbonate Supplementation in Martial Arts

The aim of this systematic review was to evaluate the effects of consuming sodium bicarbonate (NaHCO3) and to gain insight into the nature of any changes in performance following NaHCO3 supplementation among combat sport athletes. The analysis of the results provides compelling evidence in favor of acute or chronic NaHCO3 supplementation as an ergogenic substance which could have an impact on several aspects of performance in judo [23, 31, 32], taekwondo [17, 20], karate [17, 33] [28, 29], wrestling [18, 19], jiu-jitsu [32] and boxing [16].

Acute or chronic NaHCO3 supplementation is effective in the improvement of several variables of physical performance in combat sports during testing and simulated matches. Enhanced performance resulted in the increased capacity of the glycolytic system. However, the positive effects of its use are most often visible following the onset of fatigue. In addition, the use of NaHCO3 is associated with an increased concentration of lactate in the blood. This systematic review provides data relevant for sports professionals and athletes alike regarding the use of NaHCO3 as a supplement, prior or during training and matches.

Can caffeine supplementation reverse the impact of time of day on cognitive and short-term high intensity performances in young female handball players?

ABBREVIATIONS

CAF: Caffeine PLC: Placebo SRT: Simple Reaction Time AT: Attention Test SJ: Squat Jump IAT: Illinois Agility Test OT: Oral Temperature QUEST: Questionnaire RPE: Rating of Perceived Exertion PD: Peak Distance TD: Total Distance.

Influence of caffeine on the maximal isometric and concentric force produced by skinned fibers

Caffeine is one of the most famous and widely used ergogenic drugs, especially by athletes to improve sports performance. Caffeine is known to enhance muscle contraction by facilitating Ca²⁺ release from the sarcoplasmic reticulum. While the effect of caffeine on the cross-bridge dynamics has also investigated, the results is controversial. Therefore, the purpose of this study was to examine the influence of caffeine on cross-bridge dynamics using skinned fiber preparations from rabbit soleus (N = 19 in total). We performed isometric contractions at an average sarcomere length of 2.4 μm; thereafter, skinned fibers were shortened by 20% of the fiber length at a velocity of 0.1 mm/s (slow shortening) or 0.5 mm/s (fast shortening). The contractions were performed under both normal and caffeine-containing activating solution conditions to compare the isometric, slow concentric, and fast concentric forces between conditions. The isometric force did not differ between normal and caffeine-containing activating solution conditions. Similarly, the concentric forces obtained during the slow and fast shortening trials did not differ between conditions. We also measured the stiffness and the rate of force redevelopment (kTR) during the isometric contraction phase and found that these values were not different between normal and caffeine conditions. Based on these results, we conclude that the influence of caffeine on cross-bridge dynamics is negligible, and the ergogenic effect of caffeine, from the view of muscle contractility, is by facilitating Ca²⁺ release, as suggested in previous studies, and not by modulating the cross-bridge dynamics.

Acute Effects of Caffeine on Overall Performance in Basketball Players—A Systematic Review

Caffeine supplementation has become increasingly popular among athletes. The benefits of caffeine include delaying the negative effects of fatigue, maintaining a high level of physical and mental performance, and improving certain abilities necessary for sport success. Given the complex nature of basketball, caffeine could be a legal, ergogenic stimulant substance, which will positively affect overall basketball performance. The purpose of this systematic review was to summarize evidence for the effect of acute caffeine ingestion on variables related to the basketball performance. Web of Science, PubMed, Scopus and ProQuest, MEDLINE, and ERIC databases were searched up to February 2021. Studies that measured the acute effect of caffeine on basketball performance were included and analyzed. Eight studies published between 2000 and 2021 were included in the analysis. Pre-exercise caffeine intake increased vertical jump height, running time at 10 and 20 m without the ball, overall basketball performance (number of body impacts, number of free throws, rebounds, and assists) during simulated games, and reduced the time required to perform a basketball-specific agility test. Equivocal results between caffeine and placebo groups were found for aerobic capacity, free throw and three-point accuracy, and dribbling speed. Pre-exercise caffeine ingestion did not affect RPE, but insomnia and urinary excretion were increased. The pre-exercise ingestion of 3 and 6 mg/kg caffeine was found to be effective in increasing several physical performance variables in basketball players during sport-specific testing and simulated matches. However, considering the intermittent nature and complexity of basketball, and individual differences between players, future studies are needed.

Effects of acute caffeine intake on combat sports performance: A systematic review and meta-analysis

The interest in the benefits of caffeine in combat sports has grown exponentially in the last few years, evidenced by the significant rise of post-competition urine caffeine concentration. We conduct a systematic review and meta-analysis on the effects of caffeine on different performance variables in combat sports athletes. In total, we included 25 studies. All studies included had blinded, and cross-over experimental designs, and we conducted a risk of bias analysis. For nonspecific outcomes, there was an ergogenic effect of caffeine on vertical jump height (SMD: 0.38; 95% CI: 0.04, 0.71) and reaction time (SMD: -0.98, 95% CI: -1.46,-0.50). For outcomes specific to combat sports, there was an increase in the number of throws with caffeine in the Special Judo Fitness Test (SMD: 0.62; 95% CI: 0.14, 1.09). Caffeine ingestion increased the number of offensive actions during combats (SMD: 0.40; 95% CI: 0.06, 0.74). Caffeine ingestion increased the duration of offensive actions during combat (SMD: 0.58; 95% CI: 0.21, 0.96). Finally, caffeine ingestion increased blood lactate concentration after bout 1 (SMD: 1.35) bout 2 (SMD: 1.43) and bout 3 (SMD: 1.98). Overall, athletes competing in combat sports may consider supplementing with caffeine for an acute increase in exercise performance.

Effect of Caffeine Ingestion on Indirect Markers of Exercise-Induced Muscle Damage: A Systematic Review of Human Trials

The effect of caffeine on mitigating exercise-induced muscle damage (EIMD) is still poorly understood, but it was hypothesized that caffeine could contribute to decreasing delayed onset muscle soreness, attenuating temporary loss of strength, and reducing circulating levels of blood markers of muscle damage. However, evidence is not conclusive and beneficial effects of caffeine ingestion on EIMD are not always observed. Factors, such as the type of exercise that induces muscle damage, supplementation protocol, and type of marker analyzed contribute to the differences between the studies. To expand knowledge on the role of caffeine supplementation in EIMD, this systematic review aimed to investigate the effect of caffeine supplementation on different markers of muscle damage. Fourteen studies were included, evaluating the effect of caffeine on indirect muscle damage markers, including blood markers (nine studies), pain perception (six studies), and MVC maximal voluntary contraction force (four studies). It was observed in four studies that repeated administration of caffeine between 24 and 72 h after muscle damage can attenuate the perception of pain in magnitudes ranging from 3.9% to 26%. The use of a single dose of caffeine pre-exercise (five studies) or post-exercise (one study) did not alter the circulating blood levels of creatine kinase (CK). Caffeine supplementation appears to attenuate pain perception, but this does not appear to be related to an attenuation of EIMD, per se. Furthermore, the effect of caffeine supplementation after muscle damage on strength recovery remains inconclusive due to the low number of studies found (four studies) and controversial results for both dynamic and isometric strength tests.

Caffeine Supplementation Strategies Among Endurance Athletes

Caffeine is widely accepted as an endurance-performance enhancing supplement. Most scientific research studies use doses of 3–6 mg/kg of caffeine 60 min prior to exercise based on pharmacokinetics. It is not well understood whether endurance athletes employ similar supplementation strategies in practice. The purpose of this study was to investigate caffeine supplementation protocols among endurance athletes. A survey conducted on Qualtrics returned responses regarding caffeine supplementation from 254 endurance athletes (f = 134, m =120; age = 39.4 ± 13.9 y; pro = 11, current collegiate athlete = 37, recreational = 206; running = 98, triathlon = 83, cycling = 54, other = 19; training days per week = 5.4 ± 1.3). Most participants reported habitual caffeine consumption (85.0%; 41.2% multiple times daily). However, only 24.0% used caffeine supplements. A greater proportion of men (31.7%) used caffeine supplements compared with women (17.2%; p = 0.007). Caffeine use was also more prevalent among professional (45.5%) and recreational athletes (25.1%) than in collegiate athletes (9.4%). Type of sport (p = 0.641), household income (p = 0.263), education (p = 0.570) or working with a coach (p = 0.612) did not have an impact on caffeine supplementation prevalence. Of those reporting specific timing of caffeine supplementation, 49.1% and 34.9% reported consuming caffeine within 30 min of training and races respectively; 38.6 and 36.5% used caffeine 30–60 min before training and races. Recreational athletes reported consuming smaller amounts of caffeine before training (1.6 ± 1.0 mg/kg) and races (2.0 ± 1.2 mg/kg) compared with collegiate (TRG: 2.1 ± 1.2 mg/kg; RACE: 3.6 ± 0.2 mg/kg) and professional (TRG: 2.4 ± 1.1 mg/kg; RACE: 3.5 ± 0.6 mg/kg) athletes. Overall, participants reported minor to moderate perceived effectiveness of caffeine supplementation (2.31 ± 0.9 on a four-point Likert-type scale) with greatest effectiveness during longer sessions (2.8 ± 1.1). It appears that recreational athletes use lower caffeine amounts than what has been established as ergogenic in laboratory protocols; further, they consume caffeine closer to exercise compared with typical research protocols. Thus, better education of recreational athletes and additional research into alternative supplementation strategies are warranted.