Placebo in sports nutrition: a proof-of-principle study involving caffeine supplementation

Caffeine's influence on vertical jump height: a real-life collegiate student-athlete approach

BACKGROUND

Caffeine's ergogenic potential in vertical jumping remains contested, particularly at dosages compliant with collegiate athletic regulations. The NCAA enforces a caffeine urinary threshold equivalent to ~5 mg/kg body mass, yet evidence supporting its efficacy in enhancing explosive performance among trained athletes is inconsistent. This study examined whether acute caffeine ingestion at this threshold improves squat jump (SJ) and countermovement jump (CMJ) performance in NCAA Division II student-athletes, while exploring sex-specific responses and trial-to-trial variability.

METHODS

Forty NCAA Division II athletes (18 females, 22 males; 21.3 ± 2.4 years) participated in a single-blind, randomized, crossover trial. Participants ingested 5 mg/kg caffeine or placebo, followed by SJ and CMJ testing on a force platform 60 minutes post-consumption. Three trials per jump type were retained to preserve intra-individual variance. Linear mixed-effects models (LMMs) assessed fixed effects of condition, sex, and trials, with random intercepts and slopes accounting for individual variability. A priori power analyses guided sample size determination, targeting sensitivity to detect small-to-medium effects (Cohen's f ≥ 0.2).

RESULTS

Caffeine elicited trivial, non-significant differences in SJ (β =  -0.24 cm, p = 0.646) and CMJ (β =  -0.71 cm, p = 0.183) heights compared to placebo. Males outperformed females in both SJ (Δ = 9.50 cm, p < 0.001) and CMJ (Δ = 11.30 cm, p < 0.001), though no condition-by-sex interactions emerged. Trial effects were observed, with SJ improving 2.31 cm (p < 0.001) and CMJ 1.05 cm (p = 0.014) from first to second attempts, suggesting warm-up or neuromuscular potentiation. High intraclass correlation coefficients (ICC = 0.76-0.85) underscored substantial interindividual variability. Models demonstrated robust fit (conditional R2 = 0.86-0.92), with sufficient power to detect medium-to-large effects (f ≥ 0.25).

CONCLUSIONS

A 5 mg/kg caffeine dose, compliant with NCAA thresholds, did not enhance vertical jump performance in habituated collegiate athletes, challenging prior assertions of its universal ergogenicity for ballistic tasks. While sex differences in baseline performance persisted, caffeine did not modulate these disparities, implicating neuromuscular and anthropometric factors as primary determinants. The absence of ergogenic effects aligns with NCAA safety-focused policies but highlights the need for personalized dosing strategies and research into higher doses, genetic variability, and hormonal influences. Future studies should integrate biomechanical metrics and controlled hormonal assessments to elucidate caffeine's nuanced role in anaerobic power sports.

Positive and Negative Verbal Instructions Associated With Sham Ischemic Preconditioning Moderate Improvements of Knee-Extension Resistance Exercise in Trained Men

PURPOSE

To verify the effects of positive and negative verbal instructions regarding sham ischemic preconditioning (sham-IPC) on leg-extension resistance-exercise performance.

METHODS

Thirty-five trained men were randomized to 1 of 3 groups: positive expectation, negative expectation, or control. Participants completed leg-extension strength tests in 4 trials (2 familiarization, 1 baseline, and 1 experimental). Experimental trials consisted of participants' receiving sham-IPC (3 × 5 cycles at only 20 mmHg). In positive- and negative-expectation groups, participants received verbal instructions that would improve or worsen performance, respectively. Controls did not receive any verbal suggestion. Outcomes were maximum number of repetitions, maximal isometric voluntary contraction, and muscle power output.

RESULTS

Expectations about sham-IPC were significantly higher in the positive-expectation than in the negative-expectation and control groups. Participants in the positive group reported a significantly greater number of repetitions than both the negative-expectation (d = 1.11) and control groups (d = 0.77). No differences between groups were shown for maximal isometric voluntary contraction (d range = 0.05-0.67) and power output (d range = -0.08 to 1.02).

CONCLUSIONS

Our results highlight the importance of measuring expectations prior to sham-IPC, which may significantly influence the results of randomized controlled trials.

The effects of caffeine mouth rinsing on selective attention as a function of different caffeine concentrations and perceived taste intensity in recreationally active males at rest: a randomized placebo-controlled cross-over trial

RATIONALE

The effect of caffeine mouth rinsing (CAF-MR) on cognitive performance has not been thoroughly investigated.

OBJECTIVES

To evaluate the effects of different concentrations of CAF-MR on selective attention in relation to perceived taste intensity.

METHODS

A total of 30 healthy and recreationally active male subjects were included in this randomized, double-blind, placebo-controlled crossover trial. Interventions included MR for 20 s at rest with three different caffeine solutions (0.24% [60 mg/25 mL], 0.6% [150 mg/25 mL], and 1.2% [300 mg/25 mL]), MR with 25 mL water (placebo), and no MR (control). Data on Victoria Stroop Test (VST) and the perceived taste intensity were recorded at five sessions.

RESULTS

CAF-MR-300 mg intervention significantly decreased completion time (from 62.93 ± 19.07 to 57.01 ± 16.74 s, p = 0.002 in Part D), while CAF-MR-150 mg intervention significantly decreased number of errors in Part D (7.00 ± 6.21 vs. 5.63 ± 5.76, p = 0.04) and Part C (8.77 ± 8.80 vs. 7.10 ± 7.11, p = 0.02). Perceived difficulty was significantly decreased both after CAF-MR with 150 mg (5.57 ± 1.65 vs. 4.77 ± 1.98, p = 0.006) and 300 mg (5.95 ± 1.77vs. 4.67 ± 1.96, p < 0.001). Perceived taste intensity for 300 mg of caffeine was negatively correlated with completion time (r: ranged, 0.37 to 0.46, p ranged, 0.045 to 0.009) after 300 mg, 150 mg (p ranged, 0.04 to 0.005) and placebo (p ranged 0.044 to 0.03) interventions.

CONCLUSIONS

This study is the first to demonstrate that CAF-MR shows dose-dependent effects on selective attention in healthy recreational males, such as improved speed (for 300 mg caffeine), reduced error rate (for 150 mg caffeine) and decrease in perceived difficulty (for 150 and 300 mg caffeine).

Caffeine Exerts Neither Ergogenic nor Hypoalgesic Effects on Sprint Interval Exercise with Intensive Exercise-Induced Muscle Pain

Sprint interval exercise can cause transient, intense exercise-induced pain (EIP) during and several minutes after the activity. A hypoalgesic strategy for high-intensity exercise, such as sprint interval exercise, against EIP is necessary to maintain exercise habituation and improve training quality/exercise performance. Preexercise caffeine supplementation, a well-known ergogenic strategy, may improve sprint performance and alleviate EIP as the hypoalgesic strategy. However, whether preexercise caffeine supplementation exhibits both the ergogenic effect on sprint interval performance and the hypoalgesic effect on intensive EIP during and several minutes after high intensity sprint interval exercise remains unknown, and thus we investigated to clarify those points. In this double-blind, randomized, crossover trial, sixteen male collegiate athletes performed 3 sets of 30-sec all-out Wingate pedaling exercises at 2-min intervals. Participants ingested 6 mg·kg-1 caffeine or placebo via capsules at 60 min prior to exercise. Quadriceps EIP was measured using a visual analogue scale during and up to 20 min after exercise. The results showed that caffeine did not significantly affect peak or mean power during sprint interval exercise (peak power: P = 0.196, ηp 2 = 0.11, mean power: P = 0.157, ηp 2 = 0.13; interaction). No significant interactions were also found for quadriceps EIP during (P = 0.686, ηp 2 = 0.03) and immediately after exercise (P = 0.112, ηp 2 = 0.12), nor for changes in physiological responses (blood lactate and ammonia concentrations) and caffeine-induced side effects (all P > 0.05). In conclusion, caffeine had no ergogenic or hypoalgesic effects on sprint interval exercise with intensive EIP.

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.

Effect of caffeine supplementation on physical performance in a 5 km cycling time trial of healthy young adult women in different phases of the menstrual cycle: A parallel, randomized, double-blind, placebo-controlled clinical trial

BACKGROUND

Although caffeine is the most studied ergogenic aid, few studies have been conducted to evaluate the effect of caffeine supplementation among women in different phases of the menstrual cycle (MC).

AIM

To verify the effect of caffeine supplementation and the MC phase on the performance of a 5 km cycling time trial of female exercise practitioners (FEP).

METHODS

This was a parallel, double-blind, randomized, placebo-controlled clinical trial with a sample of women aged 18-35 years, all with regular MC. The caffeine (CAFG) and placebo (PLAG) groups performed the exercise test during the late follicular phase and mid-luteal phase. These time points were individually assessed according to each woman's MC. On the test day, they were instructed to intake a standardized meal. Subsequently, 30 min following the meal, volunteers consumed caffeine (6 mg·kg-1) or placebo. One hour following caffeine intake, the exercise protocol started. The participants were instructed to perform an all-out 5-km cycling time trial.

RESULTS

Twenty-one women with a mean age of 26.6 years (PLAG, n = 10; 26.7 y; CAFG, n = 11; 26.5 y) were evaluated. The mean test duration was approximately 10-min, with no effect of the MC phase (F = 0.410; p = 0.532), caffeine supplementation (F = 2.23; p = 0.156), or interaction (F = 0.298; p = 0.593). Likewise, we did not verify the effect of the MC phase (F = 0.249; p = 0.625), caffeine supplementation (F = 2.35; p = 0.146), or interaction (F = 0.585; p = 0.456) on the mean power.

CONCLUSION

Neither caffeine supplementation nor the different MC phases had an impact on the 5-km cycling TT performance of FEP.

Heal Me!-Investigating the "Red Potion" Concept and Its Influence on Gamers' Cardiovascular Endurance

The "red potion," inspired by video games, emulates the health point replenishment mechanism for injured game characters. Conversely, red ginger, known for its potential tonic properties in enhancing cardiovascular endurance, poses challenges in acquisition within specific regions. Several previous studies have highlighted the existence of an inseparable link when gamers are engaged in real-world activities, even without actively playing the game in the virtual world. This suggests the potential for the "red potion" concept to enhance the well-being of gamers in reality. A statistical ANOVA experiment involved 90 participants, all avid gamers, categorized into three groups: basic, placebo, and experimental. The basic group (BG) received a red-colored beverage without red ginger infusion or the 'red potion' concept. In contrast, the placebo group (PG) received a similar beverage described as a "red potion" but without red ginger. Lastly, the experimental group (EG) received a red ginger-infused beverage without the "red potion" concept. Despite receiving different treatments, all beverages were presented in the same red color. Participants underwent the "beep test" to assess their baseline stamina. The results revealed that both PG and EG exhibited comparable cardiovascular endurance, affirming the potential of the "red potion" concept to positively influence gamers.

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.

Caffeine Placebo Effect in Sport and Exercise: A Systematic Review

The objective of this review article is to systematically identify the caffeine placebo effect in sport and exercise activities. We selected randomized controlled trial studies to better understand the impact of caffeine and its placebo effect on sports performance. We extracted a set of articles that refer strictly to the topics of caffeine and its placebo effect in sport and exercise, considering the databases integrated to the Core Collection Web of Science and Scopus, as well as the registration of the documents in PubMed®, a system with a selection process aligned with the guidelines for the PRISMA methodology, establishing the eligibility criteria of the articles with the PICOS tool, to which a systematic review is applied. Finally, the results show that caffeine improves anaerobic capacity and endurance, while placebo perceived as caffeine can also increase performance by reducing pain and improving concentration. This finding underscores the influence of expectations and placebo on physical performance, suggesting that managing these expectations may be an effective strategy for improving athletic performance.

Caffeine Mouth Rinse Plus Ingestion Improves the 10-Km Time Trial Compared to Caffeine Mouth Rinse Alone

Background: The benefits of caffeine to physical performance have been extensively demonstrated, however, it has recently been speculated that there is an effect of the administration route on its effectiveness. Purpose: The current study investigated the effect of caffeine mouth rinse in isolation or combined with ingestion on performance in a 30-minute constant-load exercise followed by a 10-km cycling time trial. Methods: Ten physically active men performed a 30-minute constant-load exercise at 50% of the graded test Wmax, followed by a 10-km cycling time trial. Before and at the middle points of the constant-load exercise and 10-km cycling time trial, the following conditions were administered: PLA (cellulose ingestion plus mouth rinsing with magnesium sulfate), ING (5 mg.kg-1 of caffeine ingestion plus mouth rinsing with magnesium sulfate), MR (cellulose ingestion plus mouth rinsing with 1.2% caffeine), and COMB (5 mg.kg-1 of caffeine ingestion plus mouth rinsing with 1.2% caffeine). Results: During the 30-minute constant-load exercise, COMB presented a lower rating of perceived exertion (RPE) than MR (p = .04). For the 10-km time trial, the COMB was faster than MR (MR = 1363 ± 345 vs. COMB = 1291 ± 308s, Δ% = 5.57, p = .05). Mean power output was higher in COMB than PLA, ING, and MR (234 ± 15 vs. 169 ± 29, 148 ± 11, and 145 ± 12 W, respectively). There were no differences between conditions for heart rate and RPE during the 10-km time trial. Conclusion: In summary, caffeine mouth rinsing potentiated the effects of caffeine ingestion during the 10-km time trial compared to caffeine mouth rinsing alone.

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.

How Cool is That? The Effects of Menthol Mouth Rinsing on Exercise Capacity and Performance: A Systematic Review and Meta-analysis

BACKGROUND

Menthol (MEN) mouth rinsing (MR) has gained considerable interest in the athletic population for exercise performance; however, the overall magnitude of effect is unknown.

OBJECTIVE

The aim of this systematic review and meta-analysis was to determine the efficacy of menthol MEN MR and the impact it has on exercise capacity and performance.

METHODS

Three databases were searched with articles screened according to the inclusion/exclusion criteria. Three-level meta-analyses were used to investigate the overall efficacy of MEN MR and the impact it has on exercise capacity and performance. Meta-regressions were then performed with 1) mean VO2peak, 2) MEN swilling duration; 3) the MEN concentration of MR solution, 4) the number of executed swills throughout a single experiment, 5) the use of flavoured sweetened, non-caloric, or non-flavoured neutral solutions as controls, 6) mean environmental temperature at the time of exercise tests, and 7) exercise type as fixed factors to evaluate their influence on the effects of MEN MR.

RESULTS

Ten MEN MR studies included sufficient information pertaining to MEN MR and exercise performance and capacity. MR with MEN resulted in no significant change in capacity and performance (SMD = 0.12; 95% CI - 0.08, 0.31; p = 0.23, n = 1, tau21 < 0.0001, tau22 =  < 0.0001, I2 = 0%). No significant influence was detected in meta-regressions for VO2peak, (estimate: 0.03; df = 8; 95% CI - 0.03, 0.09; p = 0.27), swilling duration (5 vs. 10 s: 0.00; df = 16; 95% CI - 0.41, 0.41; p = 1.0), MEN concentration (low [0.01%] vs. high [0.1%]: - 0.08; df = 15; 95% CI - 0.49, 0.32; p = 0.67), number of swills (estimate: 0.02; df = 13; 95% CI - 0.05, 0.09; p = 0.56), the use of flavoured sweetener or non-caloric as control (non-flavoured vs. flavoured: 0.12; df = 16; 95% CI - 0.30, 0.55; p = 0.55) or mean room temperature during exercise tests (estimate: 0.01; df = 16; 95% CI - 0.02, 0.04; p = 0.62).

CONCLUSION

MEN MR did not significantly improve overall exercise capacity and performance, though those involved in endurance exercise may see benefits.

Effects of exhaustive whole-body exercise and caffeine ingestion on muscle contractile properties in healthy men

BACKGROUND

The influence of exhaustive whole-body exercise and caffeine ingestion on electromechanical delay (EMD) has been underexplored. This study investigated the effect of exhaustive cycling exercise on EMD and other parameters of muscle contractile properties and the potential ability of caffeine to attenuate the exercise-induced impairments in EMD and muscle contractile properties.

METHODS

Ten healthy men cycled until exhaustion (88±2% of V̇O2max) on two separate days after ingesting caffeine (5 mg.kg-1 of body mass) or cellulose (placebo). Parameters of muscle contractile properties of the quadriceps muscles were assessed via volitional and electrically evoked isometric contractions, performed before and 50 minutes after ingestion of the capsules, and after exercise. Muscle recruitment during volitional contractions was determined via surface electromyography.

RESULTS

Exhaustive cycling exercise did not affect volitional and relaxation EMD (P>0.05) but increased evoked EMD. In addition, the exhaustive cycling exercise also increased muscle recruitment at the beginning of volitional isometric muscle contraction (P<0.05). The peak twitch force, maximal rate of twitch force development, and twitch contraction time were all compromised after exhaustive cycling exercise (P<0.05). Acute caffeine ingestion had no effect on muscle contractile properties (P>0.05), except that caffeine increased twitch contraction time at postexercise (P<0.05).

CONCLUSIONS

Exercise-induced decline in peripheral components of the EMD might be compensated by an increase in the muscle recruitment. In addition, acute caffeine ingestion had minimal influence on exercise-induced changes in muscle contractile proprieties.

Belief That Caffeine Ingestion Improves Performance in a 6-Minute Time Trial Test without Affecting Pacing Strategy

This study aimed to analyze the placebo effect associated with caffeine ingestion on running performance.

METHODS

Thirteen recreationally trained males in long-distance running (age: 38.5 ± 11.9 years, 11.0 ± 8.8 years of running experience) performed a 6 min time trial test in each experimental condition (caffeine-informed/placebo ingested (placebo) and non-ingested (control)) separated by 7 days. The total distance covered was measured, and partial times of each 400 m were used to analyze the pacing strategy. Heart rate and kinematic variables were recorded for each split. In addition, the rate of perceived exertion and prevalence of caffeine side effects was measured using questionnaires.

RESULTS

Placebo ingestion improved running performance in the 6 min time trial test (1668 ± 139 m placebo vs. 1642 ± 158 m control, t = 2.49; p = 0.03; moderate ES = 0.69), while pacing, heart rate, RPE, and kinematic variables were similar between conditions (p > 0.05 in all cases). Minor side effects were reported.

CONCLUSIONS

Beliefs of caffeine ingestion can improve running performance at speeds around maximal aerobic speed in recreationally trained runners without affecting pacing strategy so this "nutritional" strategy could be useful in competition scenarios. As a practical application, recreationally trained runners could improve ≈5 s in 1500 m or mile competitions.

Food for thought: Physiological considerations for nutritional ergogenic efficacy

Top-class athletes have optimized their athletic performance largely through adequate training, nutrition, recovery, and sleep. A key component of sports nutrition is the utilization of nutritional ergogenic aids, which may provide a small but significant increase in athletic performance. Over the last decade, there has been an exponential increase in the consumption of nutritional ergogenic aids, where over 80% of young athletes report using at least one nutritional ergogenic aid for training and/or competition. Accordingly, due to their extensive use, there is a growing need for strong scientific investigations validating or invalidating the efficacy of novel nutritional ergogenic aids. Notably, an overview of the physiological considerations that play key roles in determining ergogenic efficacy is currently lacking. Therefore, in this brief review, we discuss important physiological considerations that contribute to ergogenic efficacy for nutritional ergogenic aids that are orally ingested including (1) the impact of first pass metabolism, (2) rises in systemic concentrations, and (3) interactions with the target tissue. In addition, we explore mouth rinsing as an alternate route of ergogenic efficacy that bypasses the physiological hurdles of first pass metabolism via direct stimulation of the central nervous system. Moreover, we provide real-world examples and discuss several practical factors that can alter the efficacy of nutritional ergogenic aids including human variability, dosing protocols, training status, sex differences, and the placebo effect. Taking these physiological considerations into account will strengthen the quality and impact of the literature regarding the efficacy of potential ergogenic aids for top-class athletes.

The effects of acute caffeine ingestion on decision-making and pass accuracy in young soccer players: A preliminary randomized controlled trial

Caffeine has been shown to benefit physical aspects of different sports. In this paper, we aimed to understand the effects of caffeine on decision-making and the accuracy of soccer passes. Twelve young soccer players (16-17 years old and 20.8±2.7kg/m2 BMI) completed the tasks once after taking 3mg/kg body mass of caffeine (CAF) and once after consuming similar amounts of placebo (PLA). For the decision-making task, participants were asked to determine the best outcome of ten simulated pre-recorded soccer events. For the soccer pass accuracy, participants performed five short- (10m) and five long passes (30m), as well as the Loughborough Soccer Passing Test. Although not statistically significant, participants were 1.67% more accurate in short- and 13.48% more accurate in long passes when they consumed caffeine compared to the placebo (14.67±2.74 vs. 14.50±2.97, p=0.34, g=0.27 and 7.50±2.84 vs. 6.83±3.13, p=0.60, g=0.14, respectively). However, participants' decision-making was 7.14% and LSPT scores were 3.49% lower when they consumed caffeine compared to the placebo (29.50±3.09 vs. 30.67±2.93, p=0.28, g=-0.30 and 55.38±11.91 vs. 57.48±12.13, p=0.08, g=-0.51 respectively). In conclusion, while the short pass accuracy remained consistent among almost all participants before and after caffeine consumption, the performance varied in the case of long passes. Moreover, most of the participants scored lower on decision-making and LSPT after consuming caffeine. This may suggest that more complex tasks with a higher number of passes might negatively be affected by low doses of caffeine ingested one hour before playing soccer. Future studies are required to elucidate the effects of caffeine consumption on distinct cognitive and passing tasks.

Turmeric supplementation improves markers of recovery in elite male footballers: a pilot study

Football match-play causes muscle damage and provokes an inflammatory response. Rapid recovery is paramount to optimising subsequent performance and reducing injury risk. Turmeric contains high concentrations of curcumin, a polyphenol that has been shown to reduce muscle damage and soreness post-exercise in recreational exercisers. However, it is unknown whether a curcumin-containing supplement can support elite footballers recovery between matches. This applied study explored whether a turmeric supplement could improve performance, subjective and physiological markers of recovery, in elite male footballers. Twenty-four elite male footballers divided into a turmeric group, who consumed 60 mL of a turmeric drink twice per day, or a control group who did not. After 96 h of rest, baseline measurements of subjective soreness (leg and whole-body), plasma creatine kinase ([CK]), plasma C-reactive protein ([CRP]), isometric mid-thigh pull (IMTP) and counter movement jump (CMJ), were collected. Following eight competitive matches, subjective leg and whole-body soreness and plasma concentrations of inflammation markers ([CK] and [CRP]) were assessed immediately (0 h), 40 and 64 h post-match. Performance markers (IMTP and CMJ) were also assessed at 40 and 64 h post-match. Percentage change from baseline showed a main effect of group (p = 0.035, p = 0.005) and time (p = 0.002, p = 0.002) for both leg and whole-body soreness, respectively. There was a group by time interaction effect (p = 0.049) for [CRP]. There were no effects of turmeric on [CK], CMJ or IMTP. This applied study is the first in elite footballers to show that a curcumin-containing supplementation may attenuate a biomarker of inflammation [CRP] and soreness post-match play.

Caffeine and sport

Caffeine is a trimethylxanthine found in coffee and several other foods and beverages. Its stimulatory effects make it an interesting strategy to boost performance for athletic populations. Scientific evidence supports its efficacy to improve high-intensity endurance exercise, explosive and high-intensity efforts, resistance exercise, team sports and combat sports, though individual variation in the ergogenic response to caffeine exists. Supplementation can be taken in many forms including dissolved in water, via capsules, coffee, energy drinks and caffeinated gum; ingestion via capsules, dissolved in water or in caffeinated gum appear to be most effective. Variability in the exercise response following caffeine supplementation may be explained by genetic factors or habitual caffeine consumption. Caffeine is an excellent supplement for athletes looking to improve their exercise performance, though some consideration of side-effects and impact on sleep are warranted.

The effect of caffeine on exercise performance is not influenced by ADORA2A genotypes, alone or pooled with CYP1A2 genotypes, in adolescent athletes

PURPOSE

This study investigated the influence of the different genotypes of ADORA2A (1976 C > T, rs 5751876), alone or pooled with CYP1A2 (163 C > A rs 762551) genotypes, on the ergogenic effects of caffeine (CAF) on various aspects of physical performance in male adolescent athletes.

METHODS

Ninety male adolescent athletes (age = 15.5 ± 2 years) were classified according to their genotypes for 1976 C > T ADORA2A (TT homozygous or C_ADORA2A allele carriers) and 163 C > A CYP1A2 (AA homozygous or C_CYP1A2 allele carriers). Participants were further divided in four groups (1-TT_ADORA2A + AA_CYP1A2; 2-TT_ADORA2A + AC/CC_CYP1A2; 3-AA_CYP1A2 + CT/CC_ADORA2A;4-AC/CC_CYP1A2 + CT/CC_ADORA2A). Using a randomized, crossover, counterbalanced, and double-blind design, participants ingested CAF (6 mg kg^-1) or a placebo (PLA, 300 mg of cellulose) one hour before performing a sequence of physical tests: handgrip strength, agility test, countermovement jump (CMJ), Spike Jump (SJ), sit-ups, push-ups, and the Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1).

RESULTS

CAF enhanced handgrip strength (CAF: 35.0 ± 9.2 kg force; PLA: 33.5 ± 8.9 kg force; p = 0.050), CMJ height (CAF: 49.6 ± 12.3 cm; PLA: 48.3 ± 13.6 cm; p = 0.013), SJ height (CAF: 54.7 ± 13.3 cm; PLA: 53.1 ± 14.8 cm; p = 0.013), number of sit-ups (CAF: 37 ± 8; PLA: 35 ± 8; p = 0.001), and distance covered on the Yoyo IR1 test (CAF: 991.6 ± 371.0 m; PLA: 896.0 ± 311.0 m; p = 0.001), This CAF-induced improvement on exercise performance was, however, independent of genotypes groups (all p > 0.05). CAF had no effect on agility (CAF: 15.8 ± 1.2 s; PLA: 15.9 ± 1.3 s; p = 0.070) and push-up (CAF: 26.6 ± 12.0; PLA: 25.0 ± 11.0; p = 0.280) tests.

CONCLUSION

The acute caffeine intake of 6.0 mg.kg^-1 improves several aspects of physical performance, which seems to be independent of ADORA2A genotypes, alone or in combination with CYP1A2 genotypes.

The effects of being told you are in the intervention group on training results: a pilot study

Little is known about the placebo effects when comparing training interventions. Consequently, we investigated whether subjects being told they are in the intervention group get better training results compared to subjects being told they are in a control group. Forty athletes (male: n = 31, female: n = 9) completed a 10-week training intervention (age: 22 ± 4 years, height: 183 ± 10 cm, and body mass: 84 ± 15 kg). After randomization, the participants were either told that the training program they got was individualized based on their force-velocity profile (Placebo), or that they were in the control group (Control). However, both groups were doing the same workouts. Measurements included countermovement jump (CMJ), 20-m sprint, one-repetition maximum (1RM) back-squat, a leg-press test, ultrasonography of muscle-thickness (m. rectus femoris), and a questionnaire (Stanford Expectations of Treatment Scale) (Younger et al. in Clin Trials 9(6):767-776, 2012). Placebo increased 1RM squat more than Control (5.7 ± 6.4% vs 0.9 ± 6.9%, [0.26 vs 0.02 Effect Size], Bayes Factor: 5.1 [BF₁₀], p = 0.025). Placebo had slightly higher adherence compared to control (82 ± 18% vs 72 ± 13%, BF₁₀: 2.0, p = 0.08). Importantly, the difference in the 1RM squat was significant after controlling for adherence (p = 0.013). No significant differences were observed in the other measurements. The results suggest that the placebo effect may be meaningful in sports and exercise training interventions. It is possible that ineffective training interventions will go unquestioned in the absence of placebo-controlled trials.

Beetroot Juice Produces Changes in Heart Rate Variability and Reduces Internal Load during Resistance Training in Men: A Randomized Double-Blind Crossover

Beetroot juice (BJ) has been used as a sport supplement, improving performance in resistance training (RT). However, its effect on the modulation of the autonomic nervous system has not yet been widely studied. Therefore, the objective of this randomized double-blind crossover study was to assess the effect of acute BJ supplementation compared to placebo in blood pressure (BP), heart rate (HR), heart rate variability (HRV) and internal load during RT measure as Root Mean Square of the Successive Differences between adjacent RR intervals Slope (RMSSD and RMSSD-Slope, respectively). Eleven men performed an incremental RT test (three sets at 60%, 70% and 80% of their repetition maximum) composed by back squat and bench press with. HR, HRV and RMSSD-Slope were measured during and post exercise. As the main results, RMSSD during exercise decrease in the BJ group compared to placebo (p = 0.023; ES = 0.999), there were no differences in RMSSD post-exercise, and there were differences in RMSSD-Slope between groups in favor of the BJ group (p = 0.025; ES = 1.104) with a lower internal load. In conclusion, BJ supplementation seems to be a valuable tool for the reduction in the internal load of exercise during RT measured as RMSSD-Slope while enhancing performance.

Are Caffeine's Effects on Resistance Exercise and Jumping Performance Moderated by Training Status?

This study aimed to explore if the effects of caffeine intake on resistance exercise and jumping performance are moderated by training status. We included ten resistance-trained and ten recreationally active males in a randomized, double-blind, crossover study. Participants were categorized into groups according to their resistance to training experience and muscular strength levels. Exercise performance outcomes included weight lifted and mean velocity during a one-repetition maximum (1RM) bench press and squat; repetitions were performed to muscular failure in the same exercises with 70% of 1RM and countermovement jump (CMJ) height. Exercise performance was evaluated on three occasions, following no substance ingestion (control), caffeine (6 mg/kg), and placebo. There was a main effect on the condition for all the performance outcomes (all p ≤ 0.02), except for the 1RM squat mean velocity (p = 0.157) and 1RM bench press mean velocity (p = 0.719). For weight lifted in the 1RM bench press, there was a significant difference when comparing the caffeine vs. control, caffeine vs. placebo, and placebo vs. control. For weight lifted in the 1RM squat, a significant difference was found when comparing the caffeine vs. control. For muscular endurance outcomes and jump height, a significant difference was found when caffeine was compared to the control or placebo. Effect sizes were trivial for muscular strength (Hedges' g: 0.04-0.12), small for the jump height (Hedges' g: 0.43-0.46), and large for muscular endurance (Hedges' g: 0.89-1.41). Despite these ergogenic effects, there was no significant training status × caffeine interaction in any of the analyzed outcomes. In summary, caffeine ingestion is ergogenic for muscular strength, endurance, and jump height. These effects are likely to be of a similar magnitude in resistance-trained and recreationally active men.

Not Another Caffeine Effect on Sports Performance Study-Nothing New or More to Do?

The performance-enhancing potential of acute caffeine consumption is firmly established with benefits for many aspects of physical performance and cognitive function summarised in a number of meta-analyses. Despite this, there remains near exponential growth in research articles examining the ergogenic effects of caffeine. Many such studies are confirmatory of well-established ideas, and with a wealth of convincing evidence available, the value of further investigation may be questioned. However, several important knowledge gaps remain. As such, the purpose of this review is to summarise key knowledge gaps regarding the current understanding of the performance-enhancing effect of caffeine and justify their value for future investigation. The review will provide a particular focus on ten research priorities that will aid in the translation of caffeine's ergogenic potential to real-world sporting scenarios. The discussion presented here is therefore essential in guiding the design of future work that will aid in progressing the current understanding of the effects of caffeine as a performance enhancer.

Deconstructing the Ergogenic Effects of Photobiomodulation: A Systematic Review and Meta-analysis of its Efficacy in Improving Mode-Specific Exercise Performance in Humans

BACKGROUND

Photobiomodulation therapy (PBMT) is defined as non-thermal electromagnetic irradiation through laser or light-emitting diode sources. In recent decades, PBMT has attracted attention as a potential preconditioning method. The current meta-analysis was conducted to assess the effectiveness of PBMT in improving mode-specific exercise performance in healthy young adults.

METHODS

A computerized literature search was conducted, ending on 15 May 2022. The databases searched were PubMed, Cochrane Central Register of Controlled Trials, Embase, SPORTDiscus, and the Physiotherapy Evidence Database. Inclusion/exclusion criteria limited articles to crossover, double-blind, placebo-controlled studies investigating the PBMT effects as a preconditioning method. The included trials were synthesized according to exercise mode (single-joint, cycling, running, and swimming). All results were combined using the standardized mean differences (SMDs) method and the 95% confidence intervals (CIs) were described.

RESULTS

A total of 37 individual studies, employing 78 exercise performance measurements in 586 participants, were included in the analyses. In single-joint exercises, PBMT improved muscle endurance performance (SMD 0.27, 95% CI 0.12-0.41; p < 0.01) but not muscle strength performance (p = 0.92). In cycling, PBMT improved time to exhaustion performance (SMD 0.35, 95% CI 0.10-0.59; p < 0.01) but had no effect on all-out sprint performance (p = 0.96). Similarly, PBMT had no effect on time to exhaustion (p = 0.10), time-trial (p = 0.61), or repeated-sprint (p = 0.37) performance in running and no effect on time-trial performance in swimming (p = 0.81).

CONCLUSION

PBMT improves muscle endurance performance in single-joint exercises and time to exhaustion performance in cycling but is not effective for muscle strength performance in single-joint exercises, running, or swimming performance metrics.

Effects of Capsaicin and Capsiate on Endurance Performance: A Meta-Analysis

Several studies have explored the effects of capsaicin and capsiate on endurance performance, with conflicting findings. This systematic review aimed to perform a meta-analysis examining the effects of capsaicin and capsiate vs. placebo on endurance performance in humans. Seven databases were searched to find eligible studies. The effects of capsaicin and capsiate on aerobic endurance (e.g., time-trials or time-to-exhaustion tests), muscular endurance (e.g., repetitions performed to muscular failure), and rating of perceived exertion (RPE) were examined in a random-effects meta-analysis. Fourteen studies (n = 183) were included in the review. Most studies provided capsaicin or capsiate in the dose of 12 mg, 45 min before exercise. In the meta-analysis for aerobic endurance, there was no significant difference between the placebo and capsaicin/capsiate conditions (Cohen’s d: 0.04; 95% confidence interval: −0.16, 0.25; p = 0.69). In subgroup meta-analyses, there were no significant differences between the placebo and capsaicin/capsiate conditions when analyzing only studies that used time-trials (p = 0.20) or time-to-exhaustion tests (p = 0.80). In the meta-analysis for muscular endurance, a significant ergogenic effect of capsaicin/capsiate was found (Cohen’s d: 0.27; 95% confidence interval: 0.10, 0.43; p = 0.002). When analyzing set-specific effects, an ergogenic effect of capsaicin/capsiate was found in set 1, set 2, and set 3 (Cohen’s d: 0.21–29). Capsaicin/capsiate ingestion reduced RPE following muscular endurance (p = 0.03) but not aerobic endurance tests (p = 0.58). In summary, capsaicin/capsiate supplementation acutely enhances muscular endurance, while the effects on aerobic endurance are less clear.

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).

Can the Brazilian Caffeine Expectancy Questionnaires Differentiate the CYP1A2 and ADORA2A Gene Polymorphisms?-An Exploratory Study with Brazilian Athletes

This study investigated the ability of the Brazilian Caffeine Expectancy Questionnaire (CaffEQ-BR), full and brief versions, to differentiate genetic profiles regarding the polymorphisms of the CYP1A2 (rs 762551) and ADORA2A (rs 5751876) genes in a cohort of Brazilian athletes. One-hundred and fifty participants were genotyped for CYP1A2 and ADORA2A. After the recruitment and selection phase, 71 (90% male and 10% female, regular caffeine consumers) completed the CaffEQ-BR questionnaires and a self-report online questionnaire concerning sociodemographic data, general health status, and frequency of caffeine consumption. The order of completion of the CaffEQ-BR questionnaires was counterbalanced. The concordance between the full and brief versions of the CaffEQ-BR was analyzed using the intraclass correlation coefficient (ICC). To determine the discriminatory capacity of the questionnaires for genotype, the receiver operating characteristic (ROC) curve was applied for sensitivity and specificity (significance level of 5%). Mean caffeine intake was 244 ± 161 mg·day−1. The frequency of AA genotypes for CYP1A2 was 47.9% (n = 34) and 52.1% (n = 37) for C-allele carriers (AC and CC). The frequencies of TT genotypes for ADORA2A were 22.7% (n = 15) and 77.3% (n = 51) for C-allele carriers (TC and CC). All CaffEQ-BR factors, for the full and brief versions, were ICCs > 0.75, except for factor 6 (anxiety/negative effects; ICC = 0.60), and presented ROC curve values from 0.464 to 0.624 and 0.443 to 0.575 for CYP1A2 and ADORA2A. Overall, the CaffEQ-BR (full and brief versions) did not show discriminatory capacity for CYP1A2 and ADORA2A gene polymorphisms. In conclusion, the CaffEQ-BR was not able to differentiate genotypes for the CYP1A2 or ADORA2A genes in this group of Brazilian athletes.

Effects of caffeine ingestion on cardiopulmonary responses during a maximal graded exercise test: a systematic review with meta-analysis and meta-regression

While the effects of caffeine ingestion on endurance performance are well known, its effects on cardiopulmonary responses during a maximal graded exercise test have been less explored. This study systematically reviewed and meta-analyzed studies investigating the effects of caffeine ingestion on cardiopulmonary responses during a maximal graded exercise test. A search was performed in four databases, and study quality was assessed using the PEDro scale. Data reported by the selected studies were pooled using random-effects meta-analysis, with selected moderator effects assessed via meta-regression. Twenty-one studies with good and excellent methodological quality were included in this review. Compared to placebo, caffeine increased peak minute ventilation (SMD = 0.33; p = 0.01) and time to exhaustion (SMD = 0.41; p = 0.01). However, meta-regression showed no moderating effects of dosage and timing of caffeine ingestion, stage length, or total length of GXT (all p > 0.05). Caffeine ingestion did not affect peak oxygen uptake (SMD = 0.13; p = 0.42), peak heart rate (SMD = 0.27; p = 0.07), peak blood lactate concentration (SMD = 0.60; p = 0.09), peak tidal volume (SMD = 0.10; p = 0.69), peak breathing frequency (SMD =0.20; p = 0.23), or peak power output (SMD = 0.22; p = 0.28). The results of this systematic review with meta-analysis suggest that caffeine increases time to exhaustion and peak minute ventilation among the cardiopulmonary variables assessed during GXT.

Caffeine reverts loss of muscular performance during the early-follicular phase in resistance-trained naturally menstruating women

The aim of this study was to compare the effects of caffeine ingestion on muscular performance during the early-follicular and mid-luteal phases of the menstrual cycle. Fourteen resistance-trained naturally menstruating women performed countermovement jump (CMJ), maximal voluntary isometric contraction (MVIC), one-repetition maximum (1-RM), and repetitions-to-failure (RF) at 80% of 1-RM in the half-squat exercise, in early-follicular and mid-luteal phases, after placebo or caffeine ingestion. The early-follicular and mid-luteal phases were identified via calendar-based counting method. The MVIC was lower in the early-follicular than mid-luteal phase (-6.2 ± 15.2 N, p < 0.05) and higher with caffeine than placebo ingestion regardless of the menstrual cycle phase (+16.8 ± 26.7 N, p < 0.05). The magnitude of gains (supplement x phase interaction, p < 0.026) in 1-RM, CMJ, and RF with caffeine ingestion was higher in the early-follicular (+16.6 ± 7.1 kg, +2.5 ± 1.6 cm, and +4.5 ± 2.6 repetitions, respectively) than in the mid-luteal phase (+7.7 ± 4.8 kg, +1.5 ± 2.0 cm, and +2.4 ± 3.1 repetitions, respectively). In conclusion, the greater ergogenic effect of caffeine during the early-follicular phase supports its use to mitigate the decline in muscular performance in this phase of the menstrual cycle.

Acute effects of sodium bicarbonate ingestion on cycling time-trial performance: A systematic review and meta-analysis of randomized controlled trials

This study aimed to investigate the isolated effects of NaHCO₃ on cycling time-trial performance. Furthermore, we investigated whether the ingestion time of NaHCO₃, standardized or individualized based on time to peak, could be effective in improving cycling time-trial performance. A systematic review was carried out on randomized placebo-controlled studies. A random-effects meta-analysis assessed the standardized mean difference (SMD) between NaHCO₃ and placebo conditions. Eighteen studies were qualitatively (systematic review) and quantitatively (meta-analysis) analysed concerning mean power output (W_mean) (n = 182) and time performance (n = 201). The reviewed studies showed a low risk of bias and homogenous results for W_mean (I² = 0%) and performance time (I²= 0%). Overall, when compared to placebo, the NaHCO₃ ingestion improved the W_mean (SMD: 0.42; 95% CI: 0.21-0.63; P = 0.001) and performance time (SMD: 0.22; 95% CI: 0.02-0.43; P = 0.03). Similarly, the NaHCO₃ ingestion using a time-to-peak strategy improved the W_mean (SMD: 0.39; 95% CI: 0.03-0.75; P = 0.04; I²= 15%) and performance time (SMD: 0.34; 95% CI: 0.07-0.61, P = 0.01, I²= 0%). The present findings reveal that NaHCO₃ ingestion has the potential to increase the overall performance time and W_mean in cycling time trials. HighlightsNaHCO₃ is an effective strategy to increase cycling time-trial performance.The standardized protocol did not improve the cycling time-trial performance parameters.The individualized time-to-peak NaHCO₃ ingestion has a positive effect on time and W_mean during cycling time-trial performance.

Caffeine ingestion increases endurance performance of trained male cyclists when riding against a virtual opponent without altering muscle fatigue

PURPOSE

Caffeine improves cycling time trial (TT) performance; however, it is unknown whether caffeine is ergogenic when competing against other riders. The aim of this study was to investigate whether caffeine improves performance during a 4-km cycling TT when riding against a virtual opponent, and whether it is associated with increased muscle activation and at the expense of greater end-exercise central and peripheral fatigue.

METHODS

Using a randomized, crossover, and double-blind design, eleven well-trained cyclists completed a 4-km cycling TT alone without supplementation (CON), or against a virtual opponent after ingestion of placebo (OP-PLA) or caffeine (5 mg^.kg^-1, OP-CAF). Central and peripheral fatigue were quantified via the pre- to post-exercise decrease in voluntary activation and potentiated twitch force, respectively. Muscle activation was continually measured during the trial via electromyography activity.

RESULTS

Compared to CON, OP-PLA improved 4-km cycling TT performance (P = 0.018), and OP-CAF further improved performance when compared to OP-PLA (P = 0.050). Muscle activation was higher in OP-PLA and OP-CAF than in CON throughout the trial (P = 0.003). The pre- to post-exercise reductions in voluntary activation and potentiated twitch force were, however, similar between experimental conditions (P > 0.05). Compared to CON, OP-PLA increased the rating of perceived exertion during the first 2 km, but caffeine blunted this increase with no difference between the OP-CAF and CON conditions.

CONCLUSIONS

Caffeine is ergogenic when riding against a virtual opponent, but this is not due to greater muscle activation or at the expense of greater end-exercise central or peripheral fatigue.

Can I Have My Coffee and Drink It? A Systematic Review and Meta-analysis to Determine Whether Habitual Caffeine Consumption Affects the Ergogenic Effect of Caffeine

OBJECTIVE

The aim was to quantify the proportion of the literature on caffeine supplementation that reports habitual caffeine consumption, and determine the influence of habitual consumption on the acute exercise response to caffeine supplementation, using a systematic review and meta-analytic approach.

METHODS

Three databases were searched, and articles screened according to inclusion/exclusion criteria. Three-level meta-analyses and meta-regression models were used to investigate the influence of habitual caffeine consumption on caffeine's overall ergogenic effect and within different exercise types (endurance, power, strength), in men and women, and in trained and untrained individuals. Sub-analyses were performed according to the following: acute relative dose (< 3, 3-6, > 6 mg/kg body mass [BM]); whether the acute caffeine dose provided was lower or higher than the mean daily caffeine dose; and the caffeine withdrawal period prior to the intervention (< 24, 24-48, > 48 h).

RESULTS

Sixty caffeine studies included sufficient information on habitual consumption to be included in the meta-analysis. A positive overall effect of caffeine was shown in comparison to placebo (standard mean difference [SMD] = 0.25, 95% confidence interval [CI] 0.20-0.30; p < 0.001) with no influence of relative habitual caffeine consumption (p = 0.59). Subgroup analyses showed a significant ergogenic effect when the caffeine dose was < 3 mg/kg BM (SMD = 0.26, 95% CI 0.12-0.40; p = 0.003) and 3-6 mg/kg BM (SMD = 0.26, 95% CI 0.21-0.32; p < 0.0001), but not > 6 mg/kg BM (SMD = 0.11, 95% CI - 0.07 to 0.30; p = 0.23); when the dose was both higher (SMD = 0.26, 95% CI 0.20-0.31; p < 0.001) and lower (SMD = 0.21, 95% CI 0.06-0.36; p = 0.006) than the habitual caffeine dose; and when withdrawal was < 24 h, 24-48 h, and > 48 h. Caffeine was effective for endurance, power, and strength exercise, with no influence (all p ≥ 0.23) of relative habitual caffeine consumption within exercise types. Habitual caffeine consumption did not modify the ergogenic effect of caffeine in male, female, trained or untrained individuals.

CONCLUSION

Habitual caffeine consumption does not appear to influence the acute ergogenic effect of caffeine.

Caffeine Combined With Sodium Bicarbonate Improves Pacing and Overall Performance During a High-Intensity Time Trial

Background: No study has demonstrated the effects of sodium bicarbonate plus caffeine (NaHCO₃ + CAF) on power output (PO) distribution (e.g., pacing), physiological parameters and energy system contribution during a 4-km cycling time trial (TT). Thus, we aimed to investigate the effects of NaHCO₃ + CAF on pacing, physiological parameters, and energy system contribution during a 4-km cycling TT. Methods: Using a double-blind and counterbalanced design, 10 cyclists performed three ingestion protocols (NaHCO₃ + CAF, NaHCO₃ and placebo) followed by a 4-km cycling TT. Results: 100 min after substance ingestion, the magnitude of change in blood pH and bicarbonate concentration [HCO₃^-] for NaHCO₃ + CAF (+0.04 ± 0.03 and +5.9 ± 1.6 mmol·L^-1, respectively, P < .05) and NaHCO₃ (+0.02 ± 0.03 and +4.1 ± 2.0 mmol·L^-1, respectively, P < .05) was more pronounced than in placebo (-0.01 ± 0.02 and 0.4 ± 0.9 mmol·L^-1, respectively). The increase in plasma lactate concentration was more pronounced in NaHCO₃ + CAF than in NaHCO₃ and placebo (P < .05). Mean ventilation and carbon dioxide production were higher in NaHCO₃ + CAF compared to NaHCO₃ and placebo (P < .05). The PO and anaerobic power output were increased at the beginning of the 4-km TT (P < .05) in NaHCO₃ + CAF compared to the other two conditions, resulting in an improved overall performance (P < .05). Conclusion: NaHCO₃ + CAF results in a higher PO and increased anaerobic contribution and respiratory parameters during a 4-km cycling TT.

Caffeine alters the breathing pattern during high-intensity whole-body exercise in healthy men

PURPOSE

The current study investigated the effect of caffeine on the breathing pattern during a high-intensity whole-body exercise.

METHODS

Using a randomized, crossover, counterbalanced, and double-blind design, twelve healthy men ingested either 5 mg.kg^-1 of caffeine or cellulose (placebo) one hour before performing a high-intensity whole-body exercise (i.e., work rate corresponding to 80% of the difference between the gas exchange threshold and maximal oxygen uptake) until the limit of tolerance. Ventilatory and metabolic responses were recorded throughout the trial and at task failure.

RESULTS

Caffeine ingestion increased time to task failure in relation to the placebo (368.1 ± 49.6 s vs. 328.5 ± 56.6 s, p = 0.005). Caffeine also increased tidal volume and inspiratory time throughout the exercise (p < 0.05). Compared to task failure with placebo, task failure with caffeine intake was marked by higher (p < 0.05) minute ventilation (134.8 ± 16.4 vs. 147.6 ± 18.2 L.min^-1), the ventilatory equivalent of oxygen consumption (37.8 ± 4.2 vs. 41.7 ± 5.5 units), and respiratory exchange ratio (1.12 ± 0.10 vs. 1.19 ± 0.11 units).

CONCLUSION

In conclusion, ingestion of caffeine alters the breathing pattern by increasing tidal volume and lengthening the inspiratory phase of the respiratory cycle. These findings suggest that caffeine affects the ventilatory system, which may account, in part, for its ergogenic effects during high-intensity whole-body exercises.

The Effect of Acute Caffeine Ingestion on Tactical Performance of Professional Soccer Players

In soccer, physical, tactical, and decision-making processes are highly important facets of successful performance. Caffeine has well established effects for promoting both physical and cognitive performance, but the translation of such benefits specifically for soccer match play is not well established. This study examined the effects of acute caffeine ingestion on tactical performance during small-sided games (SSG) in professional soccer players. Nineteen soccer players (22 ± 4 years) underwent a randomized, counterbalanced, crossover, double-blind placebo-controlled trial. The protocol consisted of 5 bouts of 5-min SSG with 3 players plus a goalkeeper in each team (3 + GK × 3 + GK) with each SSG separated by 1 min rest intervals. Tactical performance was assessed using the system of tactical assessment in soccer (FUT-SAT). Prior to each experimental trial, participants ingested caffeine (5 mg·kg⁻¹) or a placebo 60 min before the protocol. Overall, caffeine ingestion resulted in an increased ball possession time when compared to the placebo. When the offensive and defensive core principles were analyzed, the results were equivocal. Caffeine resulted in positive effects on some tactical decisions during the protocol, but it was deleterious or promoted no observed effect on other of the core tactical principles. Caffeine ingestion resulted in less offensive (during SSG3) and defensive (SSG 2, SSG3, and SSG4) errors. Caffeine ingestion also resulted in higher total offensive success during SSG 1 and SSG2, but it was detrimental during SSG3. Additionally, total defensive success was lower for the caffeine conditions during SSG 2 and SSG5 when compared to the placebo. In conclusion, caffeine influenced aspects of tactical decisions in soccer, resulting in fewer offensive and defensive errors, although it may be deleterious considering other tactical parameters. Future studies may clarify the effects of caffeine ingestion on specific decision-making parameters in soccer.

Acute effects of beetroot juice and caffeine co-ingestion during a team-sport-specific intermittent exercise test in semi-professional soccer players: a randomized, double-blind, placebo-controlled study

BACKGROUND

Beetroot juice (BJ) and caffeine (CAF) are considered as ergogenic aids among athletes to enhance performance, however, the ergogenic effects of BJ and CAF co-ingestion are unclear during team-sport-specific performance. This study aimed to investigate the acute effects of BJ and CAF co-ingestion on team-sport-specific performance, compared with placebo (PL), BJ, and CAF alone.

METHOD

Sixteen semi-professional male soccer players (age: 19.8 ± 2.2 years, body mass: 69.2 ± 6.1 kg, height: 177.3 ± 6.0 cm) completed four experimental trials using a randomized, double-blind study design: BJ + CAF, CAF + PL, BJ + PL, and PL + PL. Countermovement jump with arm swing (CMJAS) performance and cognitive function by Stroop Word-Color test were evaluated before and after the Yo-Yo Intermittent Recovery Test level 1 (YYIR1). Also, rate of perceived exertion (RPE), heart rate, and gastrointestinal (GI) discomfort were measured during each session.

RESULTS

No significant differences were shown between test conditions for total distance covered in YYIR1 (BJ + CAF: 1858 ± 455 m, CAF + PL: 1798 ± 422 m, BJ + PL: 1845 ± 408 m, PL + PL 1740 ± 362 m; p = 0.55). Moreover, CMJAS performance, cognitive function, and RPE during the YYIR1 were not significantly different among conditions (p > 0.05). However, the average heart rate during the YYIR1 was higher in CAF + PL compared to PL + PL (by 6 ± 9 beats/min; p < 0.05), and GI distress was greater in BJ + CAF compared to PL + PL (by 2.4 ± 3.6 a.u.; p < 0.05).

CONCLUSION

These results suggest, neither acute co-ingestion of BJ + CAF nor BJ or CAF supplementation alone significantly affected team-sport-specific performance compared to the PL treatment.

Effects of caffeine on central and peripheral fatigue following closed- and open-loop cycling exercises

We examined whether endurance performance and neuromuscular fatigue would be affected by caffeine ingestion during closed- and open-loop exercises. Nine cyclists performed a closed-loop (4,000-m cycling time trial) and an open-loop exercise (work rate fixed at mean power of the closed-loop trial) 60 min after ingesting caffeine (CAF, 5 mg/kg) or placebo (PLA, cellulose). Central and peripheral fatigue was quantified via pre- to post-exercise decrease in quadriceps voluntary activation and potentiated twitch force, respectively. Test sensitivity for detecting caffeine-induced improvements in exercise performance was calculated as the mean change in time divided by the error of measurement. Caffeine ingestion reduced the time of the closed-loop trial (PLA: 375.1±14.5 s vs CAF: 368.2±14.9 s, P=0.024) and increased exercise tolerance during the open-loop trial (PLA: 418.2±99.5 s vs CAF: 552.5±106.5 s, P=0.001), with similar calculated sensitivity indices (1.5, 90%CI: 0.7-2.9 vs 2.8, 90%CI: 1.9-5.1). The reduction in voluntary activation was more pronounced (P=0.019) in open- (-6.8±8.3%) than in closed-loop exercises (-1.9±4.4%), but there was no difference between open- and closed-loop exercises for the potentiated twitch force reduction (-25.6±12.8 vs -26.6±12.0%, P>0.05). Caffeine had no effect on central and peripheral fatigue development in either mode of exercise. In conclusion, caffeine improved endurance performance in both modes of exercise without influence on post-exercise central and peripheral fatigue, with the open-loop exercise imposing a greater challenge to central fatigue tolerance.

Effects of caffeine chewing gum supplementation on exercise performance: a systematic review and meta-analysis

The aim of this systematic review with meta-analysis was to determine the effect of caffeine gum (Caff-gum) on exercise performance-related outcomes. Medline, EmBase, and SPORTSDiscus, and the register ClinicalTrials.gov were searched in March 2021, for studies assessing the effect of Caff-gum in placebo-controlled protocols involving healthy adults (i.e., with no chronic diseases or health conditions). Risk of bias was assessed using the RoB 2 tool. Random-effects meta-analyses using standardized mean differences (SMD) were performed to determine the effect of Caff-gum on exercise outcomes with several sub-analyses (training status, exercise type, timing and dose) for potential modifying factors. 14 studies were included, totaling 200 participants. There was a significant overall effect of Caff-gum compared to placebo (SMD = 0.21, 95%CI: 0.10-0.32; p = 0.001). Subgroup analysis showed improved performance for trained (SMD = 0.23, 95%CI: 0.08-0.37; p = 0.004), but not for untrained (SMD = 0.14, 95%CI: -0.02-0.29; p = 0.07) individuals. Caff-gum improved both endurance (SMD = 0.27, 95%CI: 0.12-0.42; p = 0.002) and strength/power (SMD = 0.20, 95%CI: 0.03-0.37; p = 0.03) performance outcomes. Caff-gum was ergogenic when consumed within 15 min prior to initiating exercise (SMD = 0.27, 95%CI: 0.07-0.4; p = 0.01), but not when provided >15 min prior (SMD=-0.48, 95%CI= -1.7-0.82; p = 0.25). There was no significant effect of Caff-gum with doses <3 mg/kg body mass (BM) (SMD = 0.20, 95%CI: -0.03-0.43; p = 0.07), but there was a significant effect when the dose was ≥3 mg/kg BM (SMD = 0.22, 95%CI: 0.07-0.37; p = 0.01). Caff-gum supplementation may be an effective ergogenic strategy for trained athletes involved in both endurance and strength/power exercise, using a recommended dose of ≥3 mg/kg BM consumed within 15 minutes before the exercise.

Extracellular Buffering Supplements to Improve Exercise Capacity and Performance: A Comprehensive Systematic Review and Meta-analysis

BACKGROUND

Extracellular buffering supplements [sodium bicarbonate (SB), sodium citrate (SC), sodium/calcium lactate (SL/CL)] are ergogenic supplements, although questions remain about factors which may modify their effect.

OBJECTIVE

To quantify the main effect of extracellular buffering agents on exercise outcomes, and to investigate the influence of potential moderators on this effect using a systematic review and meta-analytic approach.

METHODS

This study was designed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Three databases were searched for articles that were screened according to inclusion/exclusion criteria. Bayesian hierarchical meta-analysis and meta-regression models were used to investigate pooled effects of supplementation and moderating effects of a range of factors on exercise and biomarker responses.

RESULTS

189 articles with 2019 participants were included, 158 involving SB supplementation, 30 with SC, and seven with CL/SL; four studies provided a combination of buffering supplements together. Supplementation led to a mean estimated increase in blood bicarbonate of + 5.2 mmol L^-1 (95% credible interval (CrI) 4.7-5.7). The meta-analysis models identified a positive overall effect of supplementation on exercise capacity and performance compared to placebo [ES_0.5 = 0.17 (95% CrI 0.12-0.21)] with potential moderating effects of exercise type and duration, training status and when the exercise test was performed following prior exercise. The greatest ergogenic effects were shown for exercise durations of 0.5-10 min [ES_0.5 = 0.18 (0.13-0.24)] and > 10 min [ES_0.5 = 0.22 (0.10-0.33)]. Evidence of greater effects on exercise were obtained when blood bicarbonate increases were medium (4-6 mmol L^-1) and large (> 6 mmol L^-1) compared with small (≤ 4 mmol L^-1) [β_Small:Medium = 0.16 (95% CrI 0.02-0.32), β_Small:Large = 0.13 (95% CrI - 0.03 to 0.29)]. SB (192 outcomes) was more effective for performance compared to SC (39 outcomes) [β_SC:SB = 0.10 (95% CrI - 0.02 to 0.22)].

CONCLUSIONS

Extracellular buffering supplements generate large increases in blood bicarbonate concentration leading to positive overall effects on exercise, with sodium bicarbonate being most effective. Evidence for several group-level moderating factors were identified. These data can guide an athlete's decision as to whether supplementation with buffering agents might be beneficial for their specific aims.

Acute effects of two caffeine doses on bar velocity during the bench press exercise among women habituated to caffeine: a randomized, crossover, double-blind study involving control and placebo conditions

PURPOSE

The main goal of this study was to evaluate the effectiveness of two different doses of caffeine (3 and 6 mg/kg) to enhance bar velocity during the bench press in women habituated to caffeine.

METHODS

Twelve recreationally trained women (age: 23.3 ± 0.8 years, body mass: 60.7 ± 5.7 kg, bench press one-repetition maximum (1RM): 44.3 ± 7.8 kg, daily caffeine ingestion: 5.7 ± 2.0 mg/kg/day) participated in a randomized double-blind experimental design. Each participant performed four different experimental sessions: after no supplementation (control, CON), after ingesting 3 and 6 mg/kg of caffeine (CAF-3 and CAF-6, respectively), or after ingesting a placebo (PLAC). In each experimental session, the participants performed 3 sets of 3 repetitions of the bench press exercise at 50% 1RM.

RESULTS

A two-way repeated-measures ANOVA with subsequent post hoc analyses indicated significant increases in peak velocity (p < 0.01; ES = 0.91) and mean velocity (p < 0.01; ES = 0.78) after the intake of CAF-6 compared to CON. The study did not show significant differences in bar velocity between CAF-6 and PLAC and between CAF-3 and PLAC. No significant differences in bar velocity were observed between CAF-3 and CAF-6 conditions.

CONCLUSION

These results suggest that 6 mg/kg of caffeine can be an effective dose to improve power-specific training outcomes in women habituated to caffeine. However, the ergogenic effect of 6 mg/kg of caffeine may be derived from a combination of biological effects and expectancy, as this dose was only superior to the control condition with no differences over the placebo.

The effect of mouth rinsing with different concentrations of caffeine solutions on reaction time

Caffeine mouth rinsing (CAF-MR) has been shown to improve reaction time (RT). CAF-MR studies have generally used 1.2% CAF concentrations, but the effect of using different concentrations is unknown. Therefore, we compared the effect of different concentrations of CAF-MR on RT. Forty-five trained male athletes (age: 18 ± 3 y) volunteered to participate in this double-blind, randomized controlled crossover study. Participants completed five testing sessions (Control, Placebo (water)-MR, and 1.2%, 1.8%, and 2.4% CAF-MR), with hand and foot RTs assessed immediately after MR. All CAF-MR conditions resulted in significantly faster hand and foot RT compared to Control and Placebo (all p < 0.001, except for foot RT with 1.8% CAF-MR vs. Placebo: NS). For both hand and foot RT, 1.2% and 1.8% CAF-MR did not significantly differ, but RT for 2.4% CAF-MR was significantly faster than both (p < 0.001). Improvements in RT for 2.4% CAF-MR vs. Placebo were 22% for hand RT and 21% for foot RT. In conclusion, these findings demonstrate that higher CAF-MR concentrations than those typically used can result in greater improvements in RT. This has implications for the practical use of CAF-MR to enhance performance in sports in which optimal RT is a factor of success.

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.

Effects of creatine and caffeine ingestion in combination on exercise performance: A systematic review

Creatine (CRE) and caffeine (CAF) have been used as ergogenic aids to improve exercise performance. The present study reviewed the current evidence supporting the additional use of CAF intake during or after the CRE loading on exercise performance. The search was carried out in eight databases, with the methodological quality of the studies assessed via the QualSyst tool. From ten studies that met the criteria for inclusion, six had strong, three moderate, and one weak methodological quality. CAF was ingested ∼1 h before the performance trial (5-7 mg.kg^-1) after a CRE loading period (5-6 days with 0.3 g.kg^-1.d^-1) in five studies, with the combination CAF + CRE providing additional ergogenic effect compared to CRE alone in three of these studies. Furthermore, CAF was ingested daily during the CRE loading protocol in five studies, with CAF showing additive benefits compared to CRE alone only in one study (3 g.d^-1 of CRE during 3 days + 6 mg.kg^-1 of CAF for 3 days). The combination CAF + CRE seems to provide additional benefits to exercise performance when CAF is acutely ingested after a CRE loading. There is, however, no apparent benefit in ingesting CAF during a CRE loading period.

Combined but Not Isolated Ingestion of Caffeine and Taurine Improves Wingate Sprint Performance in Female Team-Sport Athletes Habituated to Caffeine

Previous studies have investigated caffeine (CAF) and taurine (TAU) in isolation and combined during exercise in males. However, the potential synergistic effect during high-intensity exercise remains unknown in female athletes. Seventeen female team-sport athletes participated (age: 23.4 ± 2.1 years; height: 1.68 ± 0.05 m; body mass: 59.5 ± 2.2 kg). All participants were habitual caffeine consumers (340.1 ± 28.6 mg/day). A double-blind randomized crossover design was used. Participants completed four experimental trials: (i) CAF and TAU (6 mg/kg body mass of CAF + 1 g of TAU), (ii) CAF alone; (iii) TAU alone; and (iv) placebo (PLA). Supplements were ingested 60 min before a 30-s Wingate Anaerobic Test (WAnT). Heart rate and blood lactate (BL) were measured before and immediately after the WAnT; and ratings of perceived exertion (RPE) were recorded immediately after the WAnT. Peak power (PP) was significantly higher following co-ingestion of CAF+TAU compared to PLA (p = 0.03) and TAU (p = 0.03). Mean power (MP) was significantly higher following co-ingestion of CAF+TAU compared to PLA (p = 0.01). No other differences were found between conditions for PP and MP (p > 0.05). There were also no observed differences in fatigue index (FI), BL; heart rate; and RPE between conditions (p > 0.05). In conclusion, compared to PLA the combined ingestion of 6 mg/kg of CAF and 1 g of TAU improved both PP and MP in female athletes habituated to caffeine; however; CAF and TAU independently failed to augment WAnT performance.

CYP1A2 Genotype Polymorphism Influences the Effect of Caffeine on Anaerobic Performance in Trained Males

The purpose was to investigate the effects of CYP1A2 -163C > A polymorphism on the effects of acute caffeine (CAF) supplementation on anaerobic power in trained males. Sixteen trained males (age: 21.6 ± 7.1 years; height: 179.7 ± 5.6 cm; body mass: 72.15 ± 6.8 kg) participated in a randomized, double-blind, placebo (PLA) controlled crossover design. Participants supplemented with CAF (6 mg/kg of body mass) and an isovolumetric PLA (maltodextrin) in random order and separated by 7 days, before an all-out 30-s anaerobic cycling test to determine peak, average, and minimum power output, and fatigue index. Genomic deoxyribonucleic acid was extracted to identify each participants CYP1A2 genotype. Six participants expressed AA homozygote and 10 expressed C alleles. There was a treatment by genotype interaction for peak power output (p = .041, η2 = .265, observed power = 0.552) with only those expressing AA genotype showing improvement following CAF supplementation compared with PLA (CAF: 693 ± 108 watts vs. PLA: 655 ± 97 watts; p = .039), while no difference between treatments was noted in those expressing C alleles (CAF: 614 ± 92 watts vs. PLA: 659 ± 144 watts; p = .135). There were no other interaction or main effects for average or minimum power output, or fatigue index (p > .05). In conclusion, the ingestion of 6 mg/kg of CAF improved peak power output only in participants with the AA genotype compared with PLA; however, expression of the CYP1A2 did not influence average or minimum power output or fatigue index.

The Dose-Effects of Caffeine on Lower Body Maximal Strength, Muscular Endurance, and Rating of Perceived Exertion in Strength-Trained Females

Caffeine supplementation has shown to be an effective ergogenic aid enhancing athletic performance, although limited research within female populations exists. Therefore, the aim of the investigation was to assess the effect of pre-exercise caffeine supplementation on strength performance and muscular endurance in strength-trained females. In a double-blind, randomised, counterbalanced design, fourteen strength-trained females using hormonal contraception consumed either 3 or 6 mg·kg-1 BM of caffeine or placebo (PLA). Following supplementation, participants performed a one-repetition maximum (1RM) leg press and repetitions to failure (RF) at 60% of their 1RM. During the RF test, rating of perceived exertion (RPE) was recorded every five repetitions and total volume (TV) lifted was calculated. Repeated measures ANOVA revealed that RF (p = 0.010) and TV (p = 0.012) attained significance, with pairwise comparisons indicating a significant difference between 3 mg·kg-1 BM and placebo for RF (p = 0.014), with an effect size of 0.56, and for 6 mg·kg-1 BM (p = 0.036) compared to the placebo, with an effect size of 0.65. No further significance was observed for 1RM or for RPE, and no difference was observed between caffeine trials. Although no impact on lower body muscular strength was observed, doses of 3 and 6 mg·kg-1 BM of caffeine improved lower body muscular endurance in resistance-trained females, which may have a practical application for enhancing resistance training stimuli and improving competitive performance.