The effects of caffeine ingestion on isokinetic muscular strength: A meta-analysis

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.

The effect of caffeine chewing gum on muscle performance and fatigue after severe-intensity exercise: isometric vs. dynamic assessments in trained cyclists

This study investigated the effect of caffeinated chewing gum (GUMCAF) on muscle fatigue (isometric vs. dynamic) after severe-intensity cycling bouts. Fifteen trained male cyclists participated in four visits. Each visit involved two severe-intensity cycling bouts (Δ1 and Δ2) lasting 6 min, separated by a 5-min recovery period. Muscle fatigue was assessed by isometric maximal voluntary knee extension contraction (IMVC) with twitch interpolation technique and dynamically by 7 s all-out cycling sprints. Assessments were performed before GUMCAF (Pre-GUM) and after the cycling bouts (Post-Exercise). GUMCAF and placebo gum (GUMPLA) were administered in a randomized double-blind procedure with participants receiving each gum type (GUMCAF and GUMPLA) during two separate visits. The results showed no significant interaction between gum types and time for the isometric and dynamic measurements (p > 0.05). The percentage change in performance from Pre-GUM to Post-Exercise showed no significant difference between GUMCAF and GUMPLA for either the dynamic-derived TMAX (~ -17.8% and -15.1%, respectively; p = 0.551) or isometric IMVC (~ -12.3% and -17.7%, respectively; p = 0.091) measurements. Moderate to large correlations (r = 0.31-0.51) were found between changes in sprint maximal torque and maximal power output measurements and isometric force, for both gum conditions. GUMCAF was not effective in attenuating muscle force decline triggered by severe-intensity cycling exercises, as measured by both isometric and dynamic methods. The correlations between IMVC and cycling maximal torque and power output suggest caution when interpreting isometric force as a direct measure of fatigue during dynamic cycling exercises.

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.

Exploring the relationship between caffeine metabolism-related CYP1A2 rs762551 polymorphism and team sport athlete status and training adaptations

BACKGROUND

This study aimed to achieve a dual objective: to compare the frequencies of CYP1A2 rs762551 genotypes between team sport athletes and a control group, and to determine the association between the rs762551 polymorphism and changes in physical performance after a six-week training program among elite basketball players.

METHODS

The study encompassed an analysis of 504 individuals, comprising 320 athletes and 184 controls. For the Turkish cohort, DNA was isolated using the buccal swab method, and genotyping was conducted using the KASP technique. Performance assessments included the Yo-Yo IR2 and 30 m sprint tests. For Russian participants, DNA samples were extracted from peripheral blood, a commercial kit was used for DNA extraction, and genotyping of the rs762551 polymorphism was conducted using DNA microarray.

RESULT

Notably, a statistically significant linear decline in the prevalence of the CC genotype was observed with ascending levels of athletic achievement within team sports (sub-elite: 18.0%, elite: 8.2%, highly elite: 0%; p = 0.001). Additionally, the CA genotype was the most prevalent genotype in the highly elite group compared to controls (80.0% vs. 45.1%, p = 0.048). Furthermore, statistically significant improvements in Yo-Yo IR2 performance were noted exclusively among basketball players harboring the CA genotype (p = 0.048).

CONCLUSIONS

The study's findings indicate that the rs762551 CC genotype is a disadvantage in elite team sports, whereas the CA genotype provides an advantage in basketball performance.

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.

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.

Evidence-based nutritional approaches to enhance exercise adaptations

PURPOSE OF REVIEW

The purpose of this opinion paper is to provide current-day and evidence-based information regarding dietary supplements that support resistance training adaptations or acutely enhance strength-power or endurance performance.

RECENT FINDINGS

Several independent lines of evidence support that higher protein diets, which can be readily achieved through animal-based protein supplements, optimize muscle mass during periods of resistance training, and this likely facilitates strength increases. Creatine monohydrate supplementation and peri-exercise caffeine consumption also enhance strength and power through distinct mechanisms. Supplements that favorably affect aspects of endurance performance include peri-exercise caffeine, nitrate-containing supplements (e.g., beet root juice), and sodium bicarbonate consumption. Further, beta-alanine supplementation can enhance high-intensity endurance exercise efforts.

SUMMARY

Select dietary supplements can enhance strength and endurance outcomes, and take-home recommendations will be provided for athletes and practitioners aiming to adopt these strategies.

Effects of post-exercise cold-water immersion on resistance training-induced gains in muscular strength: a meta-analysis

The aim of this review was to perform a meta-analysis examining the effects of cold-water immersion (CWI) coupled with resistance training on gains in muscular strength. Four databases were searched to find relevant studies. Their methodological quality and risk of bias were evaluated using the PEDro checklist. The effects of CWI vs. control on muscular strength were examined in a random-effects meta-analysis. Ten studies (n = 170; 92% males), with 11 comparisons across 22 groups, were included in the analysis. Studies were classified as of good or fair methodological quality. The main meta-analysis found that CWI attenuated muscular strength gains (effect size [ES]: -0.23; 95% confidence interval [CI]: -0.45, -0.01; p = 0.041). In the analysis of data from studies applying CWI only to the trained limbs, CWI attenuated muscular strength gains (ES: -0.31; 95% CI: -0.61, -0.01; p = 0.041). In the analysis of data from studies using whole-body CWI, there was no significant difference in muscular strength gains between CWI and control (ES: -0.08; 95% CI: -0.53, 0.38; p = 0.743). In summary, this meta-analysis found that the use of CWI following resistance exercise sessions attenuates muscular strength gains in males. However, when CWI was applied to the whole body, there was no significant difference between CWI and control for muscular strength. Due to the attenuated gains in muscular strength found with single limb CWI, the use and/or timing of CWI in resistance training should be carefully considered and individualized.

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.

High Doses of Caffeine Increase Muscle Strength and Calcium Release in the Plasma of Recreationally Trained Men

The effects of acute caffeine supplementation on muscular strength remain unclear. We examined the effects of two different doses of caffeine on muscle strength and calcium in plasma compared to placebo using a crossover, randomized, double-blind, placebo-controlled design. Twenty-one (n = 21) recreationally resistance-trained participants were randomly assigned into three experimental conditions: 6 mg·kg bw−1 of caffeine (CF6); 8 mg·kg bw−1 of caffeine (CF8); or placebo (PLA), with a 7-day washout period between conditions. Muscular strength assessments were made for both upper (bench press) and lower body muscles (squat and deadlift). Calcium release in plasma was measured on five different occasions. Bench press (CF8: 100.1 ± 1.9 kg; PLA: 94.2 ± 2.5 kg), deadlift (CF8: 132.8 ± 3.5 kg; PLA: 120.7 ± 5.7 kg), and squat (CF8: 130.1 ± 4.9 kg; PLA 119.4 ± 5.4 kg) strength were all significantly (p < 0.001) improved in CF8 compared to PLA. Calcium release in plasma was significantly increased in CF8, whereas no changes were observed in CF6 or PLA. Overall, 8 mg·kg bw−1 of caffeine appears to be an effective dose to optimize upper and lower body muscular strength and calcium release in recreationally trained participants.

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.

Use It or Lose It? A Meta-Analysis on the Effects of Resistance Training Cessation (Detraining) on Muscle Size in Older Adults

This review aimed to explore the effect of resistance training cessation (detraining) on muscle size in older adults. Five databases were searched to find eligible studies. Their methodological quality was assessed using the PEDro checklist. The data were pooled in a random-effects meta-analysis. Six studies, with eight groups, were included in the review. Resistance training interventions lasted from 9 to 24 weeks. The detraining duration was from 12 to 52 weeks. Studies were classified as being of fair or good methodological quality. Compared to the baseline data, muscle size significantly increased following the resistance training intervention (Cohen's d: 0.99; 95% confidence interval: 0.63, 1.36). Compared to the post-resistance training data, there was a significant decrease in muscle size following training cessation (Cohen's d: -0.83; 95% confidence interval: -1.30, -0.36). In subgroup analyses, there was no significant decrease in muscle size following 12-24 weeks of training cessation (Cohen's d: -0.60; 95% confidence interval: -1.21, 0.01). There was a significant decrease in muscle size following 31-52 weeks of training cessation (Cohen's d: -1.11; 95% confidence interval: -1.75, -0.47). In summary, resistance training increases muscle size in older adults. In contrast, training cessation is associated with a decrease in muscle size. However, the loss of muscle size might be related to detraining duration, with greater muscle loss occurring during longer duration detraining periods. Future studies are required to establish the time course of muscle size changes during detraining in older adults.

How Repeatable Is the Ergogenic Effect of Caffeine? Limited Reproducibility of Acute Caffeine (3 mg.kg-1) Ingestion on Muscular Strength, Power, and Muscular Endurance

This study aimed to determine the effect of 3 mg.kg−1 acute caffeine ingestion on muscular strength, power and strength endurance and the repeatability of potential ergogenic effects across multiple trials. Twenty-two university standard male rugby union players (20 ± 2 years) completed the study. Using a double-blind, randomized, and counterbalanced within-subject experimental design. Participants completed six experimental trials (three caffeine and three placebo) where force time characteristic of the Isometric Mid-Thigh Pull (IMTP), Countermovement Jump (CMJ) and Drop Jumps (DJ) were assessed followed by assessments of Chest Press (CP), Shoulder Press (SP), Squats (SQ), and Deadlifts (DL) Repetitions Until Failure (RTF at 70% 1 RM). ANOVA indicated that caffeine improved both the CMJ and DJ (p < 0.044) and increased RTF in all RTF assessments (p < 0.002). When individual caffeine trials were compared to corresponding placebo trials, effect sizes ranged from trivial-large favoring caffeine irrespective of a main effect of treatment being identified in the ANOVA. These results demonstrate for the first time that the performance enhancing effects of caffeine may not be repeatable between days, where our data uniquely indicates that this is in part attributable to between sessions variation in caffeine’s ergogenic potential.

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).

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.

Negative Effects of Mental Fatigue on Performance in the Yo-Yo Test, Loughborough Soccer Passing and Shooting Tests: A Meta-Analysis

We aimed to examine the effects of mental fatigue on the Yo-Yo test and Loughborough soccer passing and shooting tests performance using a meta-analysis. The search for studies was performed through eight bibliographic databases (Academic Search Elite, AUSPORT, Cochrane Library, PsycInfo, PubMed/MEDLINE, Scopus, SPORTDiscus, and Web of Science). The methodological quality of the included studies was assessed using the PEDro checklist. A random-effects meta-analysis was performed for data analysis. After reviewing 599 search results, seven studies with a total of ten groups were included in the review. All studies were classified as being of good methodological quality. Mental fatigue reduced the distance covered in the Yo-Yo test (Cohen's d: -0.49; 95% confidence interval [CI]: -0.66, -0.32). In the Loughborough soccer passing test, mental fatigue increased the original time needed to complete the test (Cohen's d: -0.24; 95% CI: -0.46, -0.03), increased penalty time (Cohen's d: -0.39; 95% CI: -0.46, -0.31), and decreased performance time (Cohen's d: -0.52; 95% CI: -0.80, -0.24). In the Loughborough soccer shooting test, mental fatigue decreased points per shot (Cohen's d: -0.37; 95% CI: -0.70, -0.04) and shot speed (Cohen's d: -0.35; 95% CI: -0.64, -0.06). Overall, the findings presented in this review demonstrated that mental fatigue negatively impacts endurance-based running performance as well as soccer passing and shooting skills.

Effects of Attentional Focus on Muscular Endurance: A Meta-Analysis

Several studies explored the effects of attentional focus on resistance exercise, but their analysed outcomes most commonly involved surface electromyography variables. Therefore, the effects of attentional focus on resistance exercise performance remain unclear. The aim of this review was to perform a meta-analysis examining the acute effects of external focus vs. internal focus vs. control on muscular endurance. Five databases were searched to find relevant studies. The data were pooled in a random-effects meta-analysis. In the analysis for external vs. internal focus of attention, there were seven comparisons with 14 study groups. In the analyses for external focus vs. control and internal focus vs. control, there were six comparisons with 12 study groups. An external focus of attention enhanced muscular endurance when compared with an internal focus (Cohen's d: 0.58; 95% confidence interval (CI): 0.34 and 0.82) and control (Cohen's d: 0.42; 95% CI: 0.08 and 0.76). In the analysis for internal focus vs. control, there was no significant difference between the conditions (Cohen's d: -0.19; 95% CI: -0.45 and 0.07). Generally, these results remained consistent in the subgroup analyses for upper-body vs. lower-body exercises. From a practical perspective, the results presented in this review suggest that individuals should use an external focus of attention for acute enhancement of muscular endurance.

Effects of caffeine on rate of force development: A meta-analysis

This review aimed to conduct a meta-analysis of studies examining the effects of caffeine on rate of force development (RFD). Ten databases were searched to find relevant studies. Risk of bias (RoB) of the included studies was evaluated. Data were analyzed in a random-effects meta-analysis. Eleven studies with "some concerns" regarding RoB were included. In the main meta-analysis, there was a significant ergogenic effect of caffeine ingestion on RFD (Hedges' g = 0.37; 95% confidence interval [CI]: 0.21, 0.52; p < 0.0001). An ergogenic effect of caffeine was also found on RFD during resistance exercises (Hedges' g = 0.49; 95% CI: 0.30, 0.67; p < 0.0001), but not during the countermovement jump test (Hedges' g = 0.18; 95% CI: -0.02, 0.39; p = 0.08), with a significant difference between the subgroups (p = 0.03). Small-to-moderate (3-5 mg/kg; Hedges' g = 0.25; 95% CI: 0.09, 0.41; p = 0.002) and moderate-to-high caffeine doses (6-10 mg/kg) enhanced RFD (Hedges' g = 0.57; 95% CI: 0.30, 0.85; p < 0.0001), even though the effects were larger with higher caffeine doses (p = 0.04). Overall, caffeine ingestion increases RFD, which is relevant given that RFD is commonly associated with sport-specific tasks. From a practical perspective: (1) individuals interested in the acute enhancement of RFD in resistance exercise may consider supplementing with caffeine; and (2) given that evaluation of RFD is most commonly used for testing purposes, caffeine ingestion (3-10 mg/kg 60 min before exercise) should be standardized before RFD assessments.

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.

Acute and Long-Term Effects of Attentional Focus Strategies on Muscular Strength: A Meta-Analysis

This review aimed to perform a meta-analysis examining the following: (a) acute effects of adopting an internal focus vs. external focus of attention on muscular strength; and (b) long-term effects of adopting an internal focus vs. external focus of attention during resistance training on gains in muscular strength. We searched through five databases to find eligible studies. Random-effects meta-analyses of standardized mean differences were conducted to analyze the data. Ten studies were included. In the meta-analysis for the acute effects, there was a significant positive effect of external focus on muscular strength (standardized mean difference: 0.34; 95% confidence interval: 0.22, 0.46). In the meta-analysis for the long-term effects, there was no significant difference between training with an internal focus and external focus on muscular strength gains (standardized mean difference: 0.32; 95% confidence interval: –0.08, 0.73). In the subgroup analysis for lower-body exercises, we found a significant positive effect of training with an external focus on muscular strength gains (standardized mean difference: 0.47; 95% confidence interval: 0.07, 0.87). In summary, our findings indicate an acute increase in muscular strength when utilizing an external focus of attention. When applied over the long-term, using an external focus of attention may also enhance resistance training-induced gains in lower-body muscular strength.

Can 3 mg·kg-1 of Caffeine Be Used as An Effective Nutritional Supplement to Enhance the Effects of Resistance Training in Rugby Union Players?

The present study uniquely examined the effect of 3 mg·kg⁻¹ chronic caffeine consumption on training adaptations induced by 7-weeks resistance training and assessed the potential for habituation to caffeine’s ergogenicity. Thirty non-specifically resistance-trained university standard male rugby union players (age (years): 20 ± 2; height (cm): 181 ± 7; body mass (kg): 92 ± 17) completed the study), who were moderate habitual caffeine consumers (118 ± 110 mg), completed the study. Using a within-subject double-blind, placebo-controlled experimental design, the acute effects of caffeine intake on upper and lower limb maximal voluntary concentric and eccentric torque were measured using isokinetic dynamometry (IKD) prior to and immediately following a resistance training intervention. Participants were split into strength-matched groups and completed a resistance-training program for seven weeks, consuming either caffeine or a placebo before each session. Irrespective of group, acute caffeine consumption improved peak eccentric torque of the elbow extensors (p < 0.013), peak concentric torque of the elbow flexors (p < 0.005), total eccentric work of the elbow flexors (p < 0.003), total concentric work of the knee extensors (p < 0.001), and total concentric and eccentric work of the knee flexors (p < 0.046) following repeated maximal voluntary contractions. Many of these acute caffeine effects were still prevalent following chronic exposure to caffeine throughout the intervention. The training intervention resulted in significant improvements in upper and lower body one-repetition maximum strength (p < 0.001). For the most part, the effect of the training intervention was equivalent in both the caffeine and placebo groups, despite a small but significant increase (p < 0.037) in the total work performed in the participants that consumed caffeine across the course of the intervention. These results infer that caffeine may be beneficial to evoke acute improvements in muscular strength, with acute effects prevalent following chronic exposure to the experimental dose. However, individuals that consumed caffeine during the intervention did not elicit superior post-intervention training- induced adaptations in muscular strength.

Effects of Paracetamol (Acetaminophen) Ingestion on Endurance Performance: A Systematic Review and Meta-Analysis

Several studies explored the effects of paracetamol (acetaminophen) ingestion on endurance performance, but their findings are conflicting. Therefore, this review aimed to conduct a meta-analysis examining the effects of paracetamol ingestion on endurance performance. Five databases were searched to find relevant studies. The PEDro checklist was used to assess the methodological quality of the included studies. Data reported in the included studies were pooled in a random-effects meta-analysis. A total of ten studies with good or excellent methodological quality were included in the meta-analysis (pooled n = 141). All included studies had a randomized, double-blind, crossover design. In the main meta-analysis, there was no significant difference between the effects of placebo and paracetamol on endurance performance (Cohen's d = 0.09; 95% confidence interval (CI): -0.04, 0.22; p = 0.172). However, an ergogenic effect was found when we considered only the studies that provided paracetamol 45 to 60 min before exercise (Cohen's d = 0.14; 95% CI: 0.07, 0.21; p < 0.001). In a subgroup analysis that focused on time-to-exhaustion tests, there was a significant ergogenic effect of paracetamol ingestion (Cohen's d = 0.19; 95% CI: 0.06, 0.33; p = 0.006). There was no significant difference between placebo and paracetamol in a subgroup analysis that focused on time trial tests (Cohen's d = 0.05; 95% CI: -0.12, 0.21; p = 0.561). In conclusion, paracetamol ingestion appears to enhance performance (a) in time-to-exhaustion endurance tests and (b) when consumed 45 to 60 min before exercise.

Is Coffee a Useful Source of Caffeine Preexercise?

Caffeine is a well-established ergogenic aid, with its performance-enhancing effects demonstrated across a wide variety of exercise modalities. Athletes tend to frequently consume caffeine as a performance enhancement method in training and competition. There are a number of methods available as a means of consuming caffeine around exercise, including caffeine anhydrous, sports drinks, caffeine carbohydrate gels, and gum. One popular method of caffeine ingestion in nonathletes is coffee, with some evidence suggesting it is also utilized by athletes. In this article, we discuss the research pertaining to the use of coffee as an ergogenic aid, exploring (a) whether caffeinated coffee is ergogenic, (b) whether dose-matched caffeinated coffee provides a performance benefit similar in magnitude to caffeine anhydrous, and (c) whether decaffeinated coffee consumption affects the ergogenic effects of a subsequent isolated caffeine dose. There is limited evidence that caffeinated coffee has the potential to offer ergogenic effects similar in magnitude to caffeine anhydrous; however, this requires further investigation. Coingestion of caffeine with decaffeinated coffee does not seem to limit the ergogenic effects of caffeine. Although caffeinated coffee is potentially ergogenic, its use as a preexercise caffeine ingestion method represents some practical hurdles to athletes, including the consumption of large volumes of liquid and difficulties in quantifying the exact caffeine dose, as differences in coffee type and brewing method may alter caffeine content. The use of caffeinated coffee around exercise has the potential to enhance performance, but athletes and coaches should be mindful of the practical limitations.

Effects of Caffeine on Resistance Exercise: A Review of Recent Research

In the last few years, a plethora of studies have explored the effects of caffeine on resistance exercise, demonstrating that this field of research is growing fast. This review evaluates and summarizes the most recent findings. Given that toxic doses of caffeine are needed to increase skeletal muscle contractility, the binding of caffeine to adenosine receptors is likely the primary mechanism for caffeine's ergogenic effects on resistance exercise. There is convincing evidence that caffeine ingestion is ergogenic for (i) one-repetition maximum, isometric, and isokinetic strength; and (ii) muscular endurance, velocity, and power in different resistance exercises, loads, and set protocols. Furthermore, there is some evidence that caffeine supplementation also may enhance adaptations to resistance training, such as gains in strength and power. Caffeine ingestion is ergogenic for resistance exercise performance in females, and the magnitude of these effects seems to be similar to that observed in men. Habitual caffeine intake and polymorphisms within CYP1A2 and ADORA2A do not seem to modulate caffeine's ergogenic effects on resistance exercise. Consuming lower doses of caffeine (e.g., 2-3 mg/kg) appears to be comparably ergogenic to consuming high doses of caffeine (e.g., 6 mg/kg). Minimal effective doses of caffeine seem to be around 1.5 mg/kg. Alternate caffeine sources such as caffeinated chewing gum, gel, and coffee are also ergogenic for resistance exercise performance. With caffeine capsules, the optimal timing of ingestion seems to be 30-60 min before exercise. Caffeinated chewing gums and gels may enhance resistance exercise performance even when consumed 10 min before exercise. It appears that caffeine improves performance in resistance exercise primarily due to its physiological effects. Nevertheless, a small portion of the ergogenic effect of caffeine seems to be placebo-driven.

Ergogenic Effects of Acute Caffeine Intake on Muscular Endurance and Muscular Strength in Women: A Meta-Analysis

This meta-analysis aimed to explore the effects of caffeine ingestion on muscular endurance and muscular strength in women. Five databases were searched to find relevant studies. A random-effects meta-analysis of standardized mean differences (SMD) was performed for data analysis. Subgroup meta-analyses explored the effects of caffeine on upper-body and lower-body muscular endurance and muscular strength. Eight crossover placebo-controlled studies were included in the review. In the main meta-analysis that considered data from all included studies, there was a significant ergogenic effect of caffeine on muscular endurance (SMD = 0.25; p = 0.027) and muscular strength (SMD = 0.18; p < 0.001). In a subgroup analysis that considered only upper-body exercises, there was a significant ergogenic effect of caffeine on muscular endurance (SMD = 0.20; p = 0.007) and muscular strength (SMD = 0.17; p < 0.001). In a subgroup analysis that considered only lower-body exercises, there was no significant difference between caffeine and placebo for muscular endurance (SMD = 0.43; p = 0.092) or muscular strength (SMD = 0.16; p = 0.109). The main finding of this meta-analysis is that caffeine ingestion has a significant ergogenic effect on muscular endurance and muscular strength in women. The effects reported in this analysis are similar to those previously observed in men and suggest that women may use caffeine supplementation as an ergogenic aid for muscular performance. Future research is needed to explore the effects of caffeine on lower-body muscular endurance and muscular strength in this population.

Nutrition and physical activity interventions for the general population with and without cardiometabolic risk: a scoping review

OBJECTIVE

The objective of this scoping review was to examine the research question: In the adults with or without cardiometabolic risk, what is the availability of literature examining interventions to improve or maintain nutrition and physical activity-related outcomes? Sub-topics included: (1) behaviour counseling or coaching from a dietitian/nutritionist or exercise practitioner, (2) mobile applications to improve nutrition and physical activity and (3) nutritional ergogenic aids.

DESIGN

The current study is a scoping review. A literature search of the Medline Complete, CINAHL Complete, Cochrane Database of Systematic Reviews and other databases was conducted to identify articles published in the English language from January 2005 until May 2020. Data were synthesised using bubble charts and heat maps.

SETTING

Out-patient, community and workplace.

PARTICIPANTS

Adults with or without cardiometabolic risk factors living in economically developed countries.

RESULTS

Searches resulted in 19 474 unique articles and 170 articles were included in this scoping review, including one guideline, thirty systematic reviews (SR), 134 randomised controlled trials and five non-randomised trials. Mobile applications (n 37) as well as ergogenic aids (n 87) have been addressed in several recent studies, including SR. While primary research has examined the effect of individual-level nutrition and physical activity counseling or coaching from a dietitian/nutritionist and/or exercise practitioner (n 48), interventions provided by these practitioners have not been recently synthesised in SR.

CONCLUSION

SR of behaviour counseling or coaching provided by a dietitian/nutritionist and/or exercise practitioner are needed and can inform practice for practitioners working with individuals who are healthy or have cardiometabolic risk.

Caffeine improves biochemical and specific performance after judo training: a double-blind crossover study in a real judo training situation

Background

Nutritional ergogenic aids are foods or nutrients that can improve physical performance. Among these foods with ergogenic properties, caffeine has shown that it can increase the fat catabolism, strength, and improve the cognition and time reaction of an athlete, therefore, it is hoped that it can improve the performance of judokas. This study through a double-blind crossover (supplement X placebo) protocol, investigated the effects caffeine supplementation (single capsule containing 5 mg/kg body mass intake 60 min before the session) on biochemical, anthropometrical, physical, subjective and hemodynamic variables measured before, during and after two typical judo trainingcxs sessions (120-min: 40-min of gymnastics; 40-min of specific technics and; 40-min of judo combat).

Methods

8 high-level athletes (21.4 ± 2.0 years; 83.6 ± 15.2 kg; 1.8 ± 0.1 m; 17.9 ± 7.0 Fat%) were evaluated before and after each training for body mass, hydration, upper and lower limb power, performance in the special judo fitness test (SJFT), free fatty acids (FFA) in plasma, uric acid, glucose, lactate, heart rate, and pain. In addition, heart rate, FFA in plasma, uric acid, glucose, lactate, rating of perceived exertion and pain were assessed during the training.

Results

At 120 min, supplementation resulted in a higher concentration of plasma FFA (1.5 ± 0.5 vs. 1.0 ± 0.3 mmol/L; p = 0.047) and lactate (4.9 ± 1.8 vs. 3.0 ± 1.2 mmol/L; p = 0.047), and a lower concentration of uric acid (5.4 ± 0.9 vs. 7.0 ± 1.5 mg/dL; p = 0.04). Supplementation also resulted in performance maintenance (fatigue index) in the SJFT (Δ0.3 ± 2.0 vs Δ1.7 ± 2.5, for caffeine and placebo respectively, p = 0.046). No adverse effects were observed.

Conclusion

Based on the applied dose, intake time, and sample of this study, we can conclude that caffeine produces an ergogenic biochemical effect, and improves performance in judo athletes.

International society of sports nutrition position stand: caffeine and exercise performance

Following critical evaluation of the available literature to date, The International Society of Sports Nutrition (ISSN) position regarding caffeine intake is as follows: 1. Supplementation with caffeine has been shown to acutely enhance various aspects of exercise performance in many but not all studies. Small to moderate benefits of caffeine use include, but are not limited to: muscular endurance, movement velocity and muscular strength, sprinting, jumping, and throwing performance, as well as a wide range of aerobic and anaerobic sport-specific actions. 2. Aerobic endurance appears to be the form of exercise with the most consistent moderate-to-large benefits from caffeine use, although the magnitude of its effects differs between individuals. 3. Caffeine has consistently been shown to improve exercise performance when consumed in doses of 3-6 mg/kg body mass. Minimal effective doses of caffeine currently remain unclear but they may be as low as 2 mg/kg body mass. Very high doses of caffeine (e.g. 9 mg/kg) are associated with a high incidence of side-effects and do not seem to be required to elicit an ergogenic effect. 4. The most commonly used timing of caffeine supplementation is 60 min pre-exercise. Optimal timing of caffeine ingestion likely depends on the source of caffeine. For example, as compared to caffeine capsules, caffeine chewing gums may require a shorter waiting time from consumption to the start of the exercise session. 5. Caffeine appears to improve physical performance in both trained and untrained individuals. 6. Inter-individual differences in sport and exercise performance as well as adverse effects on sleep or feelings of anxiety following caffeine ingestion may be attributed to genetic variation associated with caffeine metabolism, and physical and psychological response. Other factors such as habitual caffeine intake also may play a role in between-individual response variation. 7. Caffeine has been shown to be ergogenic for cognitive function, including attention and vigilance, in most individuals. 8. Caffeine may improve cognitive and physical performance in some individuals under conditions of sleep deprivation. 9. The use of caffeine in conjunction with endurance exercise in the heat and at altitude is well supported when dosages range from 3 to 6 mg/kg and 4-6 mg/kg, respectively. 10. Alternative sources of caffeine such as caffeinated chewing gum, mouth rinses, energy gels and chews have been shown to improve performance, primarily in aerobic exercise. 11. Energy drinks and pre-workout supplements containing caffeine have been demonstrated to enhance both anaerobic and aerobic performance.

The Effect of Acute Caffeine Ingestion on Cognitive Dual Task Performance during Assessment of Static and Dynamic Balance in Older Adults

The present work aimed to evaluate the effect of 3 mg·kg⁻¹ caffeine consumption on the standing and dynamic balance performance of older adults and sought to establish if caffeine ingestion can modulate the influence of a cognitive dual task on balance performance. Twelve apparently healthy participants (8 females) aged >65 years (72 ± 3.7 years) completed the study. Bipedal postural sway, four square step test, timed up and go, Y-balance (anterior reach only) and force-time characteristics of sit-to-stand performance were used to assess standing and dynamic balance. Attention and working memory were assessed using a serial 3s and 7s subtraction task during seated rest and completion of the bipedal standing assessment and Y-balance test. This battery of assessments was completed on two separate occasions, once following the consumption of a non-ergogenic placebo and again following the consumption of 3 mg·kg⁻¹ caffeine. The administration of treatments was randomised, counterbalanced and double-blind. Caffeine reduced performance in the bipedal standing balance assessments, evidenced by an increase in COP_ML, COP_Path, COP_Velocity. Performance during the dynamic balance tests was unaffected, other than rate of force development during the sit-to-stand, which was improved following caffeine ingestion. The introduction of a cognitive dual task had either limited effects, or improved facets of bipedal standing balance, whilst performance during the dynamic balance task was significantly reduced. In both balance assessments, there was evidence for a reduction in the performance of the cognitive task when both the balance and cognitive tests were performed simultaneously, with this effect not modulated by caffeine consumption. These findings refute the idea that caffeine ingestion may have positive effects on balance performance. However, despite a caffeine-induced reduction in bipedal standing balance, it is unlikely that caffeine ingestion would exacerbate fall risk given the limited effects in the dynamic balance tests. Future work should establish if these effects are generalisable to older frail participants and if caffeine can modulate the detrimental effects of an acute exercise bout on balance performance.

Caffeine Timing Improves Lower-Body Muscular Performance: A Randomized Trial

Little is known about the optimal time to consume caffeine prior to exercise to maximize the ergogenic benefits of the substance.

Purpose: To determine the optimal pre-exercise time interval to consume caffeine to improve lower-body muscular performance. A secondary aim was to identify the presence of any sex differences in responses to timed caffeine administration.

Methods: Healthy, resistance-trained males (n = 18; Mean±SD; Age: 25.1 ± 5.7 years; Height: 178.4 ± 7.1 cm; Body mass: 91.3 ± 13.5 kg; Percent body fat: 20.7 ± 5.2; Average caffeine consumption: 146.6 ± 100.3 mg/day) and females (n = 11; Mean ± SD; Age: 20.1 ± 1.6 years; Height: 165.0 ± 8.8 cm; Body mass: 65.8 ± 10.0 kg; Percent bodyfat: 25.8 ± 4.2; Average caffeine consumption: 111.8 ± 91.7 mg/day) participated in this investigation. In a randomized, double-blind, placebo-controlled, crossover fashion, participants consumed 6 mg·kg⁻¹ caffeine or placebo solution at three time points: 2 h prior (2H), 1 h prior (1H), or 30 min prior (30M) to exercise testing. During three visits, caffeine was randomly administered at one time point, and placebo was administered at the other two time points. During one visit, placebo was administered at all three time points. Next, participants performed isometric mid-thigh pulls (IMTP), countermovement vertical jumps (CMVJ), and isometric/isokinetic knee extensor testing (ISO/ISOK).

Results: Caffeine administered at 1H significantly improved absolute CMVJ and ISO performance relative to placebo. Mean CMVJ jump height was significantly higher during 1H compared to 30M. However, only caffeine administered at 30M significantly improved absolute measures of isokinetic performance. Analysis of the pooled caffeine conditions revealed that muscular performance was more consistently augmented by caffeine in males compared to females.

Conclusions: Pre-exercise caffeine timing significantly modulated participant responses to the substance, with 1H exerting the most consistent ergogenic benefits relative to other time points, particularly compared to 2H. Male participants were found to respond more consistently to caffeine compared to female participants. These results suggest that active individuals can maximize the ergogenic effects of caffeine by consuming the substance ~1 h prior to the point when peak muscular performance is desired.

CYP1A2 genotype and acute ergogenic effects of caffeine intake on exercise performance: a systematic review

PURPOSE

To systematically review studies that examined the influence of the CYP1A2 -163C>A polymorphism on the ergogenic effects of caffeine and to discuss some of the reasons for the discrepancies in findings between the studies.

METHODS

This review was performed in accordance with the PRISMA guidelines. The search for studies was performed through nine databases.

RESULTS

Seventeen studies were included in the review. Based on the included studies, it seems that individuals with the AA or AC/CC genotype may experience an increase in performance following caffeine ingestion. Significant differences between genotypes were found in four studies, and all four reported a more favorable response in the AA vs. AC/CC genotype. These results suggest that if there is an actual genotype-related effect of acute caffeine supplementation, it might be in that direction. In the studies that reported such data for aerobic endurance, the findings are specific to male participants performing cycling time trials (distances of ≥ 10 km) and ingesting caffeine 60 min before exercise. For high-intensity exercise, two studies reported that genotype variations determined the response to caffeine ingestion, even though the differences were either small (~ 1 additional repetition in high-load resistance exercise set performed to muscular failure) or inconsistent (i.e., observed only in one out of eight performance tests).

CONCLUSIONS

CYP1A2 genotype variations may modulate caffeine's ergogenic effects, but the differences between genotypes were small, inconsistent, or limited to specific exercise scenarios. Future studies with larger sample sizes are needed to fully elucidate this research area.

The Effect of Dietary Nitrate Supplementation on Isokinetic Torque in Adults: A Systematic Review and Meta-Analysis

Dietary nitrate (NO3-) supplementation, which can enhance performance in exercise settings involving repeated high-intensity efforts, has been linked to improved skeletal muscle contractile function. Although muscular strength is an important component of explosive movements and sport-specific skills, few studies have quantified indices of muscular strength following NO3- supplementation, particularly isokinetic assessments at different angular velocities. We performed a systematic review and meta-analysis to determine whether dietary NO3- supplementation improves peak torque, as assessed by the gold standard method of isokinetic dynamometry, and if this effect was linked to the angular velocity imposed during the assessment. Dialnet, Directory of Open Access Journals, MEDLINE, PubMed, SciELO, Scopus, and SPORTDiscus were searched for articles using the following search strategy: (nitrate OR beet*) AND (supplement* OR nutr* OR diet*) AND (isokinetic OR strength OR "resistance exercise" OR "resistance training" OR "muscular power"). The meta-analysis of data from 5 studies with 60 participants revealed an overall effect size of -0.01 for the effect of nitrate supplementation on isokinetic peak torque, whereas trivial effect sizes ranging from -0.11 to 0.16 were observed for independent velocity-specific (90°/s, 180°/s, 270°/s, and 360°/s) isokinetic peak torque. Four of the five studies indicated that dietary NO3- supplementation is not likely to influence voluntary knee extensor isokinetic torque across a variety of angular velocities. These results suggest that NO3- supplementation does not influence isokinetic peak torque, but further work is required to elucidate the potential of NO3- supplementation to influence other indices of muscular strength, given the dearth of experimental evidence on this topic.

Effects of diet interventions, dietary supplements, and performance-enhancing substances on the performance of CrossFit-trained individuals: A systematic review of clinical studies

CrossFit (CF) is characterized as a constantly varied, high-intensity, functional movement training program, performed with little or no rest between bouts, combining strength and endurance exercises, such as running, cycling, rowing, Olympic weightlifting, power weightlifting, and gymnastic-type exercises. Several nutritional strategies are used to improve sports performance of CF practitioners; however, most of them are empirical and lack scientific evidence. Thus, the aim of this review was to determine the effects of diet intervention, dietary supplements, and performance-enhancing substances on exercise-performance parameters of CF practitioners. MEDLINE/PubMed, Web of Science, LILACS, SciELO, and Scopus databases were searched using specific Medical Subject Headings and keywords for clinical studies that enrolled CF athletes in an intervention using diet, dietary supplements, or performance-enhancing substances. Athletic performance was considered as the primary outcome. No other filters were applied. Including grey literature search, 219 studies were identified; however only 14 studies met the eligibility criteria. Two studies evaluated the effects of caffeine supplementation on exercise performance; five studies evaluated high- or low-carbohydrate effects on performance and other parameters. One study verified the effects of multi-ingredient supplementation on CF-specific performance and body composition. One study compared the intake of protein supplements on performance and body composition. Two studies assessed the effect of green tea and (-)-epicatechin on performance and other parameters. One study evaluated the effects of nitrate supplementation on exercise performance. One study investigated the effect of betaine supplementation on body composition and muscle performance. Finally, one study examined the effects of sodium bicarbonate (SB) ingestion on exercise performance and aerobic capacity. Only SB supplementation improved CF performance. These outcomes may have been obtained due to methodological limitations such as small sample size, lack of control over influencing variables, short period of exercise intervention. Despite the popularity and growing evidence about CF, little is known about the relationship between performance-enhancing substances or dietary interventions and CF performance. Given the lack of scientific evidence, new studies with potential ergogenic supplements, a better methodological model, and practical application are required.

Caffeine and Exercise: What Next?

Caffeine is a widely utilized performance-enhancing supplement used by athletes and non-athletes alike. In recent years, a number of meta-analyses have demonstrated that caffeine's ergogenic effects on exercise performance are well-established and well-replicated, appearing consistent across a broad range of exercise modalities. As such, it is clear that caffeine is an ergogenic aid-but can we further explore the context of this ergogenic aid in order to better inform practice? We propose that future research should aim to better understand the nuances of caffeine use within sport and exercise. Here, we propose a number of areas for exploration within future caffeine research. These include an understanding of the effects of training status, habitual caffeine use, time of day, age, and sex on caffeine ergogenicity, as well as further insight into the modifying effects of genotype. We also propose that a better understanding of the wider, non-direct effects of caffeine on exercise, such as how it modifies sleep, anxiety, and post-exercise recovery, will ensure athletes can maximize the performance benefits of caffeine supplementation during both training and competition. Whilst not exhaustive, we hope that the questions provided within this manuscript will prompt researchers to explore areas with the potential to have a large impact on caffeine use in the future.

What Dose of Caffeine to Use: Acute Effects of 3 Doses of Caffeine on Muscle Endurance and Strength

PURPOSE

To explore the effects of 3 doses of caffeine on muscle strength and muscle endurance.

METHODS

Twenty-eight resistance-trained men completed the testing sessions under 5 conditions: no-placebo control, placebo control, and with caffeine doses of 2, 4, and 6 mg·kg-1. Muscle strength was assessed using the 1-repetition-maximum test; muscle endurance was assessed by having the participants perform a maximal number of repetitions with 60% 1-repetition maximum.

RESULTS

In comparison with both control conditions, only a caffeine dose of 2 mg·kg-1 enhanced lower-body strength (d = 0.13-0.15). In comparison with the no-placebo control condition, caffeine doses of 4 and 6 mg·kg-1 enhanced upper-body strength (d = 0.07-0.09) with a significant linear trend for the effectiveness of different doses of caffeine (P = .020). Compared with both control conditions, all 3 caffeine doses enhanced lower-body muscle endurance (d = 0.46-0.68). For upper-body muscle endurance, this study did not find significant effects of caffeine.

CONCLUSIONS

This study revealed a linear trend between the dose of caffeine and its effects on upper-body strength. The study found no clear association between the dose of caffeine and the magnitude of its ergogenic effects on lower-body strength and muscle endurance. From a practical standpoint, the magnitude of caffeine's effects on strength is of questionable relevance. A low dose of caffeine (2 mg·kg-1)-for an 80-kg individual, the dose of caffeine in 1-2 cups of coffee-may produce substantial improvements in lower-body muscle endurance with the magnitude of the effect being similar to that attained using higher doses of caffeine.

The Influence of Caffeine Supplementation on Resistance Exercise: A Review

This paper aims to critically evaluate and thoroughly discuss the evidence on the topic of caffeine supplementation when performing resistance exercise, as well as provide practical guidelines for the ingestion of caffeine prior to resistance exercise. Based on the current evidence, it seems that caffeine increases both maximal strength and muscular endurance. Furthermore, power appears to be enhanced with caffeine supplementation, although this effect might, to a certain extent, be caffeine dose- and external load-dependent. A reduction in rating of perceived exertion (RPE) might contribute to the performance-enhancing effects of caffeine supplementation as some studies have observed decreases in RPE coupled with increases in performance following caffeine ingestion. However, the same does not seem to be the case for pain perception as there is evidence showing acute increases in resistance exercise performance without any significant effects of caffeine ingestion on pain perception. Some studies have reported that caffeine ingestion did not affect exercise-induced muscle damage, but that it might reduce perceived resistance exercise-induced delayed-onset muscle soreness; however, this needs to be explored further. There is some evidence that caffeine ingestion, compared with a placebo, may lead to greater increases in the production of testosterone and cortisol following resistance exercise. However, given that the acute changes in hormone levels seem to be weakly correlated with hallmark adaptations to resistance exercise, such as hypertrophy and increased muscular strength, these findings are likely of questionable practical significance. Although not without contrasting findings, the available evidence suggests that caffeine ingestion can lead to acute increases in blood pressure (primarily systolic), and thus caution is needed regarding caffeine supplementation among individuals with high blood pressure. In the vast majority of studies, caffeine was administered in capsule or powder forms, and therefore the effects of alternative forms of caffeine, such as chewing gums or mouth rinses, on resistance exercise performance remain unclear. The emerging evidence suggests that coffee might be at least equally ergogenic as caffeine alone when the caffeine dose is matched. Doses in the range of 3-9 mg·kg^-1 seem to be adequate for eliciting an ergogenic effect when administered 60 min pre-exercise. In general, caffeine seems to be safe when taken in the recommended doses. However, at doses as high as 9 mg·kg^-1 or higher, side effects such as insomnia might be more pronounced. It remains unclear whether habituation reduces the ergogenic benefits of caffeine on resistance exercise as no evidence exists for this type of exercise. Caution is needed when extrapolating these conclusions to females as the vast majority of studies involved only male participants.

ADOR2A C Allele Carriers Exhibit Ergogenic Responses to Caffeine Supplementation

Caffeine’s ergogenic effects on exercise performance are generally explained by its ability to bind to adenosine receptors. ADORA2A is the gene that encodes A_2A subtypes of adenosine receptors. It has been suggested that ADORA2A gene polymorphisms may be responsible for the inter-individual variations in the effects of caffeine on exercise performance. In the only study that explored the influence of variation in ADORA2A—in this case, a common polymorphism (rs5751876)—on the ergogenic effects of caffeine on exercise performance, C allele carriers were identified as “non-responders” to caffeine. To explore if C allele carriers are true “non-responders” to the ergogenic effects of caffeine, in this randomized, double-blind study, we examined the acute effects of caffeine ingestion among a sample consisting exclusively of ADORA2A C allele carriers. Twenty resistance-trained men identified as ADORA2A C allele carriers (CC/CT genotype) were tested on two occasions, following the ingestion of caffeine (3 mg/kg) and a placebo. Exercise performance was evaluated with movement velocity, power output, and muscle endurance during the bench press exercise, countermovement jump height, and power output during a Wingate test. Out of the 25 analyzed variables, caffeine was ergogenic in 21 (effect size range: 0.14 to 0.96). In conclusion, ADORA2A (rs5751876) C allele carriers exhibited ergogenic responses to caffeine ingestion, with the magnitude of improvements similar to what was previously reported in the literature among samples that were not genotype-specific. Therefore, individuals with the CT/CC genotype may still consider supplementing with caffeine for acute improvements in performance.

The Effects of Caffeine Ingestion on Measures of Rowing Performance: A Systematic Review and Meta-Analysis

The purpose of this paper was to conduct a systematic review and a meta-analysis of studies examining the acute effects of caffeine ingestion on measures of rowing performance. Crossover and placebo-controlled experiments that investigated the effects of caffeine ingestion on measures of rowing performance were included. The PEDro checklist was used to assess the methodological quality of the included studies. Seven studies of good and excellent methodological quality were included. None of the included studies examined on-water rowing. The majority of studies that were included in the meta-analysis used a 2000m rowing distance with only one using 1000m distance. Results of the main meta-analysis indicated that caffeine enhances performance on a rowing ergometer compared to placebo with a mean difference of -4.1 s (95% confidence interval (CI): -6.4, -1.8 s). These values remained consistent in the analysis in which the study that used a 1000m distance was excluded (mean difference: -4.3 s; 95% CI: -6.9, -1.8 s). We also found a significant increase in mean power (mean difference: 5.7 W; 95% CI: 2.1, 9.3 W) and minute ventilation (mean difference: 3.4 L/min; 95% CI: 1.7, 5.1 L/min) following caffeine ingestion. No significant differences between caffeine and placebo were found for the rating of perceived exertion, oxygen consumption, respiratory exchange ratio, and heart rate. This meta-analysis found that acute caffeine ingestion improves 2000m rowing ergometer performance by ~4 s. Our results support the use of caffeine pre-exercise as an ergogenic aid for rowing performance.

The Effect of Caffeine on the Velocity of Half-Squat Exercise during the Menstrual Cycle: A Randomized Controlled Trial

Recent literature confirms the ergogenic effect of acute caffeine intake to increase muscle strength and power in men. However, the information about the effect of caffeine on muscle performance in women is uncertain and it is unknown whether its ergogenicity is similar during the menstrual cycle. The goal of this investigation was to assess the effect of acute caffeine intake on mean and peak velocity of half-squat exercise during three different phases of the menstrual cycle. Thirteen trained eumenorrheic athletes (age = 31 ± 6 years; body mass = 58.6 ± 7.8 kg) participated in a double-blind, crossover and randomized experimental trial. In the early follicular (EFP), late follicular (LFP) and mid luteal phases (MLP), participants either ingested a placebo (cellulose) or 3 mg/kg/bm of caffeine in an opaque and unidentifiable capsule. In each trial, participants performed a half-squat exercise at maximal velocity with loads equivalent to 20%, 40% 60% and 80% of one repetition maximum (1RM). In each load, mean and peak velocity were measured during the concentric phase of the exercise using a rotatory encoder. In comparison to the placebo, a two-way ANOVA showed that the ingestion of 3 mg/kg/bm of caffeine increased mean velocity at 60% 1RM in EFP (Δ = 1.4 ± 2.7%, p = 0.04; ES: 0.2 ± 0.2) and LFP (Δ = 5.0 ± 10.4%, p = 0.04; ES: 0.3 ± 0.4). No other statistical differences were found for the caffeine-placebo comparison for mean velocity, but caffeine induced an ergogenic effect of small magnitude in all of the menstrual cycle phases. These results suggest that the acute intake of 3 mg/kg/bm of caffeine induces a small effect to increase movement velocity during resistance exercise in eumenorrheic female athletes. The positive effect of caffeine was of similar magnitude in all the three phases of the menstrual cycle.

Acute Enhancement of Jump Performance, Muscle Strength, and Power in Resistance-Trained Men After Consumption of Caffeinated Chewing Gum

PURPOSE

To explore the acute effects of caffeinated chewing gum on vertical-jump performance, isokinetic knee-extension/flexion strength and power, barbell velocity in resistance exercise, and whole-body power.

METHODS

Nineteen resistance-trained men consumed, in randomized counterbalanced order, either caffeinated chewing gum (300 mg of caffeine) or placebo and completed exercise testing that included squat jump; countermovement jump; isokinetic knee extension and knee flexion at angular velocities of 60 and 180°·s-1; bench-press exercise with loads corresponding to 50%, 75%, and 90% of 1-repetition maximum (1RM); and an "all-out" rowing-ergometer test.

RESULTS

Compared with placebo, caffeinated chewing gum enhanced (all Ps < .05) (1) vertical-jump height in the squat jump (effect size [ES] = 0.21; +3.7%) and countermovement jump (ES = 0.27; +4.6%); (2) knee-extension peak torque (ES = 0.21; +3.6%) and average power (ES = 0.25; +4.5%) at 60°·s-1 and knee-extension average power (ES = 0.30; +5.2%) at 180°·s-1, and knee-flexion peak torque at 60°·s-1 (ES = 0.22; +4.1%) and 180°·s-1 (ES = 0.31; +5.9%); (3) barbell velocity at 50% of 1RM (ES = 0.30; +3.2%), 75% of 1RM (ES = 0.44; +5.7%), and 90% of 1RM (ES = 0.43; +9.1%); and (4) whole-body peak power on the rowing-ergometer test (ES = 0.41; +5.0%). Average power of the knee flexors did not change at either angular velocity with caffeine consumption.

CONCLUSIONS

Caffeinated chewing gum with a dose of caffeine of 300 mg consumed 10 min preexercise may acutely enhance vertical-jump height, isokinetic strength and power of the lower-body musculature, barbell velocity in the bench-press exercise with moderate to high loads, and whole-body power.

The Effects of 3 Different Doses of Caffeine on Jumping and Throwing Performance: A Randomized, Double-Blind, Crossover Study

PURPOSE

To examine the acute effects of 3 doses of caffeine on upper- and lower-body ballistic exercise performance and to explore if habitual caffeine intake affects the acute effects of caffeine ingestion on ballistic exercise performance.

METHODS

Twenty recreationally active male participants completed medicine-ball-throw and vertical-jump tests under 4 experimental conditions (placebo and 2, 4, and 6 mg·kg-1 of caffeine).

RESULTS

One-way repeated-measures analysis of variance (ANOVA) with subsequent post hoc analyses indicated that performance in the medicine-ball-throw test improved, compared with placebo, only with a 6 mg·kg-1 dose of caffeine (P = .032). Effect size, calculated as the mean difference between the 2 measurements divided by the pooled SD, amounted to 0.29 (+3.7%). For the vertical-jump test, all 3 caffeine doses were effective (compared with placebo) for acute increases in performance (P values .022-.044, effect sizes 0.35-0.42, percentage changes +3.7% to +4.1%). A 2-way repeated-measures ANOVA indicated that there was no significant group × condition interaction effect, suggesting comparable responses between low (≤100 mg·d-1) and moderate to high (>100 mg·d-1) caffeine users to the experimental conditions.

CONCLUSION

Caffeine doses of 2, 4, and 6 mg·kg-1 seem to be effective for acute enhancements in lower-body ballistic exercise performance in recreationally trained male individuals. For the upper-body ballistic exercise performance, only a caffeine dose of 6 mg·kg-1 seems to be effective. The acute effects of caffeine ingestion do not seem to be affected by habitual caffeine intake; however, this requires further exploration.

Caffeine Supplementation for Powerlifting Competitions: An Evidence-Based Approach

In this paper, we review the effects of caffeine on muscle strength and provide suggestions for caffeine supplementation in powerlifting competitions. The currently available studies indicate that caffeine ingestion may enhance strength in two powerlifting competition events, the squat and the bench press. For the deadlift, the same might be expected even though studies directly using this event are lacking. Optimal doses of caffeine are likely in the range from 2 to 6 mg·kg⁻¹, and are highly individual. When using caffeine-containing capsules, 60 minutes pre-exercise seems to be a good timing of caffeine consumption. For other sources such as caffeinated chewing gum, a shorter period (5 to 10 min) from consumption to the start of the exercise seems to be effective. For shorter duration powerlifting competitions (e.g., 2 hours), one pre-competition dose of caffeine could be sufficient for acute performance-enhancing effects that might be maintained across all three events. For longer duration competitions (with longer rest periods between one repetition maximum attempts), there might be a benefit to repeated dosing with caffeine; for example, ingesting smaller doses of caffeine before each attempt or event. During training, powerlifters may consider ingesting caffeine only before the training sessions with the highest intensity. This approach might eliminate the attenuation of caffeine’s effects associated with chronic caffeine ingestion and would help in maximizing performance benefits from acute caffeine ingestion at the competition. Nonetheless, withdrawal from caffeine (e.g., no caffeine intake seven days before competition) does not seem necessary and may have some indirect negative effects.

Effects of caffeine and sex on muscle performance and delayed-onset muscle soreness after exercise-induced muscle damage: a double-blind randomized trial

The present study aims to investigate effects of caffeine ingestion and sex difference on muscle performance, delayed-onset muscle soreness (DOMS), and various biomarkers under exercise-induced muscle damage (EIMD). Twenty (10 male and 10 female) healthy elite college athletes were recruited. Participants ingested either caffeine (6 mg/kg) or a placebo in a randomized, double-blind, and counterbalanced fashion at 24 and 48 h following EIMD. Muscle performance, DOMS, and blood samples were taken an hour before and an hour after supplementation. Caffeine ingestion restored impaired maximal voluntary isometric contractions (MVIC: 10.2%; MVIC_post: 7.2%, both P < 0.05) during EIMD across both sexes. Following caffeine ingestion during MVIC, while affected by EIMD, an interaction was found in DOMS and serum K⁺ (both P < 0.05), with males showing greater attenuation (21.5 and 16.9%, respectively) compared with females (4.6 and 1.3%, respectively). DOMS demonstrated an inverse correlation with MVIC after caffeine ingestion both overall and among male athletes (r = -0.34 and -0.54, respectively; P < 0.05) but not among female athletes (r = -0.11; P > 0.05) under EIMD. In addition, caffeine ingestion increased postexercise serum glucose and lactate concentrations across both sexes (both P < 0.05). This is the first study to show that male athletes, compared with female athletes, experience a greater reduction in DOMS during enhanced MVIC when caffeine was consumed, suggesting men might receive greater ergogenic effects from caffeine when affected by EIMD. Furthermore, caffeine ingestion was able to restore impaired muscle power among elite collegiate athletes across both sexes.NEW & NOTEWORTHY Exercise-induced muscle damage (EIMD) reduces anaerobic/aerobic performance and increases delayed-onset muscle soreness (DOMS) during exercise. We show that acute caffeine supplementation at a dosage of 6 mg/kg seems to facilitate recovery of anaerobic muscle power and attenuate DOMS after EIMD across both sexes. Furthermore, male athletes, compared with female athletes, when caffeine was prescribed, experience a greater reduction in DOMS with better restoration of impaired maximal voluntary isometric contractions. This suggests that male athletes might benefit from the ergogenic effect of acute caffeine supplementation after the onset of EIMD.

Caffeinated Gel Ingestion Enhances Jump Performance, Muscle Strength, and Power in Trained Men

We aimed to explore the effects of caffeinated gel ingestion on neuromuscular performance in resistance-trained men. The participants (n = 17; mean ± standard deviation (SD): age 23 ± 2 years, height 183 ± 5 cm, body mass 83 ± 11 kg) completed two testing conditions that involved ingesting a caffeinated gel (300 mg of caffeine) or placebo. The testing outcomes included: (1) vertical jump height in the squat jump (SJ) and countermovement jump (CMJ); (2) knee extension and flexion peak torque and average power at angular velocities of 60°·s^-1 and 180°·s^-1; (3) barbell velocity in the bench press with loads corresponding to 50%, 75%, and 90% of one-repetition maximum (1RM); and (4) peak power output in a test on a rowing ergometer. Compared to the placebo, caffeine improved: (1) SJ (p = 0.039; Cohen's d effect size (d) = 0.18; +2.9%) and CMJ height (p = 0.011; d = 0.18; +3.3%); (2) peak torque and average power in the knee extensors at both angular velocities (d ranged from 0.21 to 0.37; percent change from +3.5% to +6.9%), peak torque (p = 0.034; d = 0.24; +4.6%), and average power (p = 0.015; d = 0.32; +6.7%) at 60°·s^-1 in the knee flexors; (3) barbell velocity at 50% 1RM (p = 0.021; d = 0.33; +3.5%), 75% 1RM (p < 0.001; d = 0.42; +5.4%), and 90% 1RM (p < 0.001; d = 0.59, +12.0%). We conclude that the ingestion of caffeinated gels may acutely improve vertical jump performance, strength, and power in resistance-trained men.