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

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Jozo Grgic at National University of Singapore
Jozo Grgic
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Abstract

In the last few years, a plethora of studies explored the effects of caffeine on resistance exercise, demonstrating that this field of research is growing fast. This review evaluated and summarized 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 those 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 to 3 mg/kg) appears to be comparably ergogenic as 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 to 60 minutes pre-exercise. Caffeinated chewing gums and gels may enhance resistance exercise performance even when consumed 10 minutes 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.
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Vol.:(0123456789)
Sports Medicine (2021) 51:2281–2298
https://doi.org/10.1007/s40279-021-01521-x
REVIEW ARTICLE
Effects ofCaffeine onResistance Exercise: AReview ofRecent Research
JozoGrgic1
Accepted: 7 July 2021 / Published online: 22 July 2021
© The Author(s), under exclusive licence to Springer Nature Switzerland AG 2021
Abstract
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 caf-
feine 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.
* Jozo Grgic
jozo.grgic@live.vu.edu.au
1 Institute forHealth andSport, Victoria University,
Melbourne, Australia
1 Introduction
Caffeine is a highly popular ergogenic aid [1, 2]. Studies
have evaluated the effects of caffeine on various components
of exercise performance, including resistance exercise [3,
4]. In 2018, we published a review that summarized and
critically evaluated the effects of caffeine supplementation
on different aspects of resistance exercise performance [4].
Since this review, over 50 new studies [5–55] have been
published that explored the effects of caffeine on resist-
ance exercise, demonstrating that this field of research is
growing fast. These studies provided novel data for (i) the
mechanisms of the ergogenic effects of caffeine on resist-
ance exercise; (ii) the general acute and long-term effects of
caffeine on resistance exercise; (iii) the effects of caffeine
in women; (iv) the relationship between habitual caffeine
intake and the ergogenic effects of caffeine supplementa-
tion; (v) the associations between genetic variations and the
individual responses to caffeine ingestion; (vi) the optimal
protocols of caffeine supplementation (i.e., dose, source, and
timing of caffeine); and (vii) the placebo effects of caffeine
on resistance exercise. Given that this is a rapidly develop-
ing field of research, the aim of this article was to provide
an updated overview of the most recent studies exploring
caffeine’s effects on resistance exercise. By doing so, it is
hoped that this article will guide research areas for future
studies on the topic and help optimize caffeine supplementa-
tion in practice.
2 Mechanisms fortheErgogenic Eects
ofCaeine onResistance Exercise
It is generally accepted that caffeine ingestion enhances
performance due to its effects on adenosine receptors (i.e.,
central mechanisms) [56, 57]. Caffeine has a similar molecu-
lar structure to adenosine [58]. Therefore, after ingestion,
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... Caffeine has a similar molecular structure to adenosine, so it acts as its antagonist, resulting in increased neurotransmitter release, increased recruitment-activation rate of motor units, and pain suppression [4]. Additional putative mechanisms involve its positive effect on muscle contraction due to increased calcium ion release and sodiumpotassium pump activity, as well as improved substrate availability [4,10,11]. ...
... The explanation for this finding remains unclear [30][31][32]. Most data on the effect of caffeine on upper-body muscular endurance show either positive [11,21,22,33] or no effects [20,23,24]. In any case, in most studies, upper-body muscular endurance is assessed through bench press, and there are insufficient data on caffeine's effect on abdominal muscle endurance. ...
... A limitation of the present study is the relatively small sample size, which is nevertheless comparable to sample sizes in other CrossFit studies on caffeine supplementation [12,13], as well as many other studies examining caffeine's effects on general exercise performance [11]. Additionally, the inclusion of only male participants limits the expansion of the findings to female CrossFit athletes, for whom the rate of caffeine metabolism may be affected by menstrual cycle phases (estrogen levels) or the use of contraceptive medications, leaving the possibility for different effects of caffeine supplementation [5]. ...
Effects of an Acute High Dose of Caffeine on Physiological Responses and Performance During a Strength-Focused CrossFit Workout: A Randomized, Double-Blind, Crossover Study
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Background: Several nutritional strategies have been used to enhance performance in CrossFit® training. This randomized, double-blind, crossover study aimed to investigate the acute effects of caffeine consumption on physiological responses and performance during a strength-focused CrossFit workout. Methods: Twelve healthy men, aged 29.2 ± 3.8 years (mean ± SD throughout), with 4.9 ± 1.9 years of CrossFit experience, completed two sessions of a specific CrossFit training program (four rounds of five exercises, 50 s exercise/10 s rest), 60 min after consuming either anhydrous caffeine (7.1 ± 0.7 mg/kg of body mass) or a placebo, aiming to perform as many repetitions as possible. The washout period was at least seven days. At the end of each round, subjective perception of fatigue was recorded using the Borg scale. Blood lactate concentration was measured before and immediately after completing the training session using a portable lactate analyzer. Data were analyzed by factorial ANOVA with repeated measures. Results: Caffeine had a negative effect on the number of sit-up repetitions in the fourth round (p = 0.012), while it did not affect any other performance parameter, rating of perceived exertion, or lactate concentration compared with the placebo. Conclusions: The results of the present study suggest that caffeine consumption does not improve performance in CrossFit training.
View
... Among the various strategies available, caffeine (CAF) supplementation and transcranial direct current stimulation (tDCS) have gained significant attention due to their potential impact on physical and cognitive performance [1,2]. CAF is a well-established ergogenic aid, known for its ability to reduce the rating of perceived exertion (RPE), increase muscle strength, and delay fatigue by acting on adenosine receptors in the central nervous system [2,3]. ...
... In isolation, the significant improvement in performance following CAF supplementation is well-documented in the literature [2,14,17,18]. Studies by Grgic [3] and Bilondi et al. [17] indicate that CAF enhances neuromuscular efficiency, reduces perceived exertion, and increases power output in resistance-based and intermittent high-intensity exercises. However, in the context of CrossFit™, CAF supplementation has shown mixed results, with studies like Fogaça et al. [35] failing to observe an impact. ...
... In this case, CAF is widely recognized for its ergogenic effects, particularly in reducing the perception of effort across various sports modalities. This effect is primarily mediated by its role as an antagonist of adenosine A1 and A2A receptors in the central nervous system, which also contributes to increased alertness and enhanced neuromuscular function [2,3,17]. Furthermore, evidence suggests that CAF influences corticomotor excitation by enhancing corticospinal tract excitability and facilitating the recruitment of motor units [14,19]. ...
Caffeine Combined with Excitatory Neuromodulation Based on Transcranial Direct Current Stimulation (tDCS) Enhances Performance in a Time-Trial CrossFit Workout: A Randomized, Placebo-Controlled, Double-Blind Study
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Background: Caffeine (CAF) and transcranial direct current stimulation (tDCS) are ergogenic strategies with potential benefits for performance, yet their combined effects remain underexplored, particularly in high-intensity functional training contexts such as CrossFit®. This randomized, double-blind, placebo-controlled crossover study aimed to investigate the impact of tDCS, with and without CAF, on performance time in the Clean & Jerk (C&J) during the benchmark WOD GRACE among competitive CrossFit® athletes. Secondarily, we aimed to compare the RPE across the different experimental conditions, as well as to establish the relationship between personal record (PR) values adjusted for body mass and the execution time of the WOD GRACE, considering different athletes' classification levels (RX Elite and RX Intermediate). Methods: Twenty participants completed four experimental conditions: CAF ingestion (400 mg) combined with anodal tDCS (CAF + a-tDCS), CAF with Sham tDCS (CAF + Sham-tDCS), placebo (PLA) with a-tDCS (PLA + a-tDCS), and PLA with Sham tDCS (PLA + Sham-tDCS). Results: The results indicated that the combination of CAF + a-tDCS significantly improved performance, reducing execution time (205.5 ± 58.0 s) compared to CAF + Sham-tDCS (218.3 ± 61.2 s; p = 0.034), PLA + a-tDCS (231.7 ± 64.1 s; p = 0.012), and PLA + Sham-tDCS (240.9 ± 66.4 s; p = 0.002). However, no significant differences were observed between CAF + Sham-tDCS and PLA + a-tDCS (p = 0.690), CAF + Sham-tDCS and PLA + Sham-tDCS (p = 0.352), or PLA + a-tDCS and PLA + Sham-tDCS (p = 0.595). Conclusions: The responder analysis revealed that 45% of participants improved performance with isolated tDCS, while 60% responded positively to CAF. No significant differences were found in RPE scores among conditions (p = 0.145). Additionally, no correlations were identified between PR values adjusted for body mass and execution time in both RX Elite (r = 0.265; p = 0.526) and RX Intermediate (r = 0.049; p = 0.901) groups, nor between training experience and performance across interventions. These findings suggest that tDCS, when combined with CAF, may serve as an effective ergogenic aid for improving performance in high-intensity functional training, whereas its isolated use does not yield meaningful benefits.
View
... Among the various strategies available, caffeine (CAF) supplementation and transcranial direct current stimulation (tDCS) have gained significant attention due to their potential impact on physical and cognitive performance [1,2]. CAF is a well-established ergogenic aid, known for its ability to reduce the rating of perceived exertion (RPE), increase muscle strength, and delay fatigue by acting on adenosine receptors in the central nervous system [2,3]. ...
... In isolation, the significant improvement in performance following CAF supplementation is well-documented in the literature [2,14,17,18]. Studies by Grgic [3] and Bilondi et al. [17] indicate that CAF enhances neuromuscular efficiency, reduces perceived exertion, and increases power output in resistance-based and intermittent high-intensity exercises. However, in the context of CrossFit™, CAF supplementation has shown mixed results, with studies like Fogaça et al. [35] failing to observe an impact. ...
... In this case, CAF is widely recognized for its ergogenic effects, particularly in reducing the perception of effort across various sports modalities. This effect is primarily mediated by its role as an antagonist of adenosine A1 and A2A receptors in the central nervous system, which also contributes to increased alertness and enhanced neuromuscular function [2,3,17]. Furthermore, evidence suggests that CAF influences corticomotor excitation by enhancing corticospinal tract excitability and facilitating the recruitment of motor units [14,19]. ...
PSYCHO-AFFECTIVE RESPONSES IN MIDDLE-AGED RECREATIONAL RUNNERS TO SELF-ADJUSTING COUNTERCLOCKWISE STIMULI.PSYCHO-AFFECTIVE RESPONSES IN MIDDLE-AGED RECREATIONAL RUNNERS TO SELF-ADJUSTING COUNTERCLOCKWISE STIMULI.
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Staying in a training program allows its practitioners to improve in daily activities, generating less energy expenditure to perform them, and in sports practice, executing movements with quality leads to achievements. Nowadays, where the population is increasingly busy and more exposed to technological conveniences, there is a great need for adjustments in training methods, whether for strength, aerobic, power, or flexibility [1]. Adherence to training involves an integrated balance between the mind and body, where the understanding of the physiological impact provided, and how this impact is individually perceived during and after physical exercise, define subsequent human behavior and its potential relationship with adherence to training [2]. The individual understanding of affective responses can be characterized as positive, that is, the perception of stimuli provided well-being and tranquility, and generally reduced tension, or negative, where the brain perceives the offered stimulus as a stressor mechanism, increasing the state of anxiety and tension [3]. We currently know that, primarily, high-intensity interval exercises are being prioritized for training prescriptions within major training centers and gyms [4, 5] However, while such a mode of exercise can exert potential benefits and rapid physiological changes, when used indiscriminately, it can provide negative affective responses and a possible strain in the practitioners' relationship with physical exercise. A possible solution to this impasse seems to be the self-selection of work speeds by the participants themselves. In this case, no matter how much they are asked and encouraged to take on a high workload, the mere perception of non-imposition and self-regulation can modulate differentiated affective responses, inducing positive interpretations. Despite the empirical nature of this theory, such phenomena still need to be more thoroughly investigated.
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... Its performanceenhancing effects have been recognized for over a century (2), with substantial evidence supporting its benefits across aerobic (3,4), anaerobic (5), and sport-specific exercises (6). Recently, as resistance exercise has gained popularity, research on caffeine's effects in this domain is also expanding (7)(8)(9). ...
... A substantial and growing body of evidence supports the performance-enhancing effects of moderate doses of caffeine (5-6 mg/ kg) on maximal strength (one-repetition maximum [1RM]) and muscular endurance (repetition to task failure at 60-70% 1RM) during bench press and/or back squat exercises (10-12), which are common among both recreational and competitive athletes. The primary mechanism is likely the role of caffeine as an adenosine receptor antagonist (8,13), which may inhibit the negative effects of adenosine on neurotransmission, perceived exertion, pain perception, and arousal (5,14,15). In addition, caffeine may increase sodiumpotassium pump activity, potentially enhancing excitation contraction coupling (5). ...
... Furthermore, two recent studies found that gum containing relatively low caffeine doses (2.5-3.6 mg/kg) enhances muscular power and explosive performance during resistance exercises (e.g., Romanian deadlift and bench press) (25,26). However, a review indicated that the effects of caffeine on power may differ from those on maximal strength (1RM) and muscular endurance (repetitions to failure) during resistance exercise (8). Thus, it remains unclear whether gum containing low-dose caffeine (3 mg/kg) also enhances maximal strength and muscular endurance. ...
Caffeinated chewing gum enhances maximal strength and muscular endurance during bench press and back squat exercises in resistance-trained men
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Full-text available
  • Jan 2025
Introduction Caffeinated chewing gum, known for its rapid absorption, has not been previously studied for its effects on maximal strength and muscular endurance in resistance exercise. The aim of this study was to determine the efficacy of caffeinated chewing gum on maximal strength and muscular endurance during bench press and back squat exercises. Methods In a randomized, double-blind design, 16 resistance-trained males (age: 21.6 ± 2.0 years, height: 176.8 ± 6.1 cm, mass: 79.6 ± 8.8 kg) chewed either caffeinated gum (3 mg/kg) or a placebo gum on two occasions, 1 week apart. After a standardized warm-up, participants chewed the gum for 5 min before performing maximal strength test (one-repetition maximum [1RM]) and muscular endurance test (60% 1RM repetitions to failure) for bench press and back squat exercises. 1RM, number of repetitions, ratings of perceived exertion and pain perception were assessed. Results Caffeinated chewing gum significantly improved 1RM in both bench press (105.3 ± 14.5 vs. 100.3 ± 13.4 kg, +5.0% [95% confidence interval (CI): 3.7–6.3%], p < 0.01) and back squat (172.3 ± 20.2 vs. 161.9 ± 22.3 kg, +6.8% [95%CI: 4.1–9.5%], p < 0.01) exercises with small effect size (Cohen’s d: 0.36 [95%CI: 0.09–0.63] and 0.49 [95%CI: 0.22–0.76], respectively), despite similar levels of pain perception and RPE (p > 0.05). It also increased the number of repetitions in both bench press (20 ± 5 vs. 17 ± 4, +18.8% [95%CI: 11.5–26.1%], p < 0.01) and back squat (37 ± 11 vs. 28 ± 8, +33.3% [95%CI: 23.1–43.4%], p < 0.01) exercises with moderate-to-large effect size (Cohen’s d: 0.76 [95%CI: 0.48–1.03] and 0.89 [95%CI: 0.60–1.16], respectively), despite similar levels of pain perception and RPE (p > 0.05). Discussion Caffeinated chewing gum (3 mg/kg) improved both maximal strength and muscular endurance during bench press and back squat exercises in resistance-trained men. This approach offers a practical and time-efficient method to improve training performance while minimizing the risk of side effects.
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... Caffeine may enhance endurance in shortduration intense exercise due to its direct action on muscles or neural processes, rather than glycogen sparing [41]. This suggests an ergogenic benefit for resistance exercises, including strength, endurance, and power [43]. These inconsistent findings underscore the need for further research on caffeine's effects on muscle fatigue resistance in short, high-intensity activities. ...
... Lower caffeine doses (2-3 mg/kg) can enhance resistance exercise performance comparably to higher doses (6 mg/kg), while even smaller amounts (~1.5 mg/kg) may still offer benefits [43]. In studies on strength athletes who regularly consume caffeine, high doses (9 and 11 mg/kg) did not significantly enhance performance during bench press repetitions [56]. ...
... Caffeine appears to improve performance in strength exercises like squats and bench presses, though evidence is limited for deadlifts. The optimal dose likely ranges from 2 to 6 mg/kg, with peak effects occurring 30-60 minutes after capsule ingestion; however, caffeinated gum may work within 5-10 minutes [43,57]. ...
Brewed for Performance: Caffeine’s Impact on Nutrition, Endurance and Strength in Sports
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Caffeine is one of the most widely consumed and studied stimulants worldwide with a long history in athletics as a performance enhancer. Although listed as a stimulant in the World Anti-Doping Agency’s (WADA’s) 2024 Monitoring Program, its use is not prohibited. Individual responses to caffeine vary widely due to factors like genetics, age, and lifestyle habits, such as smoking and diet. This paper examines caffeine's multifaced role in human metabolism, with an emphasis on athletes' training (endurance and strength) and post-exercise recovery. Our comprehensive review of literature indicates that caffeine typically ingested one hour before exercise in doses around 3-6 mg/kg raises metabolic rate, increases free fatty acids mobilization, extends time to exhaustion in running and cycling, improves maximal voluntary contraction and enhances high-speed muscular activity with low-load movements. It also blocks pain perception. These findings highlight caffeine’s role in endurance and strength sports. However, due to inconsistencies, further research is needed to develop exercise-specific protocols considering dose, timing, and training status. Caffeine aids recovery by reducing delayed - onset muscle soreness, improving glycogen resynthesis, and reducing fatigue. However, late consumption may affect sleep, requiring careful timing and dosage adjustments. Moreover, potential side and positive effects of caffeine ingestion need to be considered.
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... It increases strength and power by promoting intracellular Ca 2+ release and Na + /K + -ATPase pump activity [11,12], while also delaying fatigue onset by activating the central nervous system and blocking the adenosine receptors [13,14]. The benefits of caffeine supplementation in individual sports such as running or cycling are well established [9,10,15,16]. However, there is limited information on its ergogenic effects in team sports, which require a combination of physical and sport-specific technical and tactical skills. ...
... For each outcome, the SMD was calculated using the mean and standard deviation values from placebo and caffeine trials, along with the sample sizes and correlations between trials. Heterogeneity was assessed using the I 2 statistic and interpreted as follows: low (I 2 < 25%), moderate (25% ≤ I 2 ≤ 50%), and high (I 2 > 50%) [16]. All meta-analyses were conducted using a random-effect model. ...
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Background/Objectives: The ergogenic effects of caffeine in team sports, particularly volleyball, have received significant research attention. This study sought to examine the effects of caffeine on both volleyball-specific and general performance outcomes. Methods: This systematic review comprises 11 studies, each utilizing a blinded crossover experimental design. A meta-analysis was conducted using a random-effect model to determine the standardized mean difference (SMD), estimated by Hedges’ g, with a 95% confidence interval (CI). Results: Caffeine supplementation improved volleyball-specific outcomes, including attack and serve accuracy (SMD: 0.50; 95% CI: 0.11–0.90; p = 0.01). Regarding nonspecific outcomes, caffeine increased single-jump performance (SMD: 0.23; 95% CI: 0.02–0.44; p = 0.03), repeated-jump performance (SMD: 0.51; 95% CI: 0.05–0.96; p = 0.03), and handgrip strength (SMD: 0.23; 95% CI: 0.03–0.42; p = 0.02), while decreasing agility test completion time (SMD: −0.32; 95% CI: −0.60–0.03; p = 0.03). Furthermore, caffeine increased the frequency of positive game actions during simulated volleyball matches (SMD: 0.84; 95% CI: 0.26–1.43; p < 0.01). Conclusions: Caffeine supplementation enhances physical performance and volleyball-specific actions during competition, supporting its role as an effective ergogenic aid for volleyball players.
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... Previous research has reported that acute caffeine intake improves V mean , V peak , W mean and in muscular strength, power and endurance [21][22][23] . In muscular strength and power, different doses of caffeine, from 3 to 9 mg/ kg of body mass, promote an increase in velocity and power at 25%, 50%, 75% and 90% of 1RM 24,25 . ...
... Muscular endurance refers to skeletal muscles' ability to resist fatigue by maintaining or delaying the diminution of force and power production during repeated muscle contraction. Previous systematic reviews and meta-analyses indicate that caffeine can improve muscular endurance by a 6-7% 21,34,35 , mainly due to an increase in the number of repetitions performed per set after the acute intake of this substance [36][37][38][39] . Unfortunately, there is scarce evidence evaluating multiple performance variables during muscular endurance tests, at any load, such Muscular strength and power tests differences in mean, peak and time to reach peak velocity and power production among experimental conditions in the back squat exercise. ...
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To examine the single and combined effect of acute beetroot juice and caffeine supplementation in muscular strength, power, and endurance performance. Thirteen resistance-trained males participated in a triple-blind, cross-over, randomized controlled-trial with four conditions: (a) caffeine (CAF); (b) beetroot juice (BJ); (c) caffeine and beetroot juice (CAF + BJ); (d) placebo (PLA). Participants ingested 70 mL of beetroot juice, concentrated NO3⁻-rich beverage (BJ, 6.4 mmol NO3⁻) or PLA (~ 0.04 mmol NO3⁻) 180 min and caffeine or placebo (3 mg/kg) 60 min before the trial. Muscular strength/power was evaluated at 25%, 50%, 75%, 90% and 100%1RM and muscular endurance at 65%1RM, in bench press (BP) and back squat (BS). In all tests, mean (Vmean and Wmean) and peak (Vpeak and Wpeak) velocity and power output were measured. In BS, muscular strength/power showed a supplement-by-load effect in Vmean and Wmean (P < 0.05, ηp² = 0.167–0.173), with caffeine increased compared to placebo at 75%, 90% and 100%1RM (9–25%, P < 0.005, g = 0.51–1.47); while in muscular endurance, significant differences were found in number of repetitions, Vmean and Wmean (P < 0.05, ηp² > 0.277), in all experimental groups (CAF, BJ and CAF + BJ) compared to placebo (6–17%, P < 0.05, g = 0.46–94). No differences in muscular strength/power or endurance were found in BP. Single and combined acute beetroot juice and caffeine intake increased muscular endurance performance at 65%1RM in back squat but not in bench press exercise.
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... Nonetheless, some studies reported no discernible increase in caffeine's performance-enhancing effects on isometric or isokinetic strength [41][42][43]. In summation, current findings affirm that caffeine consumption augments isometric and isokinetic strength [44]. ...
... This approach is particularly relevant in comparing the short-term effects of caffeine on strength and power metrics, providing robust evidence to support its role as an ergogenic aid [34]. Based on previous findings and recommendations from Guest et al. [34] and Grgic et al. [44], there is a need to investigate the effects of caffeine in capsules and chewing gum. This study leverages SWC analysis to examine the individual responses to caffeine capsules and chewing gum, offering insights into their effectiveness in enhancing lower-body strength, power, and functional performance in strength-trained males. ...
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Background: Liquid-dissolved and encapsulated powder are two popular ways to consume caffeine for performance-enhancing effects. Caffeine in other delivery methods, such as chewing gums, orally dissolvable strips, gels, mouthwashes, energy drinks, and nasal sprays, is believed to be absorbed more quickly into the bloodstream. Inter-individual responses to caffeine's enhancing effects are recognized. The present study examined the inter-individual responses to the acute effects of encapsulated caffeine and caffeinated chewing gum on the lower-body isokinetic and iso-metric strength and power in strength-trained males. Method: A randomized, cross-over, placebo-controlled study was conducted with 15 strength-trained males (age: 25 ± 4 years, height: 176 ± 7 cm, weight: 75 ± 11 kg, habitual caffeine intake: 66 ± 15 mg·day −1). Participants were randomly assigned to three conditions: i) caffeinated chewing gum (CG), ii) caffeine capsule (CC), and iii) starch capsule as a placebo (PLA). Participants consumed approximately 3 to 4.5 mg·kg −1 of caffeine 60 minutes before testing. The washout period between conditions was one week. Participants performed the Sargent jump test, followed by a 5-minute active recovery (walking). Subsequently, isokinetic strength and power (60°/s and 180°/s) and isometric strength (45° and 60°) parameters were measured for knee extensor and flexor muscles. Data were analyzed using one-way repeated measures ANOVA and Bonferroni post hoc tests, with significance set at p ≤ 0.05. Responders to the caffeine conditions were identified using the smallest worthwhile change (SWC) analysis. Results: In knee extensors, 1) average peak torque and power at 60°/s were higher in CC (p = 0.045; + 11.2% and p = 0.038; + 14.1%) and CG (p = 0.044; + 7.3% and p = 0.015; + 11.4%) compared to PLA with a co-response rate of 60% and 66%, 2) maximum voluntary isometric contraction at 45° (MVIC-45°) was higher in CC compared to PLA (p = 0.031; + 10.1%), and 3) MVIC-60° was higher in CG ARTICLE HISTORY (http:// creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent. compared to PLA (p = 0.037; + 10.1%) with a co-response rate of 60%. In knee flexors, 1) time to peak torque at 60°/s was higher in CG compared to PLA (p = 0.011; + 18.2%) with a co-response rate of 46%, 2) average rate of force development at 60°/s was higher in CC (p = 0.007; + 24.1%) and CG (p = 0.050; + 20.6%) compared to PLA with a co-response rate of 53%, and 3) average power at 180°/s was higher in CC compared to PLA (p = 0.033; + 18%) with a co-response rate of 46%. However, there were no differences between other strength indicators in the knee extensors and flexors between the different conditions. Vertical jump height (VJH) was higher in CC (p = 0.001; + 5.5%) and CG (p = 0.001; + 6.) compared to PLA, with a co-response rate of 53%. Conclusion: Caffeine supplementation in CC and CG forms significantly enhanced lower-body strength, power, and vertical jump height in strength-trained males, with over ~50% of participants exceeding the SWC thresholds across key performance metrics. CC showed slightly higher responder rates for strength parameters, while CG excelled in time-dependent measures, supporting their use as effective and flexible ergogenic aids.
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... Caffeine is a well-established ergogenic aid, with research also exploring its effects on resistance exercise performance (Grgic, 2021). Evidence indicates that caffeine ingestion may enhance muscular strength, endurance, power, and velocity in resistance exercise (Grgic, 2021). ...
... Caffeine is a well-established ergogenic aid, with research also exploring its effects on resistance exercise performance (Grgic, 2021). Evidence indicates that caffeine ingestion may enhance muscular strength, endurance, power, and velocity in resistance exercise (Grgic, 2021). While the exact mechanisms by which caffeine exerts its ergogenic effects are not yet fully clear, they are generally explained by caffeine's ability to bind to adenosine receptors, which may reduce perceived exertion/pain and improve performance (McLellan et al., 2016;Guest et al., 2021). ...
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Full-text available
  • Feb 2025
This study aimed to explore the isolated and combined effects of caffeine and paracetamol (acetaminophen) on velocity and power in resistance exercise. Twenty-eight resistance-trained men and women participated in this randomized, double-blind, placebo-controlled, crossover study. The participants performed three sets of the bench press with 75% of one-repetition maximum to momentary muscular failure after ingesting a placebo, caffeine (3 mg/kg), paracetamol (1,500 mg), or caffeine + paracetamol 45 min before exercise. Velocity and power of the repetitions in each set were analysed. Compared to placebo, only isolated caffeine ingestion increased mean velocity (d = 0.34), and mean power (d = 0.17) in the first set. No significant differences between the conditions were observed for any of the analysed outcomes in the second and third sets. Our results indicate that only isolated caffeine ingestion improves velocity and power in resistance exercise, even though these effects are not consistent across all sets. Paracetamol ingestion was not ergogenic, even when combined with caffeine. These results highlight that analgesics may be ineffective in improving resistance exercise performance.
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... The emergence of sports genomics in scholarly research gained momentum following the groundbreaking discovery of the human DNA structure and the identification of initial DNA polymorphisms Angiotensin-Converting Enzyme (ACE) & Alpha-Actinin-3 (ACTN3) linked to athletic prowess [13,35,36]. Factors such as speed, strength, endurance, agility, recuperation speed, susceptibility to injuries, and the propensity for using performance-enhancing substances in elite athletes are shaped by the precise arrangement of nucleotides in the billions of base pairs in human DNA [37,38]. Current research is increasingly concentrating on examining either individual or combined gene effects to understand how genetic variations influence various athletic attributes like speed, strength, endurance, and recovery in both professional and non-professional athletes [1,[39][40][41]. ...
Assessment of male football players' physical fitness levels based on certain gene (AGT rs699 & IL-6 rs1800795) polymorphisms
Article
Full-text available
  • Apr 2025
Background: The present investigation aims to elucidate the physical fitness attributes inherent in male football players about the Angiotensinogen (AGT) rs699 and Interleukin-6 (IL-6) rs1800795 gene polymorphisms. Methods: Twenty-two male football players, aged 18 to 35 years, voluntarily enrolled in the study conducted within the North Macedonian Super League. Genomic DNA was extracted from oral epithelial cells. Genotyping procedures were then executed using real-time polymerase chain reaction (RT-PCR). All participants were actively involved in an intensive training program six days a week throughout the six-week pre-season preparation phase. The male football players underwent physical assessments both before and after the training program. Statistical analysis involved the use of the Paired-Sample t-Test to discern differences between the pre-test and post-test measurements of the male football players. Results: When stratifying the outcomes according to the IL-6 genotype and AGT genotype variables, statistically significant differences were not observed in Squat Jump (SJ), 5 m sprint, 30 m sprint, Counter Movement Jump (CMJ), Drop Jump (DJ) evaluations, and body fat percentage (p > 0.05). In contrast, statistically significant differences were observed in the Yo-Yo Intermittent Recovery Test Level 2 (Yo-Yo IRT 2), 10 m sprint, and One Repetition Maximum (1RM) bench press variables (Yo-Yo IRT 2: CC and CT p = 0.005, <0.001; 10 m sprint: CT p = 0.024; and 1RM bench press: CC, CT and TT p < 0.001, <0.001, 0.045, respectively). Significant differences were also identified in the Yo-Yo IRT 2, 10 m sprint, and 1RM bench press measurements (Yo-Yo IRT 2: CC, CG and GG p = 0.002, 0.021, 0.001; 10 m sprint: CC and GG p = 0.020, 0.028; and 1RM bench press: CC, GG p = 0.001, 0.001, respectively). Conclusions: In summary, the AGT rs699 and IL-6 rs1800795 gene polymorphisms may play a role in the adaptations induced by training in male football players.
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The acute effect of caffeine supplementation on strength, repetition sustainability, and work volume of novice bodybuilders
Article
Full-text available
  • Dec 2016
Ergogenic effects of caffeine on anaerobic maximal and submaximal peak performance, especially in resistance exercise is not clear. According to this, the purpose of this study was to investigate the acute effect of moderate amounts of caffeine on maximal strength, repetition sustainability and work volume in the upper and lower body of novice body builders. In a randomized double blind study, 15 male body builders' athletes (age of 21.16±3.9 years, height of 174.42±6.12 cm and weight of 73.25±6.71 kg) were examined. Exercise protocol was to test one repetition maximum (1RM) in the bench press and leg press and repetition sustainability of bench press and leg press with 80% 1RM in 5 sets. These tests were performed, one hour after ingesting caffeine (6 mg/kg) and placebo, in two separate sessions as similar. Muscle strength, sustainability of repetitions and volume of work (load × the number of repetitions) of upper and lower body were measured. To examine the differences between the effects of caffeine and placebo, t-test was used. The results showed that caffeine causes a significant increase in the strength of the upper and lower body (P<0.05). The repetition sustainability of upper and lower body in the first, second and third sets did not change significantly, but decreased significantly in the fourth and fifth sets. In addition, volume of work at the first to fifth set with consumption of caffeine in the body was significantly more than placebo (P<0.05). However, in the first and second set of lower body exercise was not observed significantly difference and meaningful difference was only seen in the third to fifth set between caffeine and placebo conditions (P<0.05). It seems that acute consumption of caffeine supplementation with ergogenic effect on maximal strength, sustainability of repetitions and the training volume in resistance exercise improve performance and possibly stimulate muscle for its development. Keywords
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The effects of different doses of caffeine on maximal strength and strength-endurance in women habituated to caffeine
Article
Full-text available
Purpose The main goal of this study was to assess the acute effects of 3 and 6 mg of caffeine intake per kg of body mass (b.m.) on maximal strength and strength-endurance in women habituated to caffeine. Methods Twenty-one healthy resistance-trained female students (23.0 ± 0.9 years, body mass: 59.0 ± 6.6 kg), with a daily caffeine intake of 5.8 ± 2.6 mg/kg/b.m. participated in a randomized, crossover, double-blind design. Each participant performed three experimental sessions after ingesting either a placebo (PLAC) or 3 mg/kg/b.m. (CAF-3) and 6 mg/kg/b.m. (CAF-6) of caffeine. In each experimental session, the participants underwent a 1RM test and a strength-endurance test at 50 %1RM in the bench press exercise. Maximal load was measured in the 1RM test and the time under tension, number of preformed repetitions, power output and bar velocity were registered in the strength-endurance test. Results The one-way ANOVA showed a main effect of caffeine on 1RM bench press performance (F = 14.74; p < 0.01). In comparison to the PLAC (40.48 ± 9.21 kg), CAF-3 (41.68 ± 8.98 kg; p = 0.01) and CAF-6 (42.98 ± 8.79 kg; p < 0.01) increased 1RM bench press test results. There was also a significant increase in 1RM for CAF-6 when compared to CAF-3 ( p < 0.01). There was a main effect of caffeine on time under tension during the strength-endurance test (F = 13.09; p < 0.01). In comparison to the PLAC (53.52 ± 11.44 s), CAF-6 (61.76 ± 15.39 s; p < 0.01) significantly increased the time under tension during the maximal strength-endurance test. Conclusion An acute dose of 3-to-6 mg/kg/b.m. of caffeine improves maximum strength. However, these doses of caffeine had minimal ergogenic effect on strength-endurance performance in women habituated to caffeine.
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Pre-exercise Caffeine Intake Enhances Bench Press Strength Training Adaptations
Article
Full-text available
  • Jan 2021
Previous research has identified acute caffeine intake as an effective ergogenic aid to enhance velocity and power during bench press exercise. However, no previous investigation has analyzed the effects of chronic intake of caffeine on training adaptations induced by bench press strength training. Thus, the aim of this investigation was to determine the effects of pre-exercise caffeine intake on training adaptations induced by a bench press training protocol. Using a double-blind, randomized experimental design, 16 healthy participants underwent a bench press training protocol for 4 weeks (12 sessions). Seven participants ingested a placebo and nine participants ingested 3 mg/kg/BM of caffeine before each training session. Three days before, and 3 days after the completion of the training protocol, participants performed a one-repetition maximum (1RM) bench press and force-velocity test (from 10 to 100% 1RM). From comparable pre-training values, the strength training similarly increased 1RM in the caffeine and placebo groups (+13.5 ± 7.8% vs. +11.3 ± 5.3%, respectively; p = 0.53). In the caffeine group, the strength training induced a higher mean velocity at 40%, (0.81 ± 0.08 vs. 0.90 ± 0.14 m/s), 60% (0.60 ± 0.06 vs. 0.65 ± 0.06 m/s), 70% (0.47 ± 0.05 vs. 0.55 ± 0.06 m/s), 80% (0.37 ± 0.06 vs. 0.45 ± 0.05 m/s), 90% (0.26 ± 0.07 vs. 0.34 ± 0.06 m/s), and 100% 1RM (0.14 ± 0.04 vs. 0.25 ± 0.05 m/s; p < 0.05) while the increases in the placebo group were evident only at 30 (0.95 ± 0.06 vs. 1.03 ± 0.07 m/s), 70% (0.51 ± 0.03 vs. 0.57 ± 0.05 m/s) and 80% 1RM (0.37 ± 0.06 vs. 0.45 ± 0.05 m/s) (p < 0.05). The placebo group only increased peak velocity at 60 and 70% 1RM (p < 0.05) while peak velocity increased at 10%, and from 30 to 100% 1RM in the caffeine group (p < 0.05). The use of 3 mg/kg/BM of caffeine before exercise did not modify improvements in 1RM obtained during a 4 week bench press strength training program but induced more muscle performance adaptations over a wider range of load.
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Effects of Different Doses of Caffeinated Coffee on Muscular Endurance, Cognitive Performance, and Cardiac Autonomic Modulation in Caffeine Naive Female Athletes
Article
Full-text available
  • Dec 2020
Caffeine is widely consumed among elite athletes for its well-known ergogenic properties, and its ability to increase exercise performance. However, studies to date have predominantly fo-cused on the anhydrous form of caffeine in male participants. The aim of the study was to investigate the effect of caffeinated coffee ingestion on lower-upper body muscular endurance, cognitive performance, and heart rate variability (HRV) in female athletes. A total of 17 participants (mean ± standard deviation (SD): age = 23 ± 2 years, body mass = 64 ± 4 kg, height = 168 ± 3 cm) in a random-ized cross-over design completed three testing sessions, following the ingestion of 3 mg/kg/bm of caffeine (3COF), 6 mg/kg/bm of caffeine (6COF) provided from coffee or decaffeinated coffee (PLA) in 600 mL of hot water. The testing results included: (1) repetition number for muscular endurance performance; (2): reaction time and response accuracy for cognitive performance; (3): HRV parameters , such as standard deviation of normal-to-normal (NN) intervals (SDNN), standard deviation of successive differences (SDSD), root mean square of successive differences (RMSSD), total power (TP), the ratio of low-and high-frequency powers (LF/HF), high-frequency power (HF), normalized HF (HFnu), low-frequency power (LF), and normalized LF (LFnu). A one-way repeated measures ANOVA revealed that 3COF (p = 0.024) and 6COF (p = 0.036) improved lower body muscular endurance in the first set as well as cognitive performance (p = 0.025, p = 0.035 in the post-test, respectively) compared to PLA. However, no differences were detected between trials for upper body muscular endurance (p = 0.07). Lastly, all HRV parameters did not change between trials (p > 0.05). In conclusion, ingesting caffeinated coffee improved lower body muscular endurance and cognitive performance, while not adversely affecting cardiac autonomic function.
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Caffeine Timing Improves Lower-Body Muscular Performance: A Randomized Trial
Article
Full-text available
  • Nov 2020
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.
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Placebo Effect of Caffeine on Maximal Strength and Strength Endurance in Healthy Recreationally Trained Women Habituated to Caffeine
Article
Full-text available
  • Dec 2020
Background: By using deceptive experimental designs, several investigations have observed that trained individuals may increase their performance when told they were given caffeine, when in fact they received a placebo (i.e., the placebo effect of caffeine). However, most of these investigations on the placebo effect of caffeine used individuals with low caffeine consumption or did not report habitual caffeine consumption, especially in studies analyzing resistance-based exercise. Hence, it is unknown if habitual caffeine consumers benefit from the placebo effect of caffeine on exercise performance. Thus, the aim of the present study was to analyze the placebo effect of caffeine on maximal strength and strength-endurance performance during the bench press exercise (BP) in women with mild-moderate daily consumption of caffeine. Methods: Thirteen resistance-trained women (BP one-repetition maximum (1RM) = 40.0 ± 9.7 kg) habituated to caffeine (4.1 ± 1.7 mg/kg/day) completed a deceptive randomized experimental design with two experimental trials. On one occasion, participants were told that they would receive 6 mg/kg of caffeine but received a placebo (PLAC), and on other occasions, participants did not receive any substance and were told that this was a control situation (CONT). In each experimental trial, participants underwent a 1RM BP test and a strength-endurance test consisting of performing the maximal number of repetitions at 50% of their 1RM. Results: In comparison to CONT, PLAC did not enhance 1RM (40.0 ± 10.5 kg vs. 41.0 ± 9.5 kg, respectively; p = 0.10), nor did it enhance the number of repetitions (32.2 ± 5.1 vs. 31.8 ± 4.5; p = 0.66) or mean power (130 ± 34 vs. 121 ± 26; p = 0.08) in the strength-endurance test. Conclusion: Informing participants that they were given caffeine, when in fact they received a placebo, did not modify any performance variable measured in this investigation. Thus, the use of the placebo effect of caffeine seemed an ineffective strategy to enhance muscle strength and strength endurance during the BP exercise in women with mild-moderate consumption of caffeine.
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Habitual Caffeine Consumption Does Not Interfere With the Acute Caffeine Supplementation Effects on Strength Endurance and Jumping Performance in Trained Individuals
Article
  • May 2021
The long-standing caffeine habituation paradigm was never investigated in strength endurance and jumping exercise performance through a straightforward methodology. The authors examined if habitual caffeine consumption would influence the caffeine ergogenic effects on strength endurance and jumping performance as well as perceptual responses. Thirty-six strength-trained individuals were mathematically allocated into tertiles according to their habitual caffeine consumption: low (20 ± 11 mg/day), moderate (88 ± 33 mg/day), and high consumers (281 ± 167 mg/day). Then, in a double-blind, crossover, counterbalanced fashion, they performed a countermovement vertical jump test and a strength endurance test either after caffeine (6 mg/kg) and placebo supplementation or after no supplementation (control). Perceptual responses such as ratings of perceived exertion and pain were measured at the termination of the exercises. Acute caffeine supplementation improved countermovement vertical jump performance ( p = .001) and total repetitions ( p = .004), regardless of caffeine habituation. Accordingly, analysis of absolute change from the control session showed that caffeine promoted a significantly greater improvement in both countermovement vertical jump performance ( p = .004) and total repetitions ( p = .0001) compared with placebo. Caffeine did not affect the rating of perceived exertion and pain in any exercise tests, irrespective of tertiles (for all comparisons, p > .05 for both measures). Caffeine side effects were similar in low, moderate, and high caffeine consumers. These results show that habitual caffeine consumption does not influence the potential of caffeine as an ergogenic aid in strength endurance and jumping exercise performance, thus challenging recommendations to withdraw from the habitual caffeine consumption before supplementing with caffeine.
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Nonplacebo Controls to Determine the Magnitude of Ergogenic Interventions: A Systematic Review and Meta-analysis
Article
  • Feb 2021
  • MED SCI SPORT EXER
Introduction: Placebos are used as a control treatment that is meant to be indistinguishable from the active intervention. However, where substantive placebo effects may occur, studies that do not include a nonplacebo control arm may underestimate the overall effect of the intervention (active plus placebo components). This study aimed to determine the relative magnitude of the placebo effect associated with nutritional supplements (caffeine and extracellular buffers) by meta-analysing data from studies containing both placebo and nonplacebo control sessions. Methods: Bayesian multilevel meta-analysis models were used to estimate pooled effects and express the placebo effect as a percentage of the overall intervention effect. Results: Thirty-four studies were included, with the median pooled effect size (ES0.5) indicating a very small (ES0.5=0.09 [95%CrI:0.01 to 0.17]) improvement in performance of placebo compared to control. There was no moderating effect of exercise type (capacity or performance), exercise duration or training status. The comparison between active intervention and control indicated a small to medium effect (ES0.5=0.37 [95%CrI:0.20 to 0.56]). Expressed in relative terms, the placebo effect was equivalent to 25% [75%CrI:16 to 35%] and 59% [75%CrI:34 to 94%] of the total intervention effect for buffers and caffeine. Conclusion: These results demonstrate a very small, but potentially important placebo effect with nutritional supplementation studies. A substantive proportion of supplement effects may be due to placebo effects, with the relative proportion influenced by the magnitude of the overall ergogenic effect. Where feasible, intervention studies should employ nonplacebo control-arm comparators to identify the proportion of the effect estimated to come from placebo effects and avoid underestimating the overall benefits that the physiological plus psychobiological aspects associated with an intervention provide in the real world.
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Caffeine ingestion increases the upper-body intermittent dynamic strength endurance performance of combat sports athletes
Article
  • Jan 2021
The aim of this study was to investigate the effects of caffeine ingestion on upper-body intermittent strength endurance performance of combat sports athletes. Using a double-blind and placebo-controlled crossover design, ten experienced judo and jiu-jitsu athletes performed an upper-body intermittent strength endurance protocol (four set of judogi dynamic strength endurance test, interspersed by 3-min recovery intervals) 60 min after ingesting either caffeine (5 mg·kg⁻¹) or placebo. Compared with placebo condition, caffeine ingestion significantly increased the total number of repetitions (+ 7%, P = 0.04; d = 0.44) and the maximal isometric handgrip strength (+ 5%, P = 0.03, η p ² = 0.41). Rating of perceived exertion, heart rate and blood lactate concentration increased linearly throughout the test (P < 0.05), but without significant differences between caffeine and placebo conditions (P > 0.05). Caffeine ingestion improved the upper-body intermittent strength endurance performance and maximal isometric strength of combat sports athletes. This suggests that caffeine could help to maintain high levels of maximal handgrip and endurance strength in upper limbs, especially forearm muscles, which are responsible for maintaining the grip on the opponent’s judogi. Caffeine ingestion increases the upper-body intermittent dynamic strength endurance performance of combat sports athletes
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