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Effects of Caffeine Chewing Gum on Exercise Tolerance and Neuromuscular Responses in Well-Trained Runners

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Dittrich, N, Serpa, MC, Lemos, EC, De Lucas, RD, and Guglielmo, LGA. Effects of caffeine chewing gum on exercise tolerance and neuromuscular responses in well-trained runners. J Strength Cond Res XX(X): 000-000, 2019-This study aimed to investigate the effects of caffeinated chewing gum on endurance exercise, neuromuscular properties, and rate of perceived exertion on exercise tolerance. Twelve trained male runners (31.3 ± 6.4 years; 70.5 ± 6.6 kg; 175.2 ± 6.2 cm; 9.4 ± 2.7% body fat; and V[Combining Dot Above]O2max = 62.0 ± 4.2 ml·kg·min) took part of the study. The athletes performed an intermittent treadmill test to determine maximal aerobic speed and delta 50% (Δ50%) intensity. In the following visits, they performed 2 randomized time to exhaustion tests (15.4 ± 0.7 km·h) after the ingestion of 300 mg of caffeine in a double-blind, crossover, randomized design. Maximal voluntary contraction of the knee extensor associated to surface electromyographic recording and the twitch interpolation technique were assessed before and immediately after the tests to quantify neuromuscular fatigue of the knee extensor muscles. Caffeine significantly improved exercise tolerance by 18% (p < 0.01). Neuromuscular responses decreased similarly after time to exhaustion in both exercise conditions; however, athletes were able to run a longer distance in the caffeine condition. The performance improvement induced by caffeine seems to have a neuromuscular contribution because athletes were able to run a longer distance with the same neuromuscular impairment.

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... In these studies, the doses of caffeine administered ranged from 3 to 9 mg/kg. A total of three studies [34,44,47] provided absolute doses of caffeine in the form of caffeine powder, gum, and mouth strips with doses ranging from 200 to 300 mg. The general data of the experiments included in this systematic review are depicted in Table 2. ...
... In the 21 studies included in this systematic review [7,[23][24][25][26]30,34,35,[42][43][44][45][46][47][48][49][50][51][52][53][54], there was a total sample of 254 participants, including 220 men, 19 women and 15 participants with no information about gender. The participants were all runners, of which 167 were categorized as amateur and 87 were categorized as trained runners. ...
... In these studies, the doses of caffeine administered ranged from 3 to 9 mg/kg. A total of three studies [34,44,47] provided absolute doses of caffeine in the form of caffeine powder, gum, and mouth strips with doses ranging from 200 to 300 mg. The general data of the experiments included in this systematic review are depicted in Table 2. Figure 2 displays the categorization for each RoB 2 item for each included study. ...
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Caffeine (1,3,7-trimethylxanthine) is one of the most widely consumed performance-enhancing substances in sport due to its well-established ergogenic effects. The use of caffeine is more common in aerobic-based sports due to the ample evidence endorsing the benefits of caffeine supplementation on endurance exercise. However, most of this evidence was established with cycling trials in the laboratory, while the effects of the acute intake of caffeine on endurance running performance have not been properly reviewed and meta-analyzed. The purpose of this study was to perform a systematic review and meta-analysis of the existing literature on the effects of caffeine intake on endurance running performance. A systematic review of published studies was performed in four different scientific databases (Medline, Scopus, Web of Science, and SportDiscus) up until 5 October 2022 (with no year restriction applied to the search strategy). The selected studies were crossover experimental trials in which the ingestion of caffeine was compared to a placebo situation in a single- or double-blind randomized manner. The effect of caffeine on endurance running was measured by time to exhaustion or time trials. We assessed the methodological quality of each study using Cochrane’s risk-of-bias (RoB 2) tool. A subsequent meta-analysis was performed using the random effects model to calculate the standardized mean difference (SMD) estimated by Hedges’ g and 95% confidence intervals (CI). Results: A total of 21 randomized controlled trials were included in the analysis, with caffeine doses ranging between 3 and 9 mg/kg. A total of 21 studies were included in the systematic review, with a total sample of 254 participants (220 men, 19 women and 15 participants with no information about gender; 167 were categorized as recreational and 87 were categorized as trained runners.). The overall methodological quality of studies was rated as unclear-to-low risk of bias. The meta-analysis revealed that the time to exhaustion in running tests was improved with caffeine (g = 0.392; 95% CI = 0.214 to 0.571; p < 0.001, magnitude = medium). Subgroup analysis revealed that caffeine was ergogenic for time to exhaustion trials in both recreational runners (g = 0.469; 95% CI = 0.185 to 0.754; p = 0.001, magnitude = medium) and trained runners (g = 0.344; 95% CI = 0.122 to 0.566; p = 0.002, magnitude = medium). The meta-analysis also showed that the time to complete endurance running time trials was reduced with caffeine in comparison to placebo (g = −0.101; 95% CI = −0.190 to −0.012, p = 0.026, magnitude = small). In summary, caffeine intake showed a meaningful ergogenic effect in increasing the time to exhaustion in running trials and improving performance in running time trials. Hence, caffeine may have utility as an ergogenic aid for endurance running events. More evidence is needed to establish the ergogenic effect of caffeine on endurance running in women or the best dose to maximize the ergogenic benefits of caffeine supplementation.
... Caffeine is most commonly provided using capsules, and the effectiveness of caffeine on resistance exercise is mostly established with this form. Nevertheless, several studies have evaluated the ergogenic effects of other forms of caffeine (chewing gum, gel, coffee) on resistance exercise [13,26,46,47]. One of our studies [46] evaluated the effects of consuming 300 mg of caffeinated chewing gum 10 min before exercise on mean velocity, isokinetic peak torque, and power. ...
... and mean velocity at 50%, 75%, and 90% of 1RM (Cohen's d: 0.30-0.44). Another study [13] also used 300 mg of caffeine in chewing gum provided 5 min before completing a running to exhaustion test. Before and after the running test, maximum voluntary strength was evaluated. ...
... Muscular strength declined similarly in the placebo (-18%) and caffeine condition (-14%). While this might lead to a conclusion that caffeine ingestion did not attenuate the decline in strength, such inferences might be misguided given that the consumption of caffeine chewing gum also increased running time from 33 min (placebo) to 41 min [13]. Therefore, total fatigue was not matched between the conditions, and the main finding of this study was that caffeinated chewing gums improved running performance while having the same neuromuscular impairment as the placebo condition [13]. ...
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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.
... And in a previous study, energy drink has been observed to improve VA changes slightly (Millet et al., 2003 Kalmar and Cafarelli (1999) observed about an increase in maximal VA produced by the muscles after 6 mg kg of caffeine ingestion. Four studies (Dittrich et al., 2021;Mariano et al., 2019;Santos et al., 2020;Sébastien et al., 2011) recruited athletes as subjects, and these reported a significant effect in VA, and VA indicator was evaluated using only running and jump tests. These results are somewhat unexpected as other studies. ...
... Santos et al. (2020) also observed that regardless of the supplement, postexercise VA was lower in lowperforming participants than in high-performing, and suggested that the central fatigue during a 4-km cycling test is also affected by the participants' performance levels. As depicted in Dittrich et al. (2021) research, VA was significantly decreased after the exercise, but it was not observed interaction between caffeine and placebo trials. And similar results have been found in recent studies (Ansdell et al., 2018;Bowtell et al., 2018;Camati et al., 2018;Konings et al., 2017). ...
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Background: Caffeine is often used as a stimulant during fatigue, but the standard of characteristic physiological indicators of the effect of caffeine on neuromuscular fatigue has not been unified. The purpose of this systematic review and meta-analysis is to summarize current experimental findings on the effects of caffeine on physiological indexes before and after neuromuscular fatigue, identify some characteristic neuromuscular physiological indexes to assess the potential effects of caffeine. Methods: The Preferred Reporting Items for Systematic Reviews and Meta-analyses are followed. We systematically searched PubMed, Google academic, and Web of Science for randomized controlled trials. We searched for studies on caffeine's (i) effects on neuromuscular fatigue and (ii) the influence of physiological indexes changes. Meta-analysis was performed for standardized mean differences (SMD) between caffeine and placebo trials in individual studies. Results: The meta-analysis indicated that caffeine significantly improves voluntary activation (VA) (SMD = 1.46;95%CI:0.13, 2.79; p < .00001), PTw (SMD = 1.11, 95%CI: -1.61, 3.84; p < .00001), and M-wave (SMD = 1.10, 95%CI: -0.21, 2.41; p < .00001), and a significant difference (p = .003) on measures of Peak Power (PP), and insignificant difference on measures of heart rate (HR) (I2 = 0.0, p = .84) and Maximal oxygen uptake (VO2 ) (I2 = 0.0, p = .76). Conclusion: The analysis showed that caffeine intake had a relatively large effect on VA, potentiated twitch (PTw), M-wave, which can be used as characteristic indexes of caffeine's impact on neuromuscular fatigue. This conclusion tends to indicate the effects of caffeine on neuromuscular fatigue during endurance running or jumping or muscle bending and stretching. The caffeine intake had a big effect on the electromyogram (EMG) and peak power (PP), and its effect role needs to be further verified, this conclusion tends to indicate the effect of caffeine on neuromuscular fatigue during jumping or elbow bending moment movements. HR, VO2 , maximal voluntary contraction (MVC) cannot be used as the characteristic indexes of caffeine on neuromuscular fatigue. This conclusion tends to indicate the effect of caffeine on neuromuscular fatigue during endurance exercise. However, the results of meta-analysis are based on limited evidence and research scale, as well as individual differences of participants and different physical tasks, so it is necessary to interpret the results of meta-analysis cautiously. Therefore, future research needs to explore other physiological indicators and their indicative effects in order to determine effective and accurate characteristic indicators of caffeine on neuromuscular fatigue.
... This form of caffeine absorption may minimize the risk of gastrointestinal disorders in athletes. Regarding this issue, the use of caffeinated chewing gum in doses between 2 and 6 mg/kg has been found effective in increasing performance in several types of exercise, such as cycling [10][11][12], team sportsspecific tests [13,14], endurance running [15,16] and jumping performance [17] although this is not always the case [18,19]. ...
... We have analyzed the results of this investigation taking into account the exact relative dose provided to each individual, which varied between 2.37 and 3.06 mg/kg for C + P and between 4.74 and 6.01 mg/kg for C + C, and we concluded that this small differences in relative doses did not affect the results of the investigation; (2) we did not evaluate blood caffeine concentration, thus we are unable to verify the level of blood caffeine concentration obtained with the use of chewing gum. However, previous investigations using similar caffeinated chewing gum and dosing of caffeine induced blood caffeine concentrations similar to those of caffeine capsules [9], and ergogenic effects of caffeine in sports are evident when using caffeinated chewing gum [10][11][12][13][14][15][16][17]; (3) the study analyzed the effects of caffeine intake on judo performance by only using two repetitions of the SJFT. Although this is the most common testing of judo performance in the literature [28], the use of other judo-specific testing such as the judogi grip strength test [23] or the number and duration of offensive actions during combat [24] may help to understand other potential ergogenic effects of caffeine in judo. ...
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Purpose Previous investigations have found positive effects of acute ingestion of capsules containing 4-to-9 mg of caffeine per kg of body mass on several aspects of judo performance. However, no previous investigation has tested the effectiveness of caffeinated chewing gum as the form of caffeine administration for judoists. The main goal of this study was to assess the effect of acute ingestion of a caffeinated chewing gum on the results of the special judo fitness test (SJFT). Methods Nine male elite judo athletes of the Polish national team (23.7 ± 4.4 years, body mass: 73.5 ± 7.4 kg) participated in a randomized, crossover, placebo-controlled and double-blind experiment. Participants were moderate caffeine consumers (3.1 mg/kg/day). Each athlete performed three identical experimental sessions after: (a) ingestion of two non-caffeinated chewing gums (P + P); (b) a caffeinated chewing gum and a placebo chewing gum (C + P; ~2.7 mg/kg); (c) two caffeinated chewing gums (C + C; ~5.4 mg/kg). Each gum was ingested 15 min before performing two Special Judo Fitness Test (SJFT) which were separated by 4 min of combat activity. Results The total number of throws was not different between P + P, C + P, and C + C (59.66 ± 4.15, 62.22 ± 4.32, 60.22 ± 4.08 throws, respectively; p = 0.41). A two-way repeated measures ANOVA indicated no significant substance × time interaction effect as well as no main effect of caffeine for SJFT performance, SJFT index, blood lactate concentration, heart rate or rating of perceived exertion. Conclusions The results of the current study indicate that the use of caffeinated chewing gum in a dose up to 5.4 mg/kg of caffeine did not increase performance during repeated SJFTs.
... -Caffeine can be consumed as coffee, in an anhydrous state (capsule/tablet, powder), or as chewing gum [17,24,25]. ...
... In recent studies, caffeine chewing gum (300 mg of caffeine) was also reported to help improve muscle function, such as vertical jump height and knee extension peak torque [24], as well as exercise tolerance [25]. ...
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INTRODUCTION Many athletes use nutritional supplements for their performance enhancements and training effects. However, it is unclear that some of the dietary supplements have favorable outcomes, and others may increase the risk of doping or side effects. METHODS In this review, we discuss the Australian Institute of Sport (AIS) Sports Supplement Framework’s Group A performance supplements regarding safety, legality, and effectiveness in improving sports performance. Group A supplements include caffeine, beta-alanine, bicarbonate, beetroot juice, creatine, and glycerol. RESULTS We found the use of these performance supplements could help athletes improve strength and endurance. However, the effects vary with individual athletes and depend on sports characteristics, training content, physical condition, and habits. CONCLUSIONS Therefore, a case-by-case approach is warranted to ensure their desirable effects. It is important to consult a doctor or sports nutritionist before consuming theses supplements and to monitor the individual’s response through simulation.
... More innovative intake methods, such as caffeine mouth rinsing (Ehlert et al. 2020) and caffeine chewing gum, are alternative supplementation forms (Pickering and Grgic 2019). Results are less optimistic for caffeine mouth rinsing (Ehlert et al. 2020), likely due to the lack of increased circulating caffeine with this method (Doering et al. 2014), while there is a tendency for positive results with caffeinated gum (Venier et al. 2019;Dittrich et al. 2019), although the most effective timing for caffeine gum appears to be approximately 5 min pre-exercise (Ryan et al. 2013). ...
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Caffeine is a popular ergogenic aid due to its primary physiological effects that occur through antagonism of adenosine receptors in the central nervous system. This leads to a cascade of physiological reactions which increases focus and volition, and reduces perception of effort and pain, contributing to improved exercise performance. Substantial variability in the physiological and performance response to acute caffeine consumption is apparent, and a growing number of studies are implicating a single-nucleotide polymor-phism in the CYP1A2 gene, responsible for caffeine metabolism, as a key factor that influences the acute responses to caffeine inges-tion. However, existing literature regarding the influence of this polymorphism on the ergogenic effects of caffeine is controversial. Fast caffeine metabolisers (AA homozygotes) appear most likely to benefit from caffeine supplementation, although over half of studies showed no differences in the responses to caffeine between CYP1A2 genotypes, while others even showed either a possible advantage or disadvantage for C-allele carriers. Contrasting data are limited by weak study designs and small samples sizes, which did not allow separation of C-allele carriers into their subgroups (AC and CC), and insufficient mechanistic evidence to elucidate findings. Mixed results prevent practical recommendations based upon genotype while genetic testing for CYP1A2 is also currently unwarranted. More mechanistic and applied research is required to elucidate how the CYP1A2 polymorphism might alter caffeine's ergogenic effect and the magnitude thereof, and whether CYP1A2 genotyping prior to caffeine supplementation is necessary.
... The authors' findings indicated that 300 mg; 4.2 ± 0.2 mg/kg caffeine delivered via chewing gum improved TT time, absolute power, and MPW with riders demonstrating lower RPE. To date, a few studies have identified the effects of CAF on sporting performances (Dittrich et al., 2019;Paton et al., 2015;Ranchordas et al., 2019;Russell et al., 2020); however, to the best of the authors' knowledge, this is the first to investigate caffeine intake on BMX TT performance. ...
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This study aimed to identify the acute effects of caffeinated chewing gum (CAF) on bicycle motocross (BMX) time-trial (TT) performance. In a randomized, placebo-controlled, double-blind cross-over design,14 male BMX riders (age = 20.0 ± 3.3 years; height = 1.78 ± 0.04 m; body mass = 72 ± 4 kg), consumed either (300 mg; 4.2 ± 0.2 mg/kg) caffeinated (300 mg caffeine, 6 g sugars) or a placebo (0 mg caffeine, 0 g sugars) gum, and undertook three BMX TTs. Repeated-measure analysis revealed that CAF has a large ergogenic effect on TTtime, F(1,14) = 33.570, p =.001, η2p =.71 −1.5% ± 0.4 compared with the placebo. Peak power and maximal power to weight ratio also increased significantly compared with the placebo condition, F(1, 14) = 54.666, p = .001, η2p = .79; +3.5% ± 0.6, and F(1,14) = 57.399, p = .001, η2p = .80; +3% ± 0.3, respectively. Rating of perceived exertion was significantly lower F(1, 14) = 25.020, p = .001, η2p = .64 in CAF (6.6 ± 1.3) compared with the placebo (7.2 ± 1.7). Administering a moderate dose (300 mg) of CAF could improve TT time by enhancing power and reducing the perception of exertion. BMX coaches and riders may consider consuming CAF before a BMX race to improve performance and reduce rating of perceived exertion. Keywords: caffeine, power output, sprint cycling
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Background: To date, no study has investigated the effects of acute intake of caffeinated chewing gum in female basketball players. Methods: Nine elite female basketball players participated in a randomized crossover placebo-controlled double-blind experiment. All athletes participated in two identical experimental trials 15 minutes after ingestion of (i) chewing gum containing 150 mg of caffeine (i.e.~2.3 ± 0.2 mg/kg of caffeine) or (ii) non-caffeinated chewing gum with an inert substance to produce a placebo. After the ingestion of the gum, the athletes performed the following tests: (i) a sprint test (0-20 m), (ii) agility T-test, (iii) isometric handgrip strength test, (iv) countermovement jump test, (v) free throw test, and (vi) three-point shot test. Results: No significant differences were observed in any physical or skill-based tests (p > 0.05 for all). However, the effect size in the sprint and agility T-Test, jump height test, and free-throw test was higher in the caffeine conditions, with effect sizes of small or moderate magnitude (ES = 0.31 – 0.64) over the placebo. Conclusion: From a practical perspective, the benefits of caffeinated chewing gum are minor, at least in elite athletes with a mild level of caffeine consumption.
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To date, no investigation has studied the effect of acute intake of caffeinated chewing gum on volleyball performance. Therefore, the aim of this investigation was to establish the impact of caffeinated chewing gum ingestion on physical performance in female volleyball players. Twelve high-performance volleyball female athletes participated in a randomized, crossover, placebo-controlled, and double-blind experiment. Each athlete performed two identical experimental sessions after a) ingestion of ~6.4 mg/kg of caffeine via caffeinated chewing gum, b) ingestion of non-caffeinated chewing gum as a placebo. After the ingestion of gum, athletes performed a volleyball game, and performance was assessed by a notational analysis. Just before and after the game, jump performance during block and attack actions was evaluated. The number of points obtained and the number of errors committed during serve, reception, attacking, and blocking actions were unaffected by the ingestion of caffeinated chewing gum (p from 0.066 to 0.890). However, caffeinated chewing gum increased jump attack height in comparison to the placebo (pre-game 46.0 ± 7.2 vs. 47.2 ± 6.7 cm, p = 0.032; post-game 46.3 ± 7.6 vs. 47.5 ± 6.9 cm, p = 0.022, respectively). Caffeinated chewing gum did not modify block jump height (pre-game 32.7 ± 5.5 and 33.0 ± 4.3 cm, p = 0.829; post-game: 34.8 ± 6.1, 35.4 ± 6.1 cm, p = 0.993, respectively). The ingestion of ~6.4 mg/kg of caffeine via caffeinated chewing gum was effective for improving jump attack performance in women volleyball athletes. However, this effect was not translated into better volleyball performance during a game.
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In this study we tested the hypothesis that caffeine supplementation improves neuromuscular function, which has both nutritional and clinical relevance. Fourteen male subjects (mean ± SD: 23.8 ± 2.8 years) volunteered in a double-blind, repeated-measures study with placebo (PLA) or caffeine (CAFF) (6 mg kg(-1)). Maximal voluntary isometric contractions (MVCs), evoked maximal twitch, and maximal isokinetic contractions during elbow flexion were assessed. Mechanical and electromyographic (EMG) signals from the biceps brachii muscle were recorded, and muscle fiber conduction velocity (CV) was calculated to evaluate changes in the muscle force-velocity relationship and muscle fiber recruitment. The torque-angular velocity curve was enhanced after CAFF supplementation. This was supported by a concomitant increase of CV values (8.7% higher in CAFF). Caffeine improves muscle performance during short-duration maximal dynamic contractions. The concomitant improvement of mean fiber CV supports the hypothesis of an effect of caffeine on motor unit recruitment.
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Position Statement: The position of The Society regarding caffeine supplementation and sport performance is summarized by the following seven points: 1.) Caffeine is effective for enhancing sport performance in trained athletes when consumed in low-to-moderate dosages (~3-6 mg/kg) and overall does not result in further enhancement in performance when consumed in higher dosages (>/= 9 mg/kg). 2.) Caffeine exerts a greater ergogenic effect when consumed in an anhydrous state as compared to coffee. 3.) It has been shown that caffeine can enhance vigilance during bouts of extended exhaustive exercise, as well as periods of sustained sleep deprivation. 4.) Caffeine is ergogenic for sustained maximal endurance exercise, and has been shown to be highly effective for time-trial performance. 5.) Caffeine supplementation is beneficial for high-intensity exercise, including team sports such as soccer and rugby, both of which are categorized by intermittent activity within a period of prolonged duration. 6.) The literature is equivocal when considering the effects of caffeine supplementation on strength-power performance, and additional research in this area is warranted. 7.) The scientific literature does not support caffeine-induced diuresis during exercise, or any harmful change in fluid balance that would negatively affect performance.
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Our objective was to perform a systematic review and meta-analysis of the research literature assessing the effect of caffeine ingestion on maximal voluntary contraction (MVC) strength and muscular endurance. Thirty-four relevant studies between 1939 and 2008 were included in the meta-analyses of caffeine's effects on MVC strength (n = 27 studies) and muscular endurance (n = 23 studies). Effect sizes (ES) were calculated as the standardized mean difference and meta-analyses were completed using a random-effects model. Overall, caffeine ingestion was found to result in a small beneficial effect on MVC strength (overall ES = 0.19, P = 0.0003). However, caffeine appears to improve MVC strength primarily in the knee extensors (i.e., by approximately 7%, ES = 0.37) and not in other muscle groups such as the forearm or the knee flexors. In an attempt to offer a physiological mechanism behind caffeine's ability to improve MVC strength, a meta-analysis was run on ES from nine studies that measured percent muscle activation during MVC in trials comparing caffeine versus placebo; the overall ES (0.67) was highly significant (P = 0.00008) and of moderate to large size, thus implicating an effect of caffeine on the CNS. Caffeine ingestion was also found to exert a small beneficial effect on muscular endurance (overall ES = 0.28, P = 0.00005). However, it appears caffeine improves muscular endurance only when it is assessed using open (i.e., by approximately 18%, ES = 0.37) and not fixed end point tests. Overall, caffeine ingestion improves MVC strength and muscular endurance. The effect on strength appears exclusively in the knee extensors, and the effect on muscular endurance appears only detectable with open end point tests.
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The aim of this review is to present the state of the art of the technology of detection and conditioning systems for surface electromyography (sEMG). The first part of the manuscript focuses on the sEMG electrode system technology: the electrode classification, impedance, noise, transfer function, the spatial filtering effect of surface electrode configurations, the effects of electrode geometry, and location on the recorded sEMG signal. Examples of experimental sEMG signals are provided to show the potential value of high-density sEMG electrode grids and multichannel amplifiers that allow to add spatial information to the temporal information content of the sEMG signal. Furthermore, the results of a simple simulation are reported, in order to emphasize the effects of the subcutaneous tissue layers and of the detection volume on the recorded sEMG signal. The second part of the manuscript focuses on the sEMG amplifier technology: the front end amplifier characteristics for signal conditioning, the methods for stimulation artifact reduction, filtering methods, safety requirements, and the methods for analog-to-digital conversion of the sEMG signal.
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To investigate the effects of simultaneous explosive-strength and endurance training on physical performance characteristics, 10 experimental (E) and 8 control (C) endurance athletes trained for 9 wk. The total training volume was kept the same in both groups, but 32% of training in E and 3% in C was replaced by explosive-type strength training. A 5-km time trial (5K), running economy (RE), maximal 20-m speed (V20 m), and 5-jump (5J) tests were measured on a track. Maximal anaerobic (MART) and aerobic treadmill running tests were used to determine maximal velocity in the MART (VMART) and maximal oxygen uptake (VO2 max). The 5K time, RE, and VMART improved (P < 0.05) in E, but no changes were observed in C. V20 m and 5J increased in E (P < 0.01) and decreased in C (P < 0.05). VO2 max increased in C (P < 0.05), but no changes were observed in E. In the pooled data, the changes in the 5K velocity during 9 wk of training correlated (P < 0.05) with the changes in RE [O2 uptake (r = -0.54)] and VMART (r = 0.55). In conclusion, the present simultaneous explosive-strength and endurance training improved the 5K time in well-trained endurance athletes without changes in their VO2 max. This improvement was due to improved neuromuscular characteristics that were transferred into improved VMART and running economy.
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This study compared the relationship between surface electromyographic (EMG) activity and isometric force of m. quadriceps femoris (QF) in the single-joint knee extension (KE) and the multi-joint leg press (LP) exercises. Nine healthy men performed unilateral actions at a knee angle of 90 degrees at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC). EMG was measured from m. vastus lateralis (VL), m. vastus medialis (VM), m. rectus femoris (RF), and m. biceps femoris (BF). There were no differences in maximum EMG activity of individual muscles between KE and LP. The QF EMG/force relationship was nonlinear in each exercise modality. VL showed no deviation from linearity in neither exercise, whereas VM and RF did. BF activity increased linearly with increased loads. The EMG/force relationship of all quadricep muscles studied appears to be similar in isometric multi-joint LP and single-joint KE actions at a knee angle of 90 degrees. This would indicate the strategy of reciprocal force increment among muscles involved is comparable in the two models. Furthermore, these data suggest a nonuniform recruitment pattern among the three superficial QF muscles and surface EMG recordings from VL to be most reliable in predicting force output.
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The mechanism of action underlying the ergogenic effect of caffeine is still unclear. Caffeine increases the force of muscular contraction during low-frequency stimulation by potentiating calcium release from the sarcoplasmic reticulum. Studies have also suggested an enhancement of lipid oxidation and glycogen sparing as potential mechanisms. Given that several studies have found an ergogenic effect of caffeine with no apparent metabolic effects, it is likely that a direct effect upon muscle is important. Twelve healthy male subjects were classified as habitual (n = 6) or nonhabitual (n = 6) caffeine consumers based on a 4-day diet record analysis, with a mean caffeine consumption of 771 and 14 mg/day for each group, respectively. Subjects were randomly allocated to receive caffeine (6 mg/kg) and placebo (citrate) in a double-blind, cross-over fashion approximately 100 min before a 2-min tetanic stimulation of the common peroneal nerve in a custom-made dynamometer (2 trials each of 20 and 40 Hz). Tetanic torque was measured every 30 s during and at 1, 5, and 15 min after the stimulation protocol. Maximal voluntary contraction strength and peak twitch torque were measured before and after the stimulation protocol. Caffeine potentiated the force of contraction during the final minute of the 20-Hz stimulation (P<0.05) with no effect of habituation. There was no effect of caffeine on 40-Hz stimulation strength nor was there an effect on maximal voluntary contraction or peak twitch torque. These data support the hypothesis that some of the ergogenic effect of caffeine in endurance exercise performance occurs directly at the skeletal muscle level.
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Caffeine is a common substance in the diets of most athletes and it is now appearing in many new products, including energy drinks, sport gels, alcoholic beverages and diet aids. It can be a powerful ergogenic aid at levels that are considerably lower than the acceptable limit of the International Olympic Committee and could be beneficial in training and in competition. Caffeine does not improve maximal oxygen capacity directly, but could permit the athlete to train at a greater power output and/or to train longer. It has also been shown to increase speed and/or power output in simulated race conditions. These effects have been found in activities that last as little as 60 seconds or as long as 2 hours. There is less information about the effects of caffeine on strength; however, recent work suggests no effect on maximal ability, but enhanced endurance or resistance to fatigue. There is no evidence that caffeine ingestion before exercise leads to dehydration, ion imbalance, or any other adverse effects. The ingestion of caffeine as coffee appears to be ineffective compared to doping with pure caffeine. Related compounds such as theophylline are also potent ergogenic aids. Caffeine may act synergistically with other drugs including ephedrine and anti-inflammatory agents. It appears that male and female athletes have similar caffeine pharmacokinetics, i.e., for a given dose of caffeine, the time course and absolute plasma concentrations of caffeine and its metabolites are the same. In addition, exercise or dehydration does not affect caffeine pharmacokinetics. The limited information available suggests that caffeine non-users and users respond similarly and that withdrawal from caffeine may not be important. The mechanism(s) by which caffeine elicits its ergogenic effects are unknown, but the popular theory that it enhances fat oxidation and spares muscle glycogen has very little support and is an incomplete explanation at best. Caffeine may work, in part, by creating a more favourable intracellular ionic environment in active muscle. This could facilitate force production by each motor unit.
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The purpose of this study was to evaluate the rate of absorption and relative bioavailability of caffeine from a Stay Alert chewing gum and capsule formulation. This was a double blind, parallel, randomized, seven treatment study. The treatment groups were: 50, 100, and 200 mg gum, 50, 100, and 200 mg capsule, and a placebo. Subjects consisted of 84 (n=12 per group); healthy, non-smoking, males who had abstained from caffeine ingestion for at least 20 h prior to dosing and were randomly assigned to the treatment groups. Blood samples were collected pre-dose and at 5, 15, 25, 35, 45, 55, 65, 90 min and 2, 3, 4, 6, 8, 12, 16 and 29 h post administration. Plasma caffeine levels were analyzed by a validated UV-HPLC method. Mean Tmax for the gum groups ranged from 44.2 to 80.4 min as compared with 84.0-120.0 min for the capsule groups. The Tmax, for the pooled data was significantly lower (P<0.05) for the gum groups as compared with the capsule groups. Differences in Tmax were significant for the 200 mg capsule versus 200 mg gum (P<0.05). The mean ka values for the gum group ranged from 3.21 to 3.96 h-1 and for the capsule groups ranged from 1.29 to 2.36 h-1. Relative bioavailability of the gum formulation after the 50, 100 and 200 mg dose was 64, 74 and 77%, respectively. When normalized to the total drug released from the gum (85%), the relative bioavailability of the 50, 100 and 200 mg dose were 75, 87, and 90%, respectively. No statistical differences were found for Cmax and AUCinf for comparisons of the gum and capsule formulations at each dose. Within each dose level, there were no significant formulation related differences in Cmax. No significant differences were observed in the elimination of caffeine after the gum or capsule. The results suggest that the rate of drug absorption from the gum formulation was significantly faster and may indicate absorption via the buccal mucosa. In addition, for the 100 and 200 mg groups, the gum and capsule formulations provide near comparable amounts of caffeine to the systemic circulation. These findings suggest that there may be an earlier onset of pharmacological effects of caffeine delivered as the gum formulation, which is advantageous in situations where the rapid reversal of alertness and performance deficits resulting from sleep loss is desirable.
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Competitive athletes completed two studies of 2-h steady-state (SS) cycling at 70% peak O(2) uptake followed by 7 kJ/kg time trial (TT) with carbohydrate (CHO) intake before (2 g/kg) and during (6% CHO drink) exercise. In Study A, 12 subjects received either 6 mg/kg caffeine 1 h preexercise (Precaf), 6 x 1 mg/kg caffeine every 20 min throughout SS (Durcaf), 2 x 5 ml/kg Coca-Cola between 100 and 120 min SS and during TT (Coke), or placebo. Improvements in TT were as follows: Precaf, 3.4% (0.2-6.5%, 95% confidence interval); Durcaf, 3.1% (-0.1-6.5%); and Coke, 3.1% (-0.2-6.2%). In Study B, eight subjects received 3 x 5 ml/kg of different cola drinks during the last 40 min of SS and TT: decaffeinated, 6% CHO (control); caffeinated, 6% CHO; decaffeinated, 11% CHO; and caffeinated, 11% CHO (Coke). Coke enhanced TT by 3.3% (0.8-5.9%), with all trials showing 2.2% TT enhancement (0.5-3.8%; P < 0.05) due to caffeine. Overall, 1) 6 mg/kg caffeine enhanced TT performance independent of timing of intake and 2) replacing sports drink with Coca-Cola during the latter stages of exercise was equally effective in enhancing endurance performance, primarily due to low intake of caffeine (approximately 1.5 mg/kg).
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The aim of this study was to identify the mechanisms that contribute to the decline in knee extensor (KE) muscles strength after a prolonged running exercise. During the 2 days preceding a 30-km running race [duration 188.7 +/- 27.0 (SD) min] and immediately after the race, maximal percutaneous electrical stimulations (single twitch, 0.5-s tetanus at 20 and 80 Hz) were applied to the femoral nerve of 12 trained runners. Superimposed twitches were also delivered during isometric maximal voluntary contraction (MVC) to determine the level of voluntary activation (%VA). The vastus lateralis electromyogram was recorded. KE MVC decreased from pre- to postexercise (from 188.1 +/- 25.2 to 142.7 +/- 29.7 N x m; P < 0.001) as did %VA (from 98.8 +/- 1.8 to 91.3 +/- 10.7%; P < 0.05). The changes from pre- to postexercise in these two variables were highly correlated (R = 0.88; P < 0.001). The modifications in the mechanical response after the 80-Hz stimulation and M-wave peak-to-peak amplitude were also significant (P < 0.001 and P < 0.05, respectively). It can be concluded that 1) central fatigue, neuromuscular propagation, and muscular factors are involved in the 23.5 +/- 14.9% reduction in MVC after a prolonged running bout at racing pace and 2) runners with the greatest KE strength loss experience large activation deficit.
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The purpose of this study was to compare critical velocity (CV) estimates from five mathematical models, and to examine the oxygen uptake (VO(2)) and heart rate (HR) responses during treadmill runs at the five estimates of CV. Ten subjects (six males and four females) performed one incremental test to determine maximal oxygen consumption (VO(2max)) and four or five randomly ordered constant-velocity trials on a treadmill for the estimation of CV. Five mathematical models were used to estimate CV for each subject including two linear, two nonlinear, and an exponential model. Up to five randomly ordered runs to exhaustion were performed by each subject at treadmill velocities that corresponded to the five CV estimates, and VO(2) and HR responses were monitored throughout each trial. The 3-parameter, nonlinear (Non-3) model produced CV estimates that were significantly (P < 0.05) less than the other four models. During runs at CV estimates, five subjects did not complete 60 min at the their estimate from the Non-3 model, nine did not complete 60 min at their estimate from the Non-2 model, and no subjects completed 60 min at any estimate from the other three models. The mean HR value (179 +/- 18 beats min(-1), HR(peak)) at the end of runs at CV using the Non-3 model was significantly less than the maximal HR (195 +/- 7 beats min(-1), HR(max)) achieved during the incremental trial to exhaustion. However, mean HR(peak) values from runs at all other CV estimates were not significantly different from HR(max). Furthermore, data indicated that mean HR(peak) values increased during runs at CV estimates from the third minute to the end of exercise for all models, and that these increases in VO(2) (range = 367-458 ml min(-1)) were significantly greater than that typically associated with O(2) drift ( approximately 200 ml min(-1)) for all but the exponential model, indicating a VO(2) slow component associated with CV estimates from four of the five models. However, the mean VO(2) values at the end of exercise during the runs at CV estimates for all five mathematical models were significantly less than the mean VO(2max) value. These results suggest that, in most cases, CV estimated from the five models does not represent a fatigueless task. In addition, the mean CV estimates from the five models varied by 18%, and four of the five mean CV estimates were within the heavy exercise domain. Therefore, CV would not represent the demarcation point between heavy and severe exercise domains.
Article
To investigate the effects of simultaneous explosive-strength and endurance training on physical performance characteristics, 10 experimental (E) and 8 control (C) endurance athletes trained for 9 wk. The total training volume was kept the same in both groups, but 32% of training in E and 3% in C was replaced by explosive-type strength training. A 5-km time trial (5K), running economy (RE), maximal 20-m speed ( V 20 m ), and 5-jump (5J) tests were measured on a track. Maximal anaerobic (MART) and aerobic treadmill running tests were used to determine maximal velocity in the MART ( V MART ) and maximal oxygen uptake (V˙o 2 max ). The 5K time, RE, and V MART improved ( P < 0.05) in E, but no changes were observed in C. V 20 m and 5J increased in E ( P < 0.01) and decreased in C ( P < 0.05).V˙o 2 max increased in C ( P < 0.05), but no changes were observed in E. In the pooled data, the changes in the 5K velocity during 9 wk of training correlated ( P< 0.05) with the changes in RE [O 2 uptake ( r = −0.54)] and V MART ( r = 0.55). In conclusion, the present simultaneous explosive-strength and endurance training improved the 5K time in well-trained endurance athletes without changes in theirV˙o 2 max . This improvement was due to improved neuromuscular characteristics that were transferred into improved V MART and running economy.
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Unlabelled: Caffeine improves endurance exercise performance, but its ergogenic mechanism(s) remain unclear. Purpose: This investigation sought to examine the effects of caffeine on perceptual and physiological responses to endurance exercise. Methods: Two experiments were performed. In study A, 14 participants were tested. Maximal voluntary strength (MVC) and motor-unit recruitment (%ACT) of the knee extensors and elbow flexors were tested before and 60 min after ingestion of a 5-mg·kg⁻¹ dose of caffeine or placebo and after completion of 40 min of exercise (30 min of submaximal leg or arm cycling followed by a 10-min time-trial performance). Muscle pain, RPE, and cardiorespiratory variables were assessed throughout. To determine the effects of caffeine on muscle pain and RPE during high-intensity exercise, a second study (study B) was performed. Twelve participants exercised at 95% of their gas exchange threshold (GET) and at 70% of the difference between their GET and VO(2peak) (70%Δ) after caffeine and placebo ingestion. Results: Compared to placebo, caffeine improved MVC (6.3%, P = 0.014) and %ACT (5.5%, P = 0.013) in the knee extensors, but not the elbow flexors, and reduced muscle pain (P < 0.05) and RPE (P < 0.05) during both submaximal cycling modalities. Caffeine ingestion improved time-trial performance during leg cycling (4.9% ± 6.5%, P = 0.03), but not arm crank cycling (2.1% ± 8.2%, P = 0.28), but the effect on pain and RPE was eliminated. Caffeine ingestion had no effect on pain or RPE during cycling at 95% GET and 70%Δ. Conclusions: Our results suggest that augmented strength and motor-unit recruitment, rather than reductions in pain and effort, may underlie caffeine's ergogenic effect on endurance exercise.
Article
The aim of this study was to compare the neuromuscular function of the plantar flexors following caffeine or placebo administration. Thirteen subjects (25 ± 3 years) ingested caffeine or placebo in a randomized, controlled, counterbalanced, double-blind crossover design. Neuromuscular tests were performed before and 1 h after caffeine or placebo intake. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque, and neural drive to the muscles were measured. Triceps surae muscle activation was assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0–100 ms, 100–200 ms) and maximal voluntary contraction (MVC). Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during MVC, V-wave) and peak twitch torques were evaluated. The isometric maximum voluntary torque and evoked potentials were not different. However, we found a significant difference between groups for rate of torque development in the time intervals 0–100 ms [41.1 N·m/s (95% CI: 8.3–73.9 N·m/s, P = 0.016)] and 100–200 ms [32.8 N·m/s (95% CI: 2.8–62.8 N·m/s, P = 0.034)]. These changes were accompanied by enhanced neural drive to the plantar flexors. Data suggest that caffeine solely increased explosive voluntary strength of the triceps surae because of enhanced neural activation at the onset of contraction whereas MVC strength was not affected.
Article
Unlabelled: Caffeine has many diverse physiological effects including central nervous system stimulation. Ventilatory threshold and a recently described heart rate variability threshold both have a relationship with autonomic control that could be altered by caffeine consumption. The purpose of this investigation was to determine the influence of caffeine on lactate, ventilatory, and heart rate variability thresholds during progressive exercise. Using a randomized placebo controlled, double-blind study design, 10 adults performed 2 graded maximal cycle ergometry tests with and without caffeine (5 mg·kg⁻¹). Respiratory gas exchange, blood lactate concentrations, and heart rate variability data were obtained at baseline and throughout exercise. Results: At rest, caffeine (p<0.05) increased blood lactate, oxygen consumption, carbon dioxide production, and minute ventilation. For indices of heart rate variability at rest, caffeine increased (p<0.05) the coefficient of variation, while standard deviation, and mean successive difference displayed non-significant increases. During progressive exercise, minute ventilation volumes were higher in caffeine trials but no other parameters were significantly different compared to placebo tests. Conclusion: These data demonstrate the robustness of the lactate, ventilatory and heart rate variability thresholds when challenged by a physiological dose of caffeine.
Article
The purpose of the present study was to determine the most efficacious time to administer caffeine (CAF) in chewing gum to enhance cycling performance. Eight male cyclists participated in 5 separate laboratory sessions. During the first visit, subjects underwent a graded exercise test to determine maximal oxygen consumption (VO2max). During the next 4 visits, three pieces of chewing gum were administered at three time points (120 min pre-cycling, 60 min pre-cycling, and 5 min pre-cycling). In three of the four visits, at one of the time points mentioned previously, 300 mg of CAF was administered. During the fourth visit, placebo gum was administered at all 3 time points. The experimental trials were defined as follows: Trial A (-120), Trial B (-60), Trial C (-5), and Trial D (Placebo). Following baseline measurements, time allotted for gum administration, and a standard warm-up, participants cycled at 75% VO2max for 15 min then completed a 7 kj·kg cycling time trial. Data were analyzed using a repeated measures analysis of variance. Cycling performance was improved in Trial C (-5), but not in Trial A (-120) or Trial B (-60), relative to Trial D (Placebo). Caffeine administered in chewing gum enhanced cycling performance when administered immediately prior, but not when administered 1 or 2 hr prior to cycling.
Article
The effect of oral caffeine ingestion on intense intermittent exercise performance and muscle interstitial ion concentrations was examined. The study consists of two studies (S1 and S2). In S1, 12 subjects completed the Yo-Yo intermittent recovery level 2 (Yo-Yo IR2) test with prior caffeine (6 mg/kg body wt; CAF) or placebo (PLA) intake. In S2, 6 subjects performed one low-intensity (20 W) and three intense (50 W) 3-min (separated by 5 min) one-legged knee-extension exercise bouts with (CAF) and without (CON) prior caffeine supplementation for determination of muscle interstitial K(+) and Na(+) with microdialysis. In S1 Yo-Yo IR2 performance was 16% better (P < 0.05) in CAF compared with PLA. In CAF, plasma K(+) at the end of the Yo-Yo IR2 test was 5.2 ± 0.1 mmol/l with no difference between the trials. Plasma free fatty acids (FFA) were higher (P < 0.05) in CAF than PLA at rest and remained higher (P < 0.05) during exercise. Peak blood glucose (8.0 ± 0.6 vs. 6.2 ± 0.4 mmol/l) and plasma NH(3) (137.2 ± 10.8 vs. 113.4 ± 13.3 μmol/l) were also higher (P < 0.05) in CAF compared with PLA. In S2 interstitial K(+) was 5.5 ± 0.3, 5.7 ± 0.3, 5.8 ± 0.5, and 5.5 ± 0.3 mmol/l at the end of the 20-W and three 50-W periods, respectively, in CAF, which were lower (P < 0.001) than in CON (7.0 ± 0.6, 7.5 ± 0.7, 7.5 ± 0.4, and 7.0 ± 0.6 mmol/l, respectively). No differences in interstitial Na(+) were observed between CAF and CON. In conclusion, caffeine intake enhances fatigue resistance and reduces muscle interstitial K(+) during intense intermittent exercise.
Article
The purpose of this investigation was to examine the nutritional supplement intake of athletes from a state-based sports institute. Athletes (n=72) from seven sports (kayaking, field hockey, rowing, waterpolo, swimming, athletics and netball) completed a questionnaire detailing their daily usage and rationale therefore. The large majority (63/72; 87.5+/-12.5%) of surveyed athletes reported using nutritional supplements, with no difference between female (31/36; 86.1+/-13.9%) and male (32/36; 88.9+/-11.1%) athletes. Kayakers (6.0+/-2.9) consumed a higher number of nutritional supplements than swimmers (4+/-2.2), field hockey (1.5+/-1.0), rowing (2.4+/-1.4), waterpolo (2.3+/-2.4), athletics (2.5+/-1.9) and netball (1.7+/-1.0) athletes. The athletes believed that nutritional supplements are related to performance enhancements (47/72; 65.3%), positive doping results (45/72; 62.5%), and that heavy training increases supplement requirements (47/72; 65.3%). The cohort was equivocal as to their health risks (40/72; 55.6%) or their need with a balanced diet (38/72; 52.8%). The most popular supplements were minerals (33/72; 45.8%), vitamins (31/72; 43.1%), other (23/72; 31.9%), iron (22/72; 30.6%), caffeine (16/72; 22.2%), protein (12/72; 16.7%), protein-carbohydrate mix (10/72; 13.9%), creatine (9/72; 12.5%) and glucosamine (3/72; 4.2%). The majority of supplementing athletes (n=63) did not know their supplements active ingredient (39/63; 61.9%), side effects (36/63; 57.1%) or mechanism of action (34/63; 54.0%) and admitted to wanting additional information (36/63; 57.0%). Only half of the athletes knew the recommended supplement dosages (33/63; 52.4%). The performance enhancing perception may explain the large proportion of athletes that reported using nutritional supplements, despite over half of the athletes believing that supplements are not required with a balanced diet and can cause positive doping violations.
Article
In an effort to assess the effects of caffeine ingestion on metabolism and performance during prolonged exercise, nine competitive cyclists (two females and seven males) exercised until exhaustion on a bicycle ergometer at 80% of Vo2 max. One trial was performed an hour after ingesting decaffeinated coffee (Trial D), while a second trial (C) required that each subject consume coffee containing 330 mg of caffeine 60 min before the exercise. Following the ingestion of caffeine (Trial C), the subjects were able to perform an average of 90.2 (SE +/- 7.2) min of cycling as compared to an average of 75.5 (SE +/- 5.1) min in the D Trial. Measurements of plasma free fatty acids, glycerol and respiratory exchange ratios evidenced a greater rate of lipid metabolism during the caffeine trial as compared to the decaffeinated exercise treatment. Calculations of carbohydrate (CHO) metabolism from respiratory exchange data revealed that the subjects oxidized roughly 240 g of CHO in both trials. Fat oxidation, however, was significantly higher (P less than 0.05) during the C Trial (118 g or 1.31 g/min) than in the D Trial (57 g or 0.75 g/min). On the average the participants rated (Perceived Exertion Scale) their effort during the C Trial to be significantly (P less than 0.05) easier than the demands of the D treatment. Thus, the enhanced endurance performance observed in the C Trial was likely the combined effects of caffeine on lipolysis and its positive influence on nerve impulse transmission.
Article
1. The effects of caffeine (0.2-20 mmol l-1) have been examined on calcium transients (measured with aequorin) and isometric force in intact bundles of fibres from soleus (slow-twitch) and extensor digitorum longus (EDL; fast-twitch) muscles of the rat. 2. At 25 degrees C, threshold caffeine concentration for an observable increase in resting [Ca2+]i was 0.2 and 1.0 mmol l-1 for soleus and EDL muscles respectively. Increases in resting force were first detectable at about 0.5 mmol l-1 caffeine for soleus muscles and 5.0 mmol l-1 caffeine for EDL muscles and occurred in the range 0.2-0.4 mumol l-1 [Ca2+]i for soleus and 0.7-0.9 mumol l-1 for EDL. 3. Caffeine potentiated the twitch responses of soleus and EDL in a dose-related manner. The soleus was more sensitive in this respect, with 50% potentiation occurring at 1 mmol l-1 caffeine compared with 3.5 mmol l-1 for the EDL. Concentrations of caffeine below 2 mmol l-1 potentiated Ca2+ transients associated with twitches in both soleus and EDL muscles with no apparent change in the decay rate constant. 4. High concentrations of caffeine (greater than 2 mmol l-1) further potentiated peak Ca2+ in the EDL but depressed it in the soleus. The rate of decay of the Ca2+ transient in high caffeine was significantly prolonged in the soleus but remained unaffected in the EDL. 5. The phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX) had little effect on force or [Ca2+]i at concentrations known to significantly increase intracellular cyclic AMP levels. 6. The Ca2+ transient during fused tetani was characterized by an initial peak, a decline to a plateau level and sometimes a gradual rise towards the end of the stimulus train. Peak [Ca2+]i during normal tetani ranged between 1.1 and 2.4 mumol l-1 in the soleus and 1.9 and 4.0 mumol l-1 in the EDL. 7. Caffeine potentiated both force and [Ca2+]i during tetanus. Since the increase of the Ca2+ transient was significantly greater than potentiation of force, it is likely that saturation of myofilaments occurs. The primary effect of caffeine on the Ca2+ transient was an elevation of the plateau phase. 8. Caffeine concentrations below 5 mmol l-1 potentiate twitch and tetanic force in both fast- and slow-twitch mammalian skeletal muscles primarily by increasing both the basal and stimulus-evoked release of Ca2+ from the sarcoplasmic reticulum.
Article
There is a great demand for perceptual effort ratings in order to better understand man at work. Such ratings are important complements to behavioral and physiological measurements of physical performance and work capacity. This is true for both theoretical analysis and application in medicine, human factors, and sports. Perceptual estimates, obtained by psychophysical ratio-scaling methods, are valid when describing general perceptual variation, but category methods are more useful in several applied situations when differences between individuals are described. A presentation is made of ratio-scaling methods, category methods, especially the Borg Scale for ratings of perceived exertion, and a new method that combines the category method with ratio properties. Some of the advantages and disadvantages of the different methods are discussed in both theoretical-psychophysical and psychophysiological frames of reference.
Article
This double-blind, repeated-measures study examined the effects of caffeine on neuromuscular function. Eleven male volunteers [22.3 +/- 2.4 (SD) yr] came to the laboratory for control, placebo, and caffeine (6 mg/kg dose) trials. Each trial consisted of 10 x 1-ms stimulation of the tibial nerve to elicit maximal H reflexes of the soleus, four attempts at a maximal voluntary contraction (MVC) of the right knee extensors, six brief submaximal contractions, and a 50% MVC held to fatigue. Isometric force and surface electromyographic signals were recorded continuously. The degree of maximal voluntary activation was assessed with the twitch-interpolation technique. Single-unit recordings were made with tungsten microelectrodes during the submaximal contractions. Voluntary activation at MVC increased by 3.50 +/- 1.01 (SE) % (P < 0. 01), but there was no change in H-reflex amplitude, suggesting that caffeine increases maximal voluntary activation at a supraspinal level. Neither the force-EMG relationship nor motor unit firing rates were altered by caffeine. Subjects were able to hold a 50% MVC for an average of 66.1 s in the absence of caffeine. Time to fatigue (T(lim)) increased by 25.80 +/- 16.06% after caffeine administration (P < 0.05). There was no significant change in T(lim) from pretest to posttest in the control or placebo trials. The increase in T(lim) was associated with an attenuated decline in twitch amplitude, which would suggest that the mechanism is, at least in part, peripheral.
Article
Caffeine has known ergogenic effects, some of which have been observed during submaximal isometric contractions. We used 15 subjects in a randomized, double-blind, repeated-measures experiment to determine caffeine's ergogenic effects on neuromuscular variables that would contribute to increased endurance capacity. Subjects performed repeated submaximal (50% maximal voluntary contraction) isometric contractions of the right quadriceps to the limit of endurance (T(lim)) 1 h after oral caffeine administration (6 mg/kg). Time to reach T(lim) increased by 17 +/- 5.25% (P < 0.02) after caffeine administration compared with the placebo trial. The changes in contractile properties, motor unit activation, and M-wave amplitude that occurred as the quadriceps reached T(lim) could not account for the prolonged performance after caffeine ingestion. In a separate experiment with the same subjects, we used a constant-sensation technique to determine whether caffeine influenced force sensation during 100 s of an isometric contraction of the quadriceps. The results of this experiment showed that caffeine reduced force sensation during the first 10-20 s of the contraction. The rapidity of this effect suggests that caffeine exerts its effects neurally. Based on these data, the caffeine-induced increase in T(lim) may have been caused by a willingness to maintain near-maximal activation longer because of alterations in muscle sensory processes.
Article
Acute caffeine ingestion has been found to increase blood pressure and sympathetic activity in nonhabitual coffee drinkers; however, the effects. of caffeine on parasympathetic nervous system activity have seldom been explored. After acute ingestion of caffeine in 10 normal subjects, we found blood pressures to be significantly increased, and measures of parasympathetic nervous system activity significantly decreased compared with measures after placebo ingestion.
Article
This double-blind, within-subjects experiment examined the effects of ingesting two doses of caffeine on perceptions of leg muscle pain and blood pressure during moderate intensity cycling exercise. Low caffeine consuming college-aged males (N=12) ingested one of two doses of caffeine (5 or 10 mg.kg(-1) body weight) or placebo and 1 h later completed 30 min of moderate intensity cycling exercise (60% VO2peak). The order of drug administration was counter-balanced. Resting blood pressure and heart rate were recorded immediately before and 1 h after drug administration. Perceptions of leg muscle pain as well as work rate, blood pressure, heart rate, and oxygen uptake (VO2) were recorded during exercise. Caffeine increased resting systolic pressure in a dose-dependent fashion but these blood pressure effects were not maintained during exercise. Caffeine had a significant linear effect on leg muscle pain ratings [F(2,22)=14.06; P < 0.0001; eta2=0.56 ]. The mean (+/-SD) pain intensity scores during exercise after ingesting 10 mg.kg(-1) body weight caffeine, 5 mg.kg(-1) body weight caffeine, and placebo were 2.1+/-1.4, 2.6+/-1.5, and 3.5+/-1.7, respectively. The results support the conclusion that caffeine ingestion has a dose-response effect on reducing leg muscle pain during exercise and that these effects do not depend on caffeine-induced increases in systolic blood pressure during exercise.
Article
The purpose of this study was to use the meta-analytic approach to examine the effects of caffeine ingestion on ratings of perceived exertion (RPE). Twenty-one studies with 109 effect sizes (ESs) met the inclusion criteria. Coding incorporated RPE scores obtained both during constant load exercise (n=89) and upon termination of exhausting exercise (n=20). In addition, when reported, the exercise performance ES was also computed (n=16). In comparison to placebo, caffeine reduced RPE during exercise by 5.6% (95% CI (confidence interval), -4.5% to -6.7%), with an equivalent RPE ES of -0.47 (95% CI, -0.35 to -0.59). These values were significantly greater (P<0.05) than RPE obtained at the end of exercise (RPE % change, 0.01%; 95% CI, -1.9 to 2.0%; RPE ES, 0.00, 95% CI, -0.17 to 0.17). In addition, caffeine improved exercise performance by 11.2% (95% CI; 4.6-17.8%). Regression analysis revealed that RPE obtained during exercise could account for approximately 29% of the variance in the improvement in exercise performance. The results demonstrate that caffeine reduces RPE during exercise and this may partly explain the subsequent ergogenic effects of caffeine on performance.
Article
Caffeine increases time to fatigue [limit of endurance (T(lim))] during submaximal isometric contractions without altering whole muscle activation or neuromuscular junction transmission. We used 10 male volunteers in a randomized, double-blind, repeated-measures experiment to examine single motor unit firing rates during intermittent submaximal contractions and to determine whether administering caffeine increased T(lim) by maintaining higher firing rates. On 2 separate days, subjects performed intermittent 50% maximal voluntary contractions of the quadriceps to T(lim), 1 h after ingesting a caffeine (6 mg/kg) or placebo capsule. Average motor unit firing rates recorded with tungsten microelectrodes were constant for the duration of contractions. Caffeine increased average T(lim) by 20.5 +/- 8.1% (P < 0.05) compared with placebo conditions. This increase was due to seven subjects, termed responders, who increased T(lim) significantly. Two other subjects showed no response, and a third had a shorter T(lim). Neither the increased T(lim) nor the responders' performance could be explained by alterations in firing rates or other neuromuscular variables. However, the amplitude of the evoked twitch and its maximal instantaneous rate of relaxation did not decline to the same degree in the caffeine trial of the responders; this resulted in values 20 and 30% higher at the time point matching the end of the placebo trial (P < 0.05). The amplitude of the evoked twitch and the maximal instantaneous rate of relaxation were linearly correlated (caffeine r = 0.72, placebo r = 0.80, both P < 0.001), suggesting that the increase in T(lim) may be partially explained by caffeine's effects on calcium reuptake and twitch force.
Article
The aim of the present study was to further confirm the validity of measurements for characterizing neuromuscular alterations by establishing their reliability both before and after fatigue. Thirteen men (28 +/- 5 years) volunteered to participate in two separate identical sessions requiring the performance of a sustained maximal voluntary contraction (MVC) with the quadriceps muscle for 2 min. MVC and transcutaneous electrical stimulations were used before and immediately after the fatiguing contraction to investigate the reliability of MVC torque, central activation, and peripheral variables (M-wave properties, peak twitch, peak doublet) within and between sessions. Based on previous and present results, we advise the use of (1) voluntary activation level with potentiated doublet as a reference to describe central fatigue, (2) electromyographic activity of vastus lateralis muscle as a surrogate for quadriceps for both voluntary and evoked contraction, and (3) potentiated peak doublet amplitude to investigate contractile fatigue. These findings can be useful in the choice of the parameters describing central and peripheral fatigue of the quadriceps muscle in future studies.
Article
Both time-to-exhaustion (TTE) and time-trial (TT) exercise tests are commonly used to assess exercise performance, but no study has directly examined the reliability of comparable tests in the same subjects. To evaluate the reliability of comparable TTE and TT treadmill running tests of high and moderately high exercise intensity in endurance-trained male distance runners, and to validate Hinckson and Hopkins TT prediction methods using log-log modeling from TTE results. After familiarization tests, eight endurance-trained male distance runners performed, in a randomized, counterbalanced order, eight trials consisting of two 5-km TT and two 1500-m TT, and four TTE tests run at a speed equivalent to the average speed attained during both the 5-km and 1500-m TT distances. Typical error of the estimate (TEE) expressed as a coefficient of variation for the 5-km TT, 5-km TTE, 1500-m TT, and 1500-m TTE were 2.0, 15.1, 3.3, and 13.2%, respectively. The standard error of the estimate for predicted TT running speed using log-log modeling from TTE results was 0.67%, and the predicted versus criterion reliability of this method revealed TEE values of 1.6% and 2.5% for the prediction of 5-km and 1500-m TT, respectively. The variability of 5-km and 1500-m TT tests was significantly less than for similar TTE treadmill protocols. Despite the greater variability of the TTE tests, log-log modeling using the TTE test results reliably predicted actual TT performance.
Article
The present study investigated the effect of maximal strength training on running economy (RE) at 70% of maximal oxygen consumption (V[spacing dot above]O2max) and time to exhaustion at maximal aerobic speed (MAS). Responses in one repetition maximum (1RM) and rate of force development (RFD) in half-squats, maximal oxygen consumption, RE, and time to exhaustion at MAS were examined. Seventeen well-trained (nine male and eight female) runners were randomly assigned into either an intervention or a control group. The intervention group (four males and four females) performed half-squats, four sets of four repetitions maximum, three times per week for 8 wk, as a supplement to their normal endurance training. The control group continued their normal endurance training during the same period. The intervention manifested significant improvements in 1RM (33.2%), RFD (26.0%), RE (5.0%), and time to exhaustion at MAS (21.3%). No changes were found in V[spacing dot above]O2max or body weight. The control group exhibited no changes from pre to post values in any of the parameters. Maximal strength training for 8 wk improved RE and increased time to exhaustion at MAS among well-trained, long-distance runners, without change in maximal oxygen uptake or body weight.
Effect of different protocols of caffeine intake on metabolism and endurance performance
  • G R Cox
  • B Desbrow
  • Montgomery
  • Pg
  • Anderson
  • Me
  • Bruce
  • Cr
  • T A Macrides
Cox, GR, Desbrow, B, Montgomery, PG, Anderson, ME, Bruce, CR, Macrides, TA, et al. Effect of different protocols of caffeine intake on metabolism and endurance performance. J Appl Physiol 93: 990-999, 2002.
Physiological responses at critical running speed during continuous and intermittent exhaustion tests
  • R Penteado
  • Salvador
  • Af
  • Corvino
  • Rb
  • R Cruz
  • Lisbô A Fd
  • F Caputo
Penteado, R, Salvador, AF, Corvino, RB, Cruz, R, Lisbô a, FD, Caputo, F, et al. Physiological responses at critical running speed during continuous and intermittent exhaustion tests. Sci Sport Sport 29: e99-e105, 2014.