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The Physiological and Performance Effects of Caffeine Gum Consumed During A Simulated Half-Time By Professional Academy Rugby Union Players
Abstract
Despite the prevalence of caffeine as an ergogenic aid, few studies have examined the use of caffeinated gums, especially during half-time in team sports. The physiological (blood lactate, salivary hormone concentrations) and performance (repeated sprints, cognitive function) effects of consuming caffeine gum during a simulated half-time were examined. Professional academy rugby union players (n=14) completed this double-blind, randomized, counterbalanced study. Following pre-exercise measurements , players chewed a placebo (PL) gum for five min before a standardized warm-up and completing repeated sprint testing (RSSA1). Thereafter, during a 15 min simulated half-time period, players chewed either caffeine (CAF: 400 mg; 4.1 ± 0.5 mg·kg) or PL gum for five min before completing a second repeated sprint test (RSSA2). Blood lactate, salivary testosterone and cortisol concentrations, and indices of cognitive function (i.e., reaction time and Stroop test) were measured at baseline, pre-RSSA1, post-RSSA1, pre-RSSA2 and post-RSSA2. Sprint performance was not affected by CAF (P=0.995) despite slower sprint times following the first sprint of both RSSA tests (all P<0.002). Following half-time, salivary testosterone increased by 70% (+97±58 pg·mL) in CAF versus PLA (P<0.001) whereas salivary cortisol remained unchanged (P=0.307). Cognitive performance was unaffected by time and trial (all P>0.05). Although performance effects were absent, chewing caffeine gum increased the salivary testosterone concentrations of professional rugby union players over a simulated half-time. Practitioners may therefore choose to recommend caffeine gum between successive exercise bouts due to the increases in salivary testosterone observed; a variable associated with increased motivation and high-intensity exercise performance.
... The result reported a low risk of biasness in 12 included RCTs [2,31,[33][34][35][36][37][38][39][40][41][42], while the remaining RCTs had some concerns [3,4,30,32,[43][44][45][46][47][48][49][50][51][52][53][54][55][56]. The biasness arises due to the lack of allocation concealment in the experimental procedure of RCTs. ...
... It was found that CMJ height increased irrespective of the dosage and measurement time. Reaction time was assessed in three studies [40][41][42] out of which two studies reported improvement in reaction time at 5 mg/kg and 6 mg/kg body mass of caffeine after 5 minutes and 60 minutes, respectively. The squat jump was assessed in three studies [2,35,36] at a dosage of 3 mg/kg body mass of caffeine after 60 minutes and all studies reported significant improvement. ...
... The reason for improved reaction time is due to the ability of caffeine to act as an adenosine receptor antagonist, which lowers the threshold for faster motor unit activation thus decreasing reaction time [52]. Another hypothesis that supports improved reaction time after caffeine ingestion is the adaptation in the fiber composition of the dominant muscle [40]. Another important point that needs to be addressed is the caffeine-induced calcium release from the sarcoplasmic reticulum thus altering neuromuscular transmission and possibly improving reaction time [53]. ...
Objectives
To examine the efficacy of caffeine on athletic performance, also to establish the most effective dose and form of caffeine intake that is needed to bring about a positive effect in performance.
News
Studies were searched in various electronic databases, including Web of Science, PubMed, Pedro, and CINAHL. Studies were excluded if: 1) it was conducted before January 2010; 2) caffeine was given along with other substance/exercise; 3) only abstract was available; 4) it included non-healthy athlete; 5) the population was not involved in any kind of sports; 6) Pedro score < 7. Thirty articles were included in this review after the removal of duplicates and applying exclusion criteria. A random-effect model was used in this meta-analysis to analyze the effect of caffeine on athletic performance using the standardized mean difference with a 95% confidence interval. Our meta-analysis showed that there is a significant effect, immediately (SMD: 0.82; 95% confidence interval: 0.27, 1.37; P = 0.003) and after 60 minutes (SMD: 0.26; 95% confidence interval: 0.05, 0.47; P = 0.02) of caffeine intake on jump height favouring the placebo group. There was a significant effect on reaction time (SMD: −0.40; 95% confidence interval: −0.76, −0.04; P = 0.03) and agility (SMD: −0.36; 95% confidence interval: −0.66, −0.07; P = 0.02) after 60 minutes of caffeine intake favouring the experimental group.
Prospects and projects
To back up the results presented in this study, more research into the effects of caffeine supplementation on non-athlete performance is required.
Conclusion
Caffeine supplementation is efficient in improving the reaction time and agility of an athlete. Agility and reaction time is seen to improve when an athlete is supplemented with caffeine at a dosage of 3 mg/kg of body mass and 6 mg/kg of body mass, respectively. Also, improvement in agility and reaction time favoring caffeine-supplemented group occurs after 60 minutes of caffeine ingestion.
... PBC, USA) was used to extract data from these figures. Authors of articles whose data could not be extracted directly from the manuscript via text or figures were contacted for data (Russell et al., 2020). When relative dose or mean relative dose by body mass (BM) was not included, it was obtained through dividing absolute dose by participants mean BM. ...
... All comparisons of Caff-gum were made in relation to a placebo-control session, which was reportedly colour, texture-and taste-matched to the Caff-gum intervention. However, only six of the fourteen studies reported blinding assessment (Paton et al., 2015;Paton et al., 2010;Ranchordas et al., 2018Ranchordas et al., , 2019Russell et al., 2020;Veiner et al., 2019). Only one study (Veiner et al. (2019)) confirmed that blinding of Caff-gum was effective, while others showed varying levels of blinding success (Ranchordas et al., 2018(Ranchordas et al., , 2019. ...
... Only one study (Veiner et al. (2019)) confirmed that blinding of Caff-gum was effective, while others showed varying levels of blinding success (Ranchordas et al., 2018(Ranchordas et al., , 2019. Furthermore, some studies (Paton et al., 2010(Paton et al., , 2015Russell et al., 2020) declared that participants were unable to distinguish between conditions, but without showing data to support their affirmations. This is important since expectation of caffeine intake may influence subsequent performance (Saunders, de Oliveira, et al., 2017) and measurement of caffeine expectancy may be an important factor to consider in future research (Heinz et al., 2009;Mendes et al., 2020). ...
Highlights:
This study determined the effect of Caff-gum on exercise performance, using a systematic review and meta-analysis. Fourteen studies, totalling 200 participants performing a variety of endurance and strength/power exercise tests were included. The relative Caff-gum dose ranged from 1.27-4.26 mg/kg BM and timing ranged from 120 min prior to exercise up to intra-test application.Caff-gum was shown to be an effective ergogenic aid for trained individuals involved in both endurance and strength/power exercise.Supplement dose and timing modified the efficacy of Caff-gum. Supplementation with Caff-gum was effective when provided in doses ≥3 mg/kg BM and within 15 min prior to initiating exercise.Trained endurance or strength/power athletes seeking to benefit from caffeine in the form of chewing gum should supplement within 15 min prior to initiating an exercise task, in doses ≥3 mg/kg BM.
... Furthermore, soldiers' vigilance improved when in a sleep-restricted state [43]. However, in rugby players, repeated sprint performance and cognitive ability were unaffected after chewing caffeine gum [44]. Similarly, during simulated flight procedures, pilots' cognitive and psychomotor performance was improved in those who were not well rested, compared with those who were [4], nuancing the interpretation of current research. ...
... Seven effect sizes from six studies showed that caffeine had no effect on accuracy (−0.16 [−0.41, 0.08]) [44,[54][55][56][57][58]. ...
... Six effect sizes from five studies showed that caffeine had no effect on reaction time (0.08 [−0.15, 0.31]) [44,[54][55][56][57][58]63]. ...
Background: Research in sport, military, and aerospace populations has shown that mental fatigue may impair cognitive performance. The effect of nutritional interventions that may mitigate such negative effects has been investigated. This systematic review and meta-analysis aimed to quantify the effects of nutritional interventions on cognitive domains often measured in mental fatigue research. Methods: A systematic search for articles was conducted using key terms relevant to mental fatigue in sport, military, and aerospace populations. Two reviewers screened 11,495 abstracts and 125 full texts. A meta-analysis was conducted whereby effect sizes were calculated using subgroups for nutritional intervention and cognitive domains. Results: Fourteen studies were included in the meta-analysis. The consumption of energy drinks was found to have a small positive effect on reaction time, whilst the use of beta-alanine, carbohydrate, and caffeine had no effect. Carbohydrate and caffeine use had no effect on accuracy. Conclusions: The results of this meta-analysis suggest that consuming energy drinks may improve reaction time. The lack of effect observed for other nutritional interventions is likely due to differences in the type, timing, dosage, and form of administration. More rigorous randomized controlled trials related to the effect of nutrition interventions before, during, and after induced mental fatigue are required.
... Age ↑ Cortisol, ↓ amylase in elliptical and cycle ergo meter in young males [2] ↓ cortisol, amylase in treadmill sessions in young males [2] ↑ salivary cortisol post resistance in middle-aged man [20] in superset strength training protocol Gender ↑ amylase activity post exercise in females in cycling [1] ↑ 1.5× amylase activity in males at rest, but similar cortisol levels in high intensity interval training [21] ↑ amylase and cortisol in females in the Ecomotion/ProAdventure Race World [22] -basal amylase levels higher in females in 5000 m race [23] Caffeine ↑ post-triathlon cortisol levels-microencalsulated caffeine [24] ↓ testosterone:cortisol ratio in resistance exercise [25] -caffeine gum-no changes in salivary cortisol after simulated half time by professional academy rugby union [26] ↓ salivary cortisol in repeated, high-intensity sprint exercise in competitive cyclists [26] ↑ adrenaline and cortisol levels after recovery leading to increased levels of IL-6 and IL-10 after treadmill exercise [27] -acute coffee consumption activates salivary amylase, but not salivary cortisol [28] -consumption of green tea after a taekwondo training session ↑ salivary amylase activity [29] -caffeine consumed as a cereal bar during exhaustive cycling ↑ endurance and salivary cortisol, but did not affect the salivary amylase increase post-exercise [30] ↑ salivary cortisol after caffeine administration in acute sleep deprived athletes and altered performance [31,32] -performance improved in endurance athletes [24,33] -significant performance improvement in competitive intermittent-sprint [34,35], tennis performance [36], women's rugby seven competition [37]. ...
... Age ↑ Cortisol, ↓ amylase in elliptical and cycle ergo meter in young males [2] ↓ cortisol, amylase in treadmill sessions in young males [2] ↑ salivary cortisol post resistance in middle-aged man [20] in superset strength training protocol Gender ↑ amylase activity post exercise in females in cycling [1] ↑ 1.5× amylase activity in males at rest, but similar cortisol levels in high intensity interval training [21] ↑ amylase and cortisol in females in the Ecomotion/ProAdventure Race World [22] -basal amylase levels higher in females in 5000 m race [23] Caffeine ↑ post-triathlon cortisol levels-microencalsulated caffeine [24] ↓ testosterone:cortisol ratio in resistance exercise [25] -caffeine gum-no changes in salivary cortisol after simulated half time by professional academy rugby union [26] ↓ salivary cortisol in repeated, high-intensity sprint exercise in competitive cyclists [26] ↑ adrenaline and cortisol levels after recovery leading to increased levels of IL-6 and IL-10 after treadmill exercise [27] -acute coffee consumption activates salivary amylase, but not salivary cortisol [28] -consumption of green tea after a taekwondo training session ↑ salivary amylase activity [29] -caffeine consumed as a cereal bar during exhaustive cycling ↑ endurance and salivary cortisol, but did not affect the salivary amylase increase post-exercise [30] ↑ salivary cortisol after caffeine administration in acute sleep deprived athletes and altered performance [31,32] -performance improved in endurance athletes [24,33] -significant performance improvement in competitive intermittent-sprint [34,35], tennis performance [36], women's rugby seven competition [37]. ...
... -enhanced endurance exercise performance in women [38] -hypoalgesic effect by diminishing pain [39] ↓ fatigue during repeated, high-intensity sprint exercise in competitive cyclists [26] -better exercise performance and adaptation [41] ↑ muscle carnosine proportionally with the time of use [42,43] -no significant improvements in fatigue rates during high-intensity anaerobic exercise in highly trained athletes [44] -improved biochemical parameters in regards to muscle fatigue [45] ↑ exercise capacity [46] -elimination of executive function decline post-recovery [12] -improved performance, marksmanship and target engagement speed, as well as muscle endurance [47], nut no impact on cognitive performance [48] Carbohydrates -attenuate higher plasma cortisol levels and greater immune disturbances [49][50][51] -salivary cortisol has been observed to be similar in the self-selected diet group and carbohydrate group, but increased post-exercise in the self-selected diet group [52] ↓ salivary cortisol levels as a result of increased dietary carbohydrate as part of a Dietary Guideline for Americans-based diet [53] -a high-carbohydrate diet-higher salivary cortisol response in men [54] Sodium bicarbonate -sodium bicarbonate in combination with caffeine led to a longer total distance of rowing compared to sodium bicarbonate alone or a possible additional benefit in 2000-m rowing performance when administered together with beta-alanine [55] -a small, but significant performance effect [56] ...
Athletes are exposed to a tremendous amount of stress, both physically and mentally, when performing high intensity sports with frequent practices, pushing numerous athletes into choose to use ergogenic aids such as caffeine or β-alanine to significantly improve their performance and ease the stress and pressure that is put onto the body. The beneficial or even detrimental effects of these so-called ergogenic aids can be appreciated through the use of numerous diagnostic tools that can analyze various body fluids. In the recent years, saliva samples are gaining more ground in the field of diagnostic as it is a non-invasive procedure, contains a tremendous amount of analytes that are subject to pathophysiological changes caused by diseases, exercises, fatigue as well as nutrition and hydration. Thus, we describe here the current progress regarding potential novel biomarkers for stress and physical activity, salivary α-amylase and salivary cortisol, as well as their use and measurement in combination with different already-known or new ergogenic aids.
... Scores awarded to the 13 reviewed studies are provided in Table 4. According to these scores, the methodological quality of one study (8%) was classified as excellent [38], of nine studies (69%) as very good [33,37,39,[46][47][48][49][50][51], and of three studies (23%) as good [52][53][54]. ...
... In the studies conducted by Cesareo et al. [50] and Hogervorst et al. [37], caffeine was ingested 1.5 h before the start of exercise. Furthermore, in four studies, besides administrating caffeine before the start of exercise, the supplement was also taken during exercise [37,38,49,52]. Hogervorst et al. [37] used a protocol that included the ingestion of caffeine 1 h before the test and every 20 min during the protocol. ...
... Mumford et al. [48] administered caffeine 120 min after starting a game of golf. Finally, Russell et al. [52] employed caffeine 15 min during exercise through the use of caffeinated gums. In summary, the different studies examined the effect of acute caffeine supplementation taken from 5-60 min prior to testing on cognitive performance during sports activity. ...
Cognitive functions are essential in any form of exercise. Recently, interest has mounted in addressing the relationship between caffeine intake and cognitive performance during sports practice. This review examines this relationship through a structured search of the databases Med-line/PubMed and Web of Science for relevant articles published in English from August 1999 to March 2020. The study followed PRISMA guidelines. Inclusion criteria were defined according to the PICOS model. The identified records reported on randomized cross-over studies in which caffeine intake (as drinks, capsules, energy bars, or gum) was compared to an identical placebo situation. There were no filters on participants' training level, gender, or age. For the systematic review, 13 studies examining the impacts of caffeine on objective measures of cognitive performance or self-reported cognitive performance were selected. Five of these studies were also subjected to meta-analysis. After pooling data in the meta-analysis, the significant impacts of caffeine only emerged on attention, accuracy, and speed. The results of the 13 studies, nevertheless, suggest that the intake of a low/moderate dose of caffeine before and/or during exercise can improve self-reported energy, mood, and cognitive functions, such as attention; it may also improve simple reaction time, choice reaction time, memory, or fatigue, however, this may depend on the research protocols.
... Despite the potential practical benefits of caffeine gum, few studies have investigated its effect on team sports. In a study of professional academy rugby players, 400 mg of caffeine delivered in gum failed to rescue the decrement in performance across two sprint tests (6 × 40 m) separated by a 15 min simulated half time period [24]. This lack of effect may have been because the rugby players had a mean habitual intake of caffeine of 191 ± 138 mg·d − 1 [25,26]. ...
... At the time of data collection there was only one study that had reported on the effect of caffeine gum on performance of a repeated sprint protocol. Russell et al. [24] investigated the effect of caffeine gum (400 mg of caffeine) in professional academy rugby players undertaking 2 x repeated sprint protocols (6 × 40 m) separated by a 15 min passive recovery period (to simulate half-time). Caffeine gum failed to attenuate the decrement in performance from the first set of sprints to the second. ...
... Caffeine gum failed to attenuate the decrement in performance from the first set of sprints to the second. Direct comparison with the present results is difficult because Russell et al. [24] did not report a fatigue index and their protocol was designed to investigate the ability of caffeine to rescue the decrement in performance that accompanies passive recovery between bouts of high intensity exercise. After the current study was completed, Evans et al. [26] reported that 200 mg of caffeine delivered in gum did not significantly improve performance of team sport players (soccer, rugby and hockey) completing a 10 × 40 m sprint test. ...
Background
Caffeine has been shown to enhance strength, power and endurance, characteristics that underpin performance in rugby. Caffeinated gum has attracted interest as a novel vehicle for delivering caffeine, because absorption of caffeine from gum is quick. Rapid absorption of caffeine may be useful during rugby matches when there is limited time for supplementation such as at half-time or when substitutes enter play. The purpose of this study was to determine whether a low dose of caffeine in gum improves performance in a battery of rugby-specific tests.
Methods
In a double-blind, randomized, placebo-controlled, crossover design, 17 male university-standard rugby players (mass: 85.6 ± 6.3 kg; height: 179.4 ± 6.2 cm; age: 20.4 ± 1.2 years) chewed caffeinated gum (200 mg caffeine) or a placebo gum on two occasions separated by a week. After a standardized warm-up, gum was chewed for 5 min. Subsequently, participants performed three countermovement jumps, followed by an Illinois agility test, 6 × 30 m repeated sprints, and the Yo-Yo IR-2 test; each test was separated by short rest periods.
Results
Caffeinated gum enhanced countermovement jump by 3.6% (caffeine: 43.7 ± 7.6 cm vs. placebo: 42.2 ± 6.2 cm; d = 0.22, 95% CI [0.006, 0.432]; p = 0.044). There was a greater resistance to fatigue during the 6 × 30 m repeated sprint test (fatigue index caffeine: 102.2 ± 0.9% vs. placebo: 103.3 ± 1.2%; d = 1.03, 95% CI [0.430, 1.613]; p = 0.001), and performance on the Yo-Yo IR2 was improved by 14.5% (caffeine: 426 ± 105 m, placebo: 372 ± 91 m; d = 0.55, 95% CI [0.130, 0.957]; p = 0.010). Caffeine gum had no significant effect on the Illinois agility test (caffeine 16.22 ± 1.08 s vs. placebo 15.88 ± 1.09 s; d = − 0.31, 95% CI [− 0.855, 0.240]; p = 0.271).
Conclusions
In university-standard rugby players, a low dose of caffeine (200 mg) supplied in chewing gum enhanced performance on the Yo-Yo IR-2 test and the countermovement jump test and reduced fatigue index during repeated sprints. These improvements in a battery of rugby-specific tests may transfer to enhanced performance in rugby matches.
... Thus, it is possible that not all of the assumed amount of caffeine is delivered. Indeed, several previous studies [21,63,64] also failed to show a significant improvement in physical performance after the intervention of caffeine via chewing gum. Future studies using caffeinated chewing gum have to include caffeine concentration analysis, especially when doses higher than 200 mg of caffeine are used [19]. ...
No previous study analyzed the effect of caffeinated chewing gum on volleyball-specific skills and physical performance in volleyball players. Twelve volleyball players participated ina randomized, crossover, and double-blind experiment after ingestion of (a) ~3.2 ± 0.4 mg/kg of body mass (BM) of caffeine via chewing gum or (b) non-caffeinated chewing gum (placebo) and performed: (a) a countermovement jump, (b) a squat jump, (c), an attack jump, (d) a block jump, (e) 5 and 10 m sprints, (f) a modified agility t-test, (g) an attack and service speed test, and (h) a spike and serve accuracy test. Compared to the placebo, the caffeine chewing gum supplementation significantly improved the accuracy of the attack (15 ± 4 vs. 18 ± 3 points, p = 0.02). However, the ingestion of caffeinated chewing gum had no effect on the remaining other performance tests (p from 0.12 to 1.00). A caffeine-containing chewing gum with a dose of ~3 mg/kg BM effectively improved the attack’s accuracy in volleyball players. However, this effect was not observed in better results in jumping, running, and other skill-based volleyball tests.
... During the agility and cognitive performance applied after the Wingate test protocol, while CAF significantly improved agility and cognitive performance (ICR (ms) and ICR (error rate) tasks) compared to PLA, there was no significant difference in balance performance. In addition to studies arguing that CAF affects cognitive performance [78][79][80], some studies suggest that CAF has no effect [81,82]. This study supported the potential ergogenic effect of caffeine. ...
In previous studies, the effect of single or combined intake of caffeine (CAF) and taurine (TAU) on exercise performance was investigated. However, the potential synergistic effect on physical and cognitive performance after fatigue induced by anaerobic exercise is unknown. The effects of single and combination CAF and TAU supplementation on the Wingate test in elite male boxers and to evaluate balance, agility and cognitive performance after fatigue are being investigated for the first time in this study. Twenty elite male boxers 22.14 ± 1.42 years old were divided into four groups in this double-blind, randomized crossover study: CAF (6 mg/kg of caffeine), TAU (3 g single dose of taurine), CAF*TAU (co-ingestion of 3 g single dose of taurine and 6 mg/kg of caffeine) and PLA (300 mg maltodextrin). The findings are as follows: co-ingestion of CAF*TAU, improved peak (W/kg), average (W), minimum (W) power, time to reach (s), and RPE performances compared to the PLA group significantly (p < 0.05). Similarly, it was determined that a single dose of TAU, created a significant difference (p < 0.05) in peak power (W/kg), and average and minimum power (W) values compared to the CAF group. According to the balance and agility tests performed after the Wingate test, co-ingestion of CAF*TAU revealed a significant difference (p < 0.05) compared to the PLA group. In terms of cognitive performance, co-ingestion of CAF*TAU significantly improved the neutral reaction time (ms) compared to the TAU, CAF and PLA groups. As a result, elite male boxers performed better in terms of agility, balance and cognitive function when they consumed a combination of 6 mg/kg CAF and 3 g TAU. It has been determined that the combined use of these supplements is more effective than their single use.
... It thus seems possible that part of the caffeine remains in the gum after 5 min of chewing. Interestingly, several previous investigations have found that the use of caffeinated chewing gum may not be totally effective to increase physical performance in several sport situations (Filip-Stachnik, Krawczyk, et al., 2021;Russell et al., 2020;Ryan et al., 2013). Further investigations comparing various sources of caffeine in different doses are needed to confirm this statement. ...
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.
... 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]. ...
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.
... 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. ...
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
... Different studies have found that ingestion of low-to-moderate doses of caffeine (3-6 mg·kg −1 ·bm) may have the potential to enhance performance in individual [5] and team sports [6]. In addition, previous studies investigating the ergogenic effect of acute caffeine ingestion in team sport disciplines have observed benefits of this supplementation strategy on neuromuscular performance and match-play demands [7][8][9][10]. With this background, caffeine can be considered as an ergogenic substance to increase several aspects of physical performance but a few investigations have suggested that the magnitude of the ergogenic response to acute caffeine intake may vary among individuals [11][12][13]. ...
Previous investigations have found that several genes may be associated with the interindividual variability to the ergogenic response to caffeine. The aim of this study is to analyze the influence of the genetic variations in CYP1A2 (−163C > A, rs762551; characterized such as "fast" (AA genotype) and "slow" caffeine metabolizers (C-carriers)) and ADORA2A (1976T > C; rs5751876; characterized by "high" (TT genotype) or "low" sensitivity to caffeine (C-carriers)) on the ergogenic response to acute caffeine intake in professional handball players. Thirty-one professional handball players (sixteen men and fifteen women; daily caffeine intake = 60 ± 25 mg·d −1) ingested 3 mg·kg −1 ·body mass (bm) of caffeine or placebo 60 min before undergoing a battery of performance tests consisting of a countermovement jump (CMJ), a sprint test, an agility test, an isometric handgrip test, and several ball throws. Afterwards, the handball players performed a simulated handball match (2 × 20 min) while movements were recorded using inertial units. Saliva samples were analyzed to determine the genotype of each player for the −163C > A polymorphism in the CYP1A2 gene (rs762551) and for the 1976T > C polymorphism in the ADORA2A gene (rs5751876). In the CYP1A2, C-allele carriers (54.8%) were compared to AA homozygotes (45.2%). In the ADORA2A, C-allele carriers (80.6%) were compared to TT homozygotes (19.4%). There was only a genotype x treatment interaction for the ball throwing from 7 m (p = 0.037) indicating that the ergogenic effect of caffeine on this test was higher in CYP1A2 AA homozygotes than in C-allele carriers. In the remaining variables, there were no genotype x treatment interactions for CYP1A2 or for ADORA2A. As a whole group, caffeine increased CMJ height, performance in the sprint velocity test, and ball throwing velocity from 9 m (2.8-4.3%, p = 0.001-0.022, effect size = 0.17-0.31). Thus, pre-exercise caffeine supplementation at a dose of 3 mg·kg −1 ·bm can be considered as an ergogenic strategy to enhance some neuromuscular aspects of handball performance in professional handball players with low daily caffeine consumption. However, the ergogenic response to acute caffeine intake was not modulated by CYP1A2 or ADORA2A genotypes.
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.
The aim of the present study was to explore whether caffeine (CAF) intake counteracts the morning reduction in cognitive and short-term maximal physical performances related to the daily variation pattern in young female handball players. In a randomized order, 15 active young female handball players [mean (SD) age:16.3 ± 0.8 y, height: 166.1 ± 5.3 cm; body mass: 58.7 ± 9.1 kg; BMI: 21.3 ± 3.1 kg/m²] performed the simple reaction time (SRT), the attention (AT), the squat jump (SJ), the Illinois agility (IAT) and the 5 m run shuttles (to determine total (TD) and peak (PD) distances) tests at 08:00 h and 18:00 h, 60 min after a placebo (cellulose) or CAF (6 mg·kg⁻¹) intake. The results revealed a significant diurnal variation during both the placebo and the CAF conditions, with improvement of cognitive and physical performances from 08:00 h to 18:00 h (P < .05). Moreover, the improvement of SRT and AT after CAF was better in the morning compared to the afternoon (e.g., 5.3% vs. 2.8% for SRT and 4.2% vs. 0.9% for AT). At 08:00 h and 18:00 h, SJ, IAT, TD, and PD were higher after CAF intake than Placebo (p < .05). This improvement was greater at 08:00 h than 18:00 h (e.g., 4.2% vs 1% for SJ, 1.6% vs 0.2% for IAT, 2.4% vs. 0.3% for TD, and 6% vs. 0.9% for PD). In conclusion, the dose of 6 mg·kg⁻¹ CAF intake improves the cognitive and physical performances in young female handball players and reduces the intraday variation of these parameters.
Abbreviations
CAF: Caffeine PLC: Placebo SRT: Simple Reaction Time AT: Attention Test SJ: Squat Jump IAT: Illinois Agility Test OT: Oral Temperature QUEST: Questionnaire RPE: Rating of Perceived Exertion PD: Peak Distance TD: Total Distance
To determine the acute effect of a single high-intensity interval training (HIIT) session on testosterone and cortisol levels in healthy individuals, a systematic search of studies was conducted in MEDLINE and Web of Science databases from inception to February 2020. Meta-analyses were performed to establish the acute effect of HIIT on testosterone and cortisol levels immediately after a single HIIT session, after 30 minutes, and 60 minutes (primary outcomes) and after 120 minutes, 180 minutes, and 24h (secondary outcomes, only for pre-post intervention groups). Potential effect-size modifiers were assessed by meta-regression analyses and analyses of variance. Study quality was assessed using the Cochrane's risk of bias tool and the Physiotherapy Evidence Database scale. The meta-analyses of 10 controlled studies (213 participants) and 50 pre-post intervention groups (677 participants) revealed a significant increase in testosterone immediately after a single HIIT session (d=0.92 and 0.52, respectively), which disappeared after 30 minutes (d=0.18 and -0.04), and returned to baseline values after 60 minutes (d=-0.37 and -0.16). Significant increases of cortisol were found immediately after (d=2.17 and 0.64), after 30 minutes (d=1.62 and 0.67), and 60 minutes (d=1.32 and 0.27). Testosterone and cortisol levels decreased significantly after 120 minutes (d=-0.48 and -0.95, respectively) and 180 minutes (d=-0.29 and -1.08) and return to baseline values after 24h (d=0.14 and -0.02). HIIT components and participant's characteristics seem to moderate the effect sizes. In conclusion, testosterone and cortisol increase immediately after a single HIIT session, then drop below baseline levels, and finally return to baseline values after 24h. This meta-analysis provides a better understanding of the acute endocrine response to a single HIIT session, which would certainly be valuable for both clinicians and coaches in the prescription of exercise programs to improve health and performance. Testosterone and cortisol may be used as sensitive biomarkers to monitor the anabolic and catabolic response to HIIT.
The objectives of this study were to estimate the impact of chewing time on caffeine release from gum and to understand caffeine pharmacokinetics. Caffeine release increased with chewing time (2 min < 5 min < 10 min). Furthermore, two plasma caffeine concentration peaks were observed suggesting that caffeine absorption occurs both through the oral mucosa and gastrointestinal tract. This is of practical relevance to maximise caffeine doses and to synchronise effort with peak caffeine concentration.
Reduced physical performance has been observed following the half-time period in team sports players, likely due to a decrease in muscle temperature during this period. We examined the effects of a passive heat maintenance strategy employed between successive exercise bouts on core temperature (Tcore) and subsequent exercise performance. Eighteen professional Rugby Union players completed this randomised and counter-balanced study. After a standardised warm-up (WU) and 15 min of rest, players completed a repeated sprint test (RSSA 1) and countermovement jumps (CMJ). Thereafter, in normal training attire (Control) or a survival jacket (Passive), players rested for a further 15 min (simulating a typical half-time) before performing a second RSSA (RSSA 2) and CMJ's. Measurements of Tcore were taken at baseline, post-WU, pre-RSSA 1, post-RSSA 1 and pre-RSSA 2. Peak power output (PPO) and repeated sprint ability was assessed before and after the simulated half-time. Similar Tcore responses were observed between conditions at baseline (Control: 37.06±0.05°C; Passive: 37.03±0.05°C) and for all other Tcore measurements taken before half-time. After the simulated half-time, the decline in Tcore was lower (-0.74±0.08% vs. -1.54±0.06%, p<0.001) and PPO was higher (5610±105 W vs. 5440±105 W, p<0.001) in the Passive versus Control condition. The decline in PPO over half-time was related to the decline in Tcore (r = 0.632, p = 0.005). In RSSA 2, best, mean and total sprint times were 1.39±0.17% (p<0.001), 0.55±0.06% (p<0.001) and 0.55±0.06% (p<0.001) faster for Passive versus Control. Passive heat maintenance reduced declines in Tcore that were observed during a simulated half-time period and improved subsequent PPO and repeated sprint ability in professional Rugby Union players.
A number of intermittent team sports require that two consecutive periods of play (lasting for ~30-45 min) are separated by a 10-20 min half-time break. The half-time practices employed by team-sports players generally include returning to the changing rooms, temporarily relaxing from the cognitive and physical demands of the first half, rehydration and re-fuelling strategies, addressing injury or equipment concerns, and receiving tactical instruction and coach feedback. However, the typically passive nature of these actions has been associated with physiological changes that impair performance during the second half. Both physical and cognitive performances have been found to decline in the initial stages of subsequent exercise that follows half-time. An increased risk of injury has also been observed during this period. Therefore, half-time provides sports scientists and strength and conditioning coaches with an opportunity to optimise second-half performance. An overview of strategies thought to benefit team-sports athletes is presented; specifically, the efficacy of heat maintenance strategies (including passive and active methods), post-activation potentiation, hormonal priming, and modified hydro-nutritional practices are discussed. A theoretical model of applying these strategies in a manner that compliments current practice is also offered.
Abstract The physical preparation of team sport athletes should reflect the degree to which each component of fitness is relied upon in competition. The aim of the study was therefore to establish the relationship between fitness-test data and game behaviours known or thought to be important for successful play in rugby union matches. Fitness-test measures from 510 players were analysed with game statistics, from 296 games within the 2007 and 2008 calendar years. Sprint times over 10, 20 and 30 m had moderate to small negative correlations (r) with line breaks (~0.26), metres advanced (~0.22), tackle breaks (~0.16) and tries scored (~0.15). The average time of 12 repeated sprints and percentage body fat in the forwards, and repeated sprint fatigue in the backs had moderate to small correlations with a measure of activity rate on and around the ball (-0.38, -0.17 and -0.17, respectively). These low correlations are partly due to uniformly high physical fitness as a result of selection pressures at the elite level and leave room for the identification of other key predictors. Nonetheless, physical conditioning programmes should be adapted to reflect the importance of speed, repeated sprint ability and body composition in the performance of key game behaviours during competition.
Purpose:
To assess the measures of salivary free testosterone and cortisol concentrations across selected rugby union matches according to game outcome.
Methods:
Twenty-two professional male rugby union players were studied across 6 games (3 wins and 3 losses). Hormone samples were taken 40 min before the game and 15 min after. The hormonal data were grouped and compared against competition outcomes. These competition outcomes included wins and losses and a game-ranked performance score (1-6).
Results:
Across the entire team, pregame testosterone concentrations were significantly higher during winning games than losses (P = 5.8 × 10-5). Analysis by playing position further revealed that, for the backs, pregame testosterone concentrations (P = 3.6 × 10-5) and the testosterone-to-cortisol ratio T:C (P = .038) were significantly greater before a win than a loss. Game-ranked performance score correlated to the team's pregame testosterone concentrations (r = .81, P = .049). In backs, pregame testosterone (r = .91, P = .011) and T:C (r = .81, P = .05) also correlated to game-ranked performance. Analysis of the forwards' hormone concentrations did not distinguish between game outcomes, nor did it correlate with game-ranked performance. Game venue (home vs away) only affected postgame concentrations of testosterone (P = .018) and cortisol (P = 2.58 × 10-4).
Conclusions:
Monitoring game-day concentrations of salivary free testosterone may help identify competitive readiness in rugby union matches. The link between pregame T:C and rugby players in the back position suggests that monitoring weekly training loads and enhancing recovery modalities between games may also assist with favorable performance and outcome in rugby union matches.
Abstract Recent research has challenged the typical pre-match and half-time (HT) interval warm-up (WU) routines currently used by professional soccer players. This study surveyed 2010/11 season WU strategies and their underpinning scientific reasoning and situational factors via an internet-based questionnaire, which was distributed to English Premier League and Championship practitioners, of which 43% responded. The pre-match WU duration was 30.8 (8.2) min, ranging between 15-45 min, and 89% of practitioners administered a WU of ≥ 25 min. Respondents also reported a 12.4 (3.8) min period between the end of the WU and match kick-off. Eighty-nine per cent recognised the physiological benefits of re-WUs during this "down-time" period, with 63% instructing players to engage in such activity. During HT, 58% instructed players to re-WU either on the pitch or within stadia facilities, but "unwillingness of the coach/manager" (42%) and a "lack of time" (63%) were major constraints. Practitioners reported that 2.6 (1.6) min might be available for HT re-WUs. Factors such as match regulations, league policy, and stadia facilities were not generally considered as major barriers to the delivery of WUand re-WU strategies. We suggest that researchers consider the time-demands and barriers faced by practitioners whendeveloping experimental designs to examine WU regimens.
The purpose of this study was to investigate the effectiveness of a caffeine-containing energy drink in enhancing rugby players' physical performance during a simulated match. A second purpose was to determine the urinary caffeine excretion derived from the energy drink intake. In a randomized and counterbalanced order, 26 elite rugby players (mean ± SD for age and body mass, 25 ± 2 y and 93 ± 15 kg) played 2 simulated rugby games (2 × 30 min) 60 min after ingesting (i) 3 mg of caffeine per kilogram of body mass in the form of an energy drink (Fure, ProEnergetics) or (ii) the same drink without caffeine (placebo). During the matches, the individual running distance and the instantaneous speed were measured, and the number of running actions above 20 km·h(-1) (i.e., sprints) were determined, using global positioning system devices. The number of impacts above 5 g during the matches was determined by accelerometry. The ingestion of the energy drink, compared with the placebo, increased the total distance covered during the match (4749 ± 589 vs 5139 ± 475 m, p < 0.05), the running distance covered at more than 20 km·h(-1) (184 ± 38 vs 208 ± 38 m, p < 0.05), and the number of sprints (10 ± 7 vs 12 ± 7, p < 0.05). The ingestion of the energy drink also resulted in a greater overall number of impacts (481 ± 352 vs 641 ± 366, p < 0.05) and a higher postexercise urine caffeine concentration (0.1 ± 0.1 vs 2.4 ± 0.9 μg·mL(-1), p < 0.05). The use of an energy drink with a caffeine dose equivalent to 3 mg·kg(-1) considerably enhanced the movement patterns of rugby players during a simulated match.
Purpose: The aim of this study was to examine the effects of caffeine supplementation on multiple sprint running performance.
Methods: Using a randomized double-blind research design, 21 physically active men ingested a gelatin capsule containing either caffeine (5 mg·kg-1 body mass) or placebo (maltodextrin) 1 h before completing an indoor multiple sprint running trial (12 × 30 m; repeated at 35-s intervals). Venous blood samples were drawn to evaluate plasma caffeine and primary metabolite concentrations. Sprint times were recorded via twin-beam photocells, and earlobe blood samples were drawn to evaluate pretest and posttest lactate concentrations. Heart rate was monitored continuously throughout the tests, with RPE recorded after every third sprint.
Results: Relative to placebo, caffeine supplementation resulted in a 0.06-s (1.4%) reduction in fastest sprint time (95% likely range = 0.04-0.09 s), which corresponded with a 1.2% increase in fatigue (95% likely range = 0.3-2.2%). Caffeine supplementation also resulted in a 3.4-bpm increase in mean heart rate (95% likely range = 0.1-6.6 bpm) and elevations in pretest (+0.7 mmol·L-1; 95% likely range = 0.1-1.3 mmol·L-1) and posttest (+1.8 mmol·L-1; 95% likely range = 0.3-3.2 mmol·L-1) blood lactate concentrations. In contrast, there was no significant effect of caffeine supplementation on RPE.
Conclusion: Although the effect of recovery duration on caffeine-induced responses to multiple sprint work requires further investigation, the results of the present study show that caffeine has ergogenic properties with the potential to benefit performance in both single and multiple sprint sports.
Objectives:
To re-examine the work-rate of soccer players immediately after a passive half-time interval with an alternative approach to data reduction and statistical contrasts.
Design:
Time-motion analysis data (5Hz global positioning system), were collected from 20 elite youth players (age: 17±1 years) during 21 competitive league fixtures (5±3 matches per player).
Methods:
Physical performances were categorised into total distance covered, total low-speed running (0-14.9kmh(-1)) and total high-speed running (15.0-35.0kmh(-1)). These dependent variables were subsequently time averaged into pre-determined periods of 5-, 15- and 45-min duration, and expressed in relative (mmin(-1)) terms to allow direct comparisons between match periods of different lengths. During the 15-min half-time interval players were passive (seated rest).
Results:
There was a large reduction in relative total distance covered (effect size - standardised mean difference - 1.85), low-speed running (effect size -1.74) and high-speed running (effect size -1.37) during the opening 5-min phase of the second half (46-50min) when compared to the first half mean (0-45min). When comparing the 51-55 and 56-60-min periods, effect sizes were trivial for relative total distance covered (effect size -0.13; -0.04), low-speed running (effect size -0.10; -0.11) and small/trivial for high-speed running (-0.39; 0.11).
Conclusions:
Using a more robust analytical approach, the findings of this study support and extend previous research demonstrating that players work-rate was markedly lower in the first 5-min after a passive half-time interval, although we observed this phenomenon to be transient in nature. Time-motion analysts might re-consider their data reduction methods and comparators to distinguish within-match player work-rate trends.
This investigation reports the effects of caffeinated chewing gum on fatigue and hormone response during repeated sprint performance with competitive cyclists. Nine male cyclists (mean ± SD, age 24 ± 7 years, VO(2max) 62.5 ± 5.4 mL kg(-1) min(-1)) completed four high-intensity experimental sessions, consisting of four sets of 30 s sprints (5 sprints each set). Caffeine (240 mg) or placebo was administered via chewing gum following the second set of each experimental session. Testosterone and cortisol concentrations were assayed in saliva samples collected at rest and after each set of sprints. Mean power output in the first 10 sprints relative to the last 10 sprints declined by 5.8 ± 4.0% in the placebo and 0.4 ± 7.7% in the caffeine trials, respectively. The reduced fatigue in the caffeine trials equated to a 5.4% (90% confidence limit ±3.6%, effect size 0.25; ±0.16) performance enhancement in favour of caffeine. Salivary testosterone increased rapidly from rest (~53%) and prior to treatments in all trials. Following caffeine treatment, testosterone increased by a further 12 ± 14% (ES 0.50; ± 0.56) relative to the placebo condition. In contrast, cortisol concentrations were not elevated until after the third exercise set; following the caffeine treatment cortisol was reduced by 21 ± 31% (ES -0.30; ± 0.34) relative to placebo. The acute ingestion of caffeine via chewing gum attenuated fatigue during repeated, high-intensity sprint exercise in competitive cyclists. Furthermore, the delayed fatigue was associated with substantially elevated testosterone concentrations and decreased cortisol in the caffeine trials.
The effect caffeine elicits on endurance performance is well founded. However, comparatively less research has been conducted on the ergogenic potential of anaerobic performance. Some studies showing no effect of caffeine on performance used untrained subjects and designs often not conducive to observing an ergogenic effect. Recent studies incorporating trained subjects and paradigms specific to intermittent sports activity support the notion that caffeine is ergogenic to an extent with anaerobic exercise. Caffeine seems highly ergogenic for speed endurance exercise ranging in duration from 60 to 180 seconds. However, other traditional models examining power output (i.e. 30-second Wingate test) have shown minimal effect of caffeine on performance. Conversely, studies employing sport-specific methodologies (i.e. hockey, rugby, soccer) with shorter duration (i.e. 4-6 seconds) show caffeine to be ergogenic during high-intensity intermittent exercise. Recent studies show caffeine affects isometric maximal force and offers introductory evidence for enhanced muscle endurance for lower body musculature. However, isokinetic peak torque, one-repetition maximum and muscular endurance for upper body musculature are less clear. Since relatively few studies exist with resistance training, a definite conclusion cannot be reached on the extent caffeine affects performance. It was previously thought that caffeine mechanisms were associated with adrenaline (epinephrine)-induced enhanced free-fatty acid oxidation and consequent glycogen sparing, which is the leading hypothesis for the ergogenic effect. It would seem unlikely that the proposed theory would result in improved anaerobic performance, since exercise is dominated by oxygen-independent metabolic pathways. Other mechanisms for caffeine have been suggested, such as enhanced calcium mobilization and phosphodiesterase inhibition. However, a normal physiological dose of caffeine in vivo does not indicate this mechanism plays a large role. Additionally, enhanced Na+/K+ pump activity has been proposed to potentially enhance excitation contraction coupling with caffeine. A more favourable hypothesis seems to be that caffeine stimulates the CNS. Caffeine acts antagonistically on adenosine receptors, thereby inhibiting the negative effects adenosine induces on neurotransmission, arousal and pain perception. The hypoalgesic effects of caffeine have resulted in dampened pain perception and blunted perceived exertion during exercise. This could potentially have favourable effects on negating decreased firing rates of motor units and possibly produce a more sustainable and forceful muscle contraction. The exact mechanisms behind caffeine's action remain to be elucidated.
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.
Increased professionalism in rugby has elicited rapid changes in the fitness profile of elite players. Recent research, focusing on the physiological and anthropometrical characteristics of rugby players, and the demands of competition are reviewed. The paucity of research on contemporary elite rugby players is highlighted, along with the need for standardised testing protocols.
Recent data reinforce the pronounced differences in the anthropometric and physical characteristics of the forwards and backs. Forwards are typically heavier, taller, and have a greater proportion of body fat than backs. These characteristics are changing, with forwards developing greater total mass and higher muscularity. The forwards demonstrate superior absolute aerobic and anaerobic power, and muscular strength. Results favour the backs when body mass is taken into account. The scaling of results to body mass can be problematic and future investigations should present results using power function ratios. Recommended tests for elite players include body mass and skinfolds, vertical jump, speed, and the multi-stage shuttle run. Repeat sprint testing is a possible avenue for more specific evaluation of players.
During competition, high-intensity efforts are often followed by periods of incomplete recovery. The total work over the duration of a game is lower in the backs compared with the forwards; forwards spend greater time in physical contact with the opposition while the backs spend more time in free running, allowing them to cover greater distances. The intense efforts undertaken by rugby players place considerable stress on anaerobic energy sources, while the aerobic system provides energy during repeated efforts and for recovery.
Training should focus on repeated brief high-intensity efforts with short rest intervals to condition players to the demands of the game. Training for the forwards should emphasise the higher work rates of the game, while extended rest periods can be provided to the backs. Players should not only be prepared for the demands of competition, but also the stress of travel and extreme environmental conditions.
The greater professionalism of rugby union has increased scientific research in the sport; however, there is scope for significant refinement of investigations on the physiological demands of the game, and sports-specific testing procedures.
We previously reported the existence of a descending multisynaptic, pituitary-independent, neural pathway between the hypothalamus and the testes in the male rat. Stimulation of this pathway by the intracerebroventricular (icv) injection of IL-1beta or corticotropin-releasing factor blunts the testosterone (T) response to human chorionic gonadotropin (hCG). This response is mediated at least in part by catecholamine beta-adrenergic receptor activation. The present work was performed to further investigate the role of brain catecholamines and testicular blood flow in this pathway. The icv injection of 5 microl of 200 proof ethanol (EtOH; 86 micromol) did not result in detectable levels of the drug in the general circulation and did not induce neuronal damage, but rapidly blunted hCG-induced T release while not decreasing LH levels or altering testicular blood flow. EtOH significantly up-regulated transcripts of the immediate-early gene c-fos in the paraventricular nucleus (PVN) of the hypothalamus. Lesions of the PVN blocked the inhibitory effect of IL-1beta on T, but only partially interfered with the influence of EtOH. PVN catecholamine turnover significantly increased after icv injection of IL-1beta, but not EtOH. Brain catecholamine depletion due to the neurotoxin 6-hydroxydopamine did not alter the ability of hCG to induce T release, but significantly reversed the inhibitory effect of icv EtOH or IL-1beta on this response. Collectively, these results indicate that icv-injected IL-1beta or EtOH blunts hCG-induced T secretion through a catecholamine-mediated mechanism that does not depend on either peripherally mediated effects or pituitary LH, and that the PVN plays a role in these effects.
Resistance exercise has been shown to elicit a significant acute hormonal response. It appears that this acute response is more critical to tissue growth and remodelling than chronic changes in resting hormonal concentrations, as many studies have not shown a significant change during resistance training despite increases in muscle strength and hypertrophy. Anabolic hormones such as testosterone and the superfamily of growth hormones (GH) have been shown to be elevated during 15-30 minutes of post-resistance exercise providing an adequate stimulus is present. Protocols high in volume, moderate to high in intensity, using short rest intervals and stressing a large muscle mass, tend to produce the greatest acute hormonal elevations (e.g. testosterone, GH and the catabolic hormone cortisol) compared with low-volume, high-intensity protocols using long rest intervals. Other anabolic hormones such as insulin and insulin-like growth factor-1 (IGF-1) are critical to skeletal muscle growth. Insulin is regulated by blood glucose and amino acid levels. However, circulating IGF-1 elevations have been reported following resistance exercise presumably in response to GH-stimulated hepatic secretion. Recent evidence indicates that muscle isoforms of IGF-1 may play a substantial role in tissue remodelling via up-regulation by mechanical signalling (i.e. increased gene expression resulting from stretch and tension to the muscle cytoskeleton leading to greater protein synthesis rates). Acute elevations in catecholamines are critical to optimal force production and energy liberation during resistance exercise. More recent research has shown the importance of acute hormonal elevations and mechanical stimuli for subsequent up- and down-regulation of cytoplasmic steroid receptors needed to mediate the hormonal effects. Other factors such as nutrition, overtraining, detraining and circadian patterns of hormone secretion are critical to examining the hormonal responses and adaptations to resistance training.
The premise that cognitive functioning can be influenced through dietary means has gained widespread interest. The assessment of cognitive functioning is a key method to scientifically substantiate such nutritional effects on cognition. The current paper provides a basic overview of the main concepts, issues and pitfalls of human cognitive research. General methods of cognitive assessment, selection of appropriate tests, factors that may mediate task performance and issues pertaining to the interpretation of the results are discussed.
The aim of this study was to quantify the movement patterns of various playing positions during professional rugby union match-play, such that the relative importance of aerobic and anaerobic energy pathways to performance could be estimated. Video analysis was conducted of individual players (n=29) from the Otago Highlanders during six "Super 12" representative fixtures. Each movement was coded as one of six speeds of locomotion (standing still, walking, jogging, cruising, sprinting, and utility), three states of non-running intensive exertion (rucking/mauling, tackling, and scrummaging), and three discrete activities (kicking, jumping, passing). The results indicated significant demands on all energy systems in all playing positions, yet implied a greater reliance on anaerobic glycolytic metabolism in forwards, due primarily to their regular involvement in non-running intense activities such as rucking, mauling, scrummaging, and tackling. Positional group comparisons indicated that while the greatest differences existed between forwards and backs, each positional group had its own unique demands. Front row forwards were mostly involved in activities involving gaining/retaining possession, back row forwards tended to play more of a pseudo back-line role, performing less rucking/mauling than front row forwards, yet being more involved in aspects of broken play such as sprinting and tackling. While outside backs tended to specialize in the running aspects of play, inside backs tended to show greater involvement in confrontational aspects of play such as rucking/mauling and tackling. These results suggest that rugby training and fitness testing should be tailored specifically to positional groups rather than simply differentiating between forwards and backs.
Three studies involving 108 football players were conducted to examine the reliability of a repeated-shuttle-sprint ability (RSSA) test and its ability to differentiate between players of various competitive levels and playing positions. Study 1: Short-term reliability was determined in 22 professional players completing the RSSA test (6 x 40-m sprints with 20 s of recovery between sprints) on two separate occasions. Study 2: Long-term reliability (seasonal changes) was examined in 31 professional players completing the RSSA test four times (during the preseason period, at the start, middle and end of the competitive season). Study 3: 108 players were divided and compared according to competitive level or playing position. Standard error of measurement values expressed as coefficient of variation for RSSA mean time and best time were 0.8 and 1.3 % (short-term reliability) and 0.9 and 1.2 % (long-term reliability), respectively. The smallest worthwhile changes were 0.5 % for both mean and best time. Professional players showed better RSSA performance than amateur players, and defenders displayed the lowest RSSA performance. In conclusion, the RSSA test showed adequate construct validity but only RSSA mean time showed sufficient reliability to detect large training-induced changes but not small important differences.
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.
The objective of this study was to determine if salivary free testosterone can predict an athlete's performance during back squats and sprints over time and the influence baseline strength on this relationship. Ten weight-trained male athletes were divided into 2 groups based on their 1 repetition maximum (1RM) squats, good squatters (1RM > 2.0 × body weight, n = 5) and average squatters (1RM < 1.9 × body weight, n = 5). The good squatters were stronger than the average squatters (p < 0.05). Each subject was assessed for squat 1RM and 10-m sprint times on 10 separate occasions over a 40-day period. A saliva sample was collected before testing and assayed for free testosterone and cortisol. The pooled testosterone correlations were strong and significant in the good squatters (r = 0.92 for squats, r = -0.87 for sprints, p < 0.01), but not significant for the average squatters (r = 0.35 for squats, r = -0.18 for sprints). Cortisol showed no significant correlations with 1RM squat and 10-m sprint performance, and no differences were identified between the 2 squatting groups. In summary, these results suggest that free testosterone is a strong individual predictor of squat and sprinting performance in individuals with relatively high strength levels but a poor predictor in less strong individuals. This information can assist coaches, trainers, and performance scientists working with stronger weight-trained athletes, for example, the preworkout measurement of free testosterone could indicate likely training outcomes or a readiness to train at a certain intensity level, especially if real-time measurements are made. Our results also highlight the need to separate group and individual hormonal data during the repeated testing of athletes with variable strength levels.
Previous studies have shown that visual images can produce rapid changes in testosterone concentrations. We explored the acute effects of video clips on salivary testosterone and cortisol concentrations and subsequent voluntary squat performance in highly trained male athletes (n=12). Saliva samples were collected on 6 occasions immediately before and 15 min after watching a brief video clip (approximately 4 min in duration) on a computer screen. The watching of a sad, erotic, aggressive, training motivational, humorous or a neutral control clip was randomised. Subjects then performed a squat workout aimed at producing a 3 repetition maximum (3RM) lift. Significant (P<0.001) relative (%) increases in testosterone concentrations were noted with watching the erotic, humorous, aggressive and training videos (versus control and sad), with testosterone decreasing significantly (versus control) after the sad clip. The aggressive video also produced an elevated cortisol response (% change) and more so than the control and humorous videos (P<0.001). A significant (P<0.003) improvement in 3RM performance was noted after the erotic, aggressive and training clips (versus control). A strong within-individual correlation (mean r=0.85) was also noted between the relative changes in testosterone and the 3RM squats across all video sessions (P<0.001). In conclusion, different video clips were associated with different changes in salivary free hormone concentrations and the relative changes in testosterone closely mapped 3RM squat performance in a group of highly trained males. Thus, speculatively, using short video presentations in the pre-workout environment offers an opportunity for understanding the outcomes of hormonal change, athlete behaviour and subsequent voluntary performance.
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.
Previous studies of episodic hormone secretion of the hypothalamic-pituitary-gonadal axis in normal men have produced conflicting results due to examinations of small cohorts of subjects or to limited sampling techniques. We evaluated gonadotropin and testosterone (T) secretory patterns in 20 normal men by sampling blood at 10-min intervals for luteinizing hormone (LH) and follicle-stimulating hormone (FSH). T concentrations were also analyzed at 20-min intervals in 10 subjects. A previously unappreciated spectrum of gonadotropin and T secretory patterns was observed in normal men. Both mean LH concentrations and mean LH pulse amplitudes varied fourfold between individuals. LH interpulse intervals varied from 30 to 480 min (mean 119 +/- 32). Results also suggested a relative refractory period at the level of the hypothalamus or pituitary. In three subjects, a striking nighttime accentuation of LH pulsations was noted. Through use of Fourier analysis, a diurnal variation in LH was observed in the population (P less than 0.02). Mean FSH levels showed marked variation between individual subjects, with discrete pulses rarely observed. No diurnal variation in FSH secretion was noted. Serum T concentrations determined at 6-h intervals ranged from 105 to 1,316 ng/dl between subjects. When T was measured at 20-min intervals, marked intermittent declines in the T concentrations to levels well below the normal range were observed in 3 of 10 subjects. T secretion was found to lag behind LH secretion by approximately 40 min (P less than 0.02).
The effect of caffeine ingestion on sprint performance is unclear. We have therefore investigated its effect on performance in a test that simulates the repeated sprints of team sports.
In a randomized double-blind crossover experiment, 16 male team-sport athletes ingested either caffeine (6 mg.kg-1 of body mass) or a placebo 60 min before performing a repeated 20-m sprint test. The test consisted of 10 sprints, each performed within 10 s and followed by rest for the remainder of each 10 s. The caffeine and placebo trials followed a familiarization trial, and the time between consecutive trials was 2-3 d. To allow estimation of variation in treatment effects between individuals, nine subjects performed three more trials without a supplement 7-14 d later. We estimated the smallest worthwhile effect on sprint time in a team sport to be approximately 0.8%.
Mean time to complete 10 sprints increased by 0.1% (95% likely range -1.5 to 1.7%) with caffeine ingestion relative to placebo. Individual variation in this effect was a standard deviation of 0.7% (-2.7 to 2.9%). Time to complete the 10th sprint was 14.4% longer than the first; caffeine increased this time by 0.7% (-1.8 to 3.2%) relative to placebo, and individual variation in this effect was 2.4% (-3.4 to 4.9%).
The observed effect of caffeine ingestion on mean sprint performance and fatigue over 10 sprints was negligible. The true effect on mean performance could be small at most, although the true effects on fatigue and on the performance of individuals could be somewhat larger. Pending confirmatory research, team-sport athletes should not expect caffeine to enhance sprint performance.
Caffeine enhances performance of single bouts of endurance exercise, but its effects on repeated bouts typical of those in high-intensity team sports are unclear.
To investigate effects of caffeine in a performance test simulating physical and skill demands of a rugby union game.
The study was a double-blind, randomized, crossover design in which nine competitive male rugby players ingested either caffeine (6 mg.kg(-1) body mass) or placebo (dextrose) 70 min before performing a rugby test. Each test consisted of seven circuits in each of two 40-min halves with a 10-min half-time rest. Each circuit included stations for measurement of sprint time (two straight-line and three agility sprints), power generation in two consecutive drives, and accuracy for passing balls rapidly. Interstitial fluid was sampled transdermally by electrosonophoresis before ingestion of caffeine or placebo and then before testing, at half-time, and immediately after testing; samples were assayed chromatographically for caffeine and epinephrine concentrations.
The effects of caffeine on mean performance (+/-90% confidence limits) over all 14 circuits were: sprint speeds, 0.5% (+/-1.7%) through 2.9% (+/-1.3%); first-drive power, 5.0% (+/-2.5%); second-drive power, -1.2% (+/-6.8%); and passing accuracy, 9.6% (+/-6.1%). The enhancements were mediated partly through a reduction of fatigue that developed throughout the test and partly by enhanced performance for some measures from the first circuit. Caffeine produced a 51% (+/-11%) increase in mean epinephrine concentration; correlations between individual changes in epinephrine concentration and changes in performance were mostly unclear, but there were some strong positive correlations with sprint speeds and a strong negative correlation with passing accuracy.
Caffeine is likely to produce substantial enhancement of several aspects of high-intensity team-sport performance.
Caffeine is a very common CNS stimulant that has been of interest to physiologists because of its direct effects on skeletal muscle in vitro, as well as ergogenic effects on laboratory tests of human performance. While in vitro studies have clearly demonstrated the effects of the drug on the CNS, the effects of caffeine on the voluntary activation of muscle in humans are less defined. Voluntary as well as involuntary supraspinal input, alpha motor neuron membrane properties, and afferent feedback to spinal and supraspinal neurons all modulate voluntary muscle activation, and caffeine may therefore alter muscle activation at several sites along the motor pathway. This review explores the effects of caffeine on voluntary muscle activation that have been demonstrated in recent human studies and discusses the central mechanisms that may enhance activation. Evidence of caffeine's effects on the motor evoked potential, Hoffman reflex, self-sustained firing of the alpha motor neuron, and pain and force sensation are presented as well as limitations and considerations of using the drug in human neuromuscular studies.
Caffeine is the most widely consumed psychoactive 'drug' in the world and probably one of the most commonly used stimulants in sports. This is not surprising, since it is one of the few ergogenic aids with documented efficiency and minimal side effects. Caffeine is rapidly and completely absorbed by the gastrointestinal tract and is readily distributed throughout all tissues of the body. Peak plasma concentrations after normal consumption are usually around 50 microM, and half-lives for elimination range between 2.5-10 h. The parent compound is extensively metabolized in the liver microsomes to more than 25 derivatives, while considerably less than 5% of the ingested dose is excreted unchanged in the urine. There is, however, considerable inter-individual variability in the handling of caffeine by the body, due to both environmental and genetic factors. Evidence from in vitro studies provides a wealth of different cellular actions that could potentially contribute to the observed effects of caffeine in humans in vivo. These include potentiation of muscle contractility via induction of sarcoplasmic reticulum calcium release, inhibition of phosphodiesterase isoenzymes and concomitant cyclic monophosphate accumulation, inhibition of glycogen phosphorylase enzymes in liver and muscle, non-selective adenosine receptor antagonism, stimulation of the cellular membrane sodium/potassium pump, impairment of phosphoinositide metabolism, as well as other, less thoroughly characterized actions. Not all, however, seem to account for the observed effects in vivo, although a variable degree of contribution cannot be readily discounted on the basis of experimental data. The most physiologically relevant mechanism of action is probably the blockade of adenosine receptors, but evidence suggests that, at least under certain conditions, other biochemical mechanisms may also be operational.
This study investigated the effects of caffeine on repeated, anaerobic exercise using a double-blind, randomized, crossover design. Seventeen subjects (five female) underwent cognitive (reaction time, number recall) and blood (glucose, potassium, catecholamines, lactate) testing before and after consuming caffeine (6 mg/kg), placebo, or nothing (control). An exercise test (two 60 s maximal cycling bouts) was conducted 90 min after caffeine/placebo consumption. Plasma caffeine concentrations significantly increased after caffeine ingestion, however, there were no positive effects on cognitive or blood parameters except a significant decrease in plasma potassium concentrations at rest. Potentially negative effects of caffeine included significantly higher blood lactate compared to control and significantly slower time to peak power in exercise bout 2 compared to control and placebo. Caffeine had no significant effect on peak power, work output, RPE, or peak heart rate. In conclusion, caffeine had no ergogenic effect on repeated, maximal cycling bouts and may be detrimental to anaerobic performance.
Interest in the use of caffeine as an ergogenic aid has increased since the International Olympic Committee lifted the partial ban on its use. Caffeine has beneficial effects on various aspects of athletic performance, but its effects on training have been neglected.
To investigate the acute effect of caffeine on the exercise-associated increases in testosterone and cortisol in a double-blind crossover study.
Twenty-four professional rugby-league players ingested caffeine doses of 0, 200, 400, and 800 mg in random order 1 hr before a resistance-exercise session. Saliva was sampled at the time of caffeine ingestion, at 15-min intervals throughout each session, and 15 and 30 min after the session. Data were log-transformed to estimate percent effects with mixed modeling, and effects were standardized to assess magnitudes.
Testosterone concentration showed a small increase of 15% (90% confidence limits, +/- 19%) during exercise. Caffeine raised this concentration in a dose-dependent manner by a further small 21% (+/- 24%) at the highest dose. The 800-mg dose also produced a moderate 52% (+/- 44%) increase in cortisol. The effect of caffeine on the testosterone:cortisol ratio was a small decline (14%; +/- 21%).
Caffeine has some potential to benefit training outcomes via the anabolic effects of the increase in testosterone concentration, but this benefit might be counteracted by the opposing catabolic effects of the increase in cortisol and resultant decline in the testosterone:cortisol ratio.