Enhancing physical performance in elite junior tennis players with a caffeinated energy drink

Caffeine intake and its association with nutrition, sleep, and physical activity among schoolchildren in the United Arab Emirates: a national cross-sectional study

PURPOSE

Recent surveys indicate a significant increase in total caffeine intake among schoolchildren. Limited research has been published concerning the total intake of caffeine among schoolchildren in the Middle East and Gulf Cooperation Council (GCC) countries, including the UAE.

METHODS

This cross-sectional survey estimated the total caffeine intake from foods and beverages among 10,275 schoolchildren in the UAE. Caffeine intakes were related to the European Food Safety Authority's level of no safety concern (3.0 mg/kg BW) and level of effects on sleep (1.4 mg/kg BW).

RESULTS

More than half (56.2%) of the students consumed more than 100 mg (the upper limit allowed) of caffeine from dietary sources. High intake of caffeine (> 100 mg/day) was significantly associated (p = 0.001) with reduced sleep duration, difficulty falling asleep, infrequent exercising, using smart devices for more than 2 h a day, getting a lower GPA, skipping breakfast, eating fewer servings of vegetables than recommended, frequent consumption of fast food and more frequent snack consumption.

CONCLUSION

Excessive intake of caffeine from different dietary sources coexists with unhealthy dietary and lifestyle behaviors and sleep problems. Tailoring educational programs and intervention strategies is warranted to correct the unhealthy intake of caffeine and the associated unhealthy dietary and lifestyle behaviors among schoolchildren in the UAE.

Early absorption sources of caffeine can be a useful strategy for improving female table tennis players-specific performance

BACKGROUND

The consumption of fast absorption sources containing caffeine, such as caffeinated gum and coffee mouth rinsing, has been considered a practical nutritional strategy among athletes. Therefore, this study aimed to determine the effect of early absorption sources containing caffeine on the performance of female table tennis players.

METHOD

Eighteen female table tennis players randomly participated in this randomized, double-blind, and crossover designed study. Before starting the test, the participants attended a familiarization session. In each test session, participants were randomly assigned to one of three conditions including chewing caffeinated gum (CG, n = 6), coffee mouth rinsing (CMR, n = 6) and placebo capsule (PLA, n = 6). All participants consumed caffeine with an average dose of ∼3 to 4.5 mg·kg-1. The one-week interval was considered a washout period for each condition. Each test session included measurement of functional, skill and cognitive tests. Skill tests included serve, forehand drive, backhand push and counter tests. The Cognitive function measured by color recognition test, and functional tests included agility, hand movement speed, the explosive power of the upper body and lower body, hand-eye coordination and hand grip strength tests. The collected data were analyzed (with SPSS Windows software) by repeated measure ANOVA analysis and Bonferroni post hoc test at P ≤ 0.05 level.

RESULTS

The findings of the present study illustrated that CG and CMR increased significantly agility and reduced the amounts of errors in the cognitive test compared to PLA (p < 0.05), While there was no significant difference between CG and CMR (p > 0.05). Also, CG and CMR compared to PLA and CMR compared to CG rose significantly hand movement speed and movement speed (p < 0.05), and CMR compared to PLA increased significantly hand-eye coordination, isometric hand strength, service accuracy and forehand drive (p < 0.05). However, CG compared to PLA and CMR had no significant effect on hand-eye coordination, isometric hand strength, service accuracy and forehand drive (p > 0.05). In addition, CG and CMR enhanced significantly the explosive power of the lower body compared to PLA (p < 0.05), While there was no significant difference between CG and CMR (p > 0.05). Also, CG and CMR compared to PLA and CG compared to CMR had no significant effect on the explosive power of the upper body, backhand, and counter skills (p > 0.05). Furthermore, CG increased significantly accuracy in the service test compared to PLA (p < 0.05).

CONCLUSION

According to the results, it seems that early absorption sources of caffeine (CMR and CG) are efficient strategies for improving the specific performance of female table tennis players. However, allegedly CMR and CG have a better effect on functional and cognitive tests compared to skill tests.

International society of sports nutrition position stand: energy drinks and energy shots

Position Statement: The International Society of Sports Nutrition (ISSN) bases the following position stand on a critical analysis of the literature regarding the effects of energy drink (ED) or energy shot (ES) consumption on acute exercise performance, metabolism, and cognition, along with synergistic exercise-related performance outcomes and training adaptations. The following 13 points constitute the consensus of the Society and have been approved by the Research Committee of the Society: Energy drinks (ED) commonly contain caffeine, taurine, ginseng, guarana, carnitine, choline, B vitamins (vitamins B1, B2, B3, B5, B6, B9, and B12), vitamin C, vitamin A (beta carotene), vitamin D, electrolytes (sodium, potassium, magnesium, and calcium), sugars (nutritive and non-nutritive sweeteners), tyrosine, and L-theanine, with prevalence for each ingredient ranging from 1.3 to 100%. Energy drinks can enhance acute aerobic exercise performance, largely influenced by the amount of caffeine (> 200 mg or >3 mg∙kg bodyweight [BW-1]) in the beverage. Although ED and ES contain several nutrients that are purported to affect mental and/or physical performance, the primary ergogenic nutrients in most ED and ES based on scientific evidence appear to be caffeine and/or the carbohydrate provision. The ergogenic value of caffeine on mental and physical performance has been well-established, but the potential additive benefits of other nutrients contained in ED and ES remains to be determined. Consuming ED and ES 10-60 minutes before exercise can improve mental focus, alertness, anaerobic performance, and/or endurance performance with doses >3 mg∙kg BW-1. Consuming ED and ES containing at least 3 mg∙kg BW-1 caffeine is most likely to benefit maximal lower-body power production. Consuming ED and ES can improve endurance, repeat sprint performance, and sport-specific tasks in the context of team sports. Many ED and ES contain numerous ingredients that either have not been studied or evaluated in combination with other nutrients contained in the ED or ES. For this reason, these products need to be studied to demonstrate efficacy of single- and multi-nutrient formulations for physical and cognitive performance as well as for safety. Limited evidence is available to suggest that consumption of low-calorie ED and ES during training and/or weight loss trials may provide ergogenic benefit and/or promote additional weight control, potentially through enhanced training capacity. However, ingestion of higher calorie ED may promote weight gain if the energy intake from consumption of ED is not carefully considered as part of the total daily energy intake. Individuals should consider the impact of regular coingestion of high glycemic index carbohydrates from ED and ES on metabolic health, blood glucose, and insulin levels. Adolescents (aged 12 through 18) should exercise caution and seek parental guidance when considering the consumption of ED and ES, particularly in excessive amounts (e.g. > 400 mg), as limited evidence is available regarding the safety of these products among this population. Additionally, ED and ES are not recommended for children (aged 2-12), those who are pregnant, trying to become pregnant, or breastfeeding and those who are sensitive to caffeine. Diabetics and individuals with preexisting cardiovascular, metabolic, hepatorenal, and/or neurologic disease who are taking medications that may be affected by high glycemic load foods, caffeine, and/or other stimulants should exercise caution and consult with their physician prior to consuming ED. The decision to consume ED or ES should be based upon the beverage's content of carbohydrate, caffeine, and other nutrients and a thorough understanding of the potential side effects. Indiscriminate use of ED or ES, especially if multiple servings per day are consumed or when consumed with other caffeinated beverages and/or foods, may lead to adverse effects. The purpose of this review is to provide an update to the position stand of the International Society of Sports Nutrition (ISSN) integrating current literature on ED and ES in exercise, sport, and medicine. The effects of consuming these beverages on acute exercise performance, metabolism, markers of clinical health, and cognition are addressed, as well as more chronic effects when evaluating ED/ES use with exercise-related training adaptions.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Effects of acute caffeine intake on combat sports performance: A systematic review and meta-analysis

The interest in the benefits of caffeine in combat sports has grown exponentially in the last few years, evidenced by the significant rise of post-competition urine caffeine concentration. We conduct a systematic review and meta-analysis on the effects of caffeine on different performance variables in combat sports athletes. In total, we included 25 studies. All studies included had blinded, and cross-over experimental designs, and we conducted a risk of bias analysis. For nonspecific outcomes, there was an ergogenic effect of caffeine on vertical jump height (SMD: 0.38; 95% CI: 0.04, 0.71) and reaction time (SMD: -0.98, 95% CI: -1.46,-0.50). For outcomes specific to combat sports, there was an increase in the number of throws with caffeine in the Special Judo Fitness Test (SMD: 0.62; 95% CI: 0.14, 1.09). Caffeine ingestion increased the number of offensive actions during combats (SMD: 0.40; 95% CI: 0.06, 0.74). Caffeine ingestion increased the duration of offensive actions during combat (SMD: 0.58; 95% CI: 0.21, 0.96). Finally, caffeine ingestion increased blood lactate concentration after bout 1 (SMD: 1.35) bout 2 (SMD: 1.43) and bout 3 (SMD: 1.98). Overall, athletes competing in combat sports may consider supplementing with caffeine for an acute increase in exercise performance.

Consumption and effects of caffeinated energy drinks in young people: an overview of systematic reviews and secondary analysis of UK data to inform policy

BACKGROUND

This overview and analysis of UK datasets was commissioned by the UK government to address concerns about children's consumption of caffeinated energy drinks and their effects on health and behaviour.

METHODS

We searched nine databases for systematic reviews, published between 2013 and July 2021, in English, assessing caffeinated energy drink consumption by people under 18 years old (children). Two reviewers rated or checked risk of bias using AMSTAR2, and extracted and synthesised findings. We searched the UK Data Service for country-representative datasets, reporting children's energy-drink consumption, and conducted bivariate or latent class analyses.

RESULTS

For the overview, we included 15 systematic reviews; six reported drinking prevalence and 14 reported associations between drinking and health or behaviour. AMSTAR2 ratings were low or critically low. Worldwide, across reviews, from 13% to 67% of children had consumed energy drinks in the past year. Only two of the 74 studies in the reviews were UK-based. For the dataset analysis, we identified and included five UK cross-sectional datasets, and found that 3% to 32% of children, across UK countries, consumed energy drinks weekly, with no difference by ethnicity. Frequent drinking (5 or more days per week) was associated with low psychological, physical, educational and overall well-being. Evidence from reviews and datasets suggested that boys drank more than girls, and drinking was associated with more headaches, sleep problems, alcohol use, smoking, irritability, and school exclusion. GRADE (Grading of Recommendations, Assessment, Development and Evaluation) assessment suggests that the evidence is weak.

CONCLUSIONS

Weak evidence suggests that up to a third of children in the UK consume caffeinated energy drinks weekly; and drinking 5 or more days per week is associated with some health and behaviour problems. Most of the evidence is from surveys, making it impossible to distinguish cause from effect. Randomised controlled trials are unlikely to be ethical; longitudinal studies could provide stronger evidence.

PROSPERO REGISTRATIONS

CRD42018096292 - no deviations. CRD42018110498 - one deviation - a latent class analysis was conducted.

Acute effects of dynamic versus foam rolling warm-up strategies on physical performance in elite tennis players

To date, there is a lack of information about the optimal conditions of the warm-up to lead to a better performance in elite tennis players. The aim of this study was to compare the effects of two different warm-up protocols (dynamic vs. self-myofascial release with foam rolling) on neuromuscular variables associated with physical determinants of tennis performance. Using a crossover randomised experimental design, eleven professional men tennis players (20.6 ± 3.5 years) performed either a dynamic warm-up (DWU) or a self-myofascial release with foam rolling (SMFR) protocol. DWU consisted of 8 min of dynamic exercises at increasing intensity and SMFR consisted of 8 min of rolling on each lower extremity unilaterally. Just before (baseline) and after completing warm-up protocols, players performed a countermovement jump (CMJ), the 5-0-5 agility test, a 10-m sprint test and the Straight Leg Raise and Thomas tests to assess range of motion. Compared to baseline, the DWU was more effective to reduce the time in the 5-0-5 test than SMFR (-2.23 vs. 0.44%, respectively, p = 0.042, ηp² = 0.19). However, both warm-up protocols similarly affected CMJ (2.32 vs. 0.61%, p = 0.373, ηp² = 0.04) and 10-m sprint time changes (-1.26 vs. 1.03%, p = 0.124, ηp² = 0.11). Changes in range of motion tests were also similar with both protocols (p = 0.448–1.000, ηp² = 0.00–0.02). Overall, both DWU and SMFR were effective to prepare well-trained tennis players for highly demanding neuromuscular actions. However, DWU offered a better preparation for performing change of direction and sprint actions, and hence, in high-performance tennis players, the warm-up should include dynamic exercises.

Caffeinated Drinks and Physical Performance in Sport: A Systematic Review

Caffeine (1,3,7-trimethylxanthine) is one of the most common substances used by athletes to enhance their performance during competition. Evidence suggests that the performance-enhancing properties of caffeine can be obtained by employing several forms of administration, namely, capsules/tablets, caffeinated drinks (energy drinks and sports drinks), beverages (coffee), and chewing gum. However, caffeinated drinks have become the main form of caffeine administration in sport due to the wide presence of these products in the market. The objective of this systematic review is to evaluate the different effects of caffeinated drinks on physical performance in various sports categories such as endurance, power-based sports, team sports, and skill-based sports. A systematic review of published studies was performed on scientific databases for studies published from 2000 to 2020. All studies included had blinded and cross-over experimental designs, in which the ingestion of a caffeinated drink was compared to a placebo/control trial. The total number of studies included in this review was 37. The analysis of the included studies revealed that both sports drinks with caffeine and energy drinks were effective in increasing several aspects of sports performance when the amount of drink provides at least 3 mg of caffeine per kg of body mass. Due to their composition, caffeinated sports drinks seem to be more beneficial to consume during long-duration exercise, when the drinks are used for both rehydration and caffeine supplementation. Energy drinks may be more appropriate for providing caffeine before exercise. Lastly, the magnitude of the ergogenic benefits obtained with caffeinated drinks seems similar in women and men athletes. Overall, the current systematic review provides evidence of the efficacy of caffeinated drinks as a valid form for caffeine supplementation in sport.

Effects of Energy Drink Consumption on Physical Performance and Potential Danger of Inordinate Usage

The rise in energy drink (ED) intake in the general population and athletes has been achieved with smart and effective marketing strategies. There is a robust base of evidence showing that adolescents are the main consumers of EDs. The prevalence of ED usage in this group ranges from 52% to 68%, whilst in adults is estimated at 32%. The compositions of EDs vary widely. Caffeine content can range from 75 to 240 mg, whereas the average taurine quantity is 342.28 mg/100 mL. Unfortunately, exact amounts of the other ED elements are often not disclosed by manufacturers. Caffeine and taurine in doses 3–6 mg/kg and 1–6 g, respectively, appear to be the main ergogenic elements. However, additive or synergic properties between them seem to be implausible. Because of non-unified protocol design, presented studies show inconsistency between ED ingestion and improved physical performance. Potential side effects caused by abusive consumption or missed contraindications are the aspects that are the most often overlooked by consumers and not fully elucidated by ED producers. In this review, the authors aimed to present the latest scientific information on ED components and their possible impact on improving physical performance as well as to bring emphasis to the danger of inordinate consumption.

Effects of acute caffeine ingestion on futsal performance in sub-elite players

PURPOSE

To date, no previous investigation has studied the effect of acute caffeine ingestion on futsal performance during futsal-specific testing and during a simulated match. Therefore, the aim of this investigation was to establish the effects of acute caffeine intake on futsal-specific tests and match-play running performance in male futsal players.

METHODS

Sixteen high-performance futsal players participated in a randomized, crossover, placebo-controlled and double-blind experiment. Each player completed two identical trials after ingesting either caffeine (3 mg/kg) or a placebo (cellulose). The trials consisted of a battery of futsal-specific tests (countermovement jump, 20-m sprint test, and a futsal kicking velocity and accuracy test) followed by a simulated futsal match (2 halves of 7.5 min). During the match, players' running performance was assessed with local positioning system devices.

RESULTS

In comparison to the placebo, caffeine ingestion increased jump height by 2.8% (p = 0.048; ES = 0.29) and reduced the time to complete the 20-m sprint test by -2.2% (p = 0.044; ES = - 0.54). Additionally, acute caffeine intake improved the distance covered at above 14.4 km/h by 19.6% (p = 0.021; ES = 0.58), the number of body impacts by 8.1% (p = 0.040; ES = 0.27) and the number of accelerations/decelerations by 4.2% (p = 0.044; ES = 0.57) during the simulated futsal match. However, no differences were reported in ball velocity or shooting accuracy in the futsal kicking test. There were no differences in the prevalence of side effects reported in the hours after the ingestion of the treatments.

CONCLUSION

Three mg/kg of caffeine enhanced several physical variables associated with futsal such as jump and sprint performance, and improved high-speed running and accelerations/decelerations during a simulated futsal match. Caffeine supplementation with a moderate dose can be considered as an effective ergogenic aid for futsal performance with low prevalence of side effects.

TRIAL REGISTRATION

The study was registered in ClinicalTrials.gov with the following ID: NCT04852315. The study was retrospectively registered by 18 April 2020.

Energy Drinks and Sports Performance, Cardiovascular Risk, and Genetic Associations; Future Prospects

The consumption of energy drinks (e.g., containing caffeine and taurine) has increased over the last decade among adolescents and athletes to enhance their cognitive level and improve intellectual and athletic performance. Numerous studies have shown that drinking moderate doses of such drinks produces beneficial effects, as they considerably boost the sporting performance of elite athletes in various sports, including both endurance and explosive events. However, apart from their ergogenic effects, the regular consumption of energy drinks also increases blood pressure and consequently incites problems such as hypertension, tachycardia, and nervousness, all of which can lead to cardiovascular disorders. A potential positive correlation between genetics and the moderate consumption of energy drinks and athletic performance has recently been reported; notwithstanding, a better understanding of the genetic variants involved in metabolism is a key area for future research to optimize the dose of energy drink consumed and obtain the maximal ergogenic effect in elite sports. The aim of this literature review, therefore, is to present the results of recent studies, classifying them according to the differences in the associations between energy drinks and: (i) Athletic performance; (ii) cardiovascular risk factors while practicing sports; and (iii) genetic associations and future prospects between the consumption of energy drinks and performance.

Pre-exercise Caffeine Intake Enhances Bench Press Strength Training Adaptations

Previous research has identified acute caffeine intake as an effective ergogenic aid to enhance velocity and power during bench press exercise. However, no previous investigation has analyzed the effects of chronic intake of caffeine on training adaptations induced by bench press strength training. Thus, the aim of this investigation was to determine the effects of pre-exercise caffeine intake on training adaptations induced by a bench press training protocol. Using a double-blind, randomized experimental design, 16 healthy participants underwent a bench press training protocol for 4 weeks (12 sessions). Seven participants ingested a placebo and nine participants ingested 3 mg/kg/BM of caffeine before each training session. Three days before, and 3 days after the completion of the training protocol, participants performed a one-repetition maximum (1RM) bench press and force-velocity test (from 10 to 100% 1RM). From comparable pre-training values, the strength training similarly increased 1RM in the caffeine and placebo groups (+13.5 ± 7.8% vs. +11.3 ± 5.3%, respectively; p = 0.53). In the caffeine group, the strength training induced a higher mean velocity at 40%, (0.81 ± 0.08 vs. 0.90 ± 0.14 m/s), 60% (0.60 ± 0.06 vs. 0.65 ± 0.06 m/s), 70% (0.47 ± 0.05 vs. 0.55 ± 0.06 m/s), 80% (0.37 ± 0.06 vs. 0.45 ± 0.05 m/s), 90% (0.26 ± 0.07 vs. 0.34 ± 0.06 m/s), and 100% 1RM (0.14 ± 0.04 vs. 0.25 ± 0.05 m/s; p < 0.05) while the increases in the placebo group were evident only at 30 (0.95 ± 0.06 vs. 1.03 ± 0.07 m/s), 70% (0.51 ± 0.03 vs. 0.57 ± 0.05 m/s) and 80% 1RM (0.37 ± 0.06 vs. 0.45 ± 0.05 m/s) (p < 0.05). The placebo group only increased peak velocity at 60 and 70% 1RM (p < 0.05) while peak velocity increased at 10%, and from 30 to 100% 1RM in the caffeine group (p < 0.05). The use of 3 mg/kg/BM of caffeine before exercise did not modify improvements in 1RM obtained during a 4 week bench press strength training program but induced more muscle performance adaptations over a wider range of load.

Acute Beetroot Juice Supplementation Does Not Improve Match-Play Activity in Professional Tennis Players

OBJECTIVE

Beetroot juice is a source of dietary nitrate (NO₃-) recognized as a potential ergogenic aid to enhance tolerance during endurance exercise of submaximal-to-maximal intensity. However, little is known about the effects of beetroot juice on exercise performance in intermittent sports such as tennis. The present study aimed to determine the effect of acute beetroot juice supplementation on movement patterns during a competitive tennis match in professional players.

METHODS

In a double-blind and randomized experiment, nine professional tennis players performed two experimental trials 3 h after ingesting either 70 mL of a commercially-available concentrated beetroot juice (6.4 mmol NO₃-) or placebo (0.005 mmol NO₃-). In each experimental trial, players completed a 3-set tennis match and two performance tests (i.e., serve speed and isometric handgrip strength) before and after the match. Match-play running performance was recorded using wearable GPS and accelerometer units.

RESULTS

In comparison to the placebo trial, the acute beetroot juice supplementation did not modify any match-play running performance (p = 0.178 to 0.997, d = 0.01 to 0.42). Furthermore, beetroot juice supplementation did not alter the pre-to-post match change in serve speed (p = 0.663, ηp² = 0.03) or isometric handgrip strength (p = 0.219, ηp² = 0.18).

CONCLUSIONS

The current results indicated that acute ingestion of a commercialized shot of nitrate-rich beetroot juice (70 mL containing 6.4 mmol of NO₃-) did not produce any performance benefit on tennis matchplay. Thus, acute beetroot juice supplementation seems an ergogenic aid with little value to enhance physical performance in professional tennis players.

Nutritional Ergogenic Aids in Racquet Sports: A Systematic Review

A nutritional ergogenic aid (NEA) can help athletes optimize performance, but an evidence-based analysis is required in order to support training outcomes or competition performance in specific events. Racquet sports players are regularly exposed to a high-intensity workload throughout the tournament season. The activity during a match is characterized by variable durations (2–4 h) of repeated high-intensity bouts interspersed with standardized rest periods. Medline/PubMed, Scopus, and EBSCO were searched from their inception until February 2020 for randomized controlled trials (RCTs). Two independent reviewers extracted data, after which they assessed the risk of bias and the quality of trials. Out of 439 articles found, 21 met the predefined criteria: tennis (15 trials), badminton (three trials), paddle (one trial), and squash (two trials). Among all the studied NEAs, acute dosages of caffeine (3–6 mg/kg) 30–60 min before a match have been proven to improve specific skills and accuracy but may not contribute to improve perceived exertion. Currently, creatine, sodium bicarbonate, sodium citrate, beetroot juice, citrulline, and glycerol need more studies to strengthen the evidence regarding improved performance in racquet sports.

Caffeine improves various aspects of athletic performance in adolescents independent of their 163 C > A CYP1A2 genotypes

PURPOSE

The purpose of this study was to investigate whether variations in 163 C > A CYP1A2 genotypes (rs 762 551) (AA, AC, and CC) modify the ergogenic effects of caffeine (CAF) on strength, power, muscular endurance, agility, and endurance in adolescent athletes.

METHODS

One hundred adolescents (age = 15 ± 2 years) were recruited. Participants ingested CAF (6 mg.kg^-1 ) or placebo (PLA, 300 mg of cellulose) 1 hour before performing a sequence of physical tests: handgrip strength, vertical jumps, agility test, sit-ups, push-ups, and the Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1).

RESULTS

Compared to PLA, CAF enhanced (P < .05) sit-up (CAF = 37 ± 9; PLA = 35 ± 8 repetitions) and push-up repetitions (CAF = 26 ± 11; PLA = 24 ± 11 repetitions), and increased distance covered in Yo-Yo IR1 test (CAF = 1010.4 ± 378.9; PLA = 903.2 ± 325.7 m). There was no influence of CAF on handgrip strength (CAF = 35.1 ± 8.9; PLA = 33.7 ± 8.7 kgf), countermovement jump height (CAF = 49.3 ± 12.6; PLA = 47.9 ± 13.8 cm), spike jump height (CAF = 54.2 ± 13.6; PLA = 52.9 ± 14.5 cm), and time in agility test (CAF = 15.8 ± 1.1; PLA = 15.9 ± 1.3 s, P > .05). When present, the ergogenic effect of CAF was not dependent of genotype.

CONCLUSION

CAF improves muscular endurance and aerobic performance in adolescent athletes, regardless of their 163 C > A CYP1A2 genotype.

Effects of Caffeine Ingestion on Physical Performance in Elite Women Handball Players: A Randomized, Controlled Study

PURPOSE

To investigate the effects of acute caffeine (CAFF) intake on physical performance in elite women handball players.

METHODS

A total of 15 elite women handball players participated in a randomized, double-blind study. In 2 different trials, participants ingested either a placebo (cellulose) or 3 mg of CAFF per kilogram of body mass (mg/kg bm) before undergoing a battery of neuromuscular tests consisting of handball throws, an isometric handgrip strength test, a countermovement jump, a 30-m sprint test (SV) and a modified version of the agility T test. Then, participants performed a simulated handball game (2 × 20 min), and movement patterns were recorded with a local positioning system.

RESULTS

Compared with the placebo, CAFF increased ball velocity in all ball throws (P = .021-.044; effect size [ES] = 0.39-0.49), strength in isometric handgrip strength test (350.8 [41.2] vs 361.6 [46.1] N, P = .034; ES = 0.35), and countermovement-jump height (28.5 [5.5] vs 29.8 [5.5] cm; P = .006; ES = 0.22). In addition, CAFF decreased running time in the SV (4.9 [0.2] vs 4.8 [0.3] s; P = .042; ES = -0.34). In the simulated game, CAFF increased the frequency of accelerations (18.1 [1.2] vs 18.8 [1.0] number/min; P = .044; ES = 0.54), decelerations (18.0 [1.2] vs 18.7 [1.0] number/min; P = .032; ES = 0.56), and body impacts (20 [8] vs 22 [10] impacts/min; P = .032; ES = 0.30). However, postexercise surveys about self-reported feelings of performance indicate that players did not feel increased performance with CAFF.

CONCLUSION

Preexercise ingestion of 3 mg/kg bm of CAFF improved ball-throwing velocity, jump, and sprint performance and the frequency of in-game accelerations and decelerations in elite women handball players.

Effects of Beetroot Juice Ingestion on Physical Performance in Highly Competitive Tennis Players

Beetroot juice (BJ) contains high levels of inorganic nitrate (NO₃⁻) and its intake has good evidence in increasing blood nitrate/nitrite concentrations. The ingestion of BJ has been associated with improvements in physical performance of endurance sports, however the literature in intermittent sports is scarce. The aim of this study was to investigate whether BJ could improve physical performance in tennis players. Thirteen well-trained tennis players (25.4 ± 5.1 years) participated in the study during their preparatory period for the tennis season. Subjects were randomly divided into two groups and performed a neuromuscular test battery after either BJ or placebo (PLA) consumption. Both trials were executed on two separate days, in randomized order, with one week of wash out period. The test battery consisted of serve velocity test (SVT), countermovement jump (CMJ), isometric handgrip strength (IHS), 5-0-5 agility test (5-0-5), and 10 m sprint (10-m). No significant differences were found in SVT (1.19%; p = 0.536), CMJ (0.96%; p = 0.327), IHS (4.06%; p = 0.069), 5-0-5 dominant and nondominant side (1.11–2.02%; p = 0.071–0.191) and 10-m (1.05%; p = 0.277) when comparing BJ and PLA ingestion. Thus, our data suggest that low doses of BJ (70 mL) consumption do not enhance tennis physical performance.

The acute effect of match-play on hip range of motion and isometric strength in elite tennis players

Background

Groin injuries are some of the most common injuries tennis players suffer. Several factors (e.g., post-match decrease in hip adductor (ADD) strength) have been proposed as possible mechanisms for increasing the incidence of this type of injury. However, the risk factors of developing groin injuries after a tennis match have not yet been delineated.

Objective

The aim of this study was to determine the effect of tennis match-play on isometric ADD and abductor (ABD) strength and passive hip range of motion (ROM).

Methods

Twenty-six male tennis players (20.30 ± 4.98 years) took part in this study. Participants completed an evaluation of strength and flexibility hip measurements before and after a simulated tennis match. Dominant and non-dominant passive hip ROM, ADD and ABD isometric strength, and the ADD/ABD strength ratio were measured before and immediately post-match. A global positioning system (GPS) and a session rating of perceived exertion (RPE) were used to assess the locomotive demands and internal match load.

Results

Isometric dominant ADD strength (17.8%, p ≤ 0.01) and ADD/ABD strength ratio (11.6%, p = 0.04) were lower post-match compared to the pre-match values. No between-limbs differences were observed for isometric ADD strength, ABD strength, and passive hip ROM tests. RPE showed an expected increase between pre- vs. post-match (pre- vs. post-warming-up, 3.42 ± 2.08 vs. 5.62 ± 2.29, p < 0.01). In addition, a significant relationship between ADD strength and the volume of tennis practice per week was found, stablishing that tennis players with lower volume of training per week suffered a reduction in ADD strength in their dominant limb after match-play (r = 0.420, p = 0.04).

Conclusion

The assessment of ADD strength and the ADD/ABD strength ratio in the dominant limb may be considered a post-match tool that can be used to identify players who require rest and additional recovery strategies before competing again.

Ergogenic effects of caffeine on peak aerobic cycling power during the menstrual cycle

PURPOSE

Recent investigations have established that the ingestion of a moderate dose of caffeine (3-6 mg kg^-1) can increase exercise and sports performance in women. However, it is unknown whether the ergogenicity of caffeine is similar during all phases of the menstrual cycle. The aim of this investigation was to determine the ergogenic effects of caffeine in three phases of the menstrual cycle.

METHODS

Thirteen well-trained eumenorrheic triathletes (age = 31 ± 6 years; body mass = 58.6 ± 7.8 kg) participated in a double-blind, cross-over, randomised experimental trial. In the (1) early follicular (EF); (2) preovulation (PO); (3) and mid luteal (ML) phases, participants either ingested a placebo (cellulose) or 3 mg kg^-1 of caffeine in an opaque and unidentifiable capsule. After a 60-min wait for substance absorption, participants performed an incremental maximal cycle ergometer test until volitional fatigue (25 W/min) to assess peak aerobic cycling power (Wmax).

RESULTS

In comparison to the placebo, caffeine increased Wmax in the EF (4.13 ± 0.69 vs. 4.24 ± 0.71 W kg^-1, Δ = 2.7 ± 3.3%, P = 0.01), in the PO (4.14 ± 0.70 vs. 4.27 ± 0.73 W kg^-1, Δ = 3.3 ± 5.0%; P = 0.03) and in the ML (4.15 ± 0.69 vs. 4.29 ± 0.67 W kg^-1, Δ = 3.6 ± 5.1%; P = 0.01) phases. The magnitude of the caffeine ergogenic effect was similar during all of the menstrual cycle phases (P = 0.85).

CONCLUSION

Caffeine increased peak aerobic cycling power in the early follicular, preovulatory, and mid luteal phases. Thus, the ingestion of 3 mg of caffeine per kg of body mass might be considered an ergogenic aid for eumenorrheic women during all three phases of the menstrual cycle.

Game Activity and Physiological Responses of Young Tennis Players in a Competition With 2 Consecutive Matches in a Day

Purpose: To determine whether the game activity and physiological responses of young tennis players differed depending on the session of play (eg, morning [MOR] vs afternoon [AFT]) and the final match outcome (eg, winners vs losers) during a simulated competition with 2 matches on the same day. Methods: A total of 12 well-trained male tennis players (age 14.5 [0.8] y) took part in a simulated competition of two 3-set matches separated by 3 h. All the matches were video recorded, and the participants were monitored using 10-Hz global positioning system units including a heart-rate monitor. Effect-size (ES) statistics were used to investigate the magnitudes of the differences. Results: During the AFT matches, in absolute terms, players covered longer total distance (ES = moderate) and ran more distance between 0 and ≤4 m·s−1 (ES = small to large) than in MOR matches. Total duration was also longer (ES = large) in the AFT, where the rest time between rallies was also longer (ES = very large). Heart rate was similar during AFT and MOR matches, but higher rates of perceived exertion (ES = moderate) were reported in the AFT. Only peak running velocity was observed to be likely higher for losers than for winners (ES = small). Conclusions: Game activity and physiological responses of young tennis players differ when 2 consecutive matches are played on the same day. These data might help elucidate the need for specific precompetition training loads and/or between-matches/sessions recovery strategies when facing overloaded competitions.

Trends in Energy Drink Consumption Among U.S. Adolescents and Adults, 2003-2016

INTRODUCTION

Energy drinks refer to non-alcoholic beverages that contain caffeine, amino acids, herbs, and vitamins. Although energy drinks are marketed to reduce fatigue and improve physical/mental performance, frequent consumption of these beverages has been linked to negative health consequences. The purpose of this study is to provide timely, national estimates of the percentage of energy drink consumers in the U.S. and to analyze trends in energy drink intake between 2003 and 2016.

METHODS

A total of 9,911 adolescents (aged 12-19 years); 12,103 young adults (aged 20-39 years); and 11,245 middle-aged adults (aged 40-59 years) were assessed using dietary data from the 2003-2016 National Health and Nutrition Examination Surveys. For each age group (adolescents, young adults, and middle-aged adults), logistic regression was used to estimate the proportion of energy drink consumers, and negative binomial regression was used to estimate per capita energy drink consumption, adjusting for covariates. Differences in total caffeine intake between energy drink consumers and non-consumers were examined by pooling all survey years together and using negative binomial regression. Analyses were conducted in 2018.

RESULTS

From 2003 to 2016, the prevalence of energy drink consumption increased significantly for adolescents (0.2% to 1.4%, p=0.028); young adults (0.5% to 5.5%, p<0.001); and middle-aged adults (0.0% to 1.2%, p=0.006). Per capita consumption of energy drinks increased significantly from 2003 to 2016 only for young adults (1.1 to 9.7 calories, p<0.001). Pooled across years, energy drink consumers had significantly higher total caffeine intake compared with non-consumers for adolescents (227.0 mg vs 52.1 mg, p<0.001); young adults (278.7 mg vs 135.3 mg, p<0.001); and middle-aged adults (348.8 mg vs 219.0 mg, p<0.001).

CONCLUSIONS

These findings indicate that consumption of energy drinks has grown substantially and that these drinks are a major source of caffeine among those who consume them.

Urine Caffeine Concentration in Doping Control Samples from 2004 to 2015

The ergogenic effect of caffeine is well-established, but the extent of its consumption in sport is unknown at the present. The use of caffeine was considered "prohibited" until 2004, but this stimulant was moved from the List of Prohibited Substances to the Monitoring Program of the World Anti-Doping Agency to control its use by monitoring urinary caffeine concentration after competition. However, there is no updated information about the change in the use of caffeine as the result of its inclusion in the Monitoring Program. The aim of this study was to describe the changes in urine caffeine concentration from 2004 to 2015. A total of 7488 urine samples obtained in official competitions held in Spain and corresponding to athletes competing in Olympic sports (2788 in 2004, 2543 in 2008, and 2157 in 2015) were analyzed for urine caffeine concentration. The percentage of samples with detectable caffeine (i.e., >0.1 μg/mL) increased from ~70.1%, in 2004⁻2008 to 75.7% in 2015. The median urine caffeine concentration in 2015 (0.85 μg/mL) was higher when compared to the median value obtained in 2004 (0.70 μg/mL; p < 0.05) and in 2008 (0.70 μg/mL; p < 0.05). The urine caffeine concentration significantly increased from 2004 to 2015 in aquatics, athletics, boxing, judo, football, weightlifting, and rowing (p < 0.05). However, the sports with the highest urine caffeine concentration in 2015 were cycling, athletics, and rowing. In summary, the concentration of caffeine in the urine samples obtained after competition in Olympic sports in Spain increased from 2004 to 2015, particularly in some disciplines. These data indicate that the use of caffeine has slightly increased since its removal from the list of banned substances, but urine caffeine concentrations suggest that the use of caffeine is moderate in most sport specialties. Athletes of individual sports or athletes of sports with an aerobic-like nature are more prone to using caffeine in competition.

Effects of Caffeine Supplementation on Performance in Ball Games

Although a large body of evidence exists documenting the ergogenic properties of caffeine, most studies have focused on endurance performance. However, findings from endurance sports cannot be generalized to performance in ball games where, apart from having a high level of endurance, successful athletic performances require a combination of physiological, technical and cognitive capabilities. The purpose of this review was to critically evaluate studies that have examined the effect of a single dose of caffeine in isolation on one or more of the following performance measures: total distance, sprint performance, agility, vertical jump performance and accuracy in ball games. Searches of three major databases resulted in 19 studies (invasion games: 13; net-barrier games: 6) that evaluated the acute effects of caffeine on human participants, provided the caffeine dose administered, and included a ball games specific task or simulated match. Improvements in sprint performance were observed in 8 of 10 studies (80%), and vertical jump in 7 of 8 studies (88%). Equivocal results were reported for distance covered, agility and accuracy. Minor side effects were reported in 4 of 19 studies reviewed. Pre-exercise caffeine ingestion between 3.0 and 6.0 mg/kg of body mass appears to be a safe ergogenic aid for athletes in ball games. However, the efficacy of caffeine varies depending on various factors, including, but not limited to, the nature of the game, physical status and caffeine habituation. More research is warranted to clarify the effects of caffeine on performance measures unique to ball games, such as agility and accuracy. It is essential that athletes, coaches and practitioners evaluate the risk-benefit ratio of caffeine ingestion strategies on an individual case-by-case basis.

Effect of Energy Drink Consumption on Power and Velocity of Selected Sport Performance Activities

Jacobson, BH, Hester, GM, Palmer, TB, Williams, K, Pope, ZK, Sellers, JH, Conchola, EC, Woolsey, C, and Estrada, C. Effect of energy drink consumption on power and velocity of selected sport performance activities. J Strength Cond Res 32(6): 1613-1618, 2018-Energy drinks (ED) comprise a multibillion dollar market focused on younger, active, and competitive individuals. Marketing includes claims of improved alertness and performance. The purpose of this study was to assess power (W) and velocity (m·s) of a simulated, isolated forehand stroke (FHS), and a countermovement vertical jump (CVJ) before and after ingestion of a commercially available energy shot (ES) or a placebo (PL). Healthy college-aged men and women (N = 36) volunteers were randomly placed in the ES or PL. Before and 30 minutes after ingesting either the ES or PL, participants performed 3 FHSs and CVJs. Power and velocity of each performance was measured using a linear velocity transducer and the highest value for each measure was used for subsequent analysis. The ES group demonstrated a significant (p = 0.05) increase in velocity and W for the FHS, but not for the CVJ. All measures remained unchanged in the PL group for both, the FHS and CVJ. Females demonstrated a significant increase in velocity over males in FHS, but not in CVJ. It was concluded that while the dose of stimulants in the ES was adequate to improve performance of smaller muscle groups, it may not have been sufficient to affect the larger muscle groups of the lower legs which contribute to the CVJ. While the ES used in the present study contained a caffeine dosage within the NCAA limit and did improve performance for the upper body, it must be noted that there are health risks associated with ED consumption.

A Brief Review of Handgrip Strength and Sport Performance

Cronin, J, Lawton, T, Harris, N, Kilding, A, and McMaster, DT. A brief review of handgrip strength and sport performance. J Strength Cond Res 31(11): 3187-3217, 2017-Tests of handgrip strength (HGS) and handgrip force (HGF) are commonly used across a number of sporting populations. Measures of HGS and HGF have also been used by practitioners and researchers to evaluate links with sports performance. This article first evaluates the validity and reliability of various handgrip dynamometers (HGD) and HGF sensors, providing recommendations for procedures to ensure that precise and reliable data are collected as part of an athlete's testing battery. Second, the differences in HGS between elite and subelite athletes and the relationships between HGS, HGF, and sports performance are discussed.

Health Effects and Public Health Concerns of Energy Drink Consumption in the United States: A Mini-Review

As energy drink consumption continues to grow worldwide and within the United States, it is important to critically examine the nutritional content and effects on population health of these beverages. This mini-review summarizes the current scientific evidence on health consequences from energy drink consumption, presents relevant public health challenges, and proposes recommendations to mitigate these issues. Emerging evidence has linked energy drink consumption with a number of negative health consequences such as risk-seeking behaviors, poor mental health, adverse cardiovascular effects, and metabolic, renal, or dental conditions. Despite the consistency in evidence, most studies are of cross-sectional design or focus almost exclusively on the effect of caffeine and sugar, failing to address potentially harmful effects of other ingredients. The negative health effects associated with energy drinks (ED) are compounded by a lack of regulatory oversight and aggressive marketing by the industry toward adolescents. Moreover, the rising trend of mixing ED with alcohol presents a new challenge that researchers and public health practitioners must address further. To curb this growing public health issue, policy makers should consider creating a separate regulatory category for ED, setting an evidence-based upper limit on caffeine, restricting sales of ED, and regulating existing ED marketing strategies, especially among children and adolescents.

Consumption of energy drinks by children and young people: a rapid review examining evidence of physical effects and consumer attitudes

OBJECTIVE

To examine patterns of energy drink consumption by children and young people, attitudes towards these drinks, and any associations with health or other outcomes.

DESIGN

Rapid evidence assessment and narrative synthesis.

DATA SOURCES

9 electronic bibliographic databases, reference lists of relevant studies and searches of the internet.

RESULTS

A total of 410 studies were located, with 46 meeting the inclusion criteria. The majority employed a cross-sectional design, involved participants aged 11-18 years, and were conducted in North America or Europe. Consumption of energy drinks by children and young people was found to be patterned by gender, with boys consuming more than girls, and also by activity levels, with the highest consumption observed in the most and least sedentary individuals. Several studies identified a strong, positive association between the use of energy drinks and higher odds of health-damaging behaviours, as well as physical health symptoms such as headaches, stomach aches, hyperactivity and insomnia. There was some evidence of a dose-response effect. 2 experimental studies involving small numbers of junior athletes demonstrated a positive impact on limited aspects of sports performance. 3 themes emerged from the qualitative studies: reasons for use; influences on use; and perceived efficacy and impact. Taste and energy-seeking were identified as key drivers, and branding and marketing were highlighted as major influences on young people's consumption choices. Awareness of possible negative effects was low.

CONCLUSIONS

There is growing evidence that consumption of energy drinks is associated with a range of adverse outcomes and risk behaviours in terms of children's health and well-being. However, taste, brand loyalty and perceived positive effects combine to ensure their popularity with young consumers. More research is needed to explore the short-term and long-term impacts in all spheres, including health, behaviour and education.

TRIAL REGISTRATION NUMBER

CRD42014010192.

The Activity Profile of Young Tennis Athletes Playing on Clay and Hard Courts: Preliminary Data

The aim of this study was to compare the kinematic characteristics of tennis matches between red clay and hard courts in young tennis players. Eight young tennis players performed two tennis matches on different court surfaces. The match activities were monitored using GPS units. The distance covered in different velocity ranges and the number of accelerations were analyzed. The paired t test and inference based on magnitudes were used to compare the match physical performance between groups. The total distance (24% of difference), high-intensity running distance (15 - 18 km/h) (30% of difference), the number of high-intensity activities (44% of difference), the body load (1% of difference), and accelerations >1.5 g (1.5-2 g and >2 g 7.8 and 8.1 % of difference, respectively) were significantly greater in clay court than hard court matches (p < 0.05). Matches played on the red clay court required players to cover more total and high-intensity running distances and engage in more high-intensity activities than the matches played on the hard court. Finally, on the clay court the body load and the number of accelerations performed (>1.5 g) were possibly higher than on the hard court.

Analysis of the distances covered and technical actions performed by professional tennis players during official matches

The purpose of this study was to analyse the physical and technical performances of professional tennis players during official matches. The trajectories of eight players were obtained during matches, using an automatic tracking method. The distances covered and technical performances were analysed for the first and second sets. The athletes covered (mean ± standard deviation) a total of 1702.4 ± 448.2 m in the first set, 1457.6 ± 678.1 m in the second set and 3160.0 ± 880.1 in the entire match. No differences were found between the sets for the physical variables (lateral and forward displacements, distance covered per rally, per game and per set, and the percentage of time spent in each range of velocity). However, the distances covered by the athletes during the rallies in which they were serving (median = 5.2; interquartile range (IQR) = 6.7 m) were statistically smaller than when they were returning (median = 6.2; IQR = 7.7 m). Forehand ground stroke proficiency decreased from the first (mean ± standard deviation: 75.2 ± 4.11%) to the second set (mean ± standard deviation = 65.5 ± 14.3%). In conclusion, tennis players did not present reduced physical performance from the first to the second set.