ABSTRACT
While previous studies have explored a range of factors governing the optimal use of caffeine (CAF) in athletes, limited research has explored how time of day (TOD) affects the ergogenic effects of various CAF dosages on physical performance. This study aimed to increase knowledge about how different recommended CAF doses (3 mg/kg vs. 6 mg/kg) ingested at different TODs affected maximal high-intensity physical performance and the perception of potential side effects in female athletes. In this double-blind, randomized, and counterbalanced study, 15 low CAF consumer athletes (aged 18.3 ± 0.5 y) underwent six trials, including three testing conditions assessed across two TODs: one in the morning (08:00 a.m.) and one in the evening (06:00 p.m.). During each condition, the participants ingested either a placebo, 3 mg/kg CAF (CAF (3 mg)), or 6 mg/kg CAF (CAF (6 mg)) capsules 60 min before each test with an in-between washout period of at least 72 h. In each trial, the participants performed a countermovement jumps test (CMJ), a modified agility t test (MATT), a repeated sprint ability (RSA), a rating of perceived exertion (RPE), and finally, a CAF side effects questionnaire. Our findings indicate the absence of an ergogenic effect on CMJ, MAT, and RSA performance in the evening after administering CAF (3 mg) or CAF (6 mg) compared to a placebo. Likewise, when CAF was ingested in the morning, there was an improvement in these performances with both CAF (3 mg) and CAF (6 mg), with greater improvement observed after CAF (6 mg). Additionally, neither the CAF dosage nor the TOD had a significant effect on the RPE. The occurrence of side effects increased significantly after the evening ingestion of CAF, particularly with a moderate dose of CAF (6 mg). Our findings indicate that the effectiveness of CAF depends on the TOD and CAF dosage. When ingested in the morning, a moderate dose of CAF (6 mg), rather than CAF (3 mg), is more effective in improving short-term physical performance without affecting CAF side effects in female athletes. Nevertheless, when ingested in the evening, neither dose was sufficient to enhance short-term physical performance, and both dosages increased the incidence of CAF side effects, particularly at a moderate dose.
Subject(s)
Athletes , Athletic Performance , Caffeine , Humans , Caffeine/administration & dosage , Caffeine/pharmacology , Caffeine/adverse effects , Female , Double-Blind Method , Athletic Performance/physiology , Adolescent , Young Adult , Dose-Response Relationship, Drug , Performance-Enhancing Substances/administration & dosage , Performance-Enhancing Substances/adverse effects , Drug Administration Schedule , Time Factors , Central Nervous System Stimulants/administration & dosage , Central Nervous System Stimulants/pharmacologyABSTRACT
BACKGROUND: The masculinizing effects from anabolic-androgenic steroid (AAS) appear to be different between men and women, leading to calls for more gender-specific information regarding women and AAS use. This study sought to gather perspectives from both men and women on the unique challenges surrounding women's use of AAS, irrespective of their personal use. Secondly, the study interrogated how women's AAS practices differ from those of men specifically. METHODS: The data presented in this paper come from a subsample of participants who participated in a larger study investigating women and performance and image enhancing drug (PIED) use in Australia. Participants were included in the current analysis if they were: (i) males or females who competed with or coached female strength athletes using AAS and (ii) female and male strength athletes who used AAS. The final sample comprised 21 participants of which there was a proportion of males (n = 7) and females (n = 7) using AAS. RESULTS: Women's choices in AAS selection were predominantly around oral compounds (e.g. Oxandrolone) as well as other PIEDs (e.g. Clenbuterol). Some women report the use of injectable AAS represents a change in the profile of the typical female user as it reportedly comes alongside drastic physical and psychological changes. CONCLUSIONS: The unique challenges facing women who use AAS are largely isolation and stigma, with little evidence-based practice or education being available to them online or through peer-groups. Future work may consider piloting harm reduction strategies that may be co-designed with this group.
Subject(s)
Anabolic Agents , Performance-Enhancing Substances , Humans , Male , Female , Androgens/adverse effects , Steroids , Anabolic Androgenic Steroids , Anabolic Agents/adverse effects , Testosterone Congeners/adverse effects , Performance-Enhancing Substances/adverse effectsABSTRACT
In a qualitative study on masculinity, embodiment and sexuality, we interviewed men who were recreational gym-goers about their bodywork practices in Melbourne, Australia. We also asked whether the men had used performance and image-enhancing drugs (PIEDs) as an adjunct to their bodywork practices. While none had used PIEDs, all were considering, or had considered, using them. We found that participants held varying opinions on PIED use and those who used them. The literature on PIEDs noted men's concerns with body appearance and health and focused largely on individual problematic use, but non-users were not mentioned. A second issue in the literature focused on social influences on PIED use, but again with no mention of non-users. Discussion on risk reduction as a public health response did not mention non-users either. This paper, therefore, reports on non-users' thoughts on, regular exposure to, and considerations of PIEDs and other men who use them. We propose that PIEDs might more usefully be understood as an everyday, if contradictory, consideration within most men's bodywork and health practices. We argue that PIEDs constitute a discursive practice exposing a potentiality that engages non-users also and this requires new health promotion approaches.
Subject(s)
Performance-Enhancing Substances , Male , Humans , Performance-Enhancing Substances/adverse effects , Masculinity , Australia , Health Promotion , SexualityABSTRACT
PURPOSE: The aim of this study was to systematically review evidence on the prevalence and magnitude of side effects associated with caffeine supplementation in athletes. METHODS: Systematic searches through the PubMed, VHL, Scopus, and Web of Science databases were conducted according to the PRISMA guidelines. Peer-reviewed articles written in English that reported the prevalence/percentage or magnitude/effect size of side effects after caffeine supplementation in athletes in a sports context were included. Studies were grouped by the dose of caffeine administered as follows: low = ≤ 3.0 mg/kg; moderate = from 3.1 to 6.0 mg/kg; high = ≥ 6.1 mg/kg. The magnitude of the side effects was calculated with effect sizes. RESULTS: The search retrieved 25 studies that met the inclusion/exclusion criteria with a pooled sample of 421 participants. The supplementation with caffeine produced a higher prevalence or magnitude of all side effects under investigation when compared to placebo/control situations. The prevalence (magnitude) was between 6 and 34% (ES between 0.13 and 1.11) for low doses of caffeine, between 0 and 34% (ES between -0.13 and 1.20) for moderate doses of caffeine, and between 8 and 83% (ES between 0.04 and 1.52) with high doses of caffeine. The presence of tachycardia/heart palpitations and the negative effects on sleep onset had the highest prevalence and magnitude, in athletes using supplementation with caffeine. CONCLUSION: In summary, caffeine supplementation in the doses habitually used to enhance physical performance produces several side effects, both after exercise and at least 24 h after the ingestion. However, the prevalence and magnitude of side effects with high doses of caffeine were habitually higher than with low doses of caffeine. From a practical perspective, using ~3.0 mg/kg of caffeine may be the dose of choice to obtain the ergogenic benefits of caffeine with the lowest prevalence and magnitude of side effects.
Subject(s)
Athletic Performance , Performance-Enhancing Substances , Humans , Caffeine/adverse effects , Physical Endurance , Performance-Enhancing Substances/adverse effects , Dietary SupplementsABSTRACT
The purpose of this article is to provide the school nurse with the ability to recognize performance and appearance enhancing substance use and understand treatment and prevention strategies to reduce associated health risks. The use of appearance and performance enhancing drugs and substances, also known as "doping," has been an ethical and health issue in sports for many years. It is vital that school nurses learn to recognize performance and appearance enhancing substance use to ensure student athletes and exercisers receive the care and education they need. Commonly used performance and appearance enhancing substances include anabolic-androgenic steroids, stimulants, diuretics, growth hormone, and supplements. Signs and symptoms that may look similar to other health concerns include palpitations, stunted growth, acne, severe headaches, muscle cramps, dizziness, and dehydration, but some long-term severe complications occur as well. Doping can lead to severe and sometimes permanent organ damage, including liver, kidney, and heart disease. The school nurse can play a key role by working with parents, coaches, school counselors, and educators to foster an anti-doping culture.
Subject(s)
Anabolic Agents , Doping in Sports , Performance-Enhancing Substances , School Nursing , Sports , Substance-Related Disorders , Athletes , Humans , Performance-Enhancing Substances/adverse effectsABSTRACT
The non-medical use of image- and performance-enhancing drugs (IPEDs) is widespread in the fitness and bodybuilding scene. The reasons for IPED use are often hedonistic in nature and they are used in so-called "cycles" over several weeks. The most common side effects are: testicular atrophy, acne, hypersexuality, hypertension, gynecomastia, lipid metabolism disorders, mood swings, hair loss, and policythemia. Common consequences following IPED use are: decreased libido, oligo- or azoospermia, and erectile dysfunction. To reduce undesirable side effects and consequences, IPED users often take medications for self-treatment; occasionally IPED users also mention such medications and ask for them in the general medical practice.
Subject(s)
Performance-Enhancing Substances , Exercise , Humans , Male , Performance-Enhancing Substances/adverse effectsABSTRACT
The rules of fair play in sport generally prohibit the use of performance-enhancing drugs (PEDs). The World Anti-Doping Agency (WADA) oversees global antidoping regulations and testing for elite athletes participating in Olympic sports. Efforts to enforce antidoping policies are complicated by the diverse and evolving compounds and strategies employed by athletes to gain a competitive edge. Now between the uniquely proximate 2021 Tokyo and 2022 Beijing Olympic Games, we discuss WADA's efforts to prevent PED use during the modern Olympic Games. Then, we review the major PED classes with a focus on pathophysiology, complexities of antidoping testing, and relevant toxicities. Providers from diverse practice environments are likely to care for patients using PEDs for a variety of reasons and levels of sport; these providers should be aware of common PED classes and their risks.
Subject(s)
Doping in Sports , Performance-Enhancing Substances , Sports , Athletes , Humans , Performance-Enhancing Substances/adverse effectsABSTRACT
The use of substances and medications with potential cardiovascular effects among those practicing sports and physical activity has progressively increased in recent years. This is also connected to the promotion of physical activity and exercise as core aspects of a healthy lifestyle, which has led also to an increase in sport participation across all ages. In this context, three main users' categories can be identified, (i) professional and amateur athletes using substances to enhance their performance, (ii) people with chronic conditions, which include physical activity and sport in their therapeutic plan, in association with prescribed medications, and (iii) athletes and young individuals using supplements or ergogenic aids to integrate their diet or obtaining a cognitive enhancement effect. All the substances used for these purposes have been reported to have side effects, among whom the cardiovascular consequences are the most dangerous and could lead to cardiac events. The cardiovascular effect depends on the type of substance, the amount, the duration of use, and the individual response to the substances, considering the great variability in responses. This Position Paper reviews the recent literature and represents an update to the previously published Position Paper published in 2006. The objective is to inform physicians, athletes, coaches, and those participating in sport for a health enhancement purpose, about the adverse cardiovascular effects of doping substances, commonly prescribed medications and ergogenic aids, when associated with sport and exercise.
Subject(s)
Cardiology , Doping in Sports , Performance-Enhancing Substances , Sports , Athletes/psychology , Doping in Sports/prevention & control , Doping in Sports/psychology , Exercise , Humans , Performance-Enhancing Substances/adverse effectsABSTRACT
Performance-enhancing substance (PES) use is common among young men and prior research has documented cross-sectional associations between anabolic-androgenic steroid (AAS) use and sexual risk behaviors. However, this relationship remains understudied among a longitudinal cohort of young adult men, and research on prospective associations between legal PES (e.g., creatine) use and sexual risk behaviors is lacking. The current study addressed these oversights using data from the National Longitudinal Study of Adolescent to Adult Health (N = 5,451). AAS use and legal PES use were assessed at Wave III (ages 18-26) and 10 indicators of sexual risk behavior were assessed at seven-year follow up (Wave IV; ages 24-32). Linear and logistic regression analyses were conducted adjusting for demographic and behavioral confounders. Participants who reported AAS use and legal PES use had significantly higher number of one-time sexual partners and higher odds of multiple sex partners around the same time in the past 12 months. Participants who reported AAS use had higher odds of any STI in the past 12 months. These results extend prior research on the risk behaviors and adverse effects of PES use. Health care professionals should assess for PES use among young adult men and provide guidance on healthful sexual behaviors.
Subject(s)
HIV Infections , Performance-Enhancing Substances , Substance-Related Disorders , Adolescent , Adult , Cross-Sectional Studies , Humans , Longitudinal Studies , Male , Performance-Enhancing Substances/adverse effects , Prospective Studies , Risk-Taking , Sexual Behavior , Sexual Partners , Substance-Related Disorders/epidemiology , Young AdultABSTRACT
OBJECTIVE: The use of anabolic androgenic steroids (AASs) as performance and image enhancing drugs (PIEDs), once restricted to professional athletes, now includes amateurs and regular gym visitors. AAS use is associated with psychopathology, yet this relationship is complex and not fully understood. We aimed to assess the presence of AASs and other misused substances in athletes' biological samples and link toxicological to psychopathological findings. METHODS: A multicentre, cross-sectional study in fitness centres in Italy recruited 122 professional and amateur athletes training in several sports (84 men; age range = 18-45 years). Athletes completed questionnaires, interviews, and toxicology testing for AASs, other PIEDs, illicit drugs, and non-prescribed psychotropics. Toxicology was conducted in blood, urine, and hair. RESULTS: Self-reported and toxicologically detected use rates of AASs and other misused substances showed slight-to-fair agreement (Fleiss' κ = 0.104-0.375). There was slight-to-moderate agreement among the three biological samples used for AAS testing (κ = 0.112-0.436). Thirty-one athletes (25.4%) tested positive for AASs. More sport hours/week, narcissistic or antisocial personality disorders, and higher nonplanning impulsiveness scores predicted AAS use (pseudo-R2 = 0.665). AAS users did not differ significantly from non-users in major psychopathology, but their Hypomania Checklist-32 score, which also predicted AAS use, was significantly higher (p < 0.001), suggesting increased odds for cyclothymic disorder or subthreshold hypomania. CONCLUSIONS: Our results have implications for studying AAS users, as they identify a cluster of variables that may be relevant in future understanding of AAS use risks (e.g., personality disorders). Possible disagreements between AAS assessment methods should be considered when implementing harm reduction interventions, such as needle and syringe distribution, health education, and counselling, as well as surveillance programmes.
Subject(s)
Anabolic Agents , Mental Disorders , Performance-Enhancing Substances , Adolescent , Adult , Anabolic Agents/adverse effects , Athletes , Cross-Sectional Studies , Humans , Male , Middle Aged , Performance-Enhancing Substances/adverse effects , Steroids , Young AdultABSTRACT
The misuse of dietary supplements and doping substances is commonly associated with toxicity, nutritional imbalances, and health and psychological consequences. This is alarming especially in light of the increasing prevalence of the use of dietary supplements and doping, particularly among young adults including athletes. There is evidence that education interventions can lead to improved knowledge, intentions, and practices. However, no review has summarized and evaluated the effectiveness of such interventions. The aim of this article is to review the characteristics, contents and effects of education interventions that were designed and implemented to improve knowledge, attitudes, beliefs and intentions with respect to the use of dietary supplements and doping agents in different populations. PubMed, Scopus, CINAHL, PsycInfo and Google Scholar were searched for English-language education interventions targeting dietary supplements and doping substances. A total of 20 articles were identified and have generally provided consistent findings. Most interventions reported a significant improvement in knowledge on dietary supplements and doping agents. Unfortunately, the heavy reliance on self-reported assessment tools limits the validity of these interventions, with almost all articles targeting athletes and adolescents.
Subject(s)
Dietary Supplements , Doping in Sports/methods , Health Education/methods , Health Knowledge, Attitudes, Practice , Performance-Enhancing Substances/therapeutic use , Adolescent , Adult , Athletes/psychology , Child , Doping in Sports/psychology , Female , Humans , Intention , Male , Performance-Enhancing Substances/adverse effects , Young AdultABSTRACT
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.
Subject(s)
Caffeine/adverse effects , Energy Drinks/adverse effects , Performance-Enhancing Substances/adverse effects , Physical Endurance/drug effects , Taurine/adverse effects , Adolescent , Adult , Age Factors , Child , Consumer Product Safety , Drug Interactions , Energy Intake , Humans , Nutritive Value , Recommended Dietary Allowances , Risk Assessment , Risk Factors , Young AdultABSTRACT
Creatine has been considered an effective ergogenic aid for several decades; it can help athletes engaged in a variety of sports and obtain performance gains. Creatine supplementation increases muscle creatine stores; several factors have been identified that may modify the intramuscular increase and subsequent performance benefits, including baseline muscle Cr content, type II muscle fibre content and size, habitual dietary intake of Cr, aging, and exercise. Timing of creatine supplementation in relation to exercise has recently been proposed as an important consideration to optimise muscle loading and performance gains, although current consensus is lacking regarding the ideal ingestion time. Research has shifted towards comparing creatine supplementation strategies pre-, during-, or post-exercise. Emerging evidence suggests greater benefits when creatine is consumed after exercise compared to pre-exercise, although methodological limitations currently preclude solid conclusions. Furthermore, physiological and mechanistic data are lacking, in regard to claims that the timing of creatine supplementation around exercise moderates gains in muscle creatine and exercise performance. This review discusses novel scientific evidence on the timing of creatine intake, the possible mechanisms that may be involved, and whether the timing of creatine supplementation around exercise is truly a real concern.
Subject(s)
Creatine/administration & dosage , Dietary Supplements , Exercise/physiology , Muscle, Skeletal/drug effects , Performance-Enhancing Substances/administration & dosage , Creatine/adverse effects , Creatine/metabolism , Dietary Supplements/adverse effects , Drug Administration Schedule , Female , Humans , Male , Muscle, Skeletal/metabolism , Performance-Enhancing Substances/adverse effects , Performance-Enhancing Substances/metabolism , Time Factors , Treatment OutcomeABSTRACT
The timing of sodium bicarbonate (NaHCO3) supplementation has been suggested to be most optimal when coincided with a personal time that bicarbonate (HCO3-) or pH peaks in the blood following ingestion. However, the ergogenic mechanisms supporting this ingestion strategy are strongly contested. It is therefore plausible that NaHCO3 may be ergogenic by causing beneficial shifts in the strong ion difference (SID), though the time course of this blood acid base balance variable is yet to be investigated. Twelve highly trained, adolescent swimmers (age: 15.9 ± 1.0 years, body mass: 65.3 ± 9.6 kg) consumed their typical pre-competition nutrition 1-3 hours before ingesting 0.3 gâkg BM-1 NaHCO3 in gelatine capsules. Capillary blood samples were then taken during seated rest on nine occasions (0, 60, 75, 90, 105, 120, 135, 150, 165 min post-ingestion) to identify the time course changes in HCO3-, pH, and the SID. No significant differences were found in the time to peak of each blood measure (HCO3-: 130 ± 35 min, pH: 120 ± 38 min, SID: 98 ± 37 min; p = 0.08); however, a large effect size was calculated between time to peak HCO3- and the SID (g = 0.88). Considering that a difference between time to peak blood HCO3- and the SID was identified in adolescents, future research should compare the ergogenic effects of these two individualized NaHCO3 ingestion strategies compared to a traditional, standardized approach.
Subject(s)
Acid-Base Equilibrium/physiology , Athletes , Bicarbonates/blood , Sodium Bicarbonate/administration & dosage , Adolescent , Eructation/etiology , Female , Humans , Hydrogen-Ion Concentration , Male , Nausea/etiology , Performance-Enhancing Substances/administration & dosage , Performance-Enhancing Substances/adverse effects , Performance-Enhancing Substances/chemistry , Sodium Bicarbonate/adverse effects , Sodium Bicarbonate/chemistry , SwimmingABSTRACT
Anabolic androgenic steroid (AAS) and performance-enhancing drug (PED) use is a prevalent medical issue, especially among men, with an estimated 2.9-4 million Americans using AAS in their lifetime. Prior studies of AAS use reveal an association with polycythemia, dyslipidemia, infertility, hypertension, left ventricular hypertrophy, and multiple behavioral disorders. AAS withdrawal syndrome, a state of depression, anhedonia, and sexual dysfunction after discontinuing AAS use, is a common barrier to successful cessation. Clinical resources for these patients and training of physicians on management of the patient using AAS are limited. Many men are hesitant to seek traditional medical care due to fear of judgment and lack of confidence in physician knowledge base regarding AAS. While proposed approaches to weaning patients off AAS are published, guidance on harm reduction for actively using patients remains sparse. Medical education regarding the management of AAS use disorder is paramount to improving care of this currently underserved patient population. Management of these patients must be non-judgmental and focus on patient education, harm reduction, and support for cessation. The approach to harm reduction should be guided by the specific AAS/PEDs used.
Subject(s)
Anabolic Agents , Performance-Enhancing Substances , Substance-Related Disorders , Anabolic Agents/adverse effects , Harm Reduction , Humans , Male , Performance-Enhancing Substances/adverse effects , Steroids , Testosterone Congeners/adverse effectsSubject(s)
Cysts/diagnostic imaging , Cysts/etiology , Deltoid Muscle/diagnostic imaging , Performance-Enhancing Substances/adverse effects , Plant Oils/adverse effects , Prunus armeniaca , Weight Lifting , Deltoid Muscle/pathology , Humans , Magnetic Resonance Imaging , Male , Middle Aged , Tendon Injuries/diagnostic imaging , Testosterone Congeners/adverse effects , Weight Lifting/injuriesABSTRACT
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.
Subject(s)
Athletic Performance/physiology , Energy Drinks/adverse effects , Performance-Enhancing Substances/adverse effects , Sports Nutritional Physiological Phenomena/drug effects , Sports Nutritional Physiological Phenomena/genetics , Adolescent , Athletes , Caffeine/adverse effects , Cardiovascular Diseases/chemically induced , Cardiovascular Diseases/genetics , Cognition/drug effects , Female , Heart Disease Risk Factors , Humans , Male , Taurine/adverse effectsABSTRACT
CONTEXT: Caffeine is 1 of the most popular supplements consumed by athletes, and the evidence for improving soccer performance remains limited. OBJECTIVE: To investigate and update the effects (benefits and harms) of caffeine to improve performance on soccer players. DATA SOURCES: Electronic search in Medline (via PubMed), CENTRAL, Embase, SPORTDiscus, and LILACS, from inception to March 28, 2020. STUDY SELECTION: Randomized clinical trials (RCTs) assessing the effects of caffeine on the performance of soccer players. STUDY DESIGN: Systematic review with meta-analysis. LEVEL OF EVIDENCE: Level 1. DATA EXTRACTION: Data extraction was conducted independently by 2 authors using a piloted form. We assessed methodological quality (Cochrane risk-of-bias [RoB] table) and the certainty of the evidence (GRADE [Grading of Recommendations Assessment, Development and Evaluation] approach). RESULTS: Sixteen RCTs were included. Overall methodological quality was classified as unclear to low risk of bias. When assessing aerobic endurance, meta-analyses did not demonstrate the differences between caffeine and placebo (mean difference [MD], 44.9 m; 95% confidence interval [CI], -77.7 to 167.6). Similarly, no difference was observed during time to fatigue test (MD, 169.8 seconds; 95% CI, -71.8 to 411.6). Considering anaerobic power, meta-analyses also did not find differences for vertical jump (MD, 1.01 cm; 95% CI, -0.68 to 2.69) and repeated sprint tests (MD, -0.02 seconds; 95% CI, -0.09 to 0.04), as well as reaction time agility test (MD, 0.02 seconds; 95% CI, -0.01 to 0.04) and rating of perceived exertion (MD, 0.16 points; 95% CI, -0.55 to 0.87). Regarding safety, a few minor adverse events were reported. Based on the GRADE approach, the certainty of this evidence was classified as very low to low. CONCLUSION: We found no significant improvement in soccer-related performance with caffeine compared with placebo or no intervention. However, caffeine appears to be safe.
Subject(s)
Athletic Performance/physiology , Caffeine/administration & dosage , Dietary Supplements , Performance-Enhancing Substances/administration & dosage , Soccer/physiology , Caffeine/adverse effects , Dietary Supplements/adverse effects , Exercise Test , Humans , Perception/physiology , Performance-Enhancing Substances/adverse effects , Physical Exertion/physiologyABSTRACT
BACKGROUND: The efficacy and safety of L-arginine supplements and their effect on maximal oxygen uptake (VO2 max) remained unclear. This systematic review aimed to investigate the effect of L-arginine supplementation (LAS) on VO2 max in healthy people. METHODS: We searched PubMed, Scopus, Web of Science, Cochrane, Embase, ProQuest, and Ovid to identify all relevant literature investigating the effect of LAS on VO2 max. This meta-analysis was conducted via a random-effects model for the best estimation of desired outcomes and studies that meet the inclusion criteria were considered for the final analysis. RESULTS: The results of 11 randomized clinical trials indicated that LAS increased VO2 max compared to the control group. There was no significant heterogeneity in this meta-analysis. Subgroup analysis detected that arginine in the form of LAS significantly increased VO2 max compared to the other forms (weighted mean difference = 0.11 L min-1 , I2 = 0.0%, p for heterogeneity = 0.485). CONCLUSIONS: This meta-analysis indicated that supplementation with L-arginine could increase VO2 max in healthy people. Further studies are warranted to confirm this finding and to identify the underlying mechanisms.