Ergogenic Aids to Improve Physical Performance in Female Athletes: A Systematic Review with Meta-Analysis

on studies investigating the effects of ergogenic aids (EAs) on sports performance have been carried out in the male population. Thus, the aim of this systematic review and meta-analysis was to summarize the effects in the existing literature of EAs used by female athletes on performance. A literature research was conducted, and a descriptive analysis of the articles included in the systematic review was carried out. Meta-analyses could be performed on 32 of the included articles, evaluating performance in strength, sprint, and cardiovascular capacity. A random-effects model and the standardized mean differences (SMD) 95% con dence intervals (CI) were reported. The results showed that caffeine helped to improve jumping performance, isometric strength values, and the number of repetitions until failure. Caffeine and sodium phosphate helped to improve sprint performance. Aerobic tests could be improved with the use of taurine, caffeine, and beta-alanine. No conclusive effects of beetroot juice, polyphenols, or creatine in improving aerobic performance were shown. In terms of anaerobic variables, both caffeine and sodium phosphate could help to improve repeated sprint ability. More studies are needed

until failure. Caffeine and sodium phosphate helped to improve sprint performance. Aerobic tests could be improved with the use of taurine, caffeine, and beta-alanine. No conclusive effects of beetroot juice, polyphenols, or creatine in improving aerobic performance were shown. In terms of anaerobic variables, both caffeine and sodium phosphate could help to improve repeated sprint ability. More studies are needed in female athletes that measure the effects of different EAs on sports performance, such as beetroot juice, beta-alanine or sodium phosphate, as the studies to date are scarce and there are many types of EA that need to be further considered in this population, such as creatine and taurine. Keywords:women; sports; performance; supplementation; exercise; nutrition 1. Introduction The ingestion of ergogenic aids (EA) to enhance performance has become popular in recent years and is a widely used strategy by athletes [1]. Although the terms “EA” and “nutritional supplementation” are used interchangeably in the literature, we can differentiate certain nuances between them. Nutritional supplementation would encompass sources of nutrients or other substances with a physiological or nutritional effect that complement the normal diet [2]. EA, on the other hand, include any short- and/or long- term nutritional practice that seeks to improve sports performance, to enhance training adaptations and/or to help post-exercise recovery [3]. Therefore, all EA are nutritional supplements, but not all supplements are EA. There are a plethora of sports EAs on the market that aim to achieve different indi- rect performance improvements, such as a modulation of the in ammatory response [4], reducing oxidative stress [5], improving homeostasis recovery [6], adaptation of signaling pathways [7], reducing fatigue [8], or improving aerobic [9] and short, high-intensity ex- ercise performance [10]. For some of these EAs there is solid proven scienti c evidence (e.g., caffeine (CAF), creatine (CRE), nitrate, beta-alanine (BA), and bicarbonate (SB)) [11,12] while for others there is a lack of evidence or it is very limited and inconclusive (e.g., the amino acid N-acetylcysteine or polyphenols (PPs)) [12]. Nutrients2023,15, 81.

c evidence (e.g., caffeine (CAF), creatine (CRE), nitrate, beta-alanine (BA), and bicarbonate (SB)) [11,12] while for others there is a lack of evidence or it is very limited and inconclusive (e.g., the amino acid N-acetylcysteine or polyphenols (PPs)) [12]. Nutrients2023,15, 81.

Nutrients2023,15, 81 2 of 28 One of the most used EAs is CAF due to its effect on improving force production, decreased ratings of perceived exertion and pain, and improvements in aerobic capacity, among others [13,14]. CRE is another widely used EA to improve performance in short, high-intensity exercises [15], with consistent scienti c evidence. L-carnitine, on the con- trary, although broadly used, lacks conclusive scienti c studies that prove its ergogenic effect [16]. The conclusive literature on the use of new emerging EAs such as PPs is not very extensive [17,18], although their effect as a nutritional supplement to improve health in the non-active population has been already demonstrated [19–21]. Some studies of recreational and elite athletes have shown some differences in the consumption levels of nutritional supplements and EAs in swimmers [22] and rugby players [23], while in other sports, such as handball [24], rowing [25], or fencing [26] no differences between consumption levels were found. Regarding gender differences in EA consumption, studies have mostly found a similar prevalence in the use of EA among males and females [27]. Despite this similar prevalence in EA consumption between male and female athletes, most intervention studies investigating the effects of EAs in sports performance have been carried out in the male population, with few studies showing the effects of different types of EAs in female athletes and sportswomen [13,28,29]. Due to the widely proven physiological and hormonal differences between men and women that cause the processes of absorption, distribution, metabolism, and disposal of pharmacological substances to differ [30,31], the response to EAs may not be the same. Some studies show dissimilar responses by gender to different EAs, although these are scarce [32– 34]. For instance, females could present lower changes in heart rate but higher blood pressure changes than males when consuming CAF [32]. Furthermore, they need a smaller amount of BA than men to reach the same relative increase in muscle carnosine levels [34]. Another difference is that women present higher NO2levels and have a more oxidative type of skeletal muscle than men, so they may benefit more from

in heart rate but higher blood pressure changes than males when consuming CAF [32]. Furthermore, they need a smaller amount of BA than men to reach the same relative increase in muscle carnosine levels [34]. Another difference is that women present higher NO2levels and have a more oxidative type of skeletal muscle than men, so they may benefit more from the consumption of NO3containing EAs such as beetroot juice (BJ) [28]. These differences could influence sports performance, but more research is needed to better understand the specific effects of EAs in females. It is therefore necessary to compile information about intervention studies using EAs in physically active females and sportswomen, in order to synthesize the positive, neutral, or negative effects they produce. Hence, the objective of this systematic review and meta- analysis was to summarize the effects in the existing literature of EAs used by female athletes and recreationally practitioners on performance. 2. Materials and Methods A systematic review of the literature and meta-analysis were carried out following the PRISMA guidelines and the PICOS criterion. This work was registered in PROS- PERO (CRD42022340185). 2.1. Search Strategy and Study Selection A literature search was conducted during April–June 2022 using the PubMed and Web of Science databases. A search strategy was devised using the words “female” OR “women” AND “sport” OR “exercise” AND “ergogenic aids” by including them in the “topic” section in Web of Science and in the Title/Abstract section in PubMed. The research was ltered by date, including articles from the last 15 years. No language lter was applied. The inclusion criteria were intervention studies on female athletes or recreationally active women using EAs to enhance their physical performance, both acutely and longitudi- nally. By physical performance we mean the skills deemed necessary for increased success and a reduced risk of occurrence/severity of injury when exercising and/or practicing sports (i.e., muscle strength, sprinting capacity, cardiorespiratory tness, and all their mag- nitudes and components). Studies with women over 18 years old were included with no age limit. The exclusion criteria were studies that solely included measurements on parameters other than sports

skills deemed necessary for increased success and a reduced risk of occurrence/severity of injury when exercising and/or practicing sports (i.e., muscle strength, sprinting capacity, cardiorespiratory tness, and all their mag- nitudes and components). Studies with women over 18 years old were included with no age limit. The exclusion criteria were studies that solely included measurements on parameters other than sports performance, studies which included the effects of EAs in both men and women without comparing the results by sex, and articles in which the participants used

Nutrients2023,15, 81 3 of 28 supplements without seeking ergogenic support. Conference proceedings, doctoral theses, dissertations, case studies, and other reviews and meta-analyses were excluded. Initially, 341 items were identi ed. After eliminating duplicates and ltering according to the inclusion criteria, 43 articles were included in the review and 32 in the meta-analysis. The study selection ow chart is shown in Figure.Nutrients 2023, 15, 81 3 of 29 success and a reduced risk of occurrence/severity of injury when exercising and/or prac- ticing sports (i.e., muscle strength, sprinting capacity, cardiorespiratory fitness, and all their magnitudes and components). Studies with women over 18 years old were included with no age limit. The exclusion criteria were studies that solely included measurements on parameters other than sports performance, studies which included the effects of EAs in both men and women without comparing the results by sex, and articles in which the participants used supplements without seeking ergogenic support. Conference proceed- ings, doctoral theses, dissertations, case studies, and other reviews and meta-analyses were excluded. Initially, 341 items were identified. After eliminating duplicates and filtering accord- ing to the inclusion criteria, 43 articles were included in the review and 32 in the meta- analysis. The study selection flow chart is shown in Figure 1. Figure 1. Flow chart for study selection according to PRISMA criterion. 2.2. Data Extraction Figure 1.Flow chart for study selection according to PRISMA criterion. 2.2. Data Extraction The selection of articles and the data extraction on study source, study design, study quality, participants' sample size, participants' characteristics, ergogenic substances, and performance outcomes of the interventions were conducted by three independent reviewers (CRL, OLT, and RCE). If disagreements appeared, a third author (VEF-E) was included, and the discrepancies were resolved through discussion. Trials were not excluded based on quality. A priori, the main outcomes analyzed were changes in the measures of physical per-

Nutrients2023,15, 81 4 of 28 formance triggered by the ingestion of EA. All the evaluations were performed in duplicate, independent of each other. Disagreements in the analysis were resolved through consensus. 2.3. Risk of Bias The risk of bias assessment was independently evaluated by two reviewers with the PEDro scale [35]. This tool provides information about the allocation and randomization process, the blinding process, the data obtained, and the statistical analysis. The PEDro score scale considers a rate of 0–3 `poor', 4–5 `fair', 6–8 `good', and 9–10 `excellent'. Furthermore, a total PEDro score of 8/10 is considered optimal for trials assessing complex interventions (e.g., exercise). 2.4. Statistical Analysis To analyze the data, the studies were separated according to the physical abilities examined. All the variables that assessed the same physical capacity were analyzed together. Thus, an analysis was carried out to determine performance in strength (divided into jumping and power, isometric strength, and endurance strength), sprint, and cardiovascular capacity (aerobic and anaerobic). Of the 43 articles selected in the review, 11 were discarded for the meta-analysis because they did not include suf cient data, or they analyzed other types of variables not related to exercise performance. Therefore, measurements were taken from the EA intake groups and the placebo groups to make a comparison among them. The most representative variable of the physical capacity was included in the data analysis. In those studies that included two EAs, the two corresponding variables analyzed independently with respect to the placebo group were added. The outcome measure to carry out the analysis was the standardized mean difference (SMD). A random-effects model was then tted to the data. The restricted maximum- likelihood estimator (RML) [36] was used to calculate the amount of heterogeneity (i.e., tau 2 ). In addition to the RML estimator, the Q-test for heterogeneity [37] and the I 2 statistic are detailed. If any amount of heterogeneity was noticed (i.e., tau 2 > 0, regardless of the Q-test's results), a prediction interval for the true outcomes was also given. To investigate whether studies might be outliers and/or in uential in the context

2 ). In addition to the RML estimator, the Q-test for heterogeneity [37] and the I 2 statistic are detailed. If any amount of heterogeneity was noticed (i.e., tau 2 > 0, regardless of the Q-test's results), a prediction interval for the true outcomes was also given. To investigate whether studies might be outliers and/or in uential in the context of the model, studentized residuals and Cook's distances were utilized. Studies with values greater than the 100 (1 0.05/(2 k))th percentile of a standard normal distribution were considered to be potential outliers (i.e., utilizing a Bonferroni correction with two-sidedalpha = 0.05 for k studies included in the meta-analysis). Studies which presented a Cook's distance bigger than the median plus six times the interquartile range of the Cook's distances were considered in uential. The rank correlation test and the regression test were applied to test for funnel plot asymmetry, making use of the standard error of the observed results as a predictor. To perform all the analyses, the free statistical software Jamovi was used (version 1.6.15) [38]. 3. Results The characteristics of the studies are presented in Table. The articles included dated from 2008 to 2022. Most studies were cross-sectional in nature (n= 35, 81.4%). The remaining studies incorporated interventions evaluating the longitudinal effects of EAs. Thirty- ve out of the forty-three studies had a cross-over design (81.4%) and the remaining eight articles included a speci c control group. A total sample ofn= 710 women was included in the qualitative analysis with a mean age of 26.5 years and a mean BMI of 22.7 kg/m 2 . Of the 43 studies, 20 (46.5%) were carried out with team sports players (n= 339), 10 with endurance trained athletes (23.3%,n= 144), 6 with resistance trained athletes (14.0% n= 82), 4 with recreationally active females (9.3%,n= 75), 1 with sports students (2.3%, n= 24), 1 with tennis players (2.3%,n= 17) and 1 with kayak athletes (2.3%,n= 5) (see Table).

resistance trained athletes (14.0% n= 82), 4 with recreationally active females (9.3%,n= 75), 1 with sports students (2.3%, n= 24), 1 with tennis players (2.3%,n= 17) and 1 with kayak athletes (2.3%,n= 5) (see Table).

Nutrients2023,15, 81 5 of 28 Table 1.Characteristics of the studies included in the systematic review. [Author, Journal—Year] Title Aim Sample ( n), age, BMI EA-Dosis Effects on Conclusions [Mart½n-Rincân, Nutrients—2020] Supplementation with a Mango Leaf Extract (Zynamite®) in Combination with Quercetin Attenuates Muscle Damage and Pain and Accelerates Recovery after Strenuous Damaging Exercise To examinate if Zynamite administered in combination with quercetin, interfere or not with muscle performance and promotes recovery after repeated damaging exercise Students of sports sciences (48), 23.3, 22.2 PP 140 mg of Zynamite + 140 mg of quercetin (1 h before and every 8 h thereafter for 24 h) 5 km running 10 km race followed by 100 drop jumps 140 mg Zynamite + 140 mg consumption might be effective to decrease muscle pain and damage, and to boost muscle performance recovery [Waldron, Amino Acids—2018] The effects of taurine on repeat sprint cycling after low or high cadence exhaustive exercise in females To investigate the effects of TAU vs. PLA on RSA, performed after xed incremental ramp exercise to exhaustion in women University lacrosse players (9), 22, 24.5 TAU Acute 50 mg/kg 6 10 s sprint in cycle ergometer (90 r/min or 30 r/min) Heart rate (HR) Blood lactate TAU decreased HR before exercise and enhanced end-test power output, detrimentally affecting sprint performance, regardless of cadence. Short endurance performance may improve acutely following TAU intake, but this effect may not be sustained over longer exercise periods or urge the need for longer recovery periods. [Wickham, Physiol. Rep.—2019] No effect of beetroot juice supplementation on exercise economy and performance in recreationally active females despite increased torque production To explore if acute and chronic BJ ingestion reduced de O2 cost of submaximal exercise, improved aerobic TT performance and improved skeletal muscle torque production in recreationally active females. Recreationally active (12; 12); 23; 22; 22.8; 23 BJ 6.5 mmol nitrate 2 times/day (8 days) Study 1: VO 2at 50/70 VO 2peak Study 2: MVC plantar exors BJ did not decrease submaximal exercise VO 2nor increase aerobic TT performance in recreationally active women.

improved skeletal muscle torque production in recreationally active females. Recreationally active (12; 12); 23; 22; 22.8; 23 BJ 6.5 mmol nitrate 2 times/day (8 days) Study 1: VO 2at 50/70 VO 2peak Study 2: MVC plantar exors BJ did not decrease submaximal exercise VO 2nor increase aerobic TT performance in recreationally active women.

This systematic review summarizes the effects of ergogenic aids on performance in female athletes.