Supplementation in sport has become very important. The athlete uses ergogenic products or supplements such as caffeine, seeking to improve performance in sports. Therefore, the main objective of this study was to determine the effect of caffeine on aerobic endurance in Mexican professional soccer players. A longitudinal, experimental and prospective, crossover, double-blind, placebo-controlled study was conducted. Aerobic resistance was evaluated with the Yo-Yo Intermittent Recovery Test. Sixteen athletes were included, who were applied the Yo-Yo test before the administration of caffeine. With a crossover design, athletes received caffeine or placebo and the Yo-Yo test was applied. The initial heart rate (HR) of the athletes was 11.7 ± 93.2 (caffeine) and 94.4 ± 21.7 (placebo) (P = 0.85). The final HRs were of 175.8 ± 18.1 (caffeine) and 181.9 ± 13.0 (placebo) (P = 0.28). The HRs recovery were 141.4 ± 22.0 (caffeine) and 142.3 ± 24.4 (placebo) (P = 0.92) and a recovery rate of 34.4 ± 12.5 (caffeine) and 39.6 ± 19.3 (placebo) (P = 0.37). With a total of 2532.5 ± 267.6 meters traveled (caffeine) and 2622.5 ± 285.5 meters (placebo) (P = 0.36). Through the analysis of results, it is concluded that for this sample of athletes, caffeine supplementation had no positive influence on aerobic endurance.
Keywords: Caffeine; Footballers athletes; Aerobic endurance
Caffeine (1, 3, 7, trimethylxanthine) is an alkaloid from the methylated xanthine family; it is an adenosine receptor antagonist, which is found in numerous plants.1 Caffeine is widely distributed in guarana, black tea, and chocolate; caffeine can be considered a drug, a nutrient or a drug of abuse depending on the dose and use.2 Caffeine consumption has been associated with stimulant effects on the central nervous system (CNS), misperception of exhaustion, increased mental concentration and improvement of reflexes.3 Its widespread use is due to the idea that it has exciting properties, which produce stimulation mood, and anti-soporific activity, which reduce fatigue and increase physical performance capacity.1
The sport research indicates that caffeine consumption contributes to significantly improve performance in long-term exercise.1 Likewise; caffeine also improves various aspects of performance in team sports such as skill in single or repeated "sprint" and the reaction time or increase of the precision in the pass in the football.1
According to Katch et al.4, caffeine is consumed regularly by athletes to reduce fatigue. The authors demonstrated that caffeine at a dose of 6 mg/kg can provide ergogenic aid in performance of swimmers. Regarding the dose, not always the higher intake of caffeine is better for athletes. In this regard, an improvement was found in athletic performance with 5 mg/kg; and it was found that higher doses do not cause a higher increase in the effect.4
Foskett et al.5 researched the potential benefits of caffeine on cognitive parameters and intermittent activities of career performing by a footballer. The authors found that a moderate dose (6 mg/kg) of caffeine improves accuracy and control of passes of the ball between football players; these effects are attributed to improved fine motor skills. With this evidence, the main objective of this study was to evaluate the effect of a single dose of caffeine on aerobic endurance in soccer players of a Mexican university.
A prospective, randomized, crossover, single center, double-blind, placebo-controlled study was conducted to research the effect of caffeine on aerobic endurance in soccer players of a Mexican university. The study was conducted at the University of Football and Sports Science (Spanish: Universidad de Futbol y Ciencias del Deporte), Hidalgo, Mexico. The study protocol was approved by the Ethic and Research Committees (Spanish: Comités de Ética e Investigación) at the University of Football and Sports Science, Hidalgo, Mexico, and the study was conducted according to the guidelines of the Declaration of Helsinki.
Inclusion criteria were: age ≥18 years, male gender, soccer players of the Football League Second Division of the University of Football and Sports Science from the High Performance Tuzo, registered by the Pachuca Club, and who had signed the letter of informed consent. Complete medical history was made and records of the use of liquids and caffeinated beverages. Participants had no history of allergy to caffeine or xanthines. Participants were excluded if they had conditions such as anxiety, insomnia, panic, arrhythmias, hypertension, epilepsy, liver or kidney failure, diabetes, hypo- and hyperthyroidism, gastroesophageal reflux, gastritis and peptic ulcers. Also, if they consumed methylphenidate, modafinil, nicotine, pemoline, pseudoephedrine, phenylpropanolamine or beta blockers, norfloxacin, clozapine, ciprofloxacin, enoxacin, inhibitors mono-aminooxidas (furazolidone, procarbazine, and selegiline), benzodiazepines, barbiturates, phenytoin, rifampin, theophylline, methylxanthines, clarithromycin, erythromycin, fluvoxamine, ketoconazole, tacrine, zileuton and terbinafine.
All participants underwent a clinical examination by a physician. Weight and height in participants with the use of light clothing and no shoes were measured.
A crossover design 2 x 2 (Figure 1) was used for administration of medicines (caffeine or placebo). In this case, the study was conducted in 2 periods of administration, separated by a washout period (necessary time for the drug administered in the first period to be removed in its entirety). As it was a crossover placebo-controlled design, they involved the same subjects as their own controls. In this case, the total participants were divided into 2 groups "Group A" and "Group B". In the period II, placebo was administered to the Group A and Group B received caffeine. In the period II (After a 7-day washout) the Group A now received caffeine and the Group B received placebo.
Figure 1. 2x2 crossover Design used in the study. Participants were divided into two groups.
Time 1 of the research: the Yo-Yo Intermittent Recovery Test was performed to determine the aerobic endurance for the first time.6 Heart rate was monitored with digital equipment POLAR® RC3 GPS HR model. The Yo-Yo Test, has 5 audio tracks (5 levels), each with 15 intermittent (5 levels x 15 = 75 intermittent). The athlete runs to the audio signal (signal 1) from a departure point to another (signal 2) positioned 20 meters away (marked by two straight and parallel lines) and returns to the starting point (signal 3), that is racing back and forth over a stretch of 20 meters, at a speed which increases progressively, reaching exhaustion. In each intermittent the athlete runs 40 meters (20 m forward and 20 m back). At the end the following data are recorded: the average of the level reached, the average number of intermittent reached at the last level, the average of total intermittent traveled and the average of the distance covered.
Time 2 of the research: Seven days after the first evaluation, drugs were administered, the "Group A" consumed placebo and "Group B" was given 500 mg of caffeine. One hour later the Yo-Yo test was applied for the second time under the same specifications.
Time 3 of the research: Seven days after the second evaluation, drugs were administered, the "Group A" consumed caffeine and placebo was given to the "Group B". One hour later the Yo-Yo test was applied for the third time under the same specifications.
The placebo was similar in appearance to the medication, but only containing an inert substance (rice flour). Subjects ingested the capsules with 12 ounces of bottled water. The capsules were manufactured and packaged by Liomont S.A. de C.V. (Mexico City), and they were identical in appearance.
Data were collected in a database excel, where it was included: the number of intermittent, the level at which they reached in the physical test, initial heart rate, final heart rate and finally the recovery heart rate at 1 minute after completion of the test; then data were captured in the SPSS statistical program. The t Student test was used to compare the effect of caffeine versus placebo, based on a P <0.05 to denote significant difference.
A total of 16 athletes were included in the study, with an average age of 19.4 ± 1.5 years, weight of 71.9 ± 4.7 kg and height of 1.2 ± 1.79 meters.
The aerobic resistance is defined as the ability of the body that allows exercise of greater or lesser intensity for as long as possible. In this regard, we take into account different variables in the Yo-Yo Test. In this case, the results obtained in the test during the administration of one dose of 500 mg caffeine and placebo are summarized in Tables 1 and 2.
Table 1. Effect of caffeine and placebo in the Yo-Yo Intermittent Recovery Test of 16 participants.
|Level of the test||4.6 ±0.5||4.8 ± 0.4||0.28|
|Intermittent||9.9 ±4.2||9.3 ±5.2||0.74|
|Total of intermittent||63.3 ± 6.7||65.6 ± 7.1||0.36|
|Total of meters||2532.5 ± 267.6||2622.5 ± 285.5||0.36|
Table 2. Effect of caffeine and placebo in the Yo-Yo test on 16 participants
|Initial Heart Rate||93.2 ± 11.7||94.4 ± 21.7||0.85|
|Final Heart Rate||175.8 ± 18.1||181.9 ± 13.0||0.28|
|Recovery Heart Rate||141.4 ± 22.0||142.3 ± 24.4||0.92|
|Recovery rate||34.4 ± 12.5||39.6 ± 19.3||0.37|
During supplementation of caffeine and placebo, there were no adverse reactions. Participants were evaluated and supervised by the physician and the main researcher.
According to the conditions used in the design and implementation of the present study, there was not a significant increase in aerobic endurance of the athletes. In this regard, several studies3-7 have mentioned that the ergogenic effects of caffeine in the development of certain activities of resistance, depend on a number of factors such as the kind of physical activity (type, duration and intensity), caffeine consumption, ambient temperature where the activity takes place, lipid profile or loss of body fat, body weight and sex.
In our study, the use of the Level 2, Yo-Yo Intermittent Recovery Test, was proposed to measure the aerobic endurance. Our results agree with the study of Pettersen et al.8 because they used the same test to evaluate the effect of caffeine versus placebo in two football clubs with youth categories. The authors found that caffeine did not produce significant positive effects on total distance traveled, sprints and acceleration counts.
Graham & Sprite9 mentioned that the mechanisms responsible for the improvement in prolonged endurance exercise remain vague. For example, in studies of Greer et al.10 they found no beneficial results with caffeine in the fatigue to short term in a group of active men.
Wilcox on a review11 concluded that there are few well-controlled studies that have examined the effects of caffeine on physical performance, and that the resistance results have been inconsistent, identifying factors that may confound the data on the effect of caffeine. Conlee12 summarized these factors in 3: exercise modality, power production and the dose of caffeine.
In the present study, 500 mg tablets of caffeine were supplied, which corresponds to an approximate dose of 6.9 mg/kg body weight. Some studies with team sports have found that caffeine produced effective results.13, 14 However, the authors used the combination of caffeine with other substances such as carbohydrates and energizer drinks. This could be considered as an alternative in subsequent studies.
Finally, we have to take into account the following considerations in supplementation in sports:
1. The complexity of a plan supplementation in sport is addressed to the specific needs of each subject and implicit in the sport itself, ie, the individuality of the subject, playing position and energy demands are variables to be considered in time to check the effect of a certain substance.15
2. The physiological adaptation that athletes develop as decreased heart rate at rest and rapid recovery of maximum heart rate.16
3. We have to consider the athlete's body weight at the time of dosing the amount of supplement that guarantees the ergogenic effect of the drug based on the revised references; well with other medicines it requires a quantitative analysis to be or not considered as doping.17
4. The effects of caffeine vary greatly among individuals. Therefore, it is unlikely to explain the improvement in exercise capacity and performance observed in continuous and prolonged exercise protocols in team sports.11
5. This performance can be improved or not, depending on a number of factors such as physical activity (type, duration and intensity) and also the dose of caffeine consumed or ambient temperature where the activity takes place. Which also affects the lipid profile or loss of body fat.7, 18
According to the results, it is considered that for this sample of athletes, caffeine supplementation had no positive influence on aerobic endurance. Regarding football, there is not research to substantiate the effectiveness of its use to improve not only aerobic endurance, but the power output, the sprint and accuracy (attributes conferred to caffeine).
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Itze Noriega Muro
Universidad del Futbol y Ciencias del Deporte.
San Agustín Tlaxiaca, Hidalgo.