Volleyball is a complex team sport with specific physical and physiological attributes, as well as technical and tactical on-court demands (21,31). In elite volleyball, the mean rally time is less than 12 s (32) although the players’ contact with the ball occurs within a small space zone. For these reasons, most volleyball movements are short and explosive and rely on anaerobic pathways (28). Typically, morphological (mainly height and standing reach height) and physical characteristics related to muscle explosiveness have been identified as key elements in volleyball performance (21,29). Among them, the jump ability has been reported as the most essential physical attribute for either defensive or offensive actions because it is a fundamental part of spikes, blocks, and serves (28), and jump height has been directly related to game success (22,26).
Caffeine has been proven effective to improve jump height in soccer (8,14,20), basketball (1), and rugby players (11). Moreover, the ingestion of a caffeinated drink has been effective to increase jump performance in male volleyball players (10). All these studies have determined the effectiveness of caffeine using static and isolated jumps (such as squat jumps, countermovement jumps, or repeated jumps) without the intervention of the arms. However, the characteristics of a volleyball jump include the use of the arms to block or spike. Thus, it is necessary to investigate whether caffeine is effective to improve jump performance when performing volleyball-specific movements and jumps.
Besides jump capacity, other physical abilities such as agility and speed are essential for volleyball success. Several investigations have determined the effectiveness of caffeine to improve sprinting (2,11,34), but the limited dimensions of the volleyball court preclude the attainment of maximal running velocity. A current investigation with male volleyball players has shown that the preexercise ingestion of a caffeinated energy drink reduced the time needed to complete the agility t-test, a test that mimics the movements produced in a volleyball game (10). In addition, this investigation has also revealed that the caffeinated energy drink increased the number of successful actions performed during a real volleyball game suggesting the transference from increased physical performance to real game enhancement (10).
The aim of this investigation was to determine the effects of a commercially available caffeinated energy drink (3 mg of caffeine per kg of body mass) on the physical performance of female volleyball players. We hypothesized that the preexercise ingestion of the caffeinated energy drink would improve volleyball-specific physical performance, which in turn would improve overall volleyball performance.
Thirteen young female volleyball players (25.2 ± 4.8 yr, 174 ± 9 cm of height, 64.4 ± 7.6 kg of body mass) from the same volleyball team (second division of the Spanish National league) were recruited for this investigation. All participants had prior volleyball experience of at least 6 yr and had trained for approximately 2 h·d−1, 5 d·wk−1 (including a weekly competition) during the previous year. Players were not taking medications during the study, and they had no previous history of cardiopulmonary diseases. Four participants were tested during the follicular phase of their menstrual cycle, whereas the remaining nine players were tested during the luteal phase. A preliminary analysis revealed that the results of this investigation were not affected by the menstrual cycle, and thus, all participants were treated as a single group. Before enrolling in the investigation, participants were fully informed of any risks and discomforts associated with the experiments before giving their informed written consent to participate. The study was approved by the University Ethics Committee in accordance with the latest version of the Declaration of Helsinki.
A double-blind, placebo-controlled, and randomized experimental design was used in this investigation. Each volleyball player took part in two trials under the same experimental conditions 1 wk apart to allow for complete recovery. On one occasion, participants ingested a caffeine-containing energy drink (Fure®, ProEnergetics, Spain) to provide an individualized dose of 3 mg of caffeine per kilogram of body mass. This energy drink is commercially available in powder, and the individualized amount of energy drink was dissolved in 250 mL of tap water for all participants. On another occasion, participants ingested the same amount of an identical powdered energy drink but without the caffeine content (0 mg·kg−1, placebo drink). Both the caffeinated energy drink and the placebo drink contained a slight amount of carbohydrate (6.6 mg·kg−1 in the form of maltodextrin) to sweeten the taste of the drinks. However, the amount of exogenous energy provided in the form of carbohydrate with the beverages was negligible (≈2 kcal). In addition, the two experimental beverages contained taurine (18.7 mg·kg−1), sodium bicarbonate (4.7 mg·kg−1), and l-carnitine (1.9 mg·kg−1). All of these substances were ingested in identical proportions in the two experimental trials, and the doses provided with the beverages were much lower than the minimal doses of these substances with a reported ergogenic effect (3). Beverages were ingested 60 min before the onset of the experimental trials, and an alphanumeric code was assigned to each trial by a person who was independent of the investigation to blind participants and investigators to the drink tested. This code was only unveiled after the analysis of the tests.
Two days before the first experimental trial, the volleyball players were weighed nude to calculate individual energy drink dosage. On the day of the trial, participants were encouraged to refrain from all dietary sources of caffeine, alcohol, and stimulants for the duration of the study. Twenty-four hours before each experimental trial, participants refrained from strenuous exercise and adopted a similar sleep pattern, diet, and fluid intake regimen. Diet, fluid ingestion, and sleep patterns were assessed using self-report questionnaires. Moreover, participants were encouraged to consume their habitual precompetition meal 3 h before the start of testing and replicated this before each experimental trial.
The experimental beverages were individually provided in opaque and sterilized bottles on the participants’ arrival at the stadium. The exchange of bottles between players was not allowed, and the investigators encouraged players to drink the beverage in its entirety. Then, players were weighed nude and dressed in their competition clothes. A GPS-accelerometer device (Spi-ProX; GPSports, Melbourne, Australia) and an HR monitor (Polar Team, Kempele, Finland) were attached to the participant’s chest using an adjustable harness. Participants then performed a 30-min standardized warm-up, and 60 min after the beverage intake, the players performed the following volleyball-specific tests: a) a standing spike and a jump spike with an official ball, as previously described (24), using a radar gun (ATS; Stalker, Plano, TX) to measure maximal ball velocity. The coefficient of variation (CV) of these measurements has been established at approximately 4% (35); b) a maximal spike jump measured by photoelectric cells (Optojump Next; Microgate, Bolzano, Italy), in which participants performed a two-step approach; c) squat, countermovement, and block jumps on a force platform (Quattro Jump; Kistler, Winterthur, Switzerland) as previously described (10). A previous investigation indicated that the CV for these jumps in volleyball players was between 2.1% and 2.8% (28). The stretch-shortening cycle efficiency of the leg muscles was estimated as the percentage of countermovement jump gain over squat jump height to assess muscle properties (4,17); d) a maximal manual dynamometry test for both hands measured using a dynamometer (Grip-D, Takei, Japan) with a reported CV of 1.6% (30); and e) the agility t-test as previously defined (25) and measured by infrared beams (DSD Laser System, Vitoria, Spain) with a reported CV of 3.3% (33). Each test was performed twice, and the best result was used for the statistical analysis. A rest period of 1 min was set between repetitions and 3 min between tests to allow for full recovery. The participants were previously familiarized with all the tests carried out in this investigation because their execution is part of their training routines.
Fifteen minutes after the volleyball-specific testing, players participated in a three-set simulated game played on an official wooden surface (approximately 1 h of duration). The game followed the rules of the Fédération Internationale de Volleyball (16), and the team’s coach acted as the referee to make decisions on play disputes during the game. Each volleyball team was represented on court by a setter, two receivers, two middles, and the opposite, whereas the libero substituted for middle players when they were positioned in backcourt or in defensive positions. Starting teams and player’s substitutions were replicated in both games to avoid individual playtime differences. Two video cameras (Sony Handycam HDR-XR200VE; Sony, Tokyo, Japan) set diagonally (approximately 10 m at the back of each half-court and placed at 2 m above the floor) were used to record each game action during the simulated match. Afterward, two trained and experienced observers, blinded to the experimental treatments, analyzed the games using video analysis software designed specifically for volleyball (Data Volley; DataProject, Bologna, Italy). A simplified cluster analysis based on the game action classification of this software was used to classify players’ performance in each volleyball action. Each action was classified as positive, neutral, or negative, as explained in Table 1. In the case of disagreement between observers in the evaluation of a player’s action, the observers revisualized the specific action and discussed it until they obtained a final decision/evaluation. The interobserver reliability in the analysis of the game actions presented a Cohen kappa coefficient equal to 0.89. During the game, players’ body impacts (with the GPS devices set for indoor measurement) and HR were individually measured and analyzed afterward with the specific software. The body impacts during the game represented the amount and intensity of body acceleration/deceleration (in g forces) produced during the volleyball game. Although this measurement was unspecific to differentiate among different volleyball actions (e.g., blocks, digs, and jumps), it allowed the quantification of individual body movements during the game in each experimental trial. The body impacts were categorized as follows: zone 1 = 0.0g–1.0g, zone 2 = 1.1g–2.0g, zone 3 = 2.1g–3.0g, zone 4= 3.1g–4.0g, zone 5 = 4.1g–5.0g, and zone 6 = 5.1g–6.0g.
At the end of both trials, players were required to fill out a questionnaire about their sensations of power, endurance, and perceived exertion (RPE) during the volleyball game. This questionnaire included a 1- to 10-point scale to assess each item, and participants were previously informed that 1 point meant the minimal amount of that item and 10 points meant the maximal amount of the item. In addition, participants were provided with a survey to be filled out the following morning about sleep quality, nervousness, gastrointestinal problems, and other discomforts. This survey included seven items on a yes/no scale and has been previously used to assess side effects derived from energy drink ingestion (8). This survey also included specific questions to evaluate the success of the blinding procedure.
Data were collected as previously indicated, and the results of each test were subsequently blindly introduced and analyzed into the statistical package SPSS v 20.0 (SPSS Inc., Chicago, IL). First, the Shapiro–Wilk test was used to test the normality of each variable (P > 0.05) and then a paired t-test was used to analyze the differences between the experimental beverages (caffeinated energy drink vs placebo drink). The McNemar test was also used to detect differences in side effects after beverage intake. The results are shown as mean ± SD, and the significance level was set at P < 0.05. The effect size (ES) and the 95% confidence interval were calculated to verify the caffeinated energy drink effect on players’ performance.
Diet and sleep control and blinding success
The energy intake (2059 ± 183 vs 2069 ± 184 kcal) and the proportions of protein/carbohydrate/fat in the diet (26/60/13 vs 26/60/13) were very similar between the caffeinated energy drink trial and the placebo drink trial in the 24 h before the experimental trials (P < 0.05). Similarly, the self-reported sleeping hours were similar between the experimental trials (7.9 ± 1.4 vs 7.5 ± 1.4 h). Only 31% (4 of 13) of the participants correctly guessed the order of the trials, indicating successful blinding of the participants to the interventions.
Data from all the tests performed in this investigation are presented in Table 2. In comparison with the placebo drink, the preexercise ingestion of the caffeinated energy drink significantly improved the handgrip force in both the right (P = 0.004, ES = 1.53) and left hand (P = 0.019, ES = 1.26). Maximal ball velocity was significantly greater for both standing (P = 0.023, ES = 1.22) and jumping spike tests (P = 0.038, ES = 1.4) with the caffeinated energy drink than with the placebo drink. The caffeinated energy drink also increased jump heights in all volleyball-specific jumps such as the spike jump (P = 0.024, ES = 1.22), the block jump (P = 0.044, ES = 1.11), the squat jump (P= 0.028, ES = 1.19), and the countermovement jump (P = 0.018, ES = 1.19). Moreover, the caffeinated energy drink increased peak power production during the block jump (P = 0.018, ES = 1.27), squat jump (P = 0.013, ES = 1.32), and countermovement jump (P = 0.049, ES = 1.10). However, there were no statistical differences for the stretch-shortening cycle efficiency between the caffeinated energy drink and the placebo drink (12% ± 6% vs 11% ± 7%, respectively). Finally, the caffeinated energy drink significantly reduced the time needed to complete the agility t-test (P = 0.036, ES = 1.15).
The cluster analysis of the simulated volleyball game showed that the caffeinated energy drink significantly improved the proportion of game actions classified as positive (P < 0.001, ES = 1.22), whereas the percentage of game actions categorized as negative was significantly reduced with respect to the placebo drink (P < 0.001, ES = 1.79, Table 2). Nevertheless, there were no significant differences between the experimental beverages for the proportion of game actions classified as neutral (P = 0.265, ES = 0.29). The total number of impacts during the simulated game was higher with the caffeinated energy drink than with the placebo drink (P = 0.001, ES = 0.22). Figure 1 depicts the categorization of body impacts according to the intensity of each acceleration. The ingestion of the caffeinated energy drink increased the number of impacts in all zones (P < 0.05) except for zone 4. The caffeinated energy drink also increased the mean HR (142 ± 14 vs 132 ± 14 bpm; P = 0.040, ES = 0.7) and maximal HR (185 ± 10 vs 180 ± 5 bpm; P = 0.049, ES = 0.9) during the simulated game.
Side-effects derived from the beverage intake
Caffeinated energy drink intake significantly increased perceived muscle power (6.2 ± 1.6 vs 5.1 ± 1.6; P = 0.046, ES = 0.57) during the testing when compared with the placebo drink. However, no significant differences were found for self-reported fatigue (4.8 ± 1.5 vs 3.8 ± 1.5, P = 0.083) or the endurance perception (5.8 ± 1.4 vs 5.0 ± 1.3, P = 0.090). During the hours after the testing, volleyball players showed significantly higher prevalence of nervousness (31% vs 0%, P < 0.01) and activeness (15% vs 0%, P = 0.05) with the ingestion of the caffeinated energy drink than with the placebo. The remaining side effects (insomnia, gastrointestinal discomforts, headache, and irritability) were similar between the two experimental beverages.
The aim of this investigation was to determine the efficacy of a caffeinated energy drink to improve volleyball physical performance in elite female players. For this purpose, 13 semiprofessional female players performed volleyball-specific tests and played a simulated match after the ingestion of 3 mg·kg−1 of caffeine in the form of a commercially available energy drink or a placebo drink. The preexercise ingestion of the caffeinated drink increased handgrip force, improved jump height and muscle power output during specific jumps, and reduced the time needed to complete an agility test. In addition, the caffeinated drink increased the number of game actions classified as positive during the game, whereas it reduced the number of errors. These ergogenic effects were accompanied by increased mean and maximal HR during the game and augmented prevalence of nervousness and activeness in the hours after the ingestion of the experimental drinks. All this information indicates that caffeinated energy drinks are a potential ergogenic aid to increase physical performance and the overall success of female volleyball. The ingestion of these drinks in an amount of 3 mg·kg−1 of caffeine also produces marginal side effects.
Determining the effectiveness of different strategies and training methods to enhance jump ability has been a recurrent topic in volleyball investigations (5,18,19,23,36) because jump performance is considered essential for success in this team sport. However, the efficacy of caffeine to improve volleyball performance has not been properly investigated despite this substance being one of the most frequently consumed in the sports setting (9). Previous studies have examined the effect of caffeine intake (3–6 mg·kg−1) on jump performance in other team sports such as soccer (8,14,20), rugby sevens (11), and basketball (1). To our knowledge, only a recent study has determined the effects of a caffeine-containing energy drink (3 mg·kg−1) on jump ability in male volleyball players. This investigation revealed that the caffeinated energy drink increased jump performance in squat jumps, countermovement jumps, and repeated jumps. The novelty of the present investigation is that we tested the effects of caffeinated energy drinks on traditional (e.g., squat and countermovement jumps) and volleyball-specific jumps such as the block jump and spike jump.
In agreement with the previous literature, the current investigation revealed a significant improvement in jump ability after the ingestion of a caffeinated energy drink. As is depicted in Table 2, the preexercise ingestion of the caffeinated energy drink increased jump height in all the jumps performed and the improvement was always significant and between 2.8% and 5.1%. The present results confirm the ergogenicity of caffeinated energy drinks to increase jump performance. Furthermore, caffeinated energy drinks can increase jump height during volleyball-specific actions such as blocks and spikes which in turn could be a key variable for the success of game actions.
The spike is the most common attack skill, and its importance in volleyball success has been well documented (26). Although the volleyball spike is a complex movement composed of a correct placement and approach to the ball, the effectiveness of the spike is mainly based on the height of contact with the ball and the ball velocity after the hit (6). To define the influence of caffeinated energy drinks on this specific skill, we measured ball velocity during standing and jump spikes. Interestingly, maximal ball velocity was increased by 2.4% ± 3.8% during the standing spike and 5.1% ± 4.5% during the jump spike (Table 2). A similar result has been found in male volleyball players only during the standing spike (10) or in other sports with similarities with this specific movement such as the tennis serve (15). The higher ball velocity and the higher jump height found in this investigation strongly suggest an improved capacity to perform the volleyball spike after the ingestion of caffeinated drinks, which in turn will increase the likelihood of overcoming the block of the rival team.
The small area in which volleyball is played, the specific roles of each volleyball position, and the short duration of the rallies produce those quick agile accelerations and explosive movements, which are the most habitual movements in current elite volleyball (17). Acceleration and movement velocity were measured in this study using the t-test (27). The agility t-test required players to move through a T-shaped circuit to simulate the fast movements used in volleyball digs, receptions, and blocks. Interestingly, the time needed to complete the test was 1.6% ± 3.0% shorter when the women volleyball players ingested the caffeinated energy drink. These data coincide with previous publications in which the effectiveness of caffeinated drinks was tested with this same agility test in male volleyball players (10) and college athletes (2). Thus, the use of caffeinated energy drinks might be effective to increase the acceleration and speed of volleyball-specific movements.
Apart from the tests that simulated specific attributes of volleyball, we aimed to assess the effects of caffeinated energy drinks during real game play. For this reason, the women volleyball players took part in a simulated match while each game action was videotaped for a subsequent blinded analysis by experts. In addition, the amount and intensity of the movements during the game was recorded using an accelerometer. This experimental setting increased the ecological validity of the investigation because the volleyball players participated in the game without being aware that they were being analyzed. The cluster analysis revealed that the proportion of game actions that led to a point or to obtaining a definitive advantage (e.g., positive actions) was higher after the ingestion of the caffeinated energy drink than the placebo drink (Table 2). On the other hand, the percentage of game actions that included errors (negative actions) was less with the caffeinated drink although the game actions that permitted continuity of the game (neutral actions) were similar with both experimental beverages. The cluster analysis of the volleyball game was based on a previous publication with male volleyball players (10) and the outcomes of both investigations are very similar: the ingestion of 3 mg·kg−1 of caffeine in the form of an energy drink was effective to change negative or neutral actions into successful ones. In addition, the number of body impacts during the game was higher with the ingestion of the caffeinated energy drink as has been previously found in other sports (12). A greater amount of body impacts reflects a higher number of players’ movement during the volleyball game that might indicate increased involvement of players during the game. The shift in the classification of volleyball game actions from neutral/negative to positive can be explained by the improved physical performance obtained in the above-mentioned volleyball-specific testing and increased players’ activity patterns as depicted in Figure 1.
In the real practice, team sports players sometimes consume caffeinated energy drinks during the matches besides the preexercise ingestion of these beverages. In the present investigation, volleyball players ingested the caffeinated energy drink 60 min before the onset of experimental trials, although they did not ingest any additional dose of the caffeinated energy drink during the game. Conway et al. (7) determined that dividing a caffeine dose (e.g., 3 mg·kg−1 before exercise and 3 mg·kg−1 during exercise) produces no ergogenic effect over the ingestion of a bolus dose (6 mg·kg−1 before exercise) in a group of cyclists and triathletes performing an approximately 30-min cycling time trial. It is necessary to have more scientific information to elucidate whether the ingestion of caffeine or caffeinated products during the game produces additive effects over the preexercise ingestion of these beverages.
The surveys about self-reported performance and the prevalence of adverse effects indicated that the ingestion of the caffeinated energy drink enhanced the perception of muscle power during the testing, whereas perceived fatigue or endurance capacity tended to be improved with respect to the placebo drink. Even though no discomforts were reported during testing or during the simulated game, the participants reported an increase in nervousness and activeness in the hours after the experimental trials, as previously found in other investigations with male athletes (1,13). Although the most recurrent side effect after the ingestion of caffeinated energy drinks in female athletes has been insomnia (11,20), this effect was not found in this investigation despite the trials being carried out in the afternoon. The low prevalence of side effects derived from the ingestion of 3 mg·kg−1 of caffeine in the form of an energy drink does not preclude the recommendation of these beverages to improve volleyball performance in female players.
In summary, the preexercise ingestion of an energy drink with 3 mg·kg−1 of caffeine improved handgrip force, jump performance, spike ball velocity, and quickness during volleyball-specific tests, and it also shifted a proportion of erroneous game actions into successful ones during real volleyball play. Moreover, this dose of energy drink produced only minor side effects during the following hours of the volleyball game. Thus, the use of caffeine-containing energy drinks appears to be an effective ergogenic aid to enhance the volleyball players’ physical performance, and it might represent a meaningful advantage for volleyball performance.
The authors wish to thank the subjects for their invaluable contribution to the study.
This study did not receive any funding.
The authors declare that they have no conflict of interest derived from the outcomes of this study. This study does not constitute endorsement by the American College of Sports Medicine.
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