With the recent removal of caffeine from the World Anti-Doping Agency restricted-substance list (9), many athletes may be tempted to use this formerly prohibited substance. There is strong evidence to support the theory that caffeine provides benefits to athletes involved in endurance activities, particularly in terms of improving performance in both maximal and submaximal aerobic tests across varying times and forms of exercise (4,14,21,35). Less is known about the effects of caffeine on anaerobic performance, but it appears that caffeine may provide ergogenic benefits for activities that are significantly shorter in duration than are endurance events and require more explosive movements (20,25,32,36). Growing evidence supports the theory that caffeine can improve muscle power and endurance during repeated maximal and submaximal isometric contractions (2,12,25,28,32,35,36). There is also evidence that the overall ergogenic effect of caffeine is greater in nonusers than in habitual users of the substance (3). If it is true that caffeine can improve both aerobic and anaerobic performance measures, then it may be of great value as an ergogenic aid for many team sports that demand both endurance and explosive abilities.
Basketball players derive 60–90% of their energy anaerobically and for much of the game play at or above their lactate or anaerobic thresholds (11), record heart-rate values often in excess of 170 b·min−1, and work at between 70 and 75% of their maximum oxygen uptake (MV[Combining Dot Above]O2) (30). A study conducted by Parr et al. (26) examined the maximal oxygen uptake (MV[Combining Dot Above]O2) of professional male basketball players from the U.S.A. during a treadmill test. Results from the study showed centers recorded an MV[Combining Dot Above]O2 of 41.9 ± 4.9 ml·min−1·kg−1, forwards 45.9 ± 4.3 ml·min−1·kg−1, and guards 50.0 ± 5.4 ml·min−1·kg−1, thereby indicating that endurance performance is also important.
The endurance aspect of basketball, combined with its high-intensity explosive movements, suggests that this sport is one that is well positioned to benefit from the purported benefits of caffeine, that is, an ergogenic aid with potential to improve both aerobic and anaerobic energy delivery (3,6,10,14,17,21,28,32,35). Although there is no definitive conclusion behind the mechanism through which caffeine improves endurance performance in various forms of exercise, there are a number of feasible possibilities. A proposed physiological mechanism for improving endurance with caffeine ingestion is based on the theory that caffeine ingestion is associated with an increase in free fatty acid (FFA) mobilization (10,34). This effect is, however, noticeably absent in many studies on endurance performance and caffeine ingestion (3,7,14,16,20). Nonetheless, its likelihood can be examined through consideration of differences in respiratory exchange ratios (RERs) (10,34), which are standard metabolic indicators.
Vertical-jump performance correlates with high-level anaerobic movements, such as a volleyball spike, leaping for a catch in football, a sprint start in track, and rebounding in basketball. Basketball players are often required to perform vertical jumps when fatigued. Caffeine ingestion may attenuate the decline in jumping performance that accompanies fatigue. The thinking behind this suggestion relates to the fact that the intracellular calcium ion concentrations in muscles decline markedly during fatiguing contractions, resulting in decreases in muscular force. When caffeine is applied to fatigued muscle fibers, the ryanodine receptors located within the sarcoplasmic reticulum open, restoring intracellular calcium concentrations and reversing the decline in fatigue-induced muscular force (1,31). Researchers also suggest that the rate of perceived exertion (RPE) decreases in those performing vertical jumps and treadmill tests after caffeine ingestion as a result of increased central nervous system (CNS) stimulation (7,8,36), and the restoration of intracellular calcium (1,31).
To the authors' knowledge, the effect of caffeine on vertical-jump performance, particularly after a fatiguing bout of exercise, has not been formally studied. Accordingly, the purpose of this study was to determine if caffeine would benefit aerobic and anaerobic performances of elite male basketball players.
The hypotheses are that the ingestion of caffeine by elite male basketball players will (a) increase endurance performance (MV[Combining Dot Above]O2), (b) decrease RER for any given workload, (c) decrease RPE, and (d) increase anaerobic power (reactive strength index [RSI]).
Experimental Approach to the Problem
This study followed protocols similar to those used in many other investigations regarding caffeine ingestion, for example, subjects avoiding caffeine intake for at least 48 hours before testing, and administration of the dosage at least 60 minutes before commencing the exercise test (3,7,14,20,21,25,28,32,35) to allow for maximum effect of ingested caffeine.
The dosage of caffeine was considerably less than that used in some studies (2,3,7,20,35). One of these studies (2) used doses of up to 13 mg·per kilogram of body weight (BW). A study conducted by Jenkins et al. (21), however, showed improved aerobic endurance performance among cyclists who ingested relatively low doses of caffeine—2 and 3 mg·kg BW−1, respectively. This trend was also observed in a study that found low to moderate doses of caffeine (between 3 and 6 mg·kg BW−1) were more likely to be associated with superior ergogenic effectiveness in endurance runners than were higher doses (9 mg·kg BW−1) (15). A similar study investigating time to exhaustion for male cyclists found no significant difference in performance between ingested doses of 5, 9, and 13 mg·kg BW−1; all dose levels yielded similar increases in endurance performance (27).
Aerobic parameters were investigated using a graded exercise treadmill test that included measurement of MV[Combining Dot Above]O2, RER, and blood lactate profiles. Standard protocols were used to measure RPE during the test, and measurements of subjects' RSI (4,13,23,37) were taken to allow exploration of anaerobic performance in a fatigued state. The RSI provides a measure of leg power by taking into account the height jumped and the time spent applying the downward force to produce the explosive takeoff.
Five healthy male subjects with an average age of 22 ± 1 years 7 months volunteered to take part in the experiment. The participants were basketball players performing at an elite level. The subjects all train 3 times per week and compete just below provincial representative level, playing 2 games per week. These studies were completed in early November, although the competitive season runs from the end of May until the middle of August. All the subjects were still involved in a low level of training.
All the subjects were nonsmokers, and all abstained from caffeine ingestion for 48 hours before testing and from alcohol for 24 hours before testing. The mean height and weight of the subjects was 187.4 ± 7.9 cm and 84.6 ± 8.3 kg, respectively. The players' average daily consumption of caffeine was <500 mg. The subjects were all informed (verbally and in writing) as to the nature of the experiment and the experimental risks, and all signed an informed consent document before the investigation. Because the athletes were all >18 years of age, parental consent was not required. The protocol for this study was approved by the Human Ethics Committee of the University of Canterbury.
The subjects were required to fill out a Physical Activity Readiness Questionnaire (PAR-Q) several weeks before testing to screen for any possible concerns regarding their health, including past or present medical conditions and any medication cycles they were on. If a subject mentioned a health-related concern on their PAR-Q, he was required to obtain written consent from his general practitioner to participate in the study. All the subjects had their blood pressure and resting heart-rate levels tested before commencement of the experiment to detect abnormalities not picked up by the PAR-Q, such as high blood pressure and an elevated resting heart rate.
The subjects were asked to prepare for the tests by consuming a suitable preexercise meal that was high in carbohydrates. For the second trial, they were asked to prepare in the same way as they had done for the first by eating the same or a similar meal, and following similar patterns of training to those they had completed during the lead-up to the first trial.
Each subject completed 2 trials, 1 with caffeine ingestion combined with B1 thiamine and the other with B1 thiamine alone. The B1 thiamine was used as a placebo, as the tablet containing 100 mg of caffeine also contained 10 mg of B1 thiamine. The B1 thiamine tablet had a size and shape similar to that of the tablet containing caffeine and had a similar scent.
The subjects were required to report to the laboratory 75 minutes before the start of the experiment to ensure that there was adequate time to do preliminary testing on blood pressure, resting heart rate, and blood lactate levels and for them to ingest the caffeine or placebo dosage. Quinlan et al. (29) suggest that caffeine, when taken orally, reaches a peak plasma level 30–75 minutes after ingestion. The caffeine dosage given to the subjects was 3 mg·kg BW−1 and was administered according to a double-blind procedure.
After the pretesting and a wait of 60 minutes after ingestion of the caffeine or placebo dose, the subjects were prepared for the treadmill test. The subjects were then fitted with a Polar FS1 heart-rate monitor and had their resting blood lactate levels and heart rate taken and recorded. They were asked to complete, at a comfortable pace, a run of 5–7 minutes' duration on the treadmill to warm up. Next, the subjects were additionally fitted with a CosMed K4B2, which provided breath-by-breath analysis data that included oxygen uptake, RER, and ventilation rates. Blood lactates were taken using an Accujet (used to prick the finger) and were analyzed with a Lactate Pro. The CosMed K4B2 and Lactate Pro equipment were calibrated before each test, in line with the manufacturers' instructions to ensure accuracy of results.
The test itself consisted of a graded incremental treadmill run that involved a combination of several MV[Combining Dot Above]O2 treadmill test protocols. The subjects began at a speed that they found relatively comfortable and then increased their speed by 1 km·h−1 every 3 minutes. At each 3-minute interval, blood lactate levels were recorded using Lactate Pro equipment; also noted were ratings, via the Borg Scale (5), of perceived exertion (RPE). The subjects were asked to indicate on a scale of 6–20 RPE overall (RPE-O) and RPE for their legs (RPE-L).
There was a delay of at least 7 days, but no longer than 10 days, between trials. This delay gave the subjects time to recover from fatigue from the exhaustive test in trial 1 but did not allow time for further aerobic training effects to accumulate. During the second trial, the subjects received the same protocols as those in the first trial. However, this time, speed, time, and heart-rate values on the treadmill were covered so that the subjects could not see them. This was done to eliminate the possibility that the subjects, knowing what they had achieved in the first trial, would try to better their time to exhaustion or speed achieved. Such an opportunity could have led to the subjects' times to exhaustion being completely dictated by their levels of fatigue rather than by their psychological motivation.
After completing the treadmill test and a 15-minute warm-down period, the subjects completed a maximum of 10 RSI jumps. They did this by stepping off a 45-cm step on to a pressure-sensitive timing mat, then rebounding as quickly as possible while trying to achieve as great a height as possible. Because the aim of this test was to allow examination of leg power in the form of an explosive jump, the subjects were instructed to jump as high and as quickly as they possibly could, putting maximal effort into every attempt.
The timing system connected to the mat recorded the time spent on the mat (contact time) and the time spent in the air during the rebound jump (hang time). The subjects were instructed to keep their arms to their sides to isolate the contribution to the jump from the leg muscles. They were also required to land with relatively straight legs so that hang time could be converted to a jump height using the formula height jumped = 4.905 × (hang time/2)2. From these readings, the RSI was calculated for each jump according to the formula RSI = height jumped (centimeters)/contact time (seconds) (4,13,23).
Two-sided paired t-tests were used to analyze the paired differences between caffeine and placebo trials. The statistical data analysis package used was WINKS SDA (33). This package tested a null hypothesis of no difference between trials, with an alternative hypothesis of a significant difference between trials. The 2-sided significance level to demonstrate a significant change was set at 0.05.
The MV[Combining Dot Above]O2 values achieved in both trials in this study were of a comparable standard to those found for professional basketball players (26). No significant trends were found with regard to differences in MV[Combining Dot Above]O2 achieved between the caffeine and the placebo trials; some subjects recorded a higher MV[Combining Dot Above]O2 score in their caffeine trial and others recorded a higher MV[Combining Dot Above]O2 score in their placebo trial. This result did not support hypothesis 1 and so favored the alternative hypothesis (i.e., no effect on aerobic performance from the ingestion of caffeine).
Four of the 5 subjects showed a decreased time to reach an RER value (a representation of CO2 produced over O2 consumed) of ≥1.16 in the caffeine trial—a value that is regarded as one of several physiological markers for achieving MV[Combining Dot Above]O2 (22). These 4 subjects also showed an increased RER value at each interval for the caffeine trials (Table 1), indicating a greater reliance on carbohydrate (CHO) energy stores as opposed to FFA stores. These results did not support hypothesis 2 but favored instead the alternative hypothesis that caffeine does not decrease RER in elite male basketball players. In addition to these results, 3 of the 4 subjects showed a slightly elevated blood lactate level for the caffeine trial.
The results for athletes' ratings of perceived exhaustion (Table 2) showed no significant differences between the ratings of perceived exertion, either overall (t = 1.08, p = 0.125) or for legs-only (t = 0.84, p = 0.406), in endurance performance on the treadmill test between trials where athletes ingested caffeine and those trials where they ingested the placebo.
The RSI measurements of the vertical rebound jumps showed no significant differences between the caffeine and the placebo trials (Table 3). The order of trials made no difference to these results; some subjects recorded their most proficient results in the first trial and others in the second, regardless of the dosage order. Thus, the results did not support hypothesis 4. Rather, they suggested that caffeine, in this dose, does not enhance the anaerobic performance of elite male basketball players.
The results of this study did not support the hypothesis that the specified dosages of caffeine would benefit aerobic endurance performance measures based on MV[Combining Dot Above]O2, blood lactate profiles, and RER. For 3 of the 5 athletes, there was a significant increase in RER during the trials. These results support the findings of other investigations that physiological effects alone are nonexistent or negligible (3,7,14,16,20,31). The present findings differ, however, from other investigations reporting benefits of caffeine on some endurance outcomes (3,7,14,18,21,24).
The third hypothesis that the results would show a decrease in subjects' RPE during the caffeine trial (10,12) was not supported. The lack of significant change in the average RPE value is similar to the outcome of a study by Ivy et al. (19) They found no difference in the RPE between caffeine and placebo trials among male and female cyclists in a time-trial performance.
The final hypothesis (hypothesis 4) was that there would be an increase in the subjects' reactive strength performance in vertical rebound jumps in the caffeine trial, compared with the placebo trial, because of increased CNS stimulation (9,25,28) and the caffeine restoring intracellular calcium concentrations (1). However, our study showed no significant effect of caffeine on vertical-jump performance.
The results of this study showed that elite male basketball players who ingested 3 mg·kg BW−1 of caffeine before exhaustive exercise were no more likely to experience an effect on their endurance performance than when they did not ingest caffeine. We also found no difference between caffeine ingestion and no caffeine ingestion on the players' leg power while they were doing vertical jumps in a fatigued state. The results of this study therefore suggest that there is no ergogenic benefit for male basketball players from ingesting caffeine at this dosage.
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