Submitted by David F. Vanata, Ph.D., RD, CSSD, LD; Nick Mazzino, B.S.;Robert Bergosh, Ph.D. and Paul Graham, B.S. of Ashland University in Ashland, Ohio.
Caffeine has been identified as a possible ergogenic aid for athletic performance. The objective of this study was to evaluate the effects of caffeine on sprint-distance swim trials. Caffeine dosages of 3 milligrams per kilogram (mg.kg-1) of body weight and placebos were administered via vegan capsules to 30 Division II collegiate swimmers, (60.0% males, n=18), in a single blind, crossover study design. Capsules were administered 30-minutes prior to completing a 50-yard time trial using electronic touch-pads. Urine samples were collected and analyzed via High Pressure Liquid Chromatography (HPLC) to determine the amount of caffeine excreted in the urine. Significant improvements were observed between caffeine and placebo time trials, M=27.27 seconds, SD=3.65 vs. M=27.51 seconds, SD=3.74, t(29)=2.81, p=.009, respectively. Overall, 70.0% of all swimmers improved 50-yard swim times (n=21), with 61.1% (n=11) of males improving and 83.3% (n=10) of females. There was a significant difference between urinary caffeine levels after ingesting the placebo vs. the caffeine capsules, M=.733 micrograms per milliliter (mg.ml-1), SD=1.29 vs. M=2.69 mg.ml-1, SD=2.02, t(29)= -5.34, p<.001, respectively. Following supplementation, female swimmers excreted significantly more urinary caffeine than males, M=3.59 mg.ml-1, SD=2.23 vs. M=2.09 mg.ml-1, SD=1.68, t(28)= -2.11, p=.044, respectively.
Overall, caffeine supplementation was found to significantly improve time trials of trained colligate swimmers. Additional studies are needed to identify factors associated with the variation of urinary caffeine excretion values observed between female and male athletes.
Caffeine, or 1,3,7 trimethylxanthine, is the most widely consumed drug in the world (9). In the human body caffeine acts as a central nervous system stimulant and an adenosine antagonist. As a central nervous system stimulant caffeine can have positive and negative effects. Some positive effects include increased attention, alertness, metabolic rate, and decreased fatigue. One possible mechanism of action for the effect of caffeine and delaying the onset of fatigue is the competition of caffeine with adenosine for receptor binding. Adenosine is a biochemical molecule that has inhibitory effects on the central nervous system. As adenosine binds to receptors, prevalence of fatigue increases, and arousal decreases. Caffeine binding to these receptors prevents adenosine binding, thus increasing arousal and decreasing fatigue (19). Caffeine also increases calcium permeability in sarcoplasmic reticulum and increases the sensitivity of the myofibrillar proteins to calcium by inhibiting the accumulation of cyclic AMP (2, 11). These effects of caffeine may also enhance exercise and athletic performance.
Many individuals use caffeine in order to increase athletic performance. A survey of 11-18 year-olds concluded that 25% admitted using caffeine to increase athletic performance (23). Caffeine has been shown to increase performance in a variety of athletic sports. Studies have shown that moderate daily caffeine intake has no adverse health effects. The degree of tolerance and response to caffeine varies with repeated usage (5). Most consider moderate caffeine intake to be under 300 mg of total caffeine or 6 mg.kg-1 per day. Doses between 6-9 mg.kg-1 have been shown to have adverse effects such as jitters, increased heart rate, and performance impairment. However, some studies indicate a plateau effect of caffeine around 6 mg.kg-1 (5, 10, 17, 22).
Numerous studies have shown caffeine to be an ergogenic aid to endurance athletic performance (3, 10, 13, 15, 21), with effective dosages ranging from 2-8 mg.kg-1 (5, 10, 16, 22). Investigations of the effects of caffeine on swimming have primarily been in rodent trials (6, 8). To the knowledge of the authors, the current study is the first to assess the effects of caffeine on short sprint-distance performance in intercollegiate swimmers.
The objective of this study was to investigate the impact of caffeine supplementation on athletic performance during sprint-distance, high-intensity time trials among collegiate swimmers in a single-blind, crossover study design.
The study sample consisted of Division II collegiate swimmers from a Midwestern private university (n=30, 43.3% females, M=19.5 years old, SD=1.4). All athletes were weighed, using a physician beam scale (Detecto Scale Company, Webb City, Missouri), one-week prior to caffeine supplementation to determine individual dosage levels of caffeine. Body weights of the swimmers ranged from 57.61 kg to 92.98 kg, with the mean weight being 75.25 kg, SD= 9.97 kg. At the time of the study, all participants were in-season with practices averaging 6,000 to 8,000 yards per day, six times a week. Additionally, all swimmers participated in strength training sessions three times weekly.
The study was reviewed and approved by the University Human Subject Review Board (HSRB) with signed informed consent obtained from all participants. No rewards were given for participation in this study because NCAA regulations prohibit distribution of incentives or any form of compensation. In addition, participation was voluntary and there would be no penalty for non-participation.
Procedures and Materials
Time trials for 50-yard freestyle swims were assessed on two separate occasions, 8-days apart. During each of the two assessments, participants were randomly given either a treatment (caffeine) or placebo (dextrose) vegan capsule and a glass of water. Assessments were conducted 8-days apart to allow for a “wash-out” period between the administrations of the capsules. The amount of caffeine in each treatment capsule was based on the individual body weight to supply a dosage of 3 mg.kg-1. Based on this target dosage, the amount of caffeine supplemented to the swimmers ranged from 173 mg to 279 mg per athlete. This dosage of caffeine is also possible through dietary intake while reducing the risk of physiological side effects and possible performance impairment with higher doses. Additionally, this dosage is within the acceptable limits of the International Olympic Committee (IOC) level of 12 mg.ml-1 and the National Collegiate Athletic Association (NCAA) level of 15 mg.ml-1 of urinary caffeine excretion. Pure caffeine (Carolina Biological Supply Company, Burlington, North Carolina) was chosen instead of coffee or other sources because studies have indicated that coffee may contain other ingredients that counteract the benefits of caffeine (17).
Using a crossover design, athletes received either the treatment capsule for the first trial and a placebo for the second trial, or vice versa. Investigators visibly verified that each participant swallowed the capsule prior to administering the next capsule to the following athlete.
After administering the capsules, all swimmers participated in a warm-up consisting of 2×75 yards, 2×50 yards, 4×25 yards, and 1×50 yards. This entire warm up was repeated three times and lasted for 30 minutes. Peak absorption time for caffeine has been previously determined to be between 30 and 60 minutes (3, 17).
Upon completion of the warm-up, a 50-yard time trial off the blocks was completed. All times were recorded by an electronic touch pad (Colorado Timing Systems, Loveland, Colorado). Immediately, following the completion of the timed 50-yard swim, each athlete provided a urine sample collected in a sterile container by an investigator of the same gender. Urine samples were taken directly to the laboratory for analysis to avoid any degradation of caffeine within the specimens. Urinary sample analyses were conducted with an Agilent 1100 series High Performance Liquid Chromatograph (HPLC). Each urine sample was filtered to reduce particulate matter prior to running through the HPLC. Filtration was done using a 3 ml-1 syringe and a 0.45-micrometer mesh filter. To determine urinary levels of caffeine, a calibration curve of five caffeine standards was determined for concentrations of 15 mg.ml-1, 10 mg.ml-1, 5.0 mg.ml-1, 2.5 mg.ml-1, and 1.0 mg.ml-1.
All swimmers were instructed to fast prior to each assessment session. No other dietary instructions were issued. Dietary caffeine intake was assessed for each athlete using a food frequency questionnaire (Fred Hutchinson Center, Seattle, Washington). After each supplementation trial, all participants completed a questionnaire assessing the perception about the impact of each capsule. Identical protocol and procedures were conducted at both sessions.
Paired sample t-tests were used to compare the impact of caffeine using each individual as a case and control. Independent t-tests were used to compare urinary levels of caffeine between males and females, and habitual and non-habitual caffeine users. Statistics were analyzed with an IBM Statistical Package for Social Sciences (SPSS) version 19. Statistical significance was set at .05.
Dietary Caffeine Consumption and Perceived Supplementation Effects
Analysis of caffeine food frequencies indicated that 36.7% of swimmers (n=11) were classified as habitual caffeine consumers (consuming 3 or more dietary caffeine sources weekly), with 54.5% of these habitual consumers being male (n=6). Soft drinks and coffee containing caffeine were the main dietary sources for habitual users (54.5%, n=6; 36.4%, n=4, respectively).
Self-reported qualitative data was obtained from each swimmer after supplementation of caffeine and placebo capsules. Comments from the participants indicated that 16.6% (n=5) of the swimmers reported feelings of anxiousness or jitteriness upon ingesting the caffeine capsules, while 10.0% (n=3) of the swimmers reported similar effects after ingesting the placebo capsules.
Urinary Caffeine Levels
Overall, there was a significant difference between urinary caffeine levels after ingesting the placebo vs. the caffeine capsules, M=.73 mg.ml-1, SD=1.29 vs. M=2.69 mg.ml-1, SD=2.02, t(29)= -5.34, p<.001, respectively. No significant differences in urinary caffeine levels were observed between male and female swimmers for caffeine versus placebo, M=.544 mg.ml-1, SD=1.08 vs. M=1.02 mg.ml-1, SD=1.56, t(28)= -980, p=.335, respectively. However, with the caffeine treatment, female swimmers excreted significantly more urinary caffeine versus males, M=3.59 mg.ml-1, SD=2.23 vs. M=2.09 mg.ml-1, SD=1.68, t(28)= -2.11, p=.044, respectively.
No significant differences in urinary caffeine levels were observed between habitual and non-habitual caffeine users after taking the placebo capsules, M=.80 mg.ml-1, SD=1.20 vs. M=.69 mg.ml-1, SD=1.37, t(28)= -.211, p=.834, respectively, as well as after consuming the caffeine capsules, M=2.53 mg.ml-1, SD=2.23 vs. M=2.78 mg.ml-1, SD=1.95, t(28)=.330, p=.744, respectively.
50-Yard Swim Times
Caffeine supplementation significantly improved overall 50-yard swim times when compared to placebo trials, M=27.27 seconds, SD=3.65 vs. M=27.51 seconds, SD=3.74, t(29)=2.81, p=.009, respectively. Overall, 70.0% of all swimmers improved 50-yard swim times (n=21), with 61.1% (n=11) of males improving and 83.3% (n=10) of females, although, there were no significant differences in time improvements between males and females, M=.182 seconds, SD=.47 vs. M=.304 seconds, SD=.43, t(28)= -.721, p=.477, respectively.
There were no significant improvements in 50-yard swim times between habitual and non-habitual caffeine consumers after receiving the caffeine capsules, M=.218 seconds, SD=.54 vs. M=.238 seconds, SD=.41, t(28)= -117, p=.908, respectively.
The objective of this study was to investigate the impact of caffeine supplementation on athletic performance during sprint-distance, high-intensity time trials among collegiate swimmers. Results indicated significant time improvements among swimmers when completing the time trials after supplementation with caffeine in comparison to those trials when ingesting the placebo capsules. Although the actual time improvements among the sample of swimmers may appear small, collegiate athletic events are won and decided by fractions of a second. Results from the current study are in agreement with Collomp and colleagues (1992) who demonstrated that supplementing 250 mg of caffeine was effective at improving times for 100-meter trials among trained swimmers, but not for untrained. Although caffeine dosages were based on body weight, the levels implemented in both studies would fall within the guidelines outlined by the NCAA. MacIntosh and Wright (1995) examined the effects of caffeine on swimmers, but supplemented the athletes at a dosage level twice that of the present study, (6 mg.kg-1 vs. 3 mg.kg-1, respectively) and demonstrated improvements on 1,500-meter swims. Based on these research findings, moderate caffeine supplementation of 3-6 mg.kg-1 can be beneficial in improving short-distance, high-intensity swimming performance, but possibly only among trained athletes.
On average, females improved by 0.31 seconds in the caffeine trial while the males improved on average by 0.18 seconds in the caffeine trial. Although there are studies evaluating the effects of caffeine on athletic performance including the modes of treadmill walking, resistance training, and cycling among trained (and untrained) women (1, 12, 18) none have reported findings similar to the present study with sprint-distance swimming.
Results indicated that female swimmers excreted significantly more urinary caffeine despite receiving the same relative dosage as males. This observation may be due to differences in overall body weight and muscle mass among the genders, which may affect how caffeine is absorbed and excreted in the body (14). However, further studies are needed to differentiate the possible effects of caffeine, gender, and short-distance, high intensity swimming performance.
Habitual caffeine consumption may decrease the effects of acute doses and potentially decrease individual sensitivity to caffeine ingestion (20, 24). However, no differences were observed in athletic performance in the present study between habitual and non-habitual caffeine consumers, which is also supported by others (4). Bell and colleagues (2002) investigated the effects of caffeine on cycling endurance among users and non-users of caffeine and observed benefits among the user group at 1 and 3 hour post-ingestion, and 1, 3, and 6 hours post-ingestion in the non-users. The treatment effect of caffeine was greater and longer for those individuals identified as non-users.
There were several limitations in the current study. Although subjects were instructed to fast, there is the possibility that some may have eaten food or consumed a dietary source of caffeine prior to each supplementation trial. Changes in dietary habits or caffeine consumption may have affected circulating caffeine levels during the time trials. Other uncontrolled factors such as the amount of sleep, dietary adequacy or inadequacies, or other behaviors may have affected overall athletic performance.
Results from this study indicated that caffeine ingestion of 3 mg.kg-1 was effective in improving athletic performance (swim times) of both male and female collegiate swimmers participating in short sprint-distance events, while exhibiting few reported negative side effects such as nausea, dizziness, anxiousness, or GI distress. While the athletes in this study consumed pure caffeine, additional inquiry may evaluate the impact of dietary caffeine sources as well as other dosages on performance in short sprint-distance swimming events. Additional studies may investigate the possible effect of gender with caffeine supplementation and athletic performance.
APPLICATION IN SPORT
Identifying additional applications and appropriate levels of ergogenics (such as caffeine), for sprint and short distance athletic events (such as swimming), will allow individuals to potentially improve athletic performance, while experiencing minimal side effects and staying within the guidelines of the NCAA. Results from this study will enable coaches, athletic trainers, and sports dietitians to make safe and effective recommendations regarding caffeine ingestion prior to athletic events.
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