Journal Title (Medline/Pubmed accepted abbreviation): Med Sci Sports Exerc
Page numbers: 1523-1530
Summary of background and research design:
Background: Clinical evidence for the ergogenic effects of caffeine has focused on endurance exercise performance, with only recent evidence for improvements in short-term, high-intensity performance. Further study is needed on the effect of caffeine on sport-specific responses (agility) that require both perceptual and physical responses.
Hypothesis/Purpose: Evaluate the effect of a single 6-mg/kg caffeine dose on reactive agility (RA) time and decision-making accuracy before, during, and after a team-game exercise simulation
Subjects: Ten moderately trained (7.6 hr/wk) males who competed in amateur and semiprofessional team sports participated in this study. Mean age, height, and body mass were 21.6 ± 2 years, 183.2 ± 5.6 cm, and 80.1 ± 5.3 kg, respectively.
Experimental design: Randomized, double-blind
Treatments and protocol: Participants were randomized to either caffeine (6 mg/kg) or placebo and completed a RA test; after 1 week of rest another RA test was completed under the opposite condition. A muesli bar and 500 mL of water were consumed between 60 and 90 minutes before each test, and the caffeine or placebo was consumed 60 minutes before each test. The RA test consisted of simulated, team-game exercises interspersed with 5 RA tests (total, 80 min). The RA time was assessed by both decision time (DT; stimulus point to first foot movement initiating change) and movement time (MT; movement initiation to exit gate). Decision-making accuracy was defined by whether the correct decision was made at stimulus and the correct finish gate was exited. Heart rate (HR) and rating of perceived exertion (RPE) were evaluated at warm-up, and before and immediately following completion of the test.
Summary of research findings:
- Exercise intensities were similar over time and between conditions.
- There was a main effect for time for RPE (P = .000 [NOTE: This was the P-value reported in the paper. However, such a P-value is not possible within the context of this experiment and it should have been reported as P < 0.001]).
- Total time to test completion was faster in the caffeine cohorts, but there was no significant interaction effect from time × condition (P = .536)
- Although there was no significant interaction effects from time × condition, RA time, DT, and MT were faster in the caffeine cohorts than in the placebo cohorts.
- RA time was consistently faster in both fresh and fatigued participants across all time points (P = .001).
- Significant main effects for time were found with both RA time and MT (P ≤ .039 for both).
- There was no significant interaction effect from time × condition for decision-making accuracy (P = .412).
- Qualitative analyses found very likely and likely benefits from caffeine early in performance for total time to test completion and RA time, respectively.
- Benefits were unclear for DT and possible for MT early in performance.
- Later benefits were possible to likely for all RA parameters.
Interpretation of findings/Key practice applications:
Although there were no significant interaction effects, small beneficial improvements in RA time were observed after caffeine consumption, regardless of fatigue level. However, results may have been limited by the sensitivity of the movement analysis (± 20 ms). In addition, a more realistic scenario and a larger cohort may have increased the differences observed in this study.