Purpose: Inconsistent results among studies examining the effects of
caffeine on exercise performance are potentially due to interindividual variability in
biological responses to
caffeine ingestion. The aims, therefore, of the present study were to identify high and low
caffeine responders and compare the influence of
caffeine on exercise performance and
biological responses between groups during a simulated soccer-game protocol on treadmill. Methods: Well-trained soccer players were distinguished as high (n = 11) and low (n = 9)
caffeine responders based on resting blood pressure, plasma
glycerol, nonesterified
fatty acid, and
epinephrine responses to
caffeine. Participants underwent 2 simulated soccer-game protocols on a treadmill after
caffeine (6 mg·kg-1) or placebo ingestion. Exercise performance and several
biological responses were evaluated. Results: Exercise performance did not differ between the high and low responders to
caffeine (P > .05). However, time to
fatigue (high,
caffeine: 797 [201] s vs placebo: 487 [258] s; low,
caffeine: 625 [357] s vs placebo 447 [198] s) and countermovement jump (high,
caffeine: 42.1 [5.5] cm vs placebo: 40.5 [5.7] cm; low,
caffeine: 41.0 [3.8] cm vs placebo: 38.8 [4.6] cm) improved with
caffeine relative to placebo (P < .001). Rating of perceived exertion was lower (P < .001) in high (13.4 [2.3]) than in low responders (14.3 [2.4]) with
caffeine ingestion. Conclusions:
Caffeine improved aerobic endurance and neuromuscular performance in well-trained soccer players regardless of their responsiveness to
caffeine at rest. Since no changes in substrate utilization were found with
caffeine supplementation, performance improvements could be attributed to positive effects on the central nervous system and/or neuromuscular function, although the precise mechanism remains unclear.