Abstract
Maintaining alertness and focus throughout the day is essential for productivity and performance, which contributes to caffeine being one of the most widely used ergogenic aids in sports, with over 70% of athletes consuming it for competition. Caffeine stimulates the central nervous system by blocking adenosine receptors, which increases neurotransmitter activity and enhances response time and alertness. However, habitual consumption may reduce its acute benefits through tolerance. PURPOSE: This study investigated whether acute caffeine ingestion affects reaction time differently in habitual versus low caffeine consumers. METHODS: Ten participants (7 males, 3 females, aged 18-40 years) completed two sessions in a randomized, single-blind, crossover design. Habitual caffeine consumers were defined as individuals who consumed 200 mg or more per day, whereas low caffeine consumers consumed less than 100 mg per day. Participants performed a 5-minute Psychomotor Vigilance Task 45 minutes after consuming 200 mg caffeine or a placebo. Before testing, participants were asked to refrain from caffeine for 24 hours. Participants were given a 48-hour washout period between sessions. RESULTS: The repeated-measures ANOVA showed a significant main effect of condition (F(1,8) = 116.3, p < .001, η² = 0.136) and a significant caffeine × group interaction (F(1,8) = 19.8, p = .002, η² = 0.023). Low consumers improved by 26.0 ms, which is an 8.3% improvement (95% CI [18.2, 33.8], p < .001). Habitual consumers improved by 10.8 ms, or 3.5% (95% CI [2.7, 18.9], p = .017). The confidence intervals did not overlap, which means low consumers improved about 2.4 times more than habitual consumers. CONCLUSION: After acute caffeine ingestion, both groups showed notable improvements in reaction time; however, the benefits were significantly greater in low consumers, suggesting that habitual consumption can lead to tolerance. Overall, these findings suggest that athletes may benefit from being more intentional with their caffeine intake, especially if they want to maximize its effects during competition.
Recommended Citation
Edwards, William T. and Long, Melissa
(2026)
"Effects of Acute Caffeine Ingestion on Reaction Time in Habitual and Low Caffeine Consumers: A Randomized Crossover Study,"
International Journal of Exercise Science: Conference Proceedings: Vol. 2:
Iss.
18, Article 198.
Available at:
https://digitalcommons.wku.edu/ijesab/vol2/iss18/198