<![CDATA[Background: Caffeine is commonly used as an ergogenic aid to enhance athletic performance; however, evidence regarding its effectiveness during cycling remains equivocal, particularly when performance is assessed under conditions that closely resemble real-world practice. Aims: This study examined the acute effects of caffeine ingestion on physiological and performance outcomes during a 20-minute self-paced cycling time trial in amateur cyclists. Additionally, inter-individual variability in performance responses to caffeine supplementation was explored. Methods: Eight recreationally trained male cyclists participated in a randomized, double-blind, placebo-controlled crossover pilot study. Experimental sessions were separated by a seven-day washout period. Participants ingested either caffeine (6 mg·kg⁻¹ body mass) or a placebo 60 minutes before completing a 20-minute self-paced time trial using their personal bicycles mounted on a smart trainer. Mean power output, total distance covered, and heart rate were recorded throughout the test. Individual performance responses were also evaluated. Results: No statistically significant differences were identified between caffeine and placebo conditions for heart rate, mean power output, or distance covered (p > 0.05 for all comparisons). Despite the absence of significant group-level effects, considerable inter-individual variability in percentage changes in mean power output was observed. In the exploratory analysis, three participants (37.5%) showed increases ≥2%, four (50.0%) showed changes between −2% and +2%, and one (12.5%) showed a decrease <−2%. Given the absence of repeated baseline measurements to estimate measurement error and day-to-day variability, these individual changes should not be interpreted as evidence of confirmed responsiveness to caffeine. Mild adverse effects, including increased perception of heart rate and feelings of nervousness, were reported by a subset of participants. Conclusion: Ingestion of 6 mg·kg⁻¹ of caffeine did not significantly influence physiological responses or cycling performance during a 20-minute self-paced time trial in this sample of amateur cyclists. Individual percentage changes varied across participants; however, these exploratory observations cannot establish true individual responsiveness. Larger studies incorporating repeated measurements are required to determine whether such variability reflects genuine differences in caffeine response.]]>
