Effects of Caffeine, CYP1A2 and ADORA2A Genotypes on Cycling Endurance Performance.

This randomized, double-blinded, placebo-controlled, within-subjects counter-measured study design will include 60 males and females that fall between the given age range (18-35 years).

Participants will complete five visits (~90-120 min each, 2 visits during the first week,3 visit during week 2-4) in the Laboratory at Faculty of Sports Studies of Masaryk University. All testing will take place Monday to Friday during morning hours (7-12) to minimize potential diurnal effect on sports performance. Participants will be instructed to maintain their regular diet (pre-testing meals will be replicated for all visits) and sleeping habits, avoid strenuous activity 48 hours before each visit, and abstain from caffeine one week prior to the first visit and for the duration of the data collection (4 weeks).

Sample size calculations We estimated sample size using G*Power 3.1 (Version 3.1.9.4). Effect size = 0.25, the trial would be powered to detect small but still physiologically important effect.

Alpha error = 0.025 Power (1-Beta probability) = 0.8 Number of groups = 6 - number of stratification required for genotype subgroup analysis number of measurements = 3 Sample size = based on calculation, 60 participants are required

Recruitment