Effects of Caffeine on Perceptually-Based Intensity Production During Outdoor Running

Caffeine (CAF) may enhance performance while altering estimated RPE. However, effects of caffeine on RPE production is not well understood. This study examined effects of CAF on velocity (VEL) selection during outdoor running when intensity was prescribed using RPE. Ten (n = 10) fit male runners completed a VO2 max and two running trials, CAF (6 mg· kg-1) vs. placebo (PLA). Participants ran a 2.4 km (1.5 m) bout, at prescribed RPE4, and another at prescribed RPE7, following 10 min passive recovery. Separate 2 (trial) x 6 (time point) repeated measures ANOVA's compared CAF vs. PLA for VEL and heart rate (HR). No significant main effect was found (CAF vs. PLA) for VEL (m·min-1) for RPE4 (CAF: 201.7 ± 25.8 vs. PLA: 196.0 ± 17.5) (p = 0.29) or RPE7 (CAF: 236.7 ± 19.5 vs. PLA 231.8 ± 21.3) (p = 0.30). Similarly, no main effect was found (CAF vs. PLA) for HR for RPE4 (CAF: 163 ± 12 vs. PLA: 162 ± 14) (p = 0.69) or RPE7 (CAF: 181 ± 7 vs. PLA: 178 ± 10) (p = 0.31). No significant difference was found for Session-RPE for RPE4 (CAF: 4.0 ± 0.00, PLA: 4.20 ± 0.42) (p = 0.17), however, Session-RPE for RPE7 CAF (7.10± 0.32) was significantly lower than PLA (7.50 ± 0.53) (p = 0.04). While group means show no significant differences, 9 of 20 total trials (45%) were 26 to 104 sec faster for CAF (mean difference = 54 sec) demonstrating improvement in select individuals. Future research should focus on varying responses of individuals to CAF.