Effects of caffeine ingestion on outdoor 800-m running performance: a randomized controlled crossover study with hierarchical regression analysis

Purpose Previous studies have demonstrated that caffeine ingestion improves simulated 800-m run performance; however, whether caffeine enhances 800-m performance during outdoor track running, in which environmental conditions may influence performance, remains unclear. Furthermore, it also remains unclear whether caffeine ingestion affects arterial oxygen saturation during 800-m outdoor running. Therefore, this study aimed to examine the effects of caffeine ingestion on outdoor 800-m run performance and physiological responses. Methods In a randomized, double-blind, placebo-controlled, crossover study, 14 (4 females) college middle-distance runners with an 800-m seasonal best of 128.48 ± 14.11 s ingested capsules containing either (1) placebo or (2) caffeine (6 mg/kg of body weight). Following ingestion, they performed an 800-m run on an outdoor track. To ensure consistency in pacing strategy between trials, pacemakers were employed until the 400-m mark. The first 200 m was run at 103% of the average speed calculated from each participant’s seasonal-best 800-m time, followed by 200 m at 97% of that speed, as the initial 200 m of an 800-m race is typically faster than the rest of the pace. Results The placebo and caffeine trials recorded similar running times (134.8 ± 15.1 vs 135.1 ± 15.3 s, P = 0.602). Furthermore, arterial oxygen saturation, heart rate, peak blood lactate concentration, and rating of perceived exertion were comparable between the trials. Air temperature during the run tended to be lower (17.1 ± 3.4 vs 19.2 ± 2.8 °C, P = 0.062), and the wind speed tended to be greater (2.0 ± 1.2 vs 1.2 ± 0.8 m/s, P = 0.051) in the caffeine than in the placebo trial. Hierarchical multiple regression analysis revealed that adding caffeine ingestion to a baseline model including environmental factors significantly improved the model fit ( ΔR 2 = 0.10, P = 0.039). After adjusting wind speed and air temperature, caffeine ingestion was associated with faster 800-m running time ( B = − 11.58, P = 0.039). Conclusions These findings suggest that caffeine ingestion was associated with faster outdoor 800-m running time after accounting for environmental conditions.