Potgieter, S., Smith, C., Wright, H., & Warnich, L. (2014). The effect of caffeine supplementation on Olympic distance triathletes and triathlon performance in South Africa. Medicine & Science in Sports & Exercise, 46(5), Supplement abstract number 2748.

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The study investigated the ergogenic effect of caffeine supplementation, evaluated parameters that could in part explain the mechanism of action of caffeine supplementation, and determined factors influencing the ergogenicity of caffeine supplementation, while controlling for factors influencing exercise performance. A double-blind, randomized, crossover, controlled, clinical field trial was conducted. Performance data (time to completion, rating of perceived exertion, and mood state), parameters explaining the mechanism of action (endocrine-stress response, oxidative stress, and plasma lactate), factors influencing the ergogenicity of caffeine supplementation (lifestyle, gender, and genetics) as well as data on factors that could affect triathlon performance, were collected. Triathletes (M = 14; F = 12: age-rage 27-48 years) were evaluated.

There was a 3.7% reduction in swim time and a 1.3% reduction in overall performance time in the caffeine group. Caffeine ingestion did not significantly influence mood state or rating of perceived exertion. Caffeine supplementation increased cortisol levels beyond the effect observed from exercise. Oxidative stress was more pronounced in the caffeine group, with elevated leukocyte, lymphocyte, and monocyte counts. Caffeine facilitated greater blood lactate accumulation. Lifestyle, menstrual cycle, menopause, oral contraceptive use, and CYP1A2 gene polymorphisms did not influence the effect of caffeine supplementation on performance.

Implication. "Caffeine ingestion enhanced triathlon performance, but the field effect was not as pronounced as seen in previous laboratory trials. Caffeine supplementation augments the endocrine-stress response by increasing cortisol levels beyond that observed during exercise and inducing leukocytosis, neutrophillia, and lymphocytosis, suggesting the primary ergogenic effect of the caffeine result was due to stimulation of both the central and autonomic nervous systems."

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