Effects of Acute Caffeine Ingestion on Morning Temperature, Mood, Reactive Agility and Cognitive Measures in Males: A Standardized Approach

Background/Objectives: We investigated whether ingestion of caffeine (~1 h before) was beneficial to subsequent morning (~07:30 h) mood, reactive agility, and cognitive measures in naïve-mild habitual caffeine consumers. Methods: A total of 150 recreationally active males were recruited, of whom 51 participated and completed six sessions as follows: (i) three familiarization sessions of all procedures at 12:00 h, and (ii) three experimental conditions. Participants completed caffeine and placebo trials under double-blind conditions, together with an open-label no-pill control trial using the stratified block randomization method based on baseline performance, which were counterbalanced in a crossover design into either caffeine (CAFF, 300 mg or 2.5-5.3 mg·kg-1 body weight), placebo (PLAC), or no-pill control (NoPill), both ingested at ~06:30 h. For each experimental session, on arrival at the laboratory, questions on sleep, mood states, and caffeine withdrawal were asked. A battery of cognitive performance tests was then administered (trail-making test, Rey's auditory verbal learning test, and Stroop word-colour interference test). At 30 min of rest and after a 5 min warm-up on a treadmill with associated stretches, rectal and mean skin temperatures (Tr and Tsk) were measured. Thereafter, two 90 s reactive agility tests (RATs) were undertaken, with average movement time(s) and contact number per light recorded. Data were analyzed using a general linear model with repeated measures, but the RAT measures were run as ANCOVA with mass used as a covariate. Results: The battery of cognitive tests showed no significant main effects for condition, whether the body mass of the participants was considered or not. There were no significant main effects of the experimental condition for RAT variables. There was a main effect for "light position", for mean movement time values (p 2p = 0.508), and cognitive-motor efficiency (contacts·s-1, p 2p = 0.582), where pairwise analysis showed mean movement times as higher, and cognitive-motor efficiency values indicating a lower rate of successful responses during movement for lights 1 and 5 (the furthest from the start point corresponding to light 3), rather than lights 2, 3 and 4. There were no significant interactions for condition and light for any of the variables. Conclusions: Early morning ingestion of 300 mg of caffeine had no effect on the battery of cognitive or reactive agility test measures in the population of naïve-mild habitual caffeine consumers. Caffeine ingestion had no effect on Tr, Tsk, mood, or caffeine withdrawal symptom scores, as well as tiredness or alertness, with or without consideration for body mass.