Effects of Caffeine Ingestion on Morning Cognitive and Muscle Strength Measures in Males, Where a Standardized Approach Has Been Employed

Detailed Summary

Tournament scheduling and environmental factors often require athletes to compete in the morning. Equally due to time constraints, athletes may choose to train in the morning. However, muscle power output and force production, are higher in the mid-afternoon or early evening whatever the method used, the muscle groups tested or the mode and speed of contraction. Cognitive performance is another essential determinant for many athletes that has been shown to be time-of-day and variable dependent. Considered as multifactorial, it includes many different components related to attention, accuracy, consistency, reaction time, vigilance, decision making and executive functions. Executive functions notably include the ability to plan and coordinate considered action while updating it with inhibition processes of distractions to focus attention on the relevant information. Subjective negative mood states (fatigue) and motivation levels, which are essential elements for tasks requiring higher cognitive function are poorer in the morning than the evening. Caffeine (1,3,7-trimethylxanthine) is amongst the most extensively researched ergogenic supplements within the field of sport, aimed at enhancing alertness, concentration, cognitive and physical performance. Caffeine's primary mechanism of action in the brain is the blockage of adenosine receptors, which play a central role in the regulation of sleep-wake-cycle by increasing sleep pressure throughout the activity phase. It is thought that by blocking these receptors, caffeine counteracts natural tiredness, improving attention, focus and improving overall cognitive performance. One of the few studies to investigate caffeine effects on morning cognitive performance report-ed an improvement in a simple search task 2.5 % in undergraduate students, when 4 mg.kg-1 body mass of caffeine was consumed 1-h before a 07:00 h experimental session versus Placebo. Unlike the sparce research investigating cognitive effects of morning caffeine ingestion, its effects on muscle performance have been demonstrated elsewhere. Caffeine (3 mg.kg-1 body mass) ingested 60-min before exercise increased dynamic strength and power output of upper and lower muscle groups in the morning (10:00 h) in resistance-trained men, with 4.6-5.3% improvement compared to placebo. Similarly, caffeine (3 mg.kg-1 body mass) ingested 60-min before exercise at 09:00 h improved muscular strength/power at moderate-to-high loads (75-90% 1RM) and endurance performance (65% 1RM) in the back squat while counteracting morning declines at light-load (25% 1RM) for both back squat and bench press without altering electrical activity. These benefits are likely due to increased neural activation, enhanced calcium release in muscles, and a reduction in the perception of effort during exercise, making it easier to exert maximal effort. The observation of caffeine's ability to improve morning cognitive and physical performance, may be obscured by lack of rigor and standardization in the method employed (such as timing of the ingestion and dose chosen). Many studies do not report any control condition that consider a placebo effect (no pill, familiarization of the tests to be conducted, recruit sample size based on a power calculation and no standardization of participants habitual caffeine use (low, medium or high caffeine daily users). In addition, studies have often failed to control important factors such as chronotype, time-of year, or time-of-day and participants' quality of sleep. Which specifically relates to investigations of chronobiological nature and other considerations. Objectives: To assess the effect of 300 mg caffeine (CAFF) vs placebo (PLAC) vs no-pill (NoPill) on morning a) strength and power output measured via the Biodex Isometric MVC as well as the Muscle Lab force-velocity linear encoder \[such as peak force (PF), % muscle activation, average power (AP), average velocity (AV), peak velocity (PV), mean propulsive velocity (MPV), rate of development of velocity (RDV), displacement (D) and time-to-peak velocity (tPV)\] and b) cognitive performance (including tasks of attention, memory and executive function). A population of low daily users \< 150 mg was chosen, to reduce effects of caffeine withdrawal symptoms on the non-caffeine condition on performance. As well as maximize caffeine effects at the 300 mg dose administered.

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