High-intensity, short-duration exercise became popular among people aiming to improve strength, power, and general physical condition [1]. This exercise configuration results in an acute improvement in learning and memory, as demonstrated in animal models [2]. The effects can also acutely impair attention, reaction times, and increase variability in cognitive performance [3], [4] while enhancing the performance of attentional control tasks [5].

The circadian rhythm is among the factors modulating the relationship between cognitive responses and physical exercise. Reaction time [6], working memory, subjective alertness, and visual attention [7] directly correlate with the circadian rhythm [6]. On the other hand, the relationship between the circadian rhythm and variability in cognitive responses, such as information processing, reaction time, attention, executive function, and memory, is still poorly understood [8], [9]. Therefore, it is fundamental to investigate these relations to control confounding factors like hours awake. Cognitive actions performed in the morning could show better results after a good night of sleep [7]. Indeed, cognitive performance in reaction time, inhibition, cognitive flexibility, and precision tasks have better results in the morning [7], [10].

Another factor of confusion regarding the relationship between the acute effects of exercise and cognitive performance is the chronotype [11]. Chronotype reflects a person's pattern of preferences [12], a predisposition towards activities in the morning or evening, and is usually self-assessed using questionnaires [13] with satisfactory reliable information [10]. The most used questionnaire is the “Morningness–Eveningness Questionnaire (MEQ),” which can identify different chronotypes, Definitely morning type, Moderately morning type, Neither type, Moderately evening type and Definitely evening type [14]. Changes in circadian rhythms can make it challenging to learn or solve cognitive tests at night for morning people and in the morning for afternoon people [12]. It was observed that afternoon individuals obtained lower scores than morning individuals when tests were applied at the beginning of the day [15]. Intermediate individuals receive lower scores than the morning ones when tests are completed in the morning [16]. Better performance of executive functions and better decision-making, working memory, and inhibitory control were found among individuals tested according to their chronotype [17].

The main goal of this study was to determine whether the acute effects of high-intensity short-duration exercise on cognitive performance are influenced by the time of day in healthy people.