Tracking physiological stress during prolonged virtual soccer

Extended esports play can lead to mental fatigue, resulting in slower and less precise decision-making (diminished executive control) and a variety of physiological responses indicative of impaired sensorimotor or cognitive function.

In such cases, many players reach for caffeinated or sugary drinks, but overconsumption raises health concerns such as elevated risks of obesity and diabetes. Sparkling water offers a healthier alternative, as it contains no sugar or caffeine, yet produces a similar sensation in the throat that may engage brainstem-to-prefrontal pathways linked to executive control.

In a randomized crossover study, 14 young adults played virtual soccer for three hours on two separate occasions while drinking either sparkling water or plain water. Researchers continuously tracked pupil diameter and heart rate, assessed subjective fatigue and game enjoyment hourly, tested executive function using a flanker task (in which participants must decide if stimuli flanking a central stimulus are congruent or incongruent--such as arrows pointing in the same or opposite direction), and periodically measured interstitial glucose and salivary cortisol.

Compared with plain water, sparkling water dampened subjective fatigue, boosted enjoyment, improved executive function test performance, and reduced pupil constriction. Greater pupil constriction was also associated with slower flanker-task responses, supporting pupil diameter as an easily measurable sign of cognitive fatigue.

In contrast, heart rate, interstitial glucose, and cortisol were comparable across conditions. Players drinking sparkling water also committed fewer fouls, while there were no significant changes in offensive or defensive performance metrics. These results support sparkling water consumption as an effective way to maintain mental focus during prolonged esports play without sugar or caffeine intake.