This follows research carried out by Kaplan et al, which claimed that there's a fine line between enjoying the benefits of a caffeine rush versus feeling tired and irritable. While 250g of the substance triggers feelings of elation in subjects, a measure of 500mg is more commonly associated with irritability

The study was performed on 14 active adults, 7 male and 7 female, and after taking either an energy drink or placebo they were asked to cycle for 1 hour.

During this time various things were measured including their perceived leg pain, their heart rate, their perceived exertion and their readiness to invest in physical effort both before and after the run.

The results collected tended to back up the fact that energy drinks do help during exercise. The participants reported less leg pain, less exertion, had a higher heart rate and were more ready to engage in physical activity when they had an energy drink rather than a placebo.

Another study performed by Smit et al, 2004 looked at the mental effects of energy drinks and whether they allowed you to be more tenacious when performing cognitively demanding task

Read more at: https://www.psychologized.org/energy-drinks-the-physical-and-psychological-effects/