Testing the effect of caffeine on breathing patterns during high-intensity whole-body exercise Original paper

Caffeine has a well-documented track record as an ergogenic (performance-enhancing) aid, and its effects have mostly been credited to the ability of caffeine to block adenosine receptors in the central nervous system.^[1] However, the pulmonary system is a limiting factor during high-intensity whole-body exercises, and the effects of caffeine on breathing patterns during high-intensity whole-body exercise are not well understood.

The authors of this study hypothesized that caffeine would increase tidal volume (the amount of air that moves into and out of the lungs during each respiratory cycle) and decrease respiratory frequency during high-intensity whole-body exercise.

In this randomized controlled crossover trial, 12 men (average age of 25) took 5 milligrams of caffeine per kilogram of body weight or a placebo 1 hour before performing high-intensity whole-body exercise on an ergometer to the limit of exercise tolerance.

Respiratory and metabolic responses were measured throughout the exercise test and at task failure, when the participants were unable to sustain the required work rate.

Compared to placebo, caffeine significantly extended the time to exercise failure (368.1 seconds to failure with caffeine vs. 328.5 seconds to failure with the placebo). Caffeine also significantly increased the tidal volume and inspiratory time (time taken for inhalation) throughout the exercise period but did not have a significant effect on respiratory frequency.

According to the authors, these findings suggest that caffeine altered the breathing patterns during the high-intensity exercise but maintained the same amount of air that entered the lungs in a given unit of time. They further surmised that increased tidal volume may have reduced dead space in the alveoli (the tiny air sacs of the lungs), possibly increasing ventilation. Based on these results, the authors suggested that some of the ergogenic effects of caffeine may be due to its effects on breathing.