The Effects of Low and Moderate Caffeine Doses on Cardiorespiratory Responses During Graded Exercise

Caffeine is a commonly used ergogenic aid known to influence cardiopulmonary exercise test outcomes. However, more research is needed to explore the effects of different dosages and the timing of measurements after intake. PURPOSE: This study aimed to investigate the influence of low and moderate doses of caffeine on cardiorespiratory outcomes during a graded exercise test. Specifically, the study examined the impact of 2.5 mg/kg and 5 mg/kg caffeine ingestion, measured 30 minutes after intake, on variables such as VO2, ventilation (VE), tidal volume (VT), respiratory frequency (RF), heart rate (HR), and power output (PO) at various exercise intensities: rest, gas exchange threshold (GET), respiratory compensation point (RCP), and maximal effort. METHODS: The study employed a repeated-measures, randomized, double-blind, placebo-controlled design. Young adults (10 males and 7 females) visited the laboratory on three occasions, within three weeks, to perform a graded exercise test on an electromagnetically braked cycle ergometer. Participants were asked to replicate their diet and avoid caffeine intake in the 24 hrs leading up to each trial. Prior to each trial, participants consumed either a Placebo, a 2.5 mg/kg, or 5 mg/kg caffeine drink matching in taste and color. A metabolic cart system was used to measure gas exchange and ventilation, and heart rate was monitored throughout the test. Statistical analysis was conducted using repeated-measures ANOVA to assess differences in cardiorespiratory parameters at various exercise intensities. RESULTS: There were significant differences for RF (p = 0.022; Placebo = 19.3 1/min, 2.5 mg/kg = 21.1 1/min, 5 mg/kg = 18.7 1/min) and VT at GET (p = 0.028; Placebo = 1.9, 2.5 mg/kg = 1.8 L, 5 mg/kg = 2.2 L). No significant differences were observed for other variables, including VO2, VE, HR, and PO across conditions. CONCLUSION: This study suggests that while caffeine intake may influence certain respiratory parameters such as respiratory frequency and tidal volume during graded exercise, it does not significantly impact other key cardiorespiratory variables like oxygen uptake or heart rate. These findings indicate that caffeine may have a limited but specific role in modulating respiratory mechanics during exercise.