Effects of Acute Caffeine Intake on Endurance Performance and Cardiac Autonomic Modulation in Patients with COPD

This study aimed to investigate the effects of acute caffeine (CAF) intake on heart rate, time to exhaustion, and cardiac autonomic modulation during a constant-load exercise test in patients with chronic obstructive pulmonary disease (COPD).

A counterbalanced, randomized, double-blind, placebo-controlled, and crossover design was adopted in the present study. Eleven patients diagnosed with COPD initially performed a maximal incremental exercise test on a cycle ergometer, and from 72 to 96 h later, a constant-load exercise test (60% of the peak power achieved in the maximal incremental exercise test) after ingestion of CAF (5 mg.kg^-1) or placebo (cellulose, PLA) 60 min before the test. Heart rate (HR) and heart rate variability (HRV) were continuously monitored beat-to-beat throughout the test and recovery using a portable HR monitor.

During exercise, the response of HR showed a significant effect of time (p < 0.001), but there was no main effect of condition (p = 0.76) or a time x condition interaction (p = 0.74). CAF ingestion increased time to exhaustion during the constant-load exercise test compared to PLA (p = 0.04). The CAF ingestion also reduced the magnitude of HR recovery 60 s post-exercise in comparison with PLA (p = 0.02). No other significant differences were found for HR recovery in further time points or HRV indices (p > 0.05).

In conclusion, acute CAF ingestion increased time to exhaustion in a constant-load exercise test in patients with COPD. There was no main effect of CAF on HR during exercise. Although CAF reduced HR recovery at the beginning of recovery, CAF did not seem to induce more prolonged changes on cardiac autonomic modulation post-exercise. These findings suggest CAF could be safety used as an effective ergogenic aid to optimize the endurance performance of patients with COPD.