The Effects of Caffeine on Heart Rate and Heart Rate Variability at Rest and During Submaximal Cycling Exercise

• Published in: Research quarterly for exercise and sport Vol. 96; no. 1; pp. 155 - 163
• Main Authors: Glaister, Mark, Lythgoe, Dhama, Kamath, Sahana
• Format: Journal Article
• Language: English
• Published: United States Routledge 02.01.2025
• Subjects: Adenosine receptor; Adult; autonomic; Bicycling - physiology; Caffeine - administration & dosage; Caffeine - pharmacology; Central Nervous System Stimulants - pharmacology; coffee; Cross-Over Studies; Double-Blind Method; Exercise Test; Heart Rate - drug effects; Humans; Male; methylxanthine; Middle Aged; Oxygen Consumption - physiology; Rest - physiology; autonomic; methylxanthine; Adenosine receptor; coffee
• ISSN: 0270-1367; 2168-3824; 2168-3824
• DOI: 10.1080/02701367.2024.2377303

The aim of this study was to investigate the effects of caffeine on heart rate and heart rate variability (HRV) at rest and during submaximal exercise. Using a balanced, double-blind, randomized, crossover design, 16 male cyclists (age: 37 ± 9 years; $\dot {\rm V}$ V ˙ O 2max : 4.44 ± 0.67 L·min −1 ) completed three trials in an air-conditioned laboratory. In Trial 1, cyclists completed two incremental cycling tests to establish the ${\dot {\rm V}}$ V ˙ O 2 -power output relationship and $\dot {\rm V}$ V ˙ O 2max . In trials 2 and 3, cyclists were evaluated for heart rate and HRV at rest, after which they ingested a capsule containing 5 mg·kg −1 of caffeine or placebo. Thirty-five minutes post-supplementation, additional resting heart rate and HRV readings were taken after which cyclists completed a submaximal incremental cycling test (6 min stages) at 40-80% of ${\dot {\rm V}}$ V ˙ O 2max ; with HR and HRV measurements taken in the last 5 min of each increment. HRV was determined from the root mean square of successive differences between R-R intervals. There were significant supplement × exercise intensity interactions on heart rate (p = .019) and HRV (p = .023), with post hoc tests on the latter showing that caffeine increased HRV at 40%, 50%, and 60% of ${\dot {\rm V}}$ V ˙ O 2max by 3.6 ± 4.9, 2.6 ± 2.8, and 0.6 ± 1.7 ms, respectively. There was a supplement × time interaction effect on resting HRV (p < .001), but not on heart rate (p = .351). The results of this study support the suggestion that caffeine increases the parasympathetic modulation of heart rate.Clinical trial registration number: NCT05521386.