to the editor: At scientific or clinical meetings or at other academic institutions when I argue that heart rate variability cannot be used in any simple manner to measure autonomic tone or I speak about our work on the resting bradycardia in athletes, I am faced with the problem of a disbelieving audience—disbelieving because they have been taught, as undeniable facts, that heart rate variability is a measure of autonomic tone and the resting bradycardia in athletes is the result of high vagal tone. This is despite the fact that both concepts were challenged a long time before we entered the field (3, 5). Based on changes in heart rate variability, Hughson, Flannery et al., Leicht et al., and Zuo and He in their commentaries (see Ref. 1) all support some type of role for the autonomic nervous system. However, if heart rate variability is a flawed measure as I argue, their arguments would collapse. I hope that by questioning these “undeniable facts,” others will be encouraged to enter the fray and resolve the dispute with further and more rigorous studies. I encourage neuroscientists to become involved: rather than using a flawed surrogate (heart rate variability), autonomic tone needs to be directly measured. There is a need for large studies of human athletes—most studies in the field involve small numbers of human subjects only. Future studies also need to demonstrate that autonomic blockade is complete and also understand the weaknesses of heart rate variability. Although Hughson in his commentary suggests a role for autonomic tone, he also highlights two studies of which I was unaware; his own work on treadmill-trained rats (1) and the work of Sutton et al. (4) on human subjects both demonstrate that training decreases the intrinsic heart rate, i.e., training changes the intrinsic properties of the sinus node. As suggested by Zuo and He in their commentary, perhaps the autonomic nervous system is causing these changes.
GRANTS
This work was supported by the British Heart Foundation (RG/11/18/29257).
AUTHOR CONTRIBUTIONS
M.R.B. drafted, edited and revised manuscript and approved final version of manuscript.
DISCLOSURES
No conflicts of interest, financial or otherwise, are declared by the author.
REFERENCES
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