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Exercise training bradycardia is largely explained by reduced intrinsic heart rate
Samira Bahrainy1, Wayne C Levy1, Janet M Busey2
1Division of Cardiology, Department of Medicine, VA Medical Center and University of Washington, Seattle, WA, United States.
International Journal of Cardiology
|August 7, 2016
Summary
Exercise training lowers resting heart rate (RHR) but not by increasing parasympathetic tone or decreasing beta-adrenergic response. The study suggests a reduced intrinsic heart rate is the likely cause for lower RHR in trained individuals.
Area of Science:
- Cardiology
- Exercise Physiology
- Autonomic Nervous System
Background:
- Resting heart rate (RHR) characteristically decreases following exercise training.
- Potential mechanisms include alterations in autonomic nervous system activity and intrinsic heart rate.
Purpose of the Study:
- To investigate whether increased parasympathetic tone or reduced beta-adrenergic responsiveness underlies the exercise-induced decline in RHR.
- To differentiate between autonomic and intrinsic factors influencing RHR changes post-training.
Main Methods:
- Healthy subjects (aged 18-32 and 65-80) underwent 6 months of supervised exercise training.
- Parasympathetic tone was assessed via heart rate response to atropine (parasympathetic withdrawal).
- Beta-adrenergic responsiveness was measured using isoproterenol during parasympathetic blockade.
Main Results:
- Exercise training significantly increased VO2 max and decreased RHR.
- No significant changes were observed in heart rate response to parasympathetic withdrawal or beta-adrenergic stimulation post-training.
- These findings were consistent across different age and sex subgroups.
Conclusions:
- Increased parasympathetic tone or decreased beta-adrenergic responsiveness do not explain the RHR reduction with exercise training.
- The study suggests that a decrease in intrinsic heart rate is the primary factor responsible for lower RHR after training.
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