View source for Heart Rate Variability

The time between heartbeats varies slightly, even when the average heart rate is constant. For example, a heart rate of 60 BPM is an average of one beat per second. However the actual time between heartbeats could vary so that some beats occur after 0.8 seconds, and some after 1.2 seconds. Generally, heart rate variability is greatest at rest and the variability declines as the heart rate rises. Heart rate variability is linked to aerobic fitness, with the fittest individuals having the greatest variability, and this can be used to predict [[VO2max|V̇O<sub>2</sub>max]]<ref name="HRV"/>.
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<ref name="HRV">[Heart rate variability and physical exercise. Current ... [Herz. 2006] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/17036185 </ref>
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