Researchers have devised a new way to better understand the relationship between heart rate variability (HRV) and health - a step that could enable better monitoring technologies for athletes and medical professionals.
The "lub-dub" pattern of the heart that speeds up or slows down as our activity increases or decreases is not as regular.
The new method finds that in fact, the amount of time between heartbeats can vary even at a constant heart rate and that variability is a good thing.
"When the body experiences stress - for example from exercise or extreme temperatures - it can maintain a stable blood pressure and constant body temperature in part by dialing the heart rate up or down. And HRV plays an important role in maintaining this balance," explained professor John Doyle from the California Institute of Technology.
Reduced heart rate variability (HRV) has been found to be predictive of a number of illnesses such as congestive heart failure and inflammation.
For athletes, a drop in HRV has also been linked to fatigue and over-training.
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To study how HRV helps maintain this version of "cruise control" in the human body, Doyle and his colleagues measured the heart rate, respiration rate, oxygen consumption, and carbon dioxide generation of five healthy young athletes as they completed experimental exercise routines on stationary bicycles.
By combining the data from these experiments with standard models of the physiological control mechanisms in the human body, they were able to determine the essential tradeoffs that are necessary for athletes to produce enough power to maintain an exercise workload while also maintaining the internal homeostasis of their vital signs.
"For example, the heart, lungs and circulation must deliver sufficient oxygenated blood to the muscles and other organs while not raising blood pressure so much as to damage the brain," Doyle added.
The researchers then used control theory to analyse the exercise data and found that a healthy heart must maintain certain patterns of variability during exercise to keep this complicated system in balance.
The work appeared in the journal Proceedings of the National Academy of Sciences.