If you consistently have a high average HRV and a low resting heart rate (RHR), that's generally a good thing.
In fact, higher HRV and lower RHR are often associated with better cardiovascular fitness. As aerobic fitness improves, the heart can become more efficient, often allowing it to pump more blood with each beat while the autonomic nervous system becomes better regulated. This is one reason well-trained endurance athletes frequently have both relatively high HRV and low RHR.
But there's an important qualification:
HRV and RHR are influenced by much more than cardiovascular fitness.
That means a person with a naturally high HRV and low RHR isn't necessarily more cardiovascularly fit than someone with a lower HRV and higher RHR.
The relationship is real—but it isn't universal.
Why are high HRV and low RHR often associated with good fitness?
Regular aerobic exercise produces adaptations throughout the cardiovascular and autonomic nervous systems.
As cardiovascular fitness improves, the heart can become more efficient at delivering blood throughout the body. Increased stroke volume means the heart can pump more blood with each beat, which can allow it to maintain the body's needs with fewer beats per minute at rest.
At the same time, aerobic training is associated with changes in autonomic regulation, including greater parasympathetic influence on the heart. This can contribute to higher HRV.
So, in a person who has improved their cardiovascular fitness through consistent aerobic training, it would not be unusual to see:
↑ HRV
↓ Resting heart rate
↑ VO₂max
↑ Exercise capacity
These changes can occur together because they're all influenced by the adaptations produced by aerobic training.
This is why, when we look at large groups of people, higher HRV and lower resting heart rate tend to be associated with better cardiovascular and cardiorespiratory fitness.
But that doesn't mean HRV and RHR can be used interchangeably with a measurement of fitness.
Your individual physiology matters
One of the biggest reasons HRV and RHR don't perfectly predict fitness is that people don't all start with the same physiology.
HRV varies considerably between individuals. Genetics, age, sex, body composition, medications, breathing patterns and other physiological characteristics can all influence HRV.
The same is true for RHR.
Some people naturally have a lower RHR than others, while some naturally have higher HRV.
That means two people with very different fitness levels can have surprisingly similar HRV and RHR numbers.
And two people with similar fitness levels can have very different HRV and RHR numbers.
Consider these two examples:
Person A
- Naturally high HRV
- Naturally low RHR
- Performs very little aerobic exercise
- Relatively low VO₂max
- Limited endurance
Person B
- Naturally lower HRV
- Slightly higher RHR
- Consistently performs aerobic training
- Relatively high VO₂max
- Excellent endurance
Person A could have the more favorable HRV and RHR numbers.
But Person B could be substantially more cardiovascularly fit.
That's not because HRV and RHR are misleading.
It's because they are influenced by factors other than cardiovascular fitness.
A low resting heart rate isn't automatically an athlete's heart
It's tempting to assume that a resting heart rate of 45 beats per minute means someone must be extremely fit.
That's often true in a highly trained endurance athlete—but it isn't necessarily true for everyone.
A low RHR can be influenced by genetics and individual physiology in addition to training.
And importantly, resting heart rate doesn't tell you why the heart is beating slowly.
Two people can both have a RHR of 50 bpm while arriving there through very different physiological pathways.
One may have developed a highly efficient cardiovascular system through years of aerobic training.
The other may simply have a naturally low RHR.
The number alone can't tell us the difference.
The same concept applies to HRV
A high HRV can be a favorable sign of autonomic regulation, and higher HRV is often seen in people with better cardiovascular fitness.
But HRV is also highly individual.
There is no single HRV value that defines a person as "fit."
Someone with an average HRV of 70 in Morpheus isn't necessarily more fit than someone averaging 40.
What matters is that HRV can reflect many different aspects of an individual's physiology, while cardiovascular fitness specifically describes the body's ability to perform and sustain aerobic work.
HRV is related to fitness. It isn't a direct measurement of fitness.
So what actually measures cardiovascular fitness?
If you want to know how cardiovascularly fit you are, you ultimately need to look at what your body can do during exercise.
The most established measure is VO₂max, which represents the maximum amount of oxygen the body can utilize during intense exercise.
Other useful measures include the following:
- VO₂max or estimated VO₂max
- Heart-rate response to a standardized workload
- Heart-rate recovery after exercise
- Pace or power at a given heart rate
- Lactate or ventilatory threshold
- Sustainable exercise duration
- Performance at standardized workloads
These measurements directly assess aspects of exercise capacity.
HRV and RHR provide valuable physiological information, but they shouldn't be treated as substitutes for these measures.
The important distinction
The easiest way to think about this is:
Higher HRV and lower RHR are often signs of better cardiovascular fitness.
But they are not proof of better cardiovascular fitness.
For many people, improvements in aerobic fitness will be accompanied by higher HRV and lower RHR.
But the strength of that relationship varies from person to person because HRV and RHR are influenced by many factors beyond fitness.
That's why your HRV and RHR should be interpreted in the context of your own physiology and your other data, rather than used as standalone measures of cardiovascular fitness.
The Morpheus takeaway
If you have a high average HRV and a low average RHR, that's generally favorable—and there's a very good chance those numbers reflect some degree of cardiovascular efficiency.
But don't assume they tell the whole story.
HRV and RHR can be excellent indicators that accompany good cardiovascular fitness without being direct measurements of it.
The only way to truly determine cardiovascular fitness is to assess what your cardiovascular system can do under exercise.
So think of the relationship this way:
Good cardiovascular fitness → often higher HRV and lower RHR
But, Higher HRV and lower RHR → not necessarily good cardiovascular fitness
The first relationship is common.
The second is not guaranteed.
Your physiology is individual, and your HRV and RHR should always be interpreted accordingly.