Why a higher HRV isn’t always better, and why one bad reading shouldn’t determine your workout.
Your watch says your recovery is poor. Your HRV dropped overnight. But you slept well, feel energetic and were planning a hard training session. Should you change your workout?
For many athletes, this situation has become increasingly common.
Wearable technology now gives runners, tennis players and recreational athletes access to physiological information that was once largely restricted to laboratories and research settings.
One of the most discussed metrics is Heart Rate Variability, or HRV.
But having access to data is not the same as understanding what it means.
At Costa Performance, we believe monitoring tools become valuable when they help athletes and coaches make better decisions, not when they replace judgment with a number.
What exactly is Heart Rate Variability?
Your heart does not beat like a perfectly programmed metronome.
Even when your average heart rate is 60 beats per minute, the interval between individual heartbeats is not always exactly one second.
One interval might be 980 milliseconds, the next 1,040 milliseconds, and another 995 milliseconds.
These small fluctuations are part of normal cardiovascular regulation.
Heart Rate Variability measures variations in the time intervals between successive heartbeats.
More precisely, clinical HRV analysis generally examines the intervals between normal sinus beats, commonly called NN intervals.
HRV is not the same as heart rate.
Heart rate tells us how frequently the heart beats.
HRV provides information about the pattern of variation between beats.
Both can offer useful physiological information, but they describe different characteristics of cardiovascular function.
The autonomic nervous system: why HRV changes
To understand HRV, we need to briefly explore the autonomic nervous system.
This system helps regulate functions that do not require continuous conscious control, including cardiovascular activity, digestion and aspects of thermoregulation.
Two important divisions are:
The sympathetic nervous system, involved in mobilizing physiological resources during exercise, stress and other challenges.
The parasympathetic nervous system, particularly its vagal influence on the heart, which contributes to regulating cardiac activity and beat-to-beat variability.
These systems are not simply an on/off switch, and HRV should not be interpreted as a direct measurement of a perfect balance between them.
During rest, respiratory sinus arrhythmia and cardiac vagal modulation contribute substantially to short-term HRV.
During exercise, changes in autonomic regulation, respiration and cardiovascular demands alter the pattern of heartbeat intervals.
This is why HRV can respond to training stress, recovery, sleep, illness and other physiological influences.
However, HRV is not a direct measurement of muscle recovery, psychological stress or overall readiness to perform.
It is one piece of information within a much more complex system.
Why do athletes monitor HRV?
Training challenges the body.
After exercise, multiple systems respond and adapt, including the cardiovascular, muscular, metabolic, endocrine and nervous systems.
HRV can provide information about aspects of autonomic regulation during this process.
For example, changes in HRV may occur after demanding training sessions, competitions, poor sleep, illness or periods of increased physiological stress.
In some endurance-training settings, researchers have investigated whether adjusting training according to HRV trends can help individualize exercise intensity.
The results are promising in certain contexts, but not universally consistent. HRV-guided training is not automatically superior to a well-designed conventional program.
The value of HRV depends on how it is measured, interpreted and combined with other information.
Is a higher HRV always better?
This is one of the most common misunderstandings.
Generally, higher resting HRV is often associated with greater cardiac vagal modulation under comparable measurement conditions.
But that does not mean the athlete with the highest HRV is the fittest or most recovered.
HRV varies with age, individual physiology, measurement conditions and many other factors.
Comparing your HRV with another athlete’s value is usually less informative than understanding your own normal range.
Even within the same athlete, an unusually high HRV reading does not necessarily guarantee optimal recovery.
Certain responses to accumulated training stress may involve unexpectedly elevated vagally mediated HRV, sometimes discussed in the literature in relation to parasympathetic hyperactivity. These interpretations require caution and additional evidence.
The important question is not simply whether HRV is high or low. It is whether the value makes sense within the athlete’s individual pattern and current condition.
Your baseline matters more than a single reading
Imagine two runners.
Runner A usually records an HRV around 35 milliseconds.
Runner B usually records an HRV around 75 milliseconds.
Without additional context, we cannot conclude that Runner B is recovering better.
Their values may reflect different individual physiological characteristics.
Now imagine Runner A normally records values between 32 and 40 milliseconds but experiences several mornings around 22 milliseconds.
That change may deserve attention, especially if it coincides with poor sleep, elevated resting heart rate, illness symptoms or unusual fatigue.
But even then, it is not a diagnosis.
A useful approach is to establish an individual baseline through repeated measurements under reasonably consistent conditions.
Rather than reacting to every fluctuation, look for meaningful patterns over several days.
RMSSD, SDNN and what your device actually measures
Not all HRV metrics are identical.
Two commonly used measures are:
RMSSD (Root Mean Square of Successive Differences)
RMSSD describes short-term differences between successive normal heartbeat intervals. Under appropriate resting conditions, it is widely used as an indicator associated with cardiac vagal modulation.
It is commonly used in athlete monitoring because relatively short, standardized recordings can provide useful information.
SDNN (Standard Deviation of Normal-to-Normal Intervals)
SDNN describes the overall variability of normal heartbeat intervals within a recording.
Its interpretation depends strongly on the length and conditions of measurement. An SDNN value from a 24-hour recording cannot be interpreted in the same way as one from a short morning measurement.
Some devices also present proprietary recovery or readiness scores rather than displaying raw HRV metrics.
These scores may combine HRV with sleep, resting heart rate, activity history and other information.
That can be convenient, but it is important to understand that a readiness score is an algorithmic estimate, not a direct measurement of your body’s complete recovery status.
Measurement technology also matters.
ECG records cardiac electrical activity, while many wrist-worn devices estimate pulse intervals using optical sensors.
Under suitable resting conditions, some validated devices can provide useful HRV estimates. Accuracy can vary with device, movement, signal quality and measurement protocol.
HRV and running in Florida’s heat and humidity
Consider a runner who completes a long run in Boca Raton on a hot, humid morning.
Even if the pace is relatively comfortable, the environment may substantially increase physiological strain.
High temperatures, elevated dew points, prolonged exercise and fluid losses can influence cardiovascular regulation and post-exercise recovery.
The following morning, the runner notices a lower HRV than usual.
Does that automatically mean they should skip training?
Not necessarily.
The result should be interpreted alongside several questions:
- Was the previous session longer or harder than usual?
- How was sleep quality?
- Is resting heart rate elevated?
- Is the runner experiencing unusual fatigue, soreness or illness symptoms?
- How does an easy warm-up feel compared with normal?
A lower HRV may be consistent with increased physiological stress, but it cannot identify the exact cause on its own.
This is why our CPX Running Team emphasizes understanding the relationship between pace, heart rate, perceived effort and environmental conditions.
HRV can add another useful perspective, but it does not replace those observations.
What about tennis players?
Tennis introduces different monitoring challenges.
Competitive players may experience variable match durations, repeated accelerations and decelerations, travel, irregular schedules and changes in sleep.
A player might have a relatively normal HRV reading after a tournament but still experience substantial local muscular fatigue or soreness.
Conversely, an athlete might show a lower-than-usual HRV while reporting that they feel physically capable of completing a planned session.
Neither situation should be interpreted through HRV alone.
At Costa Performance, we consider athlete monitoring most useful when objective measurements are integrated with coaching observations, athlete feedback and the demands of the sport.
The goal is not to make every training decision based on one metric.
It is to understand the athlete more completely.
Five practical rules for using HRV
1. Measure consistently.
Whenever possible, use the same validated device, measurement position and time of day. Morning measurements under standardized resting conditions are commonly used in athlete monitoring.
2. Learn your personal range.
Collect enough measurements to understand typical variability before drawing conclusions from an unusual result.
3. Look for trends rather than isolated values.
A single reading can be influenced by measurement error, breathing, sleep and numerous other factors.
4. Combine HRV with other indicators.
Resting heart rate, perceived effort, sleep, soreness, symptoms and recent training load can provide essential context.
5. Use HRV to inform decisions, not dictate them.
An unusual HRV reading may justify closer attention or a discussion about adjusting training. It should not automatically determine whether an athlete trains hard, trains easy or rests.
The bigger picture: recovery is not one number
One of the most important principles in sports performance is that adaptation is multidimensional.
Cardiovascular recovery, neuromuscular fatigue, muscle tissue recovery, psychological readiness and sport-specific performance do not necessarily follow identical timelines.
No single measurement captures all of them.
HRV provides an accessible window into aspects of cardiovascular autonomic regulation.
That is useful.
But its greatest value comes when we understand both what it can tell us and what it cannot.
At Costa Performance, our approach to strength and conditioning, athlete monitoring and recovery is built around the same principle:
Better information should lead to better questions and better training decisions.
Not simply more numbers.
Train smarter with Costa Performance
Whether you are a runner preparing for your next race or a competitive tennis player managing training and tournament demands, understanding how your body responds to stress is an important part of long-term athletic development.
At Costa Performance in Boca Raton, we combine strength and conditioning, performance assessment and individualized coaching to help athletes develop their physical capabilities.
Our CPX Running Team also brings runners together to train, share knowledge and build a stronger running community.
CPX Running Team
Saturday group runs at 7:00 AM
Meeting point: Costa Performance, Boca Raton, Florida
All paces are welcome.
Because improving performance is not just about training harder.
It’s about knowing how to train, recover and adapt.
Costa Performance | Boca Raton, Florida
