Heart Rate Variability (HRV) tracks the subtle, continuous variation in the time interval between successive heartbeats, measured in milliseconds (ms). Unlike a metronome, a healthy heart exhibits slight changes in the time between beats. This metric is a window into the function of your Autonomic Nervous System (ANS), which controls involuntary bodily functions. The ANS has two opposing branches: the sympathetic nervous system (“fight or flight”) and the parasympathetic nervous system (“rest and digest”). HRV shows the degree of fluctuation, serving as a metric for physiological resilience, recovery status, and adaptation to stress.
How Heart Rate Variability is Measured
Heart rate (HR) and heart rate variability (HRV) are distinct measurements. HR is a simple count of beats per minute (BPM), while HRV is the precise measurement of the time difference between each individual heartbeat, often called the R-R interval. This beat-to-beat timing is recorded in milliseconds (ms) and requires specialized equipment to detect these tiny fluctuations. Wearable technology, such as smart rings or watches, uses optical sensors to capture the pulse wave and measure this variability.
The variation in timing is regulated by the interplay between the two branches of the ANS. The parasympathetic branch, primarily managed by the Vagus Nerve, works to decrease the heart rate and increase variability. Conversely, the sympathetic branch works to speed up the heart rate, causing beat intervals to become more consistent and less varied. A higher HRV score reflects greater influence from the parasympathetic system, indicating that the nervous system is flexible and ready for recovery.
Interpreting High, Low, and Average HRV Scores
The question of whether a 135 ms HRV score is good is answered by noting that it is generally considered an excellent score. Most population averages for adults fall within a much lower range, typically between 20 ms and 80 ms, with averages decreasing as people age. A value of 135 ms suggests a high level of cardiovascular fitness, low chronic stress, and a nervous system that is highly adaptable and primed for recovery. This high score indicates a dominance of the parasympathetic nervous system, which is associated with better overall health and resilience.
However, the number 135 ms is not an absolute measure of health because HRV is highly individualized. Comparing your score to a population average is less important than comparing it to your own established personal baseline. The most telling sign of your health and readiness is the trend of your scores over time, not a single daily reading. A consistently low score can signal that the sympathetic system is dominant due to fatigue, illness, or excessive stress.
A sudden, sharp drop below your typical baseline is more significant than the absolute number itself. This drop suggests that your body is currently under a higher strain, whether from a challenging workout, an impending illness, or intense psychological stress. Conversely, a high score that is consistent with your long-term trend suggests a well-balanced nervous system and a strong capacity for adaptation.
Lifestyle Factors That Shift HRV
Many daily habits and circumstances can cause your HRV score to fluctuate significantly. Acute and chronic psychological stress are major negative influences, activating the sympathetic nervous system and leading to a measurable decrease in variability. Poor sleep quality or inconsistent sleep patterns disrupt restorative processes, resulting in a lower HRV as the nervous system remains in a state of mild alert. Consuming alcohol, especially in the hours before bed, suppresses parasympathetic activity and causes a noticeable drop in the nightly reading.
Illness or underlying infection will also divert the body’s resources toward defense, causing the HRV score to fall as the sympathetic system engages. On the positive side, engaging in consistent aerobic exercise over time is known to increase the baseline HRV, reflecting improved cardiac fitness and a more responsive nervous system. Proper hydration supports blood volume and circulation, helping to stabilize variability. These factors demonstrate that your HRV is a dynamic metric, constantly reacting to the immediate demands placed upon your body.
Methods for Optimizing Your HRV
Individuals looking to stabilize or raise their baseline HRV can implement several specific, actionable lifestyle changes. Practicing intentional, slow breathing exercises is one of the most direct ways to engage the parasympathetic nervous system. Diaphragmatic breathing, aiming for approximately six complete breaths per minute, has been shown to boost vagal tone and improve HRV scores. Consistent physical activity, particularly moderate-intensity movement often referred to as Zone 2 cardio, strengthens the heart and improves autonomic balance over the long term.
Establishing a fixed and predictable sleep routine is also highly effective for improving variability. Going to bed and waking up at the same time each day helps align the body’s circadian rhythm, which facilitates deeper, more restorative sleep. Incorporating daily stress management practices, such as mindfulness, meditation, or gratitude journaling, helps to actively reduce sympathetic activation. These routine practices work to condition the nervous system, allowing it to recover more efficiently and maintain a higher level of physiological readiness.