What You Need to Know About Heart Rate Variability (HRV)
Heart rate variability is a measure used to understand an athlete’s overall condition, from fitness level to health. It provides feedback on whether it’s a good time to train hard, compete, or, on the contrary, if it’s time to rest.
It is very likely that cycling enthusiasts, especially those most interested in training and physical fitness, are familiar with the term Heart Rate Variability (HRV) or its initials derived from English. However, many still do not fully understand what this term means, what it represents, or its practical applications in cycling training. For this reason, we have decided to review this topic.
1. A Bit of History
The first studies on heart rate variability date back to the 1960s. They were pilot tests conducted with Soviet cosmonauts to see how they adapted to changes in atmospheric conditions and other challenges they might face in space.
Years later, this same interest in measuring human adaptation to different stimuli extended to sports. HRV became a new parameter that both sports doctors and coaches studied closely, as earlier research had shown a strong link between changes in heart rate variability and an athlete’s fitness and health.
Polar, a pioneering company in heart rate monitors, was the first to implement HRV measurement in its devices. This opened the door to information that had previously been reserved for medical research.
Today, there are countless apps and devices that monitor heart rate variability, generate reports and trend lines, and are accessible to any user. HRV has become one of the most widespread and popular tools in recent years for monitoring an athlete’s overall condition in high-performance sports.
2. What It Really Means
In general terms, heart rate variability (HRV) refers to how regular our heartbeat is. This regularity is measured by the time, in milliseconds, between each heartbeat. Specifically, it is measured between the R-waves of each beat, which are part of the waves recorded on an electrocardiogram (ECG).
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When the interval between R-waves—or simply between beats—is very consistent and similar, HRV is considered low.
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When the interval between beats varies and is less stable, HRV is considered high.
In short, HRV reflects the regularity of our heartbeats.
3. What It Depends On
To understand what affects heart rate variability, we need to know the underlying mechanisms. Heart rate, or the rhythm of our heart, is regulated by the autonomic nervous system, which controls all involuntary functions of our body, such as digestion, body temperature, blood flow distribution, and many others.
The autonomic nervous system has two branches: the sympathetic and parasympathetic systems, which have opposite functions and inhibit each other.
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The sympathetic system accelerates processes to release energy and is associated with alertness and fatigue.
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The parasympathetic system promotes energy conservation, supports recovery, and prepares the body for physical effort.
4. How the Nervous System Affects HRV
When sympathetic activity dominates, blood sugar and cortisol levels rise, inflammation increases, and heart rate goes up, but HRV decreases, meaning the heartbeat becomes more stable between beats.
In contrast, parasympathetic activation does the opposite: it lowers blood sugar, reduces blood pressure and heart rate, and generally promotes recovery. Regarding HRV, parasympathetic dominance tends to increase variability, so the pulse becomes more variable between beats.
Because of this, low HRV values are often associated with situations that are not favorable for peak performance, whether due to fatigue, physical or mental stress, or emotional disturbances, since HRV is closely linked to the nervous system. Emotional stress can also affect HRV.
It is common to observe low HRV after intense training sessions or competitions, during very demanding training periods, during illness, or in stressful emotional situations.
A downward trend in HRV may indicate overtraining.
On the other hand, high HRV values are associated with periods when the athlete is in optimal condition, recovering energy stores, regenerating muscle tissue, and experiencing anabolic hormone activity, all of which support good performance.
Some Nuances
Monitoring HRV values allows us to better track the overall condition of a cyclist—or ourselves if we train and like to monitor all aspects of our fitness.
During training, HRV can help us see how well our body is handling the workload and whether we should continue with the plan. Conversely, it can also alert us to adjust training, for example, if we notice a trend of decreasing HRV over several days. HRV can also confirm what we might suspect based on how we feel—for instance, if we are not feeling good on the bike and don’t know why, HRV can provide objective data that something is indeed off. Emotional states can also be measured or detected through HRV, showing how they affect performance.
It is important to note that HRV can fluctuate from day to day. A single low reading does not necessarily indicate poor performance. For this reason, it is recommended to make decisions based on HRV trends over at least 4–5 days, rather than relying on a single measurement.
5. What HRV Measures
HRV measures the time, in milliseconds, between the R-waves of each heartbeat.
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When this interval is very consistent, HRV is considered low.
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When the interval is irregular, HRV is considered high.
How to Interpret It
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Low Variability → Sympathetic nervous system dominance → Lower performance capacity → Review or adjust your training (reduce load, volume, and/or intensity).
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High Variability → Parasympathetic nervous system dominance → Good adaptation to effort and potentially high performance → Able to tolerate higher training loads.
5. Ways to Measure It
There are many ways to measure HRV, some more practical, others more complex, some free, and some paid. Today, you can use mobile apps like HRV4Training or Elite HRV, which can measure your values in just a few seconds using a chest strap.
Another reliable option is using a Coospo heart rate monitor, which is capable of tracking HRV data. By pairing the monitor with the Heartool app, users can easily view and analyze their HRV values, making it a practical solution for athletes who want consistent and accurate monitoring. It also includes a five-color LED system that instantly indicates your current heart rate zone, so you can easily see your training intensity in real time.
Other alternatives include smartwatches that track HRV, or more specialized devices like WHOOP bands or OURA rings, which monitor HRV 24/7 and provide detailed reports on rest, fatigue, sleep, and overall condition, all linked to heart rate variability.
