But there\u2019s more you can learn from how your heart is functioning, based on your heart rate variability (HRV), and it\u2019s a topic of increasing interest both to athletes and the medical community.<\/p>\n
Let\u2019s take a closer look at what heart rate variability is, why it\u2019s important and how you might be able to use it to your advantage.<\/p>\n
What is heart rate variability?<\/h2>\n
According to the Harvard Medical School<\/a>, heart rate variability is \u201csimply a measure of the variation in time between each heartbeat\u201d.<\/p>\n We\u2019re used to the regular bump-bump of the heart as it beats, but this rhythm is less regular than it at first appears, with measurable differences in milliseconds in the time between successive beats.<\/p>\n \u201cThe fluctuation in your heart rate \u2013 the variance in time between the beats of your heart \u2013 is heart rate variability,\u201d says Kristen Holmes, VP of performance science at WHOOP.<\/p>\n \u201cIf your heart beats 60 times per minute, it\u2019s not actually beating once per second. For example, within that minute there may be 0.9 seconds between two beats and 1.1 seconds between two others. The greater this variability is, the more \u2018ready\u2019 your body is to perform at a high level.\u201d<\/p>\n Heart rate is controlled by your autonomic nervous system, which regulates the things that carry on without you having to think about them.<\/p>\n \u201cIt works behind the scenes, automatically regulating our heart rate, blood pressure, breathing and digestion among other key tasks,\u201d says the Harvard Medical School. \u201cThe autonomic nervous system is subdivided into two large components: the sympathetic and the parasympathetic nervous system.\u201d<\/p>\n Whereas the sympathetic nervous system manages increases in heart rate and blood pressure \u2013 the so-called \u2018fight or flight\u2019 response \u2013 the parasympathetic nervous system works in the opposite direction, slowing heart rate and reducing blood pressure \u2013 also called \u2018rest and digest\u2019.<\/p>\n The interplay between these two systems controls your heart rate, as well as other background bodily functions, working in response to external and internal stimuli.<\/p>\n Heart rate variability increases when you\u2019re more relaxed and your parasympathetic nervous system is in control, but decreases under stress when your sympathetic nervous system dominates.<\/p>\n \u201cHeart rate variability comes from the two branches of your autonomic nervous system simultaneously sending signals to your heart,\u201d adds Holmes.<\/p>\n \u201cIf your nervous system is balanced, your heart is constantly being told to beat slower by your parasympathetic system, and beat faster by your sympathetic system. This causes a fluctuation in your heart rate.\u201d<\/p>\n To track HRV, you need to be able to accurately measure the time between successive beats of the heart. More specifically, it\u2019s the RR interval, which is the period between the large peaks in heart electrical activity you see on an electrocardiogram (ECG), as featured in all good hospital dramas.<\/p>\n An electrocardiogram trace is the gold standard in tracking HRV, because the electrodes attached to your chest provide an accurate measure of the peaks.<\/p>\n In recent years, a number of wearable devices have emerged that can track HRV, including the WHOOP 4.0 strap<\/a>. It\u2019s a wrist-worn strap with a set of light-based sensors that measure your heart rate, blood oxygen levels and skin temperature.<\/p>\n HRV needs to be tracked over many heartbeats to get an accurate measurement. The data is usually expressed as a root mean square deviation, a statistical analysis that measures the spread of values.<\/p>\n \u201cHeart rate variability is a very sensitive metric that varies significantly throughout the day,\u201d says Holmes. \u201cTracking it when you\u2019re active is not always useful because it fluctuates so drastically from one moment to the next.\u201d<\/p>\n As a result, the strap takes a \u2018dynamic average\u2019 during sleep. \u201cIt\u2019s weighted towards your last slow wave sleep stage each night, when you\u2019re in your deepest period of sleep and your body is most at rest,\u201d Holmes adds. \u201cThis gives you an accurate understanding of your baseline so you can monitor your trends.\u201d<\/p>\n Many of the best cycling watches<\/a> also use optical heart rate sensors on your wrist to follow your heart rate and can identify your levels of heart rate variability. With some models, you can also use the watch alongside a heart rate strap<\/a>.<\/p>\n Garmin smartwatches, such as the Fenix 7<\/a>, use heart rate and HRV data to give you a \u2018Body Battery\u2019 number, which estimates how your energy levels are changing throughout the day. There\u2019s also the option to use a heart rate strap to get a three-minute HRV trace. HRV is something that Polar and Suunto smartwatches track and analyse too.<\/p>\n We\u2019ll go into the benefits of monitoring heart rate variability when it comes to your training later on, but there are more general advantages of keeping tabs on your HRV and how it varies over time.<\/p>\n According to the Harvard Medical School, \u201cHRV may offer a non-invasive way to signal imbalances in the autonomic nervous system.\u201d<\/p>\n \u201cWhen you have high heart rate variability, it means that your body is responsive to both sets of inputs (parasympathetic and sympathetic). That\u2019s a sign your nervous system is balanced, and that your body is very capable of adapting to its environment and performing at its best,\u201d Holmes adds.<\/p>\n \u201cBut if you have low HRV, one branch is dominating the other (usually the sympathetic) and sending stronger signals to your heart. This indicates your body is working hard for some reason \u2013 maybe you\u2019re fatigued, dehydrated, stressed, or sick and need to recover.\u201d<\/p>\n Those imbalances can come as a result of a wide range of factors, including training, lifestyle and biological factors, according to WHOOP.<\/p>\n \u201cHRV is a holistic indicator of stress,\u201d says Simon Wegerif, the founder of ithlete, a HRV tracking tool, in a podcast with TrainingPeaks<\/a>. \u201cHRV is useful partly because it\u2019s such an inclusive indicator of stress, fatigue and recovery.\u201d<\/p>\nHow is heart rate variability tracked?<\/h2>\n
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>What are the benefits of tracking heart rate variability?<\/h2>\n
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>\ufeffTraining factors<\/th> Lifestyle factors<\/th> Biological factors<\/th><\/tr><\/thead> Volume<\/td> Diet and nutrition<\/td> Age<\/td> <\/tr> Intensity<\/td> Alcohol<\/td> Gender<\/td> <\/tr> New\/unfamiliar stimuli<\/td> Circadian rhythm and sleep habits<\/td> Genetics<\/td> <\/tr> Balance between rest and workout days<\/td> Stress<\/td> Chronic health conditions<\/td> <\/tr><\/tbody><\/table>