Key Points

  • Breathing at certain paces allows for improved psychophysiological (mind-body) functioning when a person is not exercising, which can help with preparation, recovery, general stress management, and focus during a task.
  • “Heart rate variability” is the acceleration and deceleration in the rate of heartbeats.
  • A more variable heart rate is better for health and performance.
  • Heart rate variability helps quantify the physiologic changes that happen with improved breathing (deep breathing with long exhales).
  • Better breathing is not just for relaxation, it can also be used to enhance performance.


“Average heart rate” (HR) is the average number of times a heart beats over a period of time, expressed in beats per minute. Ancient Greek physicians and scientists were the first to measure HR, but it wasn’t until the 16th century that innovations also revealed how heart rate can vary in alignment with breathing (called respiratory sinus arrhythmia, or RSA). Beginning in the 1960s, with the advent of digital recording, technology again facilitated research, this time revealing the relationships between HRV and health/disease.1

Average heart rate tends to rise with stress and fall when a person is calm. At rest, those who are more prone to stress tend to have heart rates that increase more in response to a stressful situation2 and then decrease less when the source of stress goes away than for those who are less prone to stress.3 It has been suggested that this kind of heart-rate sensitivity can be explained by how well certain body mechanisms are enabled to regulate the parasympathetic (“rest and digest”) nervous system.3,4 Thus, the acceleration and deceleration of heart rate between heartbeats, called heart rate variability (HRV), can sometimes tell us more about stress and optimal performance than HR alone because HRV is a better marker of the mechanism that regulates the parasympathetic nervous system. With RSA breathing, HRs can vary in a pattern that has clear peaks and valleys in heart rate. One very simple calculation to approximate HRV is to use a heart-rate monitor to measure average maximum HR and minimum HR and then subtract the difference.5

Deep rhythmic breathing in which exhales are longer than inhales enhances HRV; that is, the range between peaks (fastest HR) and valleys (slowest HR) becomes bigger, and the variability becomes more rhythmic such that a graph of the progression between peaks and valleys would look like a sine wave.4 Breathing regularly at a pace that maximizes HRV can be good for mental and physical health and can help optimize performance. Lower HRV can serve as an indicator of mental and physical stress at one end of the continuum, whereas higher HRV can be associated with better health and performance (through improved self-regulation).

It is important to note that HRV has been researched during rest (not during exercise). Thus, current knowledge of HRV can be applied to important moments of preparation, recovery, lowering of baseline stress levels, and performance that occurs while a person is sedentary.


HR is not the same thing as HRV. Low (slow) HRs are commonly—and correctly—associated with good cardiovascular health, but low HR does not necessarily mean low stress. And HRs should not be static; they do and should constantly vary. For optimum health, low HR needs to be accompanied by high HRV.

People often think that slow diaphragmatic breathing is some “woowoo” practice of little or no merit other than a psychologically based calming effect. But biofeedback (a process that enables an individual to learn how to change physiological activity) allows us to see that this style of breathing lowers average HR and raises HRV such that peaks in HR line up with the end of an inhale and troughs in HR line up with the end of an exhale.

Facts and Evidence

A variable (not steady) HR is good for overall health and performance. “Higher HRV” represents larger ranges in fluctuation; this fluctuation is not precise, and optimal HRV can differ among individuals. Ideally, a person should have a low average HR that oscillates up and down in the ranges of at least 20 beats per minute for young, fit people and 10-12 beats per minute in older adults.6 For instance, a good, high HRV for someone with an average heart rate of 60 beats/minute might range 50 to 70 beats per minute. During optimally paced breathing exercises, where breathing (especially exhales) is much slower than most people are used to, the HRV pattern is rhythmic and gradual such that increases and decreases follow a pattern of approximately six peaks and six valleys per minute, lining up with the breathing cycle; as you breathe in, heart rate rises gradually, and as you breathe out heart rate falls gradually. These rhythmic fluctuations serve as a good indication of physical and mental health because research has consistently shown that they correlate with reduced risk of cardiac complications and less-frequent incidence of depression or anxiety.4,7-11

It is commonly known that regular exercise is good for you; it also enhances your resting HRV while both lack of exercise and over-exercise lower it.12,13 The presence or absence of this higher HRV also depends in part on how we breathe. Inhaling into the abdomen and then exhaling slowly helps promote higher HRV. Conversely, short, shallow breathing from the chest tends to elevate average HR and reduce HRV. Breathing at a rate of about six breaths per minute, with exhales almost twice as long as inhales, typically enhances HRV. Breathing in this way causes RSA (respiratory sinus arrhythmia): that is, it actually causes the rise and fall of your HR to line up with your inhales and exhales; breaths in are synchronized with increases in HR, while exhales are accompanied by decreases in HR. Breathing at this synchronous pace also allows for optimal exchange of oxygen and carbon dioxide gases between the lungs and the bloodstream.14 This synchrony augments the difference between peaks and valleys in HR and triggers very powerful reflexes in the body that influence the autonomic nervous system, i.e., heart rate, blood pressure, and breathing.

Each person has his or her own signature pace of breathing at which HRV is maximized and reflexes are working best, and this can be determined with the help of an experienced HRV biofeedback practitioner. But even when someone breathes at his/her unique optimal rate, stress can still reduce HRV, whether the stress comes from environmental demands or from negative emotions.15 One way to enhance HRV is spending some time focusing on deep breathing with long exhales, but other techniques for quieting the mind and generating positive emotions also can help.


Breath training for higher HRV, as discussed below, involves a much longer exhale than people are typically used to. When first trying this, people often feel they do not have time to inhale enough for the long exhale. This feeling usually passes after a little bit of practice, but a biofeedback practitioner can help identify optimal ratios of inhale to exhale.

Heart rate variability should be rhythmic. However, arrhythmia can represent cardiac distress, so the presence of ectopic beats (sudden jumps in heart rate) should be reviewed by a cardiologist.16 An experienced biofeedback practitioner can help a patient optimize cardiac function, in conjunction with a patient’s cardiologist when necessary, and can sometimes even provide valuable diagnostic information to a cardiologist.

Training to elevate HRV

“Breath training” can be used to enhance HRV. With this, a person learns to line up peak inhale with maximum resting heart rate and the end of exhale with minimum resting heart rate, increasing HRV by maximizing the difference between the “peak” (highest HR) and the “valley” (slowest HR).4 This optimal pace can be determined quite accurately with the assistance of a biofeedback practitioner who uses top-of-the-line equipment or less precisely through the use of moderately priced biofeedback apps and software. Many heart-rate monitors now allow one to track HRV levels over time to optimize physical training and periodization with well-timed recovery periods.

Most people have an optimal breathing rate of around six breaths per minute (although many people breathe slightly slower or slightly faster), with an exhale time much longer than they are accustomed to. At six breaths per minute, an exhale of approximately six seconds can engage the “rest and digest” mechanisms (i.e., the parasympathetic nervous system) that actively work to slow down heart rate, and an inhale of approximately four seconds momentarily stops this “braking,” allowing heart rate to speed up again. This can foster high HRV, creating more of a balance between activation and deactivation of the parasympathetic nervous system, allowing for reduced stress, improved energy, and flexibility in attention.17,18 Athletics is one domain where promising research has been demonstrating concrete benefits on performance. Though different from athletics, combat also requires anxiety management and execution of motor skills under pressure.19 Based on the training protocols used in research studies on sports performance, experts recommend training with one 20-minute breathing session twice a day for ten weeks, but even some training is better than none.20 And benefits have been noted after only ten 20-minute sessions.21,22 Further, there is nothing to suggest that there would not be continued benefits from engaging in regular training beyond 10 weeks.

Military Relevance

Low HRV, an indication of possible physical or mental distress, can be used as part of the medical diagnostic process and to help guide intervention.23-25 At the other end of the continuum, higher HRV can be associated with better health and performance (through improved self-regulation).26,27

A few small studies have been conducted in military contexts documenting links between low HRV and some negative outcomes. For example, suppressed HRV was found to be an early sign of fatigue during intense military training.13 Suppressed HRV has also been associated with a higher rate of bleeding after a severe hemorrhage, suggesting potential use for medical triage.28 In veterans of OEF/OIF, pain by itself or with mild traumatic brain injury and/or PTSD was linked with lower HRV.29 Low HRV has also been linked to military sexual trauma, particularly instances of rape.30

In treating mild traumatic brain injury and PTSD, higher HRV can signal improvement.29 Non-medication approaches such as cognitive-behavioral therapy, progressive muscle relaxation, and biofeedback can reduce symptoms of hyperarousal (feeling keyed up and on edge) and increase HRV.31,32 Research is promising that HRV biofeedback may be better than traditional treatment for symptoms of PTSD and elevating HRV.33

However it is achieved, higher HRV is associated with a sense of calm and has a positive impact on mental aspects of performance. Situational awareness (SA) in military settings (and wherever quick decisions of serious consequence must be made) is one highly relevant example. SA refers to awareness of multiple factors within a given situation, especially what is most relevant in the present moment, along with the ability to filter out less-relevant surroundings. SA involves prefrontal lobe brain activity, the hub for processes such as attention, perception, and decision-making. During a mission in a high-risk environment, it is important to be aware of surroundings such as numbers of civilians and potential for threats. Based on this information a Warfighter makes important predictions, such as the presence of a hostile with a weapon. This has major implications for decision-making.34,35

Various studies have demonstrated the link between HRV and SA in military situations, including fast-paced thinking tests, shoot-no-shoot simulations, and simulated navigation tasks.3,35 In each case, participants who had higher resting HRV performed better, experienced less stress during the tasks, and recovered more quickly after. The relative immunity to stress was evident in some reduction of HRV during the stressful period for those with higher resting HRV, while those with lower resting HRV maintained lower HRV and/or experienced even more HRV reduction. For those whose HRV decreased during stress, return to pre-task HRV was faster for those with initial higher resting HRV.


HRV is different from HR and can often tell us more. Lower HRV can help identify problems, and higher HRV can be a marker of optimal functioning; it can also be trained. Deep breathing (with long exhales) can enhance HRV and improve physical health, mental health, preparation, recovery, and performance. Training high HRV, where both the parasympathetic nervous (“rest and digest”) system (activation) and its braking system (deactivation) are optimally engaged, is a relatively new but promising direction for research. Whether a person is gifted with high resting HRV or achieves it through exercise or stress management techniques such as breathing and/or biofeedback, this balanced state is associated with optimal health and performance.

Written by Tim Herzog and first published by the Human Performance Resource Center.


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