COVID-19 - CT-Scan

Breathing and HRV biofeedback in pulmonary rehabilitation after COVID 19

COVID-19, the disease caused by the new coronavirus, can cause lung complications such as pneumonia and, in the most severe cases, acute respiratory distress syndrome, or ARDS. Sepsis, another possible complication of COVID-19, can also cause lasting harm to the lungs and other organs. While most people recover from pneumonia of various causes without any lasting lung damage, pneumonia associated with COVID-19 may be severe. Even after the disease has passed, lung injury may result in breathing difficulties that might take months to improve. The sooner patients are put on a pulmonary rehabilitation after COVID-19, the quicker and more fully their lung function is restored, and, consequently, the function of the central nervous system, muscle, gastrointestinal, and other organ systems that affected by coronavirus infection restored too.


SARS-CoV-2, the virus that causes COVID-19, is part of the coronavirus family.

When the virus gets in your body, it comes into contact with the mucous membranes that line your nose, mouth, and eyes. The virus enters a healthy cell and uses the cell to make new virus parts. It multiplies, and the new viruses infect nearby cells.

Think of your respiratory tract as an upside-down tree. The trunk is your trachea or windpipe. It splits into smaller and smaller branches in your lungs. At the end of each branch are tiny air sacs called alveoli. This is where oxygen goes into your blood and carbon dioxide comes out.

As the infection travels the respiratory tract, then the immune system fights back. The lungs and airways swell and become inflamed. This can start in the alveoli of one part of the lung and spread to the nearby alveoli of other parts.

In pneumonia, air sacs in the lungs fill with fluid, limiting their ability to take in oxygen and causing shortness of breath, cough, and other symptoms.

Doctors can see signs of respiratory inflammation on a chest X-ray or CT scan.

On a chest CT, they may see something they call “ground-glass opacity” because it looks like the frosted glass on a shower door.

 (a) Axial thin-section non-contrast CT scan shows diffuse bilateral confluent and patchy ground-glass (solid arrows) and consolidative (dashed arrows) pulmonary opacities. (b) The disease in the right middle and lower lobes has a striking peripheral distribution (arrow). [Radiological Society of North America].


The effect of COVID-19 will vary greatly over the course of the disease, with most people experiencing some of the following symptoms:

  • fever,
  • cough, sputum production, shortness of breath,
  • fatigue,
  • anorexia,
  • myalgia,
  • central nervous system manifestations (such as headaches, migraines, dizziness, and ataxia),
  • and peripheral nervous system manifestations (such as nerve pain, speech, vision, and taste problems).

While some of these symptoms may resolve naturally, some people may have impairments that persist; particularly following a prolonged hospital and ICU stay.

Doctors in Hong Kong (March 13, 2020) reported the findings of the first follow-up clinics of recovered Covid-19 patients. They suppose that some recovered patients have lost between 20% to 30% of their previous lung function (South China Morning Post). The doctors report that lung scans of recovered patients also reveal substantial lung damage.

Researchers had revealed that at the six weeks after hospital discharge, more than half of the patients had at least one persistent symptom, predominantly breathlessness and coughing, and CT scans still showed lung damage in 88% of patients. However, by the time of 12 weeks after discharge, the symptoms had improved and lung damage was reduced to 56% (COVID-19 Patients Suffer Long-Term Lung and Heart Damage – But They Can Recover With Time – By European Lung Foundation, September 7, 2020). There’s the initial injury to the lungs, followed by scarring. Over time, the tissue heals, but it can take three months to a year or more for a person’s lung function to return to pre-COVID-19 levels.

In the recovery period, people with COVID-19 may be expected to present with significant muscle wasting in both the locomotor and respiratory muscles. This may contribute to ongoing breathlessness and fatigue, reduced exercise capacity, poor balance, and loss of functional independence (Rehabilitation following COVID-19 in the pulmonary rehabilitation setting. JUNE 2020. Respiratory Network).


Changes in the anatomical and physiological properties of the tissues and organs of the chest as a result of the disease (decreased elasticity of the lungs, chest tissues, etc.) lead to an increase in the energy cost of ventilation. The work of the respiratory muscles, aimed at overcoming elastic and bronchial resistance, increases significantly. The increase in the energy cost of ventilation and the depletion of the respiratory muscles form the basis of shortness of breath and a feeling of lack of air – a complex of sensations that is put into the concept of “shortness of breath”. Many pulmonary diseases lead to a decrease in the respiratory surface of the lungs and the development of such ventilation disorders as a restrictive syndrome. The decrease in lung volumes is caused not only by the hardening of the lung tissue but the limitation of the mobility of the lung itself due to the development of adhesions that prevent it from expanding. With concomitant pleural inflammation, there is a deliberate limitation of the chest excursion due to severe pain syndrome.

The tasks of exercise therapy in pulmonology are to achieve regression of reversible and stabilize irreversible changes in the lungs, the formation of compensation, and normalization of function.

  • General tonic effect: stimulation of metabolic processes, increase in neuropsychic tone, recovery, and increase of tolerance to physical activity, stimulation of immune processes;
  • Preventive effect: mastery of breathing control technique, an increase of the protective function of the respiratory tract, reduction of intoxication;
  • Pathogenic (therapeutic) effect: improvement of external respiration functions, correction of the “mechanics” of breathing, acceleration of resorption in inflammatory processes, improvement of bronchial patency, removal, or reduction of bronchospasm, regulation of external respiration functions and increase in its reserves.

In exercise therapy classes for respiratory pathology, the following are used:

  1. general tonic exercises, which improve the function of all organs and systems, activate breathing (moderate and high-intensity exercises are used to stimulate external respiration functions; low-intensity exercises do not have a training effect on the cardiovascular and respiratory systems);
  2. special (breathing) exercises that strengthen the respiratory muscles, increase the mobility of the chest and diaphragm; promote stretching of pleural adhesions; reduce congestion in the respiratory system, facilitate sputum excretion, improve the respiratory mechanism, coordination of breathing and movement;
  3. various methods of breathing gymnastics aimed at correcting the prevailing pathological process;
  4. in order to relax tense muscle groups, autogenous training, post-isometric muscle relaxation technique, physical exercises to relax associative and segmental muscles, therapeutic massage using myofascial release techniques, segmental reflex massage can be used. Taking into account myofascial changes in muscles, the most effective physical exercises are movements with the participation of segmental and associative muscles.

Performing breathing exercises requires compliance with the basic laws of breathing:

  • before any physical activity it is necessary to remove residual air from the lungs, for which it is necessary to exhale through the lips folded into a tube;
  • inhalation is mainly (80%) carried out by the diaphragm, while the muscles of the shoulder girdle should be relaxed;
  • the duration of the exhalation should be approximately 1.5-2 times longer than the inhalation;
  • inhalation is carried out when the chest is extended, exhalation – when it is compressed (for example, when bending over).

The exhalation is usually carried out by relaxing the muscles involved in inhalation, under the influence of the gravity of the chest, i.e. delayed exhalation occurs with the dynamic inferior work of these muscles. Removal of air from the lungs is provided by the elastic forces of the lung tissue.
Forced exhalation occurs when the muscles that produce the exhalation contract; strengthening of exhalation is achieved by tilting the head forward, bringing the shoulders together, lowering the arms, flexion of the trunk, raising the legs forward. With breathing exercises, you can freely change the breathing rate.

More often, exercises are used in a voluntary slowing down of the respiratory rate (in this case it is recommended to count to oneself): the exercise reduces the speed of air movement and reduces the resistance to its passage through the airways. Increased breathing frequency increases breathing speed. Learning to consciously regulate breathing begins with static exercises; use exercises in rhythmic static breathing, which leads to a decrease in respiratory movements due to their deepening, while the strength of the respiratory muscles increases and the intercostal muscles are toned.

Breathing with additional resistance (inhalation through lips folded into a tube, through a tube, inflation of rubber toys) reduces the frequency and increases the depth of breathing, activates the work of the respiratory muscles. It is recommended to breathe through the nose, as this moistens and purifies the inhaled air; irritation of the receptors of the upper respiratory tract reflexively expands the bronchioles, deepens breathing, and increases blood oxygen saturation.

If necessary, to spare the affected lung, apply the initial positions that limit the mobility of the chest from the affected side (lying on the affected side).

Using weights in the form of sandbags when performing breathing exercises helps to strengthen the abdominal muscles, intercostal muscles, and increase the mobility of the diaphragm.

For dosing physical activity, a change in the initial position, pace, amplitude, degree of muscle tension, the number and duration of the exercises performed, rest pauses, and relaxation exercises are used.

    The Breather functions as both an inspiratory muscle trainer and expiratory muscle trainer with adjustable dials for independent resistance settings for inhalation and exhalation, making it the ULTIMATE device for respiratory care. Think of it as a lung trainer, supporting respiratory health and efficiency by promoting diaphragmatic (belly) breathing.
    This inspiratory exerciser benefits those who are undergoing respiratory treatment. The Breather is a respiratory trainer or respiratory exerciser that improves lung strength and capacity by improving oxygen uptake to vital organs.
    The Breather is used by those affected by COPD, CHF, dysphagia, and neuromuscular disease. Continued use has shown to improve dyspnea, peak cough flow, laryngeal function, QOL, vent weaning, and speech and swallowing performance.
    PN Medical, creators of The Breather, offer a self-paced, online video protocol training for therapists; patients, and consumers. Additionally, with the Breather Coach mobile app, you can track and monitor your progress from your phone.
  • There are 5 expiratory and 6 inspiratory adjustable independent pressure settings. So you can adjust the resistance on each inhalation and each exhalation. The higher the setting, the higher the resistance.


The Breather exercise optimizes the blood flow to your working muscles, increasing your performance capacity, and extending your limits of exercise. It improves the strength of your diaphragm and other respiratory muscles while maximizing lung function. The exercise strengthens your cardiac system and circulation, thereby reducing your blood pressure and improving your sleep.

Special techniques of breathing exercises are used:

Sound gymnastics – special breathing exercises, consisting of pronouncing consonant sounds in a certain way – buzzing (zh, z), sibilant and hissing (s, f, ts, ch, sh), growling (r) and their combinations. In this case, the vibration of the vocal cords is transmitted to the smooth muscles of the bronchi, lungs, chest, relaxing the spasmodic bronchi and bronchioles. The goal of sound gymnastics is to develop the correct ratio of inhalation and exhalation – 1: 2 (1.5). All sounds should be pronounced in a strictly defined way, depending on the purpose of gymnastics. For example, in bronchial asthma, buzzing, growling, hissing sounds are pronounced loudly, energetically, exciting, and in chronic obstructive bronchitis with severe respiratory failure – softly, quietly, acceptable in a whisper (soothing).

Method of volitional elimination of deep breathing (VEDB) K.P. Buteyko – the technique was developed by the Novosibirsk doctor K.P. Buteyko in 1960 and is aimed at volitional correction of incorrect (deep) breathing with a gradual complete rejection of it, since deep breathing causes a lack of carbon dioxide in the blood, a change in the acid-base state towards alkalosis and tissue hypoxia (with a lack of carbon dioxide in the body, oxygen firmly binds to hemoglobin and does not enter cells and tissues). The main tasks of the VEDB method are:

  • to normalize the ratio of inhalation and exhalation,
  • to reduce the speed and depth of inhalation,
  • to develop a compensatory pause after a long and calm exhalation,
  • to normalize the carbon dioxide content in the blood,
  • to reduce the number of asthma attacks, to prevent their occurrence.

Paradoxical breathing exercises help relieve an attack of suffocation. Gymnastics is called “paradoxical” because inhalation and exhalation are performed simultaneously with the movements of the arms, trunk, and legs, which complicate this phase of breathing. When the chest is compressed, inhalation is made, when the chest expands, exhale. The inhalation should be short, sharp, noisy, active, forced by the diaphragm; exhalation occurs passively, spontaneously. Inhalation is carried out only through the nose, exhalation independently, passively (so that it is not audible), preferably through the mouth, you should not delay exhalation. The mechanism of action of paradoxical respiratory gymnastics on the body consists of restoring disturbed nasal breathing, improving the drainage function of the bronchi, activating the work of the diaphragm and chest muscles. Gymnastics promotes the resorption of inflammatory formations, the restoration of normal lymph and blood supply, the elimination of local congestion. Elimination of morphological changes in the bronchopulmonary system enhances gas exchange in the alveoli, tissue respiration, and leads to an increase in oxygen absorption by tissues, which has a positive effect on metabolic processes. The coordination of breathing and movement helps to restore the regulation of breathing by the central nervous system, improves the psychoemotional state, and has a general tonic effect.

Modern oriental respiratory systems, which are currently popular (qigong, tai chi, hatha yoga, etc.) are based on voluntary regulation of the depth and frequency of breathing, control of the correct ratio of inhalation and exhalation. In this case, the active participation of the diaphragm in the breathing process, as well as training in concentration and relaxation, are required. It is important to learn certain types of breathing (upper chest, costal, diaphragmatic) and full breathing. Eastern breathing techniques are mainly distributed by enthusiasts and are used in alternative medicine, since these breathing techniques also carry a philosophical meaning with the ultimate goal of achieving harmony and gaining full health on their own, using the body’s hidden reserves and willpower.

The criterion for determining whether a given technique is appropriate is the state of health after exercise. In general, all physical exercise, in addition to directly improving peripheral muscle function, improves motivation, improves mood, reduces symptoms of illness, and has a positive effect on the cardiovascular system.

For people with COVID-19 presenting for pulmonary rehabilitation after COVID-19, it is important to consider that with the reduced gas transfer, exercise desaturation may occur. Therefore, monitoring of oxygen saturation and use of supplemental oxygen may be necessary during pulmonary rehabilitation after COVID-19.

Pulmonary rehabilitation after COVID-19, including physical and psychological components, should be available for patients as soon as possible and it should continue for weeks if not months after they have been discharged from the hospital in order to give patients the best chances of a good recovery. Thus, the risk of patient disability after suffering pneumonia is reduced.


Respiratory (breathing) and Heart Rate Variability (HRV) Biofeedback is a relatively new method of teaching people to change the parameters of respiration and cardiac activity. Recent research indicates the effectiveness of these biofeedback modalities in the treatment of many medical and psychological conditions, including:

     – anxiety disorders,
     – depression,
     – asthma,
     – chronic obstructive pulmonary disease,
     – cardiovascular diseases,
     – cardiac rehabilitation,
     – hypertension of various origins,
     – chronic fatigue,
    – chronic muscle pain,
    – post-traumatic stress disorder (PTSD),
    – insomnia
    – and other conditions, as well as to improve performance and professional efficiency.

Since the onset of the coronavirus pandemic, breathing and HRV biofeedback have found widespread use in pulmonary rehabilitation after COVID-19.

Breathing and HRV biofeedback is not a separate form of therapy/training, but part of a larger multimodal team approach to pulmonary rehabilitation after COVID-19.

What is the mechanism of action and effectiveness of breathing and HRV biofeedback in pulmonary rehabilitation after COVID-19?

The HRV biofeedback technique includes training in breathing at the resonant frequency of the cardiovascular system. Breathing at this rate causes the heart rate to increase and decrease in the same phase with breathing. The heart rate increases with inhalation and decreases with exhalation. Then the efficiency of gas exchange in the respiratory tract is maximal. The higher the HRV indicator (that is, the greater the difference in heart rate during inhalation and exhalation), the higher the degree of organism adaptation to the different external and internal stressors influence.

HRV biofeedback stimulates a specific reflex in the cardiovascular system, which has a specific rhythm. It is called “baroreflex” and helps control blood pressure. It also helps control emotional reactivity and improves breathing efficiency. Baroreflex is controlled by the nucleus of the solitary tract located in the brainstem. This center communicates directly with the amygdala, the center of emotional control, through a pathway through the islet. It is perhaps for this reason that various studies have shown the beneficial effects of respiratory biofeedback and HRV in the treatment of anxiety, phobias, and depression.

When blood pressure goes up, the baroreflex causes the heart rate to go down, and when blood pressure goes down, the heart rate goes up. This causes a rhythm in heart rate fluctuations. When a person breathes at this exact rhythm (which varies among people, generally between 4.5 and 6.5 times a minute), the baroreflex system resonates.

How to find the frequency for each person at which the baroreflex system resonates?

This will be the frequency that produces the biggest swings in heart rate between inhaling and exhaling. To find this frequency person should try to breathe at various rates per minute to find the exact frequency at which the cardiovascular system resonates. This will be his/her resonance breathing frequency. This frequency varied from individual to individual, but it is approximately 0.1 Hz or six breaths per minute. When people breathe at this frequency, the baroreflex system is stimulated and strengthened, and through projections to other systems in the body (e.g., inflammatory and limbic systems), other events occur that produce the many beneficial effects of HRV biofeedback. These changes are achieved with the help of HRV biofeedback training.

Controlled breathing at a rate of about six breaths per minute enhances internal regulation and creates a balanced respiratory cycle that causes pronounced fluctuations in the autonomic nervous system: from parasympathetic to sympathetic and back with each respiratory cycle. HRV is a measure of the continuous interaction of sympathetic and parasympathetic influences on heart rate, which provides information about autonomic flexibility and thus represents the ability to respond in a regulated manner. Resonance of the baroreflex circuit induces maximal respiratory sinus arrhythmia, which causes severe fluctuations in vascular tone, heart rate, and blood pressure. This ideal balance of relaxation and alertness restores homeostatic function, optimizes neurovisceral integration, promotes efficient gas exchange in the lungs, reduces pain perception, stimulates anti-inflammatory processes, and increases resistance to physical and emotional stress.

Thus, patients with COVID-19 are advised to breathe under control at a rate of six breaths per minute in the early stages of the disease to promote beneficial neuromodulation and prevent vascular and immuno-inflammatory complications.

Pulmonary rehabilitation after COVID-19, that include the breathing and HRV biofeedback in the complex of the rehabilitation program accelerates the process of restoration of lung function, muscle (both respiratory and skeletal muscles) tone, gastrointestinal tract function, psychoemotional state and has a preventive effect in the development of pulmonary complications after the coronavirus infection.


Today, thanks to the development of technology, there are many HRV and breathing biofeedback devices for personal use at home.

A variety of companies have developed and presented a range of commercial products ranging from $ 80 to $ 200.
The main requirement for HRV and breathing biofeedback devices for personal use are: the equipment must have a sensor for measuring heart rate (heart rate variability) using an electrocardiogram (ECG) and a respiration sensor using a breathing belt (recording the respiratory rate).

The most effective home-use device for breathing and HRV biofeedback is the eSense Respiration and eSense Pulse HRV Biofeedback devices that allow providing individual training in home comfort.

Tinké™ from Zensorium – pulse sensor for iOS and Android for heart rate variability (HRV).

The only tracker that measures your

  • heart rate,
  • heart rate variability,
  • respiratory rate,
  • blood oxygen saturation.
HRV in Sports Performance

Heart Rate Variability in Athletes

The analysis of heart rate variability in athletes performance has become established and recognized in the past 2 decades as a non-invasive method for evaluation of the body’s reaction to training loads, recovery methods and overtraining syndrome (OTS). HRV (Heart Rate Variability) training should be in every athlete’s vocabulary. HRV unlocks high-level information that can be used to optimize performance and training for athletes of any level.

As an athlete, you’re always looking for that 1% improvement in every aspect of your game. But as elite athletes get better and the margin for improvement narrows, actually achieving a 1% improvement becomes harder. With that in mind, athletes are conditioned to revert to the “train harder” mentality in order to grab that 1%. This mentality doesn’t always work because much too often overtraining and injuries occur as a result. If you want to make sure your body is peaking at the right moments, having insight into HRV becomes that coveted 1% all athletes are looking for.

Heart rate variability (HRV) represents variations between consecutive heartbeats (beat to beat or R-R interval) over time. This beat to beat variation in heart rhythm is considered normal and even desirable. The disappearance of variations between consecutive heartbeats is a result of autonomic dysfunction which can be associated with neurological, cardiovascular and psychiatric disease states. There is a large body of evidence reporting that higher variability of heart rhythm is associated with reduced mortality, improved quality of life and better physical fitness. (Learn more about Heart Rate Variability here).

The physiological background of HRV is complex and affected by circulating hormones, baroreceptors, chemoreceptors and muscle afferents. An important factor that influences HRV is respiratory sinus arrhythmia – the natural variation in heart rate (HR) that occurs during breathing. During inspiration, HR increases whereas during expiration HR decreases. The autonomic nervous system (ANS) through sympathetic (SNS) and parasympathetic (PNS) pathways regulates the function of internal organs and the cardiovascular system. Sympathetic activity (“fight or flight”) increases an athlete’s cardiac contractility, heart rate, breathing, and muscle tension during training or competition. In contrast, parasympathetic (vagal) stimulation (“rest and digest”) reduces an athlete’s heart rate, relaxes muscles, and allows for digestion. Any source of stress (psychological, physical or illness) will provoke disturbance in the ANS and consequently in HRV. The long-term presence of an imbalance between sympathetic and parasympathetic tone can impair the performance of athletes. By providing a unique look into nervous system activity, HRV data allows athletes to strike the right balance between training and recovery.

Heart rate variability in athletes


During exercise, HRV is reduced (shorter R-R intervals) and heart rate is increased as a result of augmented SNS and attenuated PNS activity. Not only are the intervals between R-R peaks shorter, but they also become more uniform (reduced R-R variability).

The relationship between sympathetic and parasympathetic activity during exercise depends directly on training intensity. During physical activity, sympathetic nerves can increase cardiac output to 2 to 3 times the resting value.

Caution should be taken when interpreting HRV analysis during exercise. At high exercise intensities (>90% VO2 max) increased breathing frequency will cause an increase in vagal contribution (higher PNS activity) caused purely by the mechanical properties of the heart and not a neural contribution of the ANS. This means that actual SNS activity at higher exercise intensities will be masked by PNS activity as a result of a higher frequency of respiration. Therefore, during an incremental test to exhaustion, the athlete has to be instructed to maintain a stable respiration rate as much as possible.


Distribution of training loads is a fundamental component of periodization. The elements which comprise training load are training volume and intensity. The interplay between these two elements will define the total training load. Higher training loads will cause a greater degree of ANS disturbance and sympathovagal imbalance. Post-exercise HRV analysis appears to be a valuable indicator to evaluate variations in performance level and can indirectly reflect training loads. There is evidence that HRV parameters are highly correlated with intensity and volume of exercise and are inversely related to the level of training load.


On the assumption that physical activity causes stress (a stimulus), the body will respond with a stress reaction on different physiological levels. In addition to a stress reaction, adaptation processes occur during the recovery period. If the magnitude of the stress stimulus (training load) is high enough (overload principle) to evoke a reaction of the body, then the response will be proportional to the stress level and, as a result, greater training effects will be accomplished (adaptation).

In order to reach higher performance levels in sport, it is essential to understand that well-designed and integrated rest periods are of great importance. Recovery after training is considered an integral part of the training methodology. There is no improvement in performance if there is a lack of optimal recovery. Problems occur when the demands are so frequent that the body is not able to adapt. This means that the body will continuously be under sympathetic domination during rest as well as during activity.

Most athletes and sport science personnel understand the importance of recovery after exercise, which is defined as the return of body homeostasis after training to pre-training or near pre-training levels.

Recovery involves getting adequate rest in between training sessions/competition to allow the body to repair and strengthen itself in preparation for the subsequent bout. Optimal athletic performance is supported when recovery to pre-training or near pre-training levels is allowed. If recovery is insufficient, hindrance of physiological adaptation and reduced athletic performance should be expected. Recovery plays a major role in minimizing the negative effects of training (fatigue) while retaining the positive effect (improved fitness/strength/performance). If recovery is not monitored following exercise, fatigue may accumulate and become excessive prior to competition, resulting in reduced athletic performance and, potentially, overtraining syndrome. In its essence, the overtraining syndrome is characterized by a combination of excessive overload in training stress and inadequate recovery, leading to fatigue and decreased performance.

Heart rate variability in athletes performance: Train-Recover-Perform

Every training session can be considered as stress to the body, which in turn causes disturbance of homeostasis and ANS modulation. These changes in ANS activity are manifested by increased sympathetic or/and decreased parasympathetic activity of the ANS and are reflected by HRV parameters. One crucial aspect of recovery is sleep, during which parasympathetic activity should dominate; however, an optimal recovery state is generally characterized by the parasympathetic (vagal) predominance of ANS regardless of the time of the day.

There are a variety of parameters that can be used to measure post-exercise recovery (VO2 max, creatine kinase, C-reactive protein, plasma cortisol, blood leukocyte, myeloperoxidase protein level, and glutathione status). But these methods are mostly invasive, time-consuming and expensive for everyday use. Accordingly, the importance of a non-invasive, easy and affordable method to evaluate recovery is obvious. Thus, HRV technology is being increasingly used to evaluate the status and level of recovery.

Long-term high-intensity training sessions gradually decrease the parasympathetic component of HRV which increases during the rest period. The sympathetic component demonstrates the opposite tendency.

The reactivation of parasympathetic activity of HRV to pre-exercise levels as quickly as possible significantly improves the recovery process of athletes. The inability to return HRV parameters to pre-exercise or optimal levels in a reasonable time is considered a chronic disturbance in ANS activity, which can lead to overtraining.

Today, HRV-based devices and software assist in the recovery analysis of athletes, providing easily interpretable data to trainers and athletes. The most common procedure used to evaluate recovery level involves overnight measurement (nocturnal) of HRV, although systems that can assess a quick recovery index (5-minute measurement) are available as well.


Sometimes the line between optimal performance level and overtraining is very thin.

Overtraining syndrome (OTS) is the result of the long-term imbalance between stress (internal and/or external) and recovery periods. There is a large body of evidence implying that significant cardiac autonomic imbalance between the two ANS pathways (sympathetic and parasympathetic) occurs due to overtraining syndrome.

In the literature, there are conflicting results about ANS modulation in overtrained athletes, with some studies reporting a predominance of sympathetic and some of the parasympathetic autonomic tone during an overtrained period. These disputed results might be explained by the description of different types of overtraining.

Two types of OTS have been reported: sympathetic and parasympathetic overtraining, with each having specific physiological characteristics.

Sympathetic tone







Parasympathetic tone





Loss of motivation


Early stages of performance impairment are characterized by sympathetic domination of ANS at rest which is often referred to as an “overreaching state” or “short-term overtraining”, meaning that the disturbance of homeostasis was not high and/or long enough to provoke a chronic overtraining state and therefore the time needed for full recovery of all physiological systems typically encompasses a few days to several weeks.

The increased sympathetic tone is generally observed in sports where a higher intensity of exercise dominates. If the overreaching state (sympathetic autonomic tone domination) continues a longer period of time, OTS and domination over of parasympathetic autonomic tone will develop. Parasympathetic OTS dominates in sports which are characterized by high training volume.


Analysis of heart rate variability in athletes performance has become a widely accepted method for non-invasive evaluation of ANS modulation during and after exercise. In order to overcome the aforementioned disadvantages, the signal of the recording must contain a minimum of 5 minutes of HRV fluctuation in order to get reliable results.

In the last 5 years, the number of devices and software programs/apps using HRV technology has increased exponentially. The current trend in software engineering is to make all wireless sensors for capturing and transmitting of HRV data compatible with smartphones. Hardware and software engineers are continuously improving the accuracy of sensors that record and receive HRV signals (heart rate belts, wireless technologies, and protocols), as well as HRV analysis techniques (software, mathematical models). This provides the trainer and athlete quick and easy analysis of HRV data during and after a training workout (training load, recovery and overtraining).


HRV provides an excellent objective status of the autonomic nervous system. The primary goal is reducing injuries, decreasing overreaching, improving player health, increasing adaptation, and learning more about training. But the winning requires that talent is available and optimized in performance, not just uninjured. The essence of monitoring heart rate variability in athletes is to drive a routine and accountability process for winning. The data collected from HRV can guide athletes like a compass to a training program blueprint, but only if the commitment exists with everyone. Winning requires talent and preparation, and while only a few can be on top of the mountain, HRV can increase those odds if used properly.



  • RMSSD is the most commonly used and trusted metric. It is a clear marker of parasympathetic activity (recovery). RMSSD has been shown to be linked to performance changes, fatigue states, overreaching and overtraining. The return of RMSSD to baseline after exercise has been related to the clearance of plasma catecholamine, lactate, and other metabolic byproducts in addition to the restoration of fluid balance and body temperature. Therefore, RMSSD is considered a global marker of homeostasis that reflects various facets of recovery and may explain why planning intense training when HRV is at or above baseline may be useful for improving endurance performance.
  • Duration: 60 seconds to 2 minutes in the morning is the ideal measurement protocol in terms of reliability and practical applicability in team settings. Night measurements are also a valid method.
  • Frequency: at least three days per week are required to establish a valid baseline. More measurements can be beneficial, up to 5 ideally. If compliance is an issue, give priority to the three days in the middle of the week, far from matches to avoid residual fatigue.

Data analysis: baseline HRV and the coefficient of variation (CV) are the most important parameters to look at.

  • HRV baseline: computed as the average HRV over a week (or using 3-5 days if daily measurements are difficult to obtain). It should be analyzed with respect to an athlete’s normal values. Normal values are a statistical way to represent historical data collected in the previous 30 to 60 days, which should give us insights on where we expect HRV baseline to be, provided no significant stressors are present. In case of such significant stressors or issues in responding to training or lifestyle stressors, the baseline will deviate from the expected normal values.
  • CV: coefficient of variation, or the amount of day to day variability in HRV.


Pre-season: load can be adjusted based on individual responses as shown in baseline HRV and CV. In particular:

  • Athletes showing a reduced HRV and increased CV most likely are struggling with the load and might benefit from reduced load or other recovery strategies (sleep, diet, yoga or other ways to reduce non-training related stress for example).
  • Athletes showing a stable or increasing HRV are most likely coping well with the increased load.
  • Athletes showing a reduced CV are most likely coping well with the increased load unless their baseline HRV is reducing or going below normal. In this case, the reduced CV might highlight an inability to respond to training.

During the season: the same patterns can be used throughout the season to understand individual responses to changes in training load. HRV should be used as a continuous feedback loop more than as a value to optimize towards a certain value. Staff working with athletes and physiological measures should give priority to baseline and CV changes in order to determine individual responses and adaptations.


• HRV is an indication of your resilience – the ability of the nervous system to respond and recover from physical or psychological stressors;
• HRV values depend on the length of the measurement
– 5 minutes = short term HRV
– 24 hours = long term HRV;
• HRV is age and gender-dependent;
• HRV has a circadian rhythm;
• HRV may change day to day with your biorhythm or due to emotional or physical stress;
• HRV is depended on body position;
• Chronic low HRV is an indication of systemic health (psychological or physical) issues;

Circadian Rhythm of HRV
HRV and body position
  • HRV measurement should be provided for the same length of time each day (3 minutes typical);
  • HRV should be taken at the same time each day
    – First thing in the morning is recommended
  • HRV should be taken in the same position
    – Lying down
    – Sitting
    – Standing


Heart Rate Variability (HRV) refers to the variable time between individual heartbeats. HRV can be accurately measured by an ECG. A basic heart rate monitor can also be used to provide this data, but the HRV will not be as accurate.
In the past, only elite athletes and their coaches had access to HRV data because devices that measure ECG were extremely expensive and difficult to wear.

In the last 5 years, innovations in wireless technology have significantly increased the number of devices on the market which are using HRV indices to control and manage the training processes of athletes. Now, with accessible, wearable and user-friendly technology like eSense Pulse wearable ECG monitor, everyone from professional athletes to weekend warriors can use HRV data to enhance their training.


While using eSense Pulse, the eSense App displays the current heart rate and the target heart rate during recording, in the overview area. The target heart rate can be adjusted at any time in the settings of your eSense App. You can either set the target heart rate directly or set it as a percentage of the predicted maximum heart rate. By default, the target heart rate value is set as 85% of the predicted maximum HR.

The predicted maximum heart rate is calculated with the following formula: Predicted Maximum Heart Rate = (220 – your age in years). Normally you should maintain your heart rate below your target level (85% of a predicted maximum heart rate, based on your age, and your medical conditions).

HRV focuses on the distance between peaks. In the eSense App, the SDNN (Standard deviation of all NN intervals) and RMSDD (Root Mean Square of the Successive Differences) is one of a few time-domain tools used to assess heart rate variability, the successive differences being neighboring RR intervals) values both relate to the time-interval between peaks, but RMSDD best shows parasympathetic or “rest and digest” activity. Accurate RMSDD measurements can also be taken in 60 seconds or less, which makes RMSDD quick and easy.


As a training tool, the power of HRV comes from establishing an RMSDD baseline. To establish a baseline, an athlete simply needs to wake up, strap on the eSense Pulse for a minute, and take a reading each day for one week. At the end of the week, if they average all of their RMSDD measurements, they will have a baseline RMSDD number.

In the future, if their RMSDD numbers fall below their baseline in the morning, they will know to ease off on training for optimal performance. If their RMSDD number goes above their baseline, they are more than recovered and can take on a challenging workout. In other words, higher RMSDD numbers correspond with more parasympathetic activity or a more recovered state.


In a perfect world, an athlete’s mind and body would be in total sync, and athletes would intuitively know how hard to push themselves. In reality, athletes may start to gradually stop making progress without knowing exactly why. They are either over or undertraining. They may attribute their fatigue to not working hard enough when, in fact, they are working too hard. HRV measurements like RMSDD give athletes an objective way to justify a rest day, or on the other end of the spectrum, prompt them to increase the intensity and volume of the training. Heart rate variability in athletes used to be available to only world-class athletes, but with technologies like eSense Pulse, HRV analysis can be used by cyclists, runners, endurance athletes of all kinds, and even gym enthusiasts.


Bojan Makivic, Pascal Bauer – Heart Rate Variability Analysis in Sport, Utility, Practical Implementation, and Future Perspectives. Aspetar Sports Medicine Journal, p.326-331 –

Simon Wegerif. – Using Heart Rate Variability to Schedule the Intensity of Your Training. –

Cian Carroll. – Monitoring An Athlete’s Internal Response: A Comprehensive Guide To Analysing Heart Rate Variability & Heart Rate Recovery. –