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 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% of 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 tones 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 AND AFTER EXERCISE (INDICATORS OF STRESS/TRAINING LOAD)
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.
TRAINING LOAD
The distribution of training loads is a fundamental component of periodization. The elements that comprise the 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 the intensity and volume of exercise and are inversely related to the level of training load.
RECOVERY AND HEART RATE VARIABILITY IN ATHLETES PERFORMANCE
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 in the body, then the response will be proportional to the stress level and, as a result, greater training effects will be accomplished (adaptation).
To reach higher performance levels in sports, 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 sports 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/competitions 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 before 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.
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 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). However, 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.
THE USE OF HEART RATE VARIABILITY IN ATHLETES: OVERTRAINING AND HOW AVOID IT?
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 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
Insomnia
Irritability
Tachycardia
Agitation
Hypertension
Restlessness
Parasympathetic tone
Fatigue
Bradycardia
Depression
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 for a longer period, OTS and domination over of parasympathetic autonomic tone will develop. Parasympathetic OTS dominates in sports which are characterized by high training volume.
LIMITATIONS, IMPROVEMENTS AND FUTURE PERSPECTIVES OF ANALYSIS OF HEART RATE VARIABILITY IN ATHLETES PERFORMANCE
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. To overcome the aforementioned disadvantages, the signal of the recording must contain a minimum of 5 minutes of HRV fluctuation 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 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 with quick and easy analysis of HRV data during and after a training workout (training load, recovery, and overtraining).
THE GOAL OF MONITORING OF HRV IN ATHLETES PERFORMANCE
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.
MEASUREMENT PROTOCOL
Metric:
- 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.
Insights:
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 ADDITIONAL INFORMATION AND PRACTICAL RECOMMENDATION
• 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;
- 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
ESENSE PULSE WEARABLE ECG MONITOR
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.
TARGET HEART RATE
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.
HOW CAN RMSDD BE USED TO CALCULATE HRV AND PLAN OPTIMAL ATHLETIC TRAINING?
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.
RMSDD AND HRV LET YOU KNOW WHEN AND HOW TO TRAIN
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.
References
Bojan Makivic, Pascal Bauer – Heart Rate Variability Analysis in Sport, Utility, Practical Implementation, and Future Perspectives. Aspetar Sports Medicine Journal, p.326-331 – www.aspetar.com/journal
Simon Wegerif. – Using Heart Rate Variability to Schedule the Intensity of Your Training. – https://www.trainingpeaks.com/
Cian Carroll. – Monitoring An Athlete’s Internal Response: A Comprehensive Guide To Analysing Heart Rate Variability & Heart Rate Recovery. – https://statsports.com/
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