Heart rate variability in athletes has gained significant attention as a crucial indicator of physical fitness and recovery. This metric reflects the body’s ability to adapt to stress and is particularly valuable for monitoring the training and performance of athletes. Analyzing the HRV of athletes, coaches, and trainers can gain insights into an athlete’s autonomic nervous system activity, recovery status, and overall well-being. Understanding heart rate variability (HRV) helps optimize training loads and plays a vital role in preventing overtraining and injuries. In this article, we will explore the importance of HRV in athletes, its impact on performance, and how it can be effectively utilized to enhance athletic outcomes.
Athletes’ Pursuit of Improvement and the Role of HRV
As an athlete, you always look for that 1% improvement in every aspect of your game. However, as elite athletes improve and the margin for improvement narrows, 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. If you want to ensure 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. When variations between consecutive heartbeats disappear, autonomic dysfunction is often the cause. This dysfunction can link to neurological, cardiovascular, and psychiatric diseases. Many studies show that higher heart rhythm variability relates to reduced mortality, improved quality of life, and enhanced physical fitness. (Learn more about Heart Rate Variability here).
Physiological Background and HRV’s Impact on Athletes’ Performance
The physiological background of HRV is complex and affected by circulating hormones, baroreceptors, chemoreceptors, and muscle afferents. An important factor influencing HRV is respiratory sinus arrhythmia – the natural variation in heart rate (HR) 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. During training or competition, sympathetic activity (“fight or flight”) increases an athlete’s cardiac contractility, heart rate, breathing, and muscle tension.
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 athletes’ performance.
HRV data offers a unique view into nervous system activity. This insight helps athletes find 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 due to 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. When exercise intensity exceeds 90% of VO2 max, breathing frequency rises. This increase boosts vagal contribution, or PNS activity, due purely to the heart’s mechanical properties rather than any neural input from the ANS. As a result, PNS activity, driven by faster respiration, can mask actual SNS activity at these higher intensities. To ensure accurate results, the athlete should maintain a stable respiration rate as much as possible during an incremental test to exhaustion.
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 greater ANS disturbance and sympathovagal imbalance. Post-exercise HRV analysis appears to be a valuable indicator for evaluating 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 training load level.
RECOVERY AND HEART RATE VARIABILITY IN ATHLETES PERFORMANCE
Understanding Stress, Adaptation, and Recovery in Training
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 recovery. Suppose the magnitude of the stress stimulus (training load) is high enough (overload principle) to evoke a reaction in the body. In that case, 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 crucial. Recovery after training is considered an integral part of the training methodology. Performance will not improve if there is a lack of optimal recovery. Problems occur when the demands are so frequent that the body cannot adapt. This means the body will continuously be under sympathetic domination during rest and activity.
Most athletes and sports science personnel understand the importance of recovery after exercise, defined as the return of body homeostasis after training to pre-training or near pre-training levels.
The Role of Recovery and Its Impact on Performance
Recovery involves getting adequate rest 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 permitted. If recovery is insufficient, hindrance of physiological adaptation and reduced athletic performance should be expected. Recovery plays a major role in minimizing the harmful effects of training (fatigue) while retaining the positive impact (improved fitness/strength/performance).
Without monitoring recovery after exercise, fatigue can build up and become excessive before competition. This buildup reduces athletic performance and may even lead to overtraining syndrome. The overtraining syndrome occurs when training stress is too high, and recovery is insufficient, causing fatigue and decreased performance.
Every training session stresses the body and disturbs homeostasis and ANS modulation. These changes in ANS activity manifest as increased sympathetic activity or decreased parasympathetic activity, which reflects in HRV parameters. One crucial aspect of recovery is sleep, during which parasympathetic activity should dominate. However, an optimal recovery state typically features parasympathetic (vagal) predominance of the ANS, regardless of the time of day.
HRV as a Noninvasive Tool for Monitoring Recovery
Various parameters 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 noninvasive, easy, and affordable method to evaluate recovery is obvious. Thus, HRV technology is 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 of the period. The sympathetic component demonstrates the opposite tendency.
Reactivating HRV’s parasympathetic activity to pre-exercise levels as quickly as possible significantly improves athletes’ recovery. When HRV parameters cannot return to pre-exercise or optimal levels within a reasonable time, this indicates a chronic disturbance in ANS activity. Such a disturbance can lead to overtraining.
Today, HRV-based devices and software assist in athletes’ recovery analysis, providing easily interpretable data to trainers and athletes. The most common procedure to evaluate recovery level involves overnight measurement (nocturnal) of HRV, although systems that can assess a quick recovery index (5-minute measurement) are also available.
THE USE OF HEART RATE VARIABILITY IN ATHLETES: OVERTRAINING AND HOW AVOID IT?
Sometimes, the line between optimal performance level and overtraining is skinny.
Overtraining syndrome (OTS) results from a long-term imbalance between stress (internal and external) and recovery periods. A large body of evidence implies that overtraining syndrome causes significant cardiac autonomic imbalance between the two ANS pathways (sympathetic and parasympathetic).
The literature contains conflicting results about ANS modulation in overtrained athletes. Some studies report a predominance of sympathetic and parasympathetic autonomic tone during an overtrained period. The description of different types of overtraining might explain these disputed results.
Two types of OTS have been reported: sympathetic and parasympathetic overtraining, each with specific physiological characteristics.
Sympathetic tone
Insomnia
Irritability
Tachycardia
Agitation
Hypertension
Restlessness
Parasympathetic tone
Fatigue
Bradycardia
Depression
Loss of motivation
The early stages of performance impairment feature sympathetic domination of the ANS at rest. This condition is often called an “overreaching state” or “short-term overtraining.” This means that the disturbance of homeostasis was not high and long enough to provoke a chronic overtraining state. Therefore, the time needed to fully recover all physiological systems typically encompasses several days to weeks.
Sports that require higher exercise intensity generally show increased sympathetic tone. If the overreaching state (sympathetic autonomic tone domination) continues for longer, OTS and domination of parasympathetic autonomic tone will develop. Parasympathetic OTS dominates in sports 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 noninvasive evaluation of ANS modulation during and after exercise. To overcome the aforementioned disadvantages, the recording signal 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) and 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. However, 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 appropriately used.
MEASUREMENT PROTOCOL
Metrics
- RMSSD is the most commonly used and trusted metric. It is a clear marker of parasympathetic activity (recovery). RMSSD is 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 restoring fluid balance and body temperature.
Therefore, RMSSD serves as a global marker of homeostasis, reflecting various aspects of recovery. This marker may explain why planning intense training when HRV is at or above baseline can help improve endurance performance. - Duration: 60 seconds to 2 minutes in the morning is the ideal measurement protocol for reliability and practical applicability in team settings. Night measurements are also a valid method.
- Frequency: To establish a valid baseline, at least three days per week are required. More measurements can be beneficial, up to five ideally. If compliance is an issue, prioritize the three days in the middle of the week, far from matches, to avoid residual fatigue.
Data analysis: The most important parameters to examine are baseline HRV and the coefficient of variation (CV).
- HRV baseline: computed as the average HRV over a week (or 3-5 days if daily measurements are challenging to obtain). An athlete’s average values should be analyzed. Typical values are a statistical way to represent historical data collected in the previous 30 to 60 days. This should give us insights into where we expect the 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 typical values.
- CV: Coefficient of Variation, or the amount of day-to-day variability in HRV.
Insights
Pre-session: 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 struggle with the load and might benefit from reduced load or other recovery strategies (sleep, diet, yoga, or different ways to minimize non-training-related stress, for example).
- Athletes showing a stable or increasing HRV are likely coping well with the increased load.
- Athletes showing a reduced CV likely cope well with the increased load unless their baseline HRV reduces or goes below average. In this case, the reduced CV might highlight an inability to respond to training.
The same patterns throughout the session can help you understand individual responses to changes in training load. Use HRV as a continuous feedback loop rather than a target to optimize toward a specific value. Staff working with athletes and physiological measures should prioritize baseline and CV changes 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 dependent 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. An ECG can accurately measure HRV. A basic heart rate monitor can also provide this data, but the HRV will not be as accurate.
Only elite athletes and their coaches had access to HRV data in the past because devices that measure ECG were costly and difficult to wear.
In the last five years, innovations in wireless technology have significantly increased the number of devices on the market that use HRV indices to control and manage athletes’ training processes. Now, with accessible, wearable, and user-friendly technology like the 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 it directly or as a percentage of the predicted maximum heart rate. By default, the target heart rate value is 85% of the expected maximum HR.
The predicted maximum heart rate is calculated using 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 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 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?
The power of HRV as a training tool comes from establishing an RMSDD baseline. To establish a baseline, an athlete 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 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 only to world-class athletes. However, with technologies like eSense Pulse, HRV analysis can be used by cyclists, runners, endurance athletes, 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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