This article is an introduction to the principles of training adaptation, ANS cardiac control, and the use of Heart Rate Variability (HRV) as a tool to monitor training load, fatigue, and recovery. With focus on the ithlete HRV mobile app.
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Page updated: 11/12/2017
- Training Adaptation: Stimulus and Recovery
- The Beat-To-Beat Variability of Heart Rate
The ANS plays a dynamic role in the regulation of pain, inflammation and tissue repair (Ackermann et al., 2016). Thus, some authors have postulated that monitoring HRV, as an indirect measurement of ANS homeostasis, has the potential to indicate early signs of somatic tissue overload prior to the onset of pain or fully developed injury (Gisselman et al., 2016). It is hypothesised that, relative to each athlete’s baseline HRV measurements, imbalances in the parasympathetic and sympathetic nervous systems may indicate an athlete is in a state of ongoing repair and recovery versus an athlete who is adapting positively to training load (Gisselman et al., 2016). HRV measurements may therefore be used to improve our understanding of the mediators and moderators in the workload-injury relationship (Windt et al., 2017). (Sean, 2017).
Training Adaptation: Stimulus and Recovery
The purpose of training is to stimulate the body to adapt and compensate positively in effort to improve performance for a given task or action. Depending on the training phase, the stimulus is modified to increase or decrease fatigue, allowing adequate recovery, and to prevent overtraining.
Training Load (TL) can be defined as a stimulus composed of: skill (specificity), intensity (exertion), volume (amount), and duration (time). What you are doing, how hard, how much, and for how long.
When adequate TL is regularly applied (frequency), along with adequate recovery (compensation), positive metabolic, cardiovascular, and neuromuscular adaptation occurs. Progressive increases in TL are required to stimulate progressively greater adaptation over time. Overcompensation (also called supercompensation) results from consistently applying TL above previous adaptation levels.
Apart from specific training blocks where the object is to acutely overreach (via excessive TL relative to recovery), TL is applied following adequate recovery, which provides greater training capacity, allowing for greater training volume, leading to greater adaptation over time.
If the balance is out between TL and recovery (i.e. repeated overreaching), adaptation plateaus or at worse recedes. Overtraining can be thought of as “recovery debt” and could lead to sickness or injury, and therefore (ironically) less training and positive adaptation over time.
Excessive and rapid increases in training loads are likely responsible for a large proportion of non-contact, soft-tissue injuries. However, physically hard (and appropriate) training develops physical qualities, which in turn protects against injuries. (Gabbett, 2016).
In contrary to the nf-OR [non-functional overreaching] stage, f-OR [functional overreaching] is often intentionally induced by coaches – typically through periods of intensified training such as training camp periods – with the intent that the temporary performance decrement is followed by a taper-induced performance supercompensation. (Aubry, 2015).
Overtraining—an accumulation of training and/or non-training stress resulting in long-term decrement in performance capacity with or without related physiological and psychological signs and symptoms of maladaptation in which restoration of performance capacity may take several weeks or months. (Lehmann, 1999).
Performance decrements are common, but this can simply be due to fatigue. Or it can be because of extreme fatigue, often referred to as overreaching, which is observed usually after a block of hard training or a training camp. Athletes who come back from a training camp usually perform worse at first, but after sufficient recovery typically see a major jump in their performance as the reward for the hard work during the camp. Overreaching had therefore been described as functional overreaching. (The term functional overreaching was described in a consensus paper by Professor Romain Meeusen from the Free University in Brussels and colleagues from various Universities all over the world). Athletes go through a phase like this because it is necessary to improve. (Jeukendrup, 2015)
But I will leave the detailed discussion on training periodisation, overtraining, functional overreaching (f-OR), non-functional overreaching (nf-OR), and overtraining syndrome (OTS) for a future article.
Quite simply, getting your recovery right provides you the capacity to train harder and thus progressively improve. The same goes for nutrition: eat to increase your training capacity.
How do we know if we are getting the balance right?
Monitoring training and fatigue could get pretty complicated, especially in regards to choosing what is specifically being measured: time, technique, maximal effort, repeat efforts, perception of exertion or effort, perception of fatigue and recovery, illness, injury, biochemistry, body composition, sleep, psychology, sensations…
As a coach, I will modify Training Load (TL) in response to feedback during the training session, and from cumulative feedback over time. Feedback measures I use are…
Physiological Change: Total Body Mass (TBM), Lean Body Mass (LBM). Circumference measurements. Positive or negative relative to performance, goals, diet, supplementation.
Training Performance: Intensity, volume, density (volume over duration), RPE scores (see next point). Was the session completed as prescribed. Performance tests. Progression or regression.
Rating of Perceived Exertion (RPE): After every last skill/movement set, the client rates their exertion out of 10. They also provide an overall RPE score for the whole training session. Was their perceived exertion correct relative to given TL and recovery expectation.
Heart Rate Variability (HRV): Each morning my clients take an ithlete HRV reading along with subjective scores (sleep, fatigue, stress, muscle soreness, etc) which provides some indication of the recent TL effect, cumulative TL effect, and their level of fatigue or recovery from it.
Which after such lengthy introduction leads us neatly into the very subject of the article…
The Beat-To-Beat Variability of Heart Rate
Your heart rate (HR) or pulse changes to match your physical exertion, how stressed or relaxed you are, and is influenced by your breathing: HR increases on inhalation, decreases on exhalation.
What you might not know is that a heart rate of 60 bpm (beats per minute) does not mean that each beat is exactly one second apart. There are variations in the intervals between each consecutive heart beat.
Heart rate is inversely proportional to the interval. That being the greater the time (R distance) between each R-R interval, the lower heart rate is, and vice versa: shorter equals faster.
Now these dynamic rather than fixed beat-to-beat intervals correspond to the shortening "fight-or-flight" sympathetic and lengthening "rest-and-digest" parasympathetic nerve control of the heart.
The Autonomic Nervous System (ANS)
Collectively called the Autonomic Nervous System (ANS), the sympathetic (SNS) and parasympathetic (PNS) "vagal" nerves originate from the Central Nervous System (CNS) and dually innervate (supply with nerves) target organs regulating the functions of the body generally not under our conscious control or will.
Both the SNS and PNS, along with the hypothalamic–pituitary–adrenal (HPA) axis govern the body's dynamic homeostasis (balance) during situations of stress and recovery. The HPA axis is the intertwining of the CNS and endocrine (hormonal) system: the neuroendocrine system.
The SNS can be thought of as being stimulatory: preparing, priming, and focusing various physiological systems during increased physical or mental needs. The opposing (albeit complementary rather than antagonistic) PNS is involved in promoting the maintenance and recovery of the body during rest.
Sympathetic (SNS) nerves stimulate catecholamine (epinephrine, norepinephrine) release, increase heart rate and force contraction, dilate pupils, dilate lung bronchiole, dilate blood vessels, increase blood flow to skeletal muscle, activate sweat secretion, constrict sphincters and decrease gastrointestinal motility (digestion slows). This is the fight-or-flight or sympathoadrenal nervous response you experience being chased by a tiger, or when someone says: "We need to talk".
Parasympathetic (PNS) nerves do the opposite: decrease heart rate, relax blood vessels, constrict pupils, intensify digestion, increase sexual arousal, increase and maintain blood flow to the sexual organs (more stress, less PNS). Hence referred to as the rest-and-digest or feed-and-breed nervous response. The response you have eating a nice breakfast, reading a book, or even cuddling. Although, caffeine will actually stimulate a SNS response; not to mention post-cuddles.
Though cardiac function is a product of multiple physiological interactions, the ANS is dominant in the control of heart rate: conduction velocity (nerve signal), contractility (self-contraction), and relaxation.
Both branches of the ANS innervate the heart's sinotrial (SA) node controlling the rate of electrical impulses that initiate heart beat. If left unaffected, this “pacemaker” would spontaneously maintain an intrinsic heart rate of 100-115 bpm. But heart rate is reduced and maintained at 60-80 bpm by the parasympathetic vagus nerve; and for heart rate to increase, vagal tone is reduced whilst sympathetic tone is increased. Thus this reciprocal change in SNS and PNS activity allows for heart rate to dynamically increase or decrease depending on needs. E.g. Increasing exercise intensity.
So as there is opposing control of heart rate by these two nervous systems, and the cardiac adjustments are reflected in the varying distances between adjacent heart beats; by measuring the variability of heart rate we can "read" which branch of the ANS is currently predominating control.
RMSSD: The Measure of Heart Rate Variability (HRV)
A number of parameters exist to determine Heart Rate Variability (HRV), but for the purpose of monitoring recovery status and physiological adaptation to training, RMSSD is most commonly used.
If you look back at the ECG diagram earlier; RMSSD is simply the Root Mean Square of the Successive Differences (distances) between adjacent R-R intervals established over a period (domain) of time. Log transformed RMSSD (LnRMSSD) is generally used to establish "HRV score".
RMSSD is commonly used as an index of vagally (Vagus Nerve) mediated cardiac control… provides an easily acquired and interpretable figure in a short period of time that reflects parasympathetic activity which is quite useful for monitoring the effects of training and in the manipulation of training loads. (Flatt, 2013)
As RMSSD is used as a measure of Autonomic Nervous System (ANS) cardiac control, the SNS/PNS driven beat-to-beat variability of heart rate; RMSSD established "HRV" score can serve as a contextually useful "rough measure" of our sympathetic-to-parasympathetic nervous system balance.
|↓ Low: Heart Rate Variability (HRV)||↑ High: Heart Rate Variability (HRV)|
|↑ High: Resting Heart Rate (RHR)||↓ Low: Resting Heart Rate (RHR)|
|↑ High: Sympathetic (SNS) activity||↑ High: Parasympathetic (PNS) activity|
|↑ High: Stress / Fatigue||↑ High: Rest / Recovery|
HRV readings are normally taken first thing in the morning, sitting down, and before doing anything physically strenuous or mentally stressful which would affect resting heart rate. Sitting, standing or lying prone all affect HRV, as does breathing rate which is why paced breathing is recommended. HRV should be taken at the same time and in the same way.
Low HRV (relative to your established baseline), indicates higher basal sympathetic cardiac control. The question to ask then is why are you “stressed”? Is it correctly correlated with anything you know: How well did you sleep? How hard was your training yesterday? Are you getting sick?
High HRV (relative to your established baseline) is generally an indication of the ability of the ANS to respond to the changing demands placed on the body. You can think of it as "nervous system reserve", the better you are rested and recovered the more dynamically responsive your heart is. Lower HRV has been shown to correspond with poor cardiovascular health, and HRV is influenced (generally increased) by cardiovascular training, but I will discuss this at a later date.
HRV is individual, and unlike blood pressure, there is no standard or threshold value for what is "high". HRV scores should then interpreted against your own individual mean score and correlating data (TL, RPE, etc). What is a low HRV score for you might be high for others and vice versa.
An optimal level of HRV within an organism reflects healthy function and an inherent self-regulatory capacity, adaptability, or resilience. (McCraty, 2015).
The changes in the HRV indices indicate the ability of the autonomic nervous system to respond to multiple physiological and environmental stimuli, such as breathing, physical exercise, mental stress, hemodynamic and metabolic changes, and sleep and posture changes, as well as compensating for disorders resulting from illness. (De Silva, 2015).
Relative to each athlete’s baseline HRV measurements, imbalances in PNS and SNS activity may indicate an athlete is in a state of ongoing repair and recovery versus an athlete who is adapting positively to training load. (Gisselman, 2016).
In the case of elite athletes, increasing HRV values (as competition approaches) may be a sign of positive adaptation and/or coping with training load, while reductions in HRV in the week/days before pinnacle events may represent increasing freshness and readiness to perform. (Plews, 2013)
Using Heart Rate Variability (HRV) to Guide Training and Recovery
For training adaptation to occur over time, the training stimulus needs to be matched to recovery, allowing you to consistently increase your training volume through an increased capacity to do more.
Tracking your HRV over time and correlating it with other data such as Physiological Change, Training Performance, Rating of Perceived Exertion (RPE) and subjective measures of sleep quality, muscle soreness, stress levels… allows you to identify patterns in your training-to-recovery balance.
More often than not, training sessions are either governed by set programming, or completely left to subjective feelings of fatigue or readiness. Both approaches are not always optimal. Some days you may need to completely disregard your normal schedule, and some days you could actually do more than was planned.
Understanding when to pull-back from your normal training schedule or programming is essential to training longevity. Leaving some "in the tank" often allows you to achieve training consistency long term and thus greater training volume over time. The always "go hard or go home" attitude may actually keep you at home longer.
More so if you are repeatedly under-recovering in relation to your training, your training programming is non-optimal. In a future post (and potential video talk), I will provide more real-world examples of using HRV to adjust and balance training load, intensity and recovery.
Why Tracking Heart Rate Variability (HRV) is Useful
Taking your HRV reading daily lets you plan ahead with knowledge of what your body is best suited to on that day. When your reading is good compared to your baseline, it’s having confidence that your body is able to cope with the training demands you put on it. (ithlete HRV).
- Aids you in monitoring your acute / chronic response to training loads and blocks
- Aids you in adjusting your acute / chronic training loads and blocks relative to recovery
- Aids you in identifying recovery / fatique patterns related to acute / chronic training loads and blocks
But importantly HRV is not a lot of things, and most certainly not a direct measure or indication of your training adaption or level of fatigue.
A low HRV reading cannot tell you about your glycogen levels, your testosterone levels, your CNS fatigue. The other way around if your HRV level is high, it just means that cardiac ANS-wise you might be able to train or perform well, but whether the other systems are recovered, HRV does not tell you. In the end you still might have suboptimal training load and training response! Never follow blindly what a singular HRV test is telling you, always take other factors into account as well. (Kraaijenhof, 2014).
Heart Rate Variability (HRV) indicates the status of your cardiac autonomic system which has been shown to correlate with other measures providing you some view to your training capacity and adaptation.
Tracking HRV is useful, just don't make it more than what it is.
Heart Rate Variability (HRV) Apps, Hardware, and Training Courses
- HRV mobile apps
- HRV training courses
- Notable HRV resources
- HRVtraining - Andrew Flatt PhD(c), CSCS
- Heart Rate Variability (HRV) - Science For Sport
- 2016 Google Hangout with Simon Wegerif (ithlete), Dr. Mike T Nelson (MikeTNelson), and Dr. Marco Altini (HRV4Training) discussing their understanding of the application of HRV: pros, cons and whether or not monitoring HRV is actually useful at all. Watch the hangout here: Heart Rate Variability (HRV) - In Application.
Aubry, A., Hausswirth, C., Louis, J., Coutts, A. J., Buchheit, M., & Le Meur, Y. (2015). The Development of Functional Overreaching Is Associated with a Faster Heart Rate Recovery in Endurance Athletes. Plos One, 10(10), e0139754. http://doi.org/10.1371/journal.pone.0139754
Autonomic Regulation of Sexual Function. Neuroscience. 2nd edition. http://www.ncbi.nlm.nih.gov/books/NBK11157/
CV Physiology: Control Of Heart Rate. Cvphysiology.com. http://www.cvphysiology.com/Arrhythmias/E010.htm
Da Silva, V. P., De Oliveira, N. A., Silveira, H., Mello, R. G. T., & Deslandes, A. C. (2015). Heart rate variability indexes as a marker of chronic adaptation in athletes: A systematic review. Annals of Noninvasive Electrocardiology, 20(2), 108–118. http://doi.org/10.1111/anec.12237
Dong, J. (2016). The role of heart rate variability in sports physiology (Review). Experimental and Therapeutic Medicine, 1531–1536. http://doi.org/10.3892/etm.2016.3104
Flatt, A. (2013). RMSSD: The HRV Value provided by ithlete and BioForce. HRVtraining. https://hrvtraining.com/2013/07/04/rmssd-the-hrv-value-provided-by-ithlete-and-bioforce/
Flatt, A. Beardsley. C. (2014). Andrew Flatt Explains How To Use HRV Information. Strength & Conditioning Research. http://www.strengthandconditioningresearch.com/2014/11/18/andrew-flatt-hrv/
Gabbett, T. J. (2016). The training-injury prevention paradox: should athletes be training smarter and harder? British Journal of Sports Medicine, 1–9. http://doi.org/10.1136/bjsports-2015-095788
Gisselman, A. S., Baxter, G. D., Wright, A., Hegedus, E., & Tumilty, S. (2016). Musculoskeletal overuse injuries and heart rate variability: Is there a link? Medical Hypotheses, 87, 1–7. http://doi.org/10.1016/j.mehy.2015.12.003
Halson, S. L. (2014). Monitoring Training Load to Understand Fatigue in Athletes. Sports Med, 44(Suppl 2), S139–147. http://doi.org/10.1007/s40279-014-0253-z
Issurin, V. B. (2010). New Horizons for the Methodology and Physiology of Training Periodization, 40(3), 189–206. http://doi.org/10.2165/11319770-000000000-00000
Issurin, V. B. (2015). Benefits and Limitations of Block Periodized Training Approaches to Athletes' Preparation: A Review. Sports Medicine. http://doi.org/10.1007/s40279-015-0425-5
ithlete HRV. Optimize performance. http://www.myithlete.com/what-is-hrv/optimize-perfomance/
Jeukendrup, A. Overtraining: is it real? http://www.mysportscience.com/single-post/2015/03/02/Overtraining-is-it-real
Kiviniemi, A. M., Hautala, A. J., Kinnunen, H., Nissil??, J., Virtanen, P., Karjalainen, J., & Tulppo, M. P. (2010). Daily exercise prescription on the basis of hr variability among men and women. Medicine and Science in Sports and Exercise, 42(7), 1355–1363. http://doi.org/10.1249/MSS.0b013e3181cd5f39
Kraaijenhof, H. (2014). HRV…. what could it mean to me? http://helpingthebesttogetbetter.com/?p=680
Kreider, R. B. Role of Amino Acids in Reducing Fatigue and Overtraining. ISSN Brazil 2015. http://bit.ly/1q0mP81
McCraty, R., & Shaffer, F. (2015). Heart rate Variability: new perspectives on physiological Mechanisms, assessment of self-regulatory Capacity, and Health risk. Global Advances in Health and Medicine, 4(1), 45–61. http://doi.org/10.7453/gahmj.2014.073
Principles of Training. IAAF. http://bit.ly/1RhxRwr
Plews D Laursen P Stanley J Kilding A Buchheit M. (2013). Training adaptation and heart rate variability in elite endurance athletes: Opening the door to effective monitoring. Sports Medicine. http://doi.org/10.1007/s40279-013-0071-8
Sean Williams, Thomas Booton, Matthew Watson, Daniel Rowland, Marco Altini. (2017) Heart Rate Variability is a Moderating Factor in the Workload-Injury Relationship of Competitive CrossFit™ Athletes. Journal of Sports Science and Medicine (16), 443 - 449. http://www.jssm.org/hf.php?id=jssm-16-443.xml
Stanley, J., Peake, J. M., & Buchheit, M. (2013). Cardiac parasympathetic reactivation following exercise: Implications for training prescription. Sports Medicine, 43(12), 1259–1277. http://doi.org/10.1007/s40279-013-0083-4
Syv, H. (2010). Effects of Exercise Intensity on Recovery of the Autonomic Nervous System Immediately After Exercise and During Sleep, and on Subjective and Objective Sleep Quality. http://urn.fi/URN:NBN:fi:jyu-201103011834