Ensuring progression and providing client feedback are two cornerstones of any successful training experience. Being able to demonstrate quantifiable change in an individuals conditioning or strength are what indicates to both client and coach that training stress is being effectively managed.
However, whilst measuring our training loads through examples such as total tonnage (load x volume) provide some indication, it often fails to consider the direct impact on the individual at the centre of the training experience and their physiological, emotional and cognitive response to training.
Finding ways in which we can incorporate biological feedback into the training environment is key in understanding what’s changing with a client or athlete holistically.
Biofeedback: the use of electronic monitoring of a normally automatic bodily function in order to train someone to acquire voluntary control of that function.
One of the first biofeedback measures integrated within our system at IFT was the use of live in-session Heart Rate Monitoring (HRM).
This provides not only the coach with a clear indicator of imposed cardiovascular demands and recovery during sessions, but greatly improves the level of understanding and awareness that individuals have with their own bodily systems. This simple measure of biofeedback has greatly influenced the achievable outcomes of what we do on a sessional, weekly and periodic training cycle.
Whilst HRM has provided a large change in biofeedback within sessions, the search remained for a measure that could provide an indicator of recovery and training readiness outside of sessions.
In our early exploration, assessing measures such as resting Heart Rate day-to-day, indicated too much variation on a daily basis to effectively manage training load and cause adaptation. Whilst HR may have been low on a particular day, it could not be interpreted as indicating a positive or negative training adaption with numerous variables needing to be considered in why the outcome was so.
Trialling with weekly measures of the coefficient of variation in resting heart rate, again saw disagreement in resting HR and perceived physiological readiness for training sessions. The question still remained, what is actually being measured and what does it imply for training…
It has been through a strong interest and drive for greater understanding of the influence of the nervous system on physiological performance and recovery, that began research into Heart Rate Variability as a biofeedback tool to monitor training load, stress and subsequent recovery.
This introduction has profoundly changed the way in which we view neurological influences on training and recovery at the most fundamental of levels.
What is HRV?
As a broad overview, Heart Rate Variability (HRV) is the time interval between one heart beat and another.
Many of us will be familiar with the concept of a resting heart rate, the number of beats our heart makes within a 60 second period, or beats per minute (bpm). We commonly think of this number to be between 60 and 90 bpm in general populations, and often way below 60 bpm in more athletic individuals.
Yet something we often don’t consider in this measure, is that this is not a fixed pulse number.
A heart rate average of 60bpm over 60secs actually doesn’t equate to a set-standard of 1 beat per second over the time. We have a large degree of oscillation between beats, some occurring quicker than a 1sec interval, others slower.
This rhythm occurs due to the natural influence that respiration has on our cardiorespiratory system. As we inhale, our heart rate actually increases as we switch to more sympathetic activity (fight, flight, freeze). As we exhale, a parasympathetic (rest and digest) activity, our heart rate slows. This phenomenon is known as Respiratory Sinus Arrhythmia.
It’s the link between the heart and the vagal nerve, who’s innervation with the heart mediates parasympathetic activity, that enables this autonomic nervous system influence on heart rate.
HRV is a measure of this natural occurrence in heart rate oscillation.
A high measure of HRV, indicating a high level of fluctuation and oscillation, is a indicator of someone with a low level of stress and a greater level of resiliency towards the daily stressors of life. They demonstrate a system with good variability to deal with moving between periods of stress and recovery, engaging the appropriate state, sympathetic or parasympathetic, to achieve such variability.
An individual demonstrating a low-degree of variability more similar to a standard 1-sec interval basis, indicates a system that is more dominated by the sympathetic state in particular. This individual, demonstrates a greater degree of sympathetic stress within the body and a lack of resiliency in the face of day-to-day stressors.
Even with limited physical demands, the biological system within is still having to deal with social, emotion or physiological stress, its yet to enter recovery mode.
Our thoughts, emotions and external experience of our environment are deeply coupled with this rhythmic oscillation of our cardiac system. As well as being further influenced by our age, gender and level of physical fitness amongst other individual factors.
HRV is therefore, a global marker of measuring the flexibility of our cardiovascular autonomous nervous system.
To understand what specifically is being measured through HRV, an easy place to begin is with a visual of an electrocardiogram. This is the image we often see on screens when an individual is having their heart rate monitor in the medical setting.
This snippet of an ECG demonstrates the QRS Complex.
This mid-section, in which we see a small drop (Q) large spike (R) and subsequent fall (S), corresponds to the depolarisation of the right and left ventricles of the heart during a single beat.
In measurement of HRV, it is the time interval between the R portion of the QRS Complex and the subsequent beat that is measured. This is commonly referred to as the R-R Interval. We are therefore measuring the influence that Respiratory Sinus Arrhythmia has on the R-R Interval of our heart rate.
HRV can be calculated based upon either a time-domain analysis such as through R-R Intervals and the root mean square of successive R-R Intervals (RMSSD) to provide a figure of HRV. Or alternatively through spectral measures from frequency domain analysis using low and high frequency measures of sympathetic and parasympathetic activity as an indicator of sympathovagal balance.
For the purpose of this Insight and its relationship to training, we will be referring only to the time-domain analysis of RMSSD.
Measurement of HRV therefore provides a snap shot of an individuals nervous system flexibility to adapt to an imposed stress.
When we consider the impact of imposed stress on the body, whilst the degree of intensity may vary, the body is non-specific in it’s response to a stressful situation whether it be psychological, emotional, physiological. The outcome remains the same.
HRV can therefore be seen as a biofeedback tool for assessing not only from a psycho-social standpoint, how well we are handling what life throws at us on a day-to-day basis, but also our physiological response to training stress. Whether we are sufficiently recovered from a cardiorespiratory standpoint to perform at a high level in a subsequent workout.
The role that HRV can play within our conditioning programme is naturally obvious, providing us with a biofeedback tool that tells us when our cardiorespiratory system has rebounded back to a level in which it can handle training stress again.
However how does HRV apply within resistance training settings?
Whilst HRV doesn’t provide a valid measure of muscular damage expected from a training stimulus, nor does it represent the neuromuscular abilities of the CNS for heavy-resistance training, the role of the cardiovascular system in the removal of waste products as a result of resistance training should not be underestimated in repeat performance and recovery.
For an in depth look, take a read of the following blog on The Oxidative System and Strength Training.
In short, our oxidative system powers the capacity for an individual to recovery optimally from anaerobic activity, such as those seen within resistance training, due to the systems large-scale capacity to remove the bi-products associated with anaerobic activity.
Whilst not directly indicative of the readiness of a musculoskeletal system for further stress, it does indicate a cardiovascular autonomous nervous system that is not under immediate threat and tightened activity of sympathetic systems. Therefore a global indicator of training readiness.
Measurement of HRV is becoming increasingly more practical and affordable, with many Apps such as HRV4Training and Sweatbeat, now work alongside simple heart rate monitors such as the Polar H7 to provide a research-approved measure of HRV via RMSSD.
Whilst the necessary measurement and formulaic approach may seem long-winded and confusing to some, many Apps now convert an RMSSD figure into a 1-100 scale which provides a simple yet effective measure of daily training readiness.
Due to the many factors associated with an individual HRV score, providing averages of HRV is a challenging prospect, however Joel Jamieson an industry leading Strength and Conditioning Coach and HRV expert, outlines typical HRV scores in the following classifications.
As coaches, trainers and clients, we are all looking for ways in which we can maximise the outcomes of our training. Finding ways in which we can better understanding our own biology, training readiness and recovery is an important part of the process.
Whilst HRV was favour those individuals performing predominately within cardiorespiratory activities such as running, cycling and swimming, it has potentially game-changing influence within the way we approach not only conditioning, but the strength element of our training.
Utilising HRV as an indicator of readiness, trialling how training sessions and life daily stressors impact on the central nervous system through this measure, is something that we strongly recommend in better understanding each of our own biological health.
This has been just the beginning of our deep-dive into how HRV can be a vital biofeedback mechanism for health and fitness. For more information look out for further posts around the topic, or take a look at the following sources from industry-leading individuals around the topic of Heart Rate Variability.