HRV training interventions
Heart Rate Variability (HRV) training is one of the most popular and effective biofeedback training methods. It is used clinically, sometimes alongside neurofeedback approaches and it is widely used in training for sports and other peak performance domains.
There are a number of reasons why it has become so popular as we shall see. As HRV training impacts greatly on stress and anxiety issues it has become common to build this into a broad variety of training programmes - perhaps as a lead in. It lends itself to home training once the fundamentals have been taught and is a useful preparation for a neurofeedback session.
What is Heart Rate Variability?
Everyone knows that the heart beats in a regular fashion as it circulates oxygenated blood around the body. We understand that the heart speeds up when we exercise or even walk quickly and we sense that it slows down again as we rest.
What many people do not realise is that the heart rate (time between beats) naturally varies too. In fact in healthy individuals the heart rate variability tends to be relatively high. Prolonged stress amongst other factors can rob us of this natural and health variability. Lack of variability is associated with poor health.
When working with HRV measurements we often rely on a Blood Volume Pulse (BVP) sensor that slips over the finger. This allows us to record the ebb and flow of bood to the finger tip and from that we can derive the Inter-Beat Interval (IBI) - the time interval between adjacent heart beats.
When we have recorded a set of IBI data we in effect have a set of time intervals. We can calculate the standard deviation of this set and derive what is referred to as the SDRR (or SDNN once any errors and artefacts are corrected). This in effect is the varibility of the heart rate.
Sometimes clients who do not feel themselves to be particularly anxious or stressed notice that training with HRV improved their focus and concentration; hinting at the potential for peak performance training.
With the NeXus range we can implement a Stress Test built into the BioTrace+ software and this is a great approach for many clinical and peak performance applications. The reason for this is that clients can quickly get a sense of how sensitive their physiological state is to even minor stress - they can see how particular signals respond and see how they can learn to control these signals. We prefer to use a multimodal approach with multiple sensors - BVP for heart rate, EMG of trapezius muscles, respiration rate via a belt sensor, skin temperature at a finger tip and GSR (electrodermal activity) on the fingers.
From the point of view of the trainer, they get to see which of the client's signals are most sensitive to stress and this is extremely helpful in deciding on a biofeedback training approach.
To interpret the patterns of heart rate variability a number of terms were defined back in 1996 to label the energy contained in different frequency ranges of the HRV signal.
- Very low frequency (VLF)
- Low frequency (LF) and
- High frequency (HF)
VLF is typically considered to span the frequency range less than 0.04 Hz. This may reflect sympathetic nervous system activity to some extent.
LF is typically spanning the frequency range 0.04 to 0.15 Hz and we would expect and encourage this range to exhibit the highest power. It is suggested that this reflects the degree of balance between the sympathetic and parasympathetic branches of the autonomic nervous system.
HF is considered to be spanning the frequency range 0.15 to 0.4 Hz and reflect parasympathetic activity. The ratio of LF/HF is often calculated and is normally around 1.5 to 2. A typical display from BioTrace+ software with a NeXus 10 unit is shown here.
On the right hand side is a column with the IBI values in milliseconds. The frequency spectrum of the data with the statistics is shown with the chart. Notice the large peak around 0.1 Hz which reflects that fact that this is a resonant frequency for this persons cardiovascular system.
Every person's heart has it's own resonant frequency which is often close to 0.1 Hz although it tends to be less for men than women. Stature also influences this rate. When such as resonant frequency is achieved and activated you will note the strong connection between the breathing pattern and heart rate changes.
Goals of training HRV
The usual goal in training is to increase the heart rate variations. When this is achieved we see an increase in SDNN and the maximum change will occur when the client breathes at the resonant frequency of their cardiovascular system. With BioTrace+ we can assist the process of training the person to find their resonant frequency with an inbuilt breath pacer. This can provide a simple indication (biofeedback) that is used to guide the clients breathing pattern. Often it is necessary to very gradually adjust the breathing rate in small steps to allow the person to adapt whilst observing the captured data.
Learning to find and work with this resonant frequency has broad application as it is reflective of autonomic system balance - defusing stress and enhancing focus and concentration.