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print articleHRV by ithlete

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Monitoring Heart Rate Variability (HRV) is so much more valuable than just monitoring heart rate.

https://www.myithlete.com/

 


Heart rate variability (HRV) is a relatively new method for assessing the effects of stress on your body. It is measured as the time gap between your heart beats that varies as you breathe in and out. Research evidence increasingly links high HRV to good health and a high level of fitness, whilst decreased HRV is linked to stress, fatigue and even burnout.

ithlete measures your HRV, as well as your resting heart rate, every morning during a one minute test. After you have built up a baseline over a few days, the ithlete software algorithms compare your daily readings with baseline to determine if any significant changes have taken place. These are reflected in traffic lights for  the day’s training and in a chart to help you track trends.

HRV as a tool to monitor overtraining

Dr. Gavin Sandercock,
Director of Centre for Sports & Exercise Science,
University of Essex

Simple measures of the small changes in each beat of your heart can provide a wealth of information on the health of your heart and nervous system; such measures are called heart rate variability or HRV. Originally applied to assess the risks for patients who suffered a heart attack, HRV analysis is now becoming a standard tool in sports science research and coaching practice.

Since researchers first found significant changes in the nervous systems of athletes involved in hard training for the rowing world championships (Iellamo, 2002), a number of studies have tried to use HRV as a tool to monitor overtraining. In general such studies show that HRV is much lower in overtrained athletes than healthy ones (Mourot, 2004).

The problem is, when you are overtrained it is too late. It might take weeks or months to get back to full fitness, so what you need is a daily measure to tell you how well your nervous system is doing. Daily monitoring using standard HRV methods have shown that listening to you heart via HRV can not only stop you overtraining but actually make your training more effective. (Manzi, 2009).

The idea is quite simple. Monitor your HRV every morning and train as normal. If your HRV drops significantly, take this as an early warning that you are overloading the system. A small drop is OK as long as you recover. Training is, after all, about stress and recovery and a hard session, especially on top of accumulated fatigue, will lower your HRV.

But if your HRV stays low even with rest you could be on the edge of trouble. In my opinion, using daily HRV to monitor training stress is the best thing you can do to make your training safe and effective. So listen to your heart.

Learn more about Overtraining

What is heart rate variability (HRV)?

Measurement of HRV for use in monitoring training and recovery involves analysis of the heart’s beat-to-beat variation. By accurately measuring the time interval between heartbeats, the detected variation can be used to measure the psychological and physiological stress and fatigue on the body during training. Generally speaking the more relaxed and unloaded (free from fatigue) the body is, the more variable the time between heartbeats. HRV data can indicate the impact of fatigue due to prior exercise sessions, hydration levels, stress and even the degree of performance anxiety, nervousness or other external stressful influences. Studies have shown that it varies within individuals according to size of left ventricle (inherited trait), fitness level, exercise mode (endurance or static training) and skill (economy of exercise). Body position, temperature, humidity, altitude, state of mood, hormonal status, drugs and stimulants all have an effect on HRV, as do gender and age.

Heart rate variability is measured by calculating the time between R spikes on an ECG trace

HRV measurement

Measure your HRV

How to determine the right amount of training

In practice, it’s difficult to assess accurately the effect of training on the body. How do you fix your training load? How well is your body adapting to the training? Is there any accumulated fatigue and how much rest do you need for recovery? Other questions that you need to ask are – how do I know I am getting the right training effect? Have I improved? Am I over or under training? There is a tendency for training to be extreme with a prevalence of over training and under recovery. There is a general belief amongst athletes that ‘working hard’ is always a virtue when it comes to improving fitness. Equally at the social end of participation (charity running for example) many competitors are under prepared for the physiological effort required. The ithlete app is a commercially available product to assist those serious about their training in using HRV to improve athletic performance.

General adaptation syndrome

General adaptation syndrome

Enhance your training

Why is it important to recover from training?

At rest your body system is in balance. To achieve a training effect, you need to disturb this balance by putting the body under an adaptive stress to which it can react. This stress is known as training and your body’s reaction to training is called a training effect. Well-timed rest is one of the most important factors of any training programme. The effects of training sessions can be negligible or even detrimental if insufficient rest & recovery is built in.

Typically, HRV measurements demonstrate a significant and progressive decrease in the HRV index measured by ithlete during long-term heavy training followed by a significant increase during resting. Continuous hard training with insufficient recovery will slowly lead to lower performance and a long-term state of overtraining.

When overtrained, even a long period of recovery may not be enough to return performance to the original level. The body needs time for recovery after a single high-intensity session, or a hard training period of several days, or even after a low-intensity but long training session. Without rest, adaptation to the training load will not occur.

How does HRV stress & recovery analysis work?

The ithlete application requires a simple one minute test first thing every every morning, whilst you wear a regular heart rate monitor chest strap or finger sensor. During the test you breathe deeply and relax, so that you minimise the effect of external stressors on the HRV index and focus on what your body is telling you about the impact of your training. After you have performed the test for a few mornings (ideally in a quiet period of training or recovery), you will start to see daily variations around an average (the blue line). Once your normal value has been established, the Daily Change indication will give you a recommendation for today’s training intensity depending on the difference from your previous measurements.

People use the device in different ways – some like to do their measurement immediately on getting out of bed, whilst some prefer to wake up a little first (but no coffee or tea before the measurement please!). Some get familiar with their normal value range as a number and judge the impact of their training from that, whilst others like to look for patterns on the chart. The Weekly & Monthly Change indicators also help you see the trends during periods of intensive training, when you can expect to see sustained decreases, or tapering before an event, when you should see a very healthy increase.

Our ithlete training guide

Conclusion

HRV is a relatively simple, but effective, tool for regular checks of progress during endurance training programmes. Overtraining or under recovery are real issues that athletes and coaches alike need to consider. Overload periods need to be used with caution and additional rest periods or reduced intensity training sessions introduced to ensure athletes are optimising their training and recovery time. Close to a competition, monitoring of taper activities can be undertaken to ensure that the athlete competes in a fully recovered state.

The ithlete heart rate variability monitor is a powerful tool for athletes and coaches, providing useful information which can be used to adjust training programmes to best effect.

Visit the store

Follow these four easy steps to get started with ithlete today!

Heart rate sensor

Choose a heart rate sensor

To measure heart rate variability (HRV) with ithlete you’ll need a heart rate sensor. You have the option to use an ithlete finger sensor or chest strap monitor. If you have a recent iPhone, iPad or Android device you may like to use our Bluetooth Smart chest strap monitor, or alternatively grab a Polar type analogue strap (we also offer one of these) and an ithlete ECG receiver to pick up the signal. Visit the ithlete store to find your preferred sensor.

ithlete display

Download the ithlete app

ithlete is available on both iOS and Android devices and can be downloaded from the App Store or Google Play. If you do want to check your model of smartphone or tablet is compatible check our FAQ page.

Apple App StoreGoogle Play Store

ithlete measurement

One minute daily measurement

After waking each morning relax and sit comfortably, slip on a chest strap or finger sensor and follow the on screen instructions to get an accurate reading of your heart rate variability. Taking the measurement couldn’t be simpler and in 60 seconds you will have a personalised training recommendation for the day.

Wheelchair athlete

Reap the benefits of training with ithlete

The idea is quite simple. Training is all about stress and recovery. A hard session, lack of sleep, mental stress etc. will lower your number. If your reading drops significantly, take this as an early warning that you are overloading the system. On the other hand a high score lets you know you should make the most out of the day. Benefits of this include avoiding overtraining, workout optimisation, guilt free rest days, improved performance and much more!

Introduction

Simon Wegerif

Founder Simon Wegerif explains how ithlete was designed in response to an athlete’s genuine need to train smart.

‘Like many endurance athletes, I had used a heart rate monitor for years. It helped me measure how hard my body was working during training as well as keeping me just to the right side of the red line during competition. In search of more effective ways to develop my limited talents, I began investigating smarter training methods that would improve my performance whilst avoiding injury due to overtraining. This is how I found out about heart rate variability (HRV).

I was quickly convinced that I should incorporate HRV in my own athletic training. I looked around for a commercial product but could find nothing that included important measurement criteria such as colour-coded readiness indicators, the ability to visualize trends graphically, and the simplicity of a quick morning test that anyone can fit into his or her daily routine.

I concluded that there was no easy-to-use, affordable product that provided a convenient daily measure of HRV. As a professional engineer, with a long career in consumer electronics & signal processing, building such an HRV product seemed a worthwhile challenge.

During 2009, I read over 500 research papers on HRV and consulted cardiologists, coaches and trainers. My device had to be scientifically valid, practical, and uncomplicated to use. During this research, and following patent applications in the US, UK and EU, I was invited to establish sports and medical research collaborations on HRV application in cardiac rehabilitation and elite sports training.  By mid 2009, I had completed the first working ithlete smartphone app and a prototype receiver which was the first able to record heart rate on an iPhone.’

The following material is based on extracts from US patent 8666482 and links to relevant supporting research, and explains how ithlete measures HRV and creates training indications for the user.

Scientific basis for the ithlete measurement

Choice of HRV parameter

Many parameters have been for measuring HRV over the last 30 years. They fall into three types: time domain, frequency domain and entropy (chaos) measures.  Very few of these are suitable for use outside the laboratory by untrained users with limited time available for measurement.  We chose RMSSD (Root Mean Square of the Successive Differences), a time domain parameter that correlates very highly with more complex frequency domain measure HF (High Frequency), without requiring a breathing rate greater than 9 breaths per minute or stationarity of underlying heart rate. The raw RMSSD measure has poor statistical properties, so I decided to apply natural Log (Ln) transformation, which allows common statistical measures such as standard deviation (SD) and coefficient of variation (CV) to be used. This article provides a more in-depth rationale for this choice.

Measurement duration

Users need to fit the measurement into their daily morning routine, so it is important that it should not take very long.  We established that 1 minute is sufficient for a very good level of scientific validity whilst being short enough to maximize user compliance. Although just 30 seconds is sufficient for RMSSD from a signal processing perspective, the 1 minute measure of LnRMSSD has now been validated in a peer reviewed journal paper, which reports an intraclass correlation of 0.98 (0.93, 0.99) and 0.0 bias (LoA 0.22) for the 1 minute measure compared to the criterion measure of 5 minutes.

Measurement time of day

Morning wake was chosen as the optimum time of day for the following reasons:

  • Measurement first thing in the morning provides an indication of recovery following sleep without influence from food and drink (including caffeine), and daily physical or mental stresses.
  • Knowledge of the HRV value first thing in the morning allows the user to alter training or activity plans for the day ahead.
  • Relevant, commonly used subjective recovery parameters such as sleep quality, general fatigue, stress and muscle soreness can be recorded at the same time as the HRV measure, giving a more complete picture of the impact of lifestyle factors impacting recovery and readiness to train.

Sensor types

Sensors need to be carefully selected and well cared for, as the precision measurement of every interbeat interval is a demanding task, and much more so than giving an indication of average heart rate at rest or during exercise. Traditionally, medical grade ECG has been used for HRV studies and clinical practice.  (See this article’s charts for more on the evolution of heart rate sensors suitable for HRV use) Polar™ type chest band sensors have been validated for HRV use, and these are now available with Bluetooth Smart™ (BLE, 4.0) transmission, but not all manufacturers’ products transmit the required R-R intervals over Bluetooth, and even worse, some transmit inaccurate data. Certain pulse sensors have also recently been validated for HRV measurement in smartphone applications.

Researchers at the University of Alabama have now performed a comprehensive validation of the ithlete Finger Sensor in a young athletic population in seated, standing and supine positions. Full text is available here.

Measurement accuracy

HRV was first analysed in clinical settings using hand measurements of ECG rhythm strips, and then by recorders which digitized at 128Hz, giving an accuracy of approx. 8 milliseconds.  This has steadily improved over the years to 1-2 milliseconds and this is the range chosen also for ithlete, with the strap based measurements aiming for 1-1.5 milliseconds and the finger pulse sensor for 2 milliseconds precision.  Insufficient accuracy leads to bias in the results, which is not constant, but dependent on the measured value.

Validation of the ithlete measurement accuracy when used with a chest strap can be found here.

And for the finger sensor here.

There has been interest recently in the use of smartphone cameras for HR & HRV measurement.  Reasonable estimates of resting HR can be obtained using this technology, but the time resolution of the camera at 30-60 frames per second is far too low for reliable HRV measurement.

Measurement repeatability & breathing rate

Many studies have shown that HRV is affected by respiratory activity – both breathing rate and depth. HRV measurement using LnRMSSD under free breathing resting conditions is not reliable (Coefficient of Variation = 12% reported by Al Haddad et al 2011). However, researchers have found that controlled (paced) breathing overcomes the problems experienced with free breath and improves reliability and repeatability of HRV results.

When implementing paced breathing, it is important to avoid stressing the user by making them breathe at a significantly different rate to that which they are comfortable with.  The rate of 7.5 breaths per minute chosen for ithlete back in 2009 has recently been endorsed by researchers who found that this was the average free breathing rate of a group of club runners at rest (Saboul 2013).

HRV result scale

The raw transformed LnRMSSD measure of HRV occupies a range of 2.5 to 4.5 for healthy individuals and as such is not very friendly or intuitive for non scientific users. A scaling factor of 20 was introduced in order to improve intelligibility so that the fittest athletes would tend to be in the range 90-100.  The scale does not have a hard stop, and occasionally ithlete readings as high as 115 have been reported.  This represents very marked respiratory sinus arrhythmia where the highest heart rate during inspiration is about twice that observed at the end of expiration.

Another beneficial property of the 20x scaling is that one unit represents about 0.25 standard deviations for a user who is careful with their measurement practice, and is therefore the lowest value likely for the smallest worthwhile change (SWC, W. Hopkins). This property means that whole numbers can be reported and eliminates the need for values after the decimal point.

Baseline comparison

Since the first prototypes of ithlete, a 7 day weekly moving HRV average has been used as an individual baseline from which to identify significant changes.  This has also been validated as best practice in this review by Plews (2013).

Identifying normal & abnormal daily readings

Daily readings are compared with the baseline described above to determine whether they are within the normal range.  The Smallest Worthwhile Change (SWC, Hopkins) is set at 1 standard deviation (SD) for the purposes of traffic light user indications. If a reading is more than 1 SD below baseline, it is marked amber as a warning to the user.  If the following day’s reading also meets the same criteria, it is marked red as a strong warning to the user that their HRV is below normal range.

As well as flagging HRV values below normal for the user, the ithlete algorithms also indicate HRV values very significantly above baseline as signs of possible parasympathetic dominance/ adrenal fatigue, especially when combined with abnormally low resting HR.

Identifying normal & abnormal trends

HRV response to progressive overload in runners was studied by V. Pichot et al (2002), and their findings are embedded in the ithlete weekly and monthly change indications to flag when overload may become maladaptive (i.e. excessive and difficult to recover from). Indications are progressive with amber and red flags. Conversely, during taper (the period at the end of a training block when loading is reduced) and rest periods, beneficial upwards trends are flagged green. Rapid rises in HRV over successive days which are unlikely to be the result of tapering but rather onset of adrenal fatigue are also flagged.

Additional data recording

As well as HRV and resting HR, ithlete also allows users to capture the following objective & subjective variables:

  • Training load (arbitrary units)
  • Sleep quality (Visual Analog Scale, VAS 1 -9)
  • Fatigue (VAS 1 -9)
  • Muscle soreness (VAS 1 -9)
  • Stress level (VAS 1 -9)
  • Mood (VAS 1 -9)
  • Diet (VAS 1 -9)

These are presented graphically so that users can visually identify relationships between HRV and lifestyle factors, allowing them to experiment with changes.


 

Date Inserted: 03 June 2018
Last Updated: 15 July 2018
 
Have questions or comments on this article? email me

 

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