We first met Simon Wegerif from leading Heart Rate Variability training app/sensor developers ithlete at the Training Peaks Endurance Coaching Summit up in Manchester back in November.
He's doing some really interesting work that's helping athletes optimise their training plans by monitoring (and then responding to) the signs of fatigue that can be found by measuring the time gap between heart beats. He's worked with a number of elite athletes and organisations, including Arsenal FC.
If you read our blog on avoiding overtraining and burnout with personal interest then this one's well worth a read...
What is Heart Rate Variability (HRV)?
Heart rate variability (HRV) is an excellent method for assessing the effects of stress on your body. Research evidence over the past decade has increasingly linked high HRV to good health and a high level of fitness, whilst decreased HRV is linked to stress, fatigue and even burnout.
HRV measures the time gap between your heart beats, which vary as you breathe in and out. 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.
HRV is measured as the variation in time gap between the R waves on an ECG / EKG trace, also known as the R-R interval:
What can HRV tell me about my 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. This likely stems from the 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 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 so 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.
How do I measure HRV myself?
One way to measure your heart rate variability for training is with HRV app ithlete.
ithlete measures your HRV, as well as your resting heart rate and a number of wellness metrics every morning during a one minute test, whilst you wear a dedicated finger sensor or use a regular heart rate monitor chest strap.
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, ithlete’s Daily Change indication will give you a recommendation for today’s training intensity depending on the difference from your previous measurements.
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.
Morning wake is the optimum time of day to take your HRV 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.
- Commonly used wellness and 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.
HRV and Resting Heart Rate
A combined view of HRV together with resting heart rate (RHR) can tell us even more about the body’s state of stress and readiness to train.
This is because HRV largely reflects the state of the parasympathetic (‘rest and digest’) nervous system whereas resting HR is more affected by the sympathetic (‘fight or flight’) branch.
ithlete Pro’s Training Guide is a unique chart that plots your daily readings in the chart shown below that allows you to see not only what zone (green / amber / red) you are in that day, but also how close you are to the zone boundary, and what the trend is:
If your daily reading is in the top left corner, your body is stressed, by illness or an imbalance of training and recovery.
Dehydration can also stress your body significantly – a research study in 2015 found that dehydration reduced HRV and increased resting metabolic rate.
The decreased HRV reflects a delayed return to the ‘rest and digest’ state that we need in order to rebuild and restore the body’s reserves.
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.
If you're interested, you can learn more about the science behind HRV on our research pages. Or, if you're interested in incorporating HRV into your training, you can get 10% off our sensors and/or an annual ithlete Pro subscription using the code Precision_Hydration at myithlete.com before the end of June.
Simon Wegerif is an inventor and biomedical engineer. Previously an executive with Philips Electronics in the UK and Silicon Valley, he started as a pioneer of digital broadcasting at the BBC. Simon oversees all business activities and product development. Simon is a competitive cyclist and has completed a number of triathlons including Ironman distance.