Unless you’ve been living under a rock for the last couple of years, there’s a good chance that you will have come across the term heart rate variability (or HRV for short). Popularised by the likes of wearable tech brand Whoop, it is the latest performance data especially when more long-term lifestyle stressors work and family can be harder to change training.
But what is this new three-letter acronym? And can it actually make a difference to your mile splits, or is it simply another thing to track?
What is heart rate variability?
'Technically speaking, heart rate variability refers to quantifying the difference between consecutive heartbeats,' explains Marco Altini, founder of the smartphone app HRV4Training. Every time your heart beats, the gap between each thump isn’t exactly the same. It these milliseconds that form the basis of your heart rate’s variability.
HRV is useful because it provides a picture of your autonomic nervous system’s (ANS) status. Your ANS is the part of the nervous system that controls the body’s automatic processes (heart rate, blood pressure, breathing) and is made up of two branches – sympathetic and parasympathetic. The former instructs your heart to beat faster, while the latter tells it to beat slower.
'By quantifying heart rate variability, we have an objective way to quantify the activity of the ANS, and we can understand how the body responds to stress,' says Altini. 'Parasympathetic is the one that is in charge of rest or relaxation – when we are at rest, we are always predominantly parasympathetic.' In this state, your ANS is balanced and your HRV is high – a rare metric where irregularity is a good thing.
'If we are under more stress, then the parasympathetic activity will be reduced,' says Altini. This is when the sympathetic nervous system starts to dominate proceedings, your heart beat becomes more regular and your HRV therefore drops. It’s not always a bad thing though.
'The sympathetic nervous system is the one that kicks in when we are exercising, so heart rate is increased.' He adds that millennia ago, danger to life – the fight or flight response – would have also made it kick in. But other stressors (psychological, lifestyle) can also cause the sympathetic to dominate, leaving less in the tank when you need it for exercise.
HRV isn’t a new-fangled metric, either. It has been a trusted tool of scientific literature for more than 50 years. It’s just that its application and accessibility have changed in recent times.
'We don't need to get people to the lab,' says Altini. 'Now you just measure at home when you're rested. By measuring every day, you can see how your own data changes in response to stress over time – so if you're sick or travelling, if you train hard, or if anything else impacts your stress level, then you can see it.'
Heart rate variability by age
Like a lot of performance metrics, time is against you when it comes to HRV. 'It typically reduces and this could be just a process of the autonomic nervous system degrading as we age,' explains Altini.
That said, there is a large overlap in the range of values that can be considered ‘normal’, so you could be 60 years old and have the same HRV as a 20-year-old.
What is good heart rate variability?
There is no such thing as a ‘good’ HRV for two reasons. Firstly, there is a genetic element to it, so your HRV is completely personal to you – what is ‘optimal’ for you might be a low score for someone else and vice versa.
Also, it’s not possible to gain any insight from just a one-off reading. Instead, you start to build a picture over time.
'We understand what is your normal by measuring for several weeks,' says Altini. On a day-to-day basis, if your HRV is within your normal range, it shows that you are more rested or recovered, while if it’s lower, it’s an indication that your nervous system is suppressed.
'Tools always show us the daily measurement first because that's what you just did, but at the same time, if we look at the bigger picture and it shows that HRV is increasing, that is typically a good trend,' he explains. 'Trending higher or staying stable typically means that there is a positive response to the stressors you're facing. In the context of training, if you're doing a very intense or high volume block and your HRV doesn’t drop, you are responding well.'
There is also the opposite of this, where your HRV starts to trend downwards. 'If it drops, then you should change something because the stressors – either training or lifestyle – are too much for you, and this will impact your training response.'
What are the benefits of using heart rate variability to guide your training?
Physical activity is a stressor that causes your sympathetic nervous system to dominate, but your HRV’s status before you’ve even laced up your trainers can determine whether your body is ready and recovered enough Some big factors that sink HRV acutely are.
'The timing of the stressors matters,' says Altini. 'If we have a training plan, it's not just the plan that matters, but it's also when you apply that stress. HRV allows us to do that in a smarter way because we can apply the stressor when we are ready to assimilate it and respond better.'
When your HRV is within your normal range, there’s a higher chance that you will reap the intended physiological benefits of that lung-busting session. If it’s below your baseline, you don’t have to avoid training completely, but you’ll be better off swerving an interval or tempo run for a lower-intensity workout, metric that brands claim can help transform your.
'If we go and do the hard sessions when our values are suppressed, it’s unlikely to lead to the same positive outcome because the body is just not in a state in which we will respond positively to that stimulus,' he adds.
Factors that affect heart rate variability
Your heart rate variability is affected by three key types of stressors – training, lifestyle, and biological. Each can have a positive and negative impact on your HRV, but can all combine in different ways to determine the status of your ANS.
'Suppressed values mean you should try to look at altering some of the changeable variables,' says Altini. 'Training is an easy one because we have more control over it.' In this situation, taking it easy on days when your levels are below normal might be enough to reverse the dip. But what if you’ve been skipping interval sessions and it’s made no difference?
'A beginners guide to heart rate variability sickness and alcohol intake.' He adds that if your readings are inconsistent, it might be an idea to limit certain detrimental behaviours and focus on the positive ones (sleeping, staying hydrated, eating well) to get a better understanding of how your HRV is responding to training. Lifestyle isn’t limited by what you consume either and can include harder-to-quantify (and change) psychological stressors – work and family.
Finally, your biology plays a key role in your HRV. As already highlighted, as you age, it will gradually trend downwards. But for a proportion of the population, there is a monthly cycle that can cause fluctuations.
'For people that have a regular menstrual cycle, there’s typically a suppression during the second phase and the other way around during the first phase. It’s important to know because if you see a suppression, it's just a normal variation that is triggered by the other changes you have in hormones during this cycle.'
How to improve your heart rate variability
Improving your heart rate variability is as simple as sticking to the factors that affect heart rate variability positively – training when your HRV is showing you’re ready and rested and dropping the intensity when you’re not, getting enough sleep, and eating a well-balanced diet.
Reducing factors that negatively affect your HRV can also have a transformative impact. One of the easiest and quickest ways to boost it is by Health & Injuries, especially when more long-term lifestyle stressors (work and family) can be harder to change.
Best heart rate variability monitors
Whoop 4.0
This wearable tracks your HRV, as well as your sleep, recovery, and daily effort to provide a holistic overview of your current health status. The accompanying app provides insights as well as advice on how ready you are to train.
and moving your hard miles to later in the week when your HRV is back to normal; whoop.com
HRV4Training app
This app-based approach sees you hold your finger over your phone’s camera to take measurements of your HRV. It will tell you each day whether you’re ready or not for a high-intensity session and can be linked with Strava to track the effect of training on your data.
£8.99 (one-off payment); hrv4training.com
Oura Ring Generation
Part of a new breed of finger-based wearables to hit the market, the latest Oura ring tracks your sleep, activity and ‘readiness’ (aka HRV) without the intrusiveness of a band. It too has an accompanying app, providing easy-to-understand graphs of your metrics and guidance on how to improve them.
$299 Best wireless headphones; ouraring.com
