Sophie Raworth on her new fascination with heart rate variability
My Garmin has turned me into an addict. I have become hooked on alcohol-free beer. It all began a few months ago when I was flicking through data on my new watch after a long weekend of late nights and wine. Something called HRV status had plummeted from green into red. I had no idea what HRV was but started to notice very quickly that every time I didn’t sleep well, trained too hard or had a few drinks, I would wake up the next morning and my HRV number would have halved overnight. What did it all mean? And was it important? I decided to find out.
HRV stands for heart rate variability – it’s the variance in time between each heartbeat, measured in milliseconds. If your heart rate is 60 beats a minute, for example, it’s not beating exactly on the second, every second. Sometimes it’s fractionally faster, sometimes slower. What controls it is your autonomic nervous system – the network of nerves in charge of unconscious processes like breathing and heart beats. It has two branches that compete with each. The sympathetic nervous system – known as the fight or flight response – tells the heart to speed up. The parasympathetic – the rest and digest – tells it to calm down. The HRV measurement is essentially an average number you’re left with after the two have battled it out overnight.
Dr Marco Altini is a scientist and an ultrarunner who specialises in HRV and its impact on training. ‘HRV is a marker of our response to physiological stress, when measured under certain conditions,’ he says. ‘If it’s measured at rest, first thing in the morning or during the night, HRV can provide us with a useful indication of our body’s stress response. If our HRV is normal after a high-intensity session, it doesn’t mean we didn’t experience stress. It means we have responded well to that stress because our training and fitness allowed our body to bounce back to normal by the time we measured HRV again during the night or the following morning.’ If, however, your HRV is suddenly low, it means your heart has been working harder than usual, with shorter gaps between each beat. Dr Altini says tracking HRV data can be valuable. ‘It helps us realise the impact of certain acute stressors like alcohol, travel, high-intensity training, heat or altitude, and then helps us make adjustments whenever possible so we can try to prevent chronic negative stress responses, like burnout and overtraining.’
The science has been around for a long time, but wearables mean more and more of us now have access to it. If, like me, you’d never heard of it before, you’ll now be wondering what a good HRV number is. The answer is, it depends on your age and sex. The number will fall as you get older but it tends to be higher in athletes and especially masters athletes, who can have HRV numbers similar to 25-year-olds. But it’s very individual to you and the best way to find out is by monitoring it for a few weeks to see what your baseline is.
Ultrarunner and coach Robbie Britton has been experimenting with HRV data over the last few months to see if it’s worthwhile. ‘HRV is useful and yes you can take it seriously,’ he tells me, ‘but it’s not infallible, it’s not perfect. Experiment with monitoring it alongside how you feel. See how work, diet, sleep, stress and training impact your HRV and you can find ways to help you improve your training and recovery.’
The ultrarunner, Sophie Power, who’s just become the fastest woman to run the length of Ireland, says HRV is really important to her, particularly given the high mileage she runs. It’s one of the first things she checks when she wakes up every morning. ‘I think as runners it’s sometimes difficult to listen to our body because we want to go out and push ourselves. We try to ignore all our niggles. We also ignore our nervous system. If you work with your HRV data for a while, it is quite a good way of holding yourself back when you really want to train hard, knowing that if you did train hard when your levels are low, you won’t get the fitness benefits from that session. My HRV levels tell me that I’m sick before I’m sick. Or that I’ve had a really rough night’s sleep. It is also a good way of keeping healthy habits. It tells my coach if I’ve been drinking the night before. If you have two glasses of wine, your HRV goes down.’
I can vouch for that. I have now cut right back the amount of wine I was drinking, often choosing alcohol-free beer instead. And I see the difference. My numbers had been in the mid-50s, not bad for my age, for quite some time. Interestingly though, they suddenly fell again recently after I was diagnosed with a fractured ankle and ordered into a boot and onto crutches. Sophie Power isn’t surprised when I tell her this. ‘Anytime I’m injured my body is in repair mode. The injury isn’t just physical stress – it’s mental stress, emotional stress and it’s interesting to see it in the numbers when those things happen. It’s just fascinating to see how your body operates.’
Elsey Davis is another top British ultra runner who has monitored her HRV data too. But she says her new coach prefers her to listen to her body rather than rely on the stats. ‘The problem with HRV,’ she says, ‘is that there’s very little research into what it really means within the realms of sport. I still keep half an eye on it out of interest and if it’s lower for more than a few days I try to figure out why that is, if it’s not something obvious like not enough food or sleep.’
Robbie Britton still keeps a close eye on his HRV levels. He says he has found it useful for gauging his post-race recovery after his last 100km race across Sweden. But like Elsey’s coach, he says it’s important not to get too hooked on the vast amounts of data from our watches and other wearables. ‘The numbers should be there to guide, to advise, but not to dictate how we behave or feel,’ he says. ‘I remember my wife asking me how I slept the night before and I actually thought, “Well, what did the watch say?” instead of just answering how I felt.’
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