This is a guest article by Simon Wegerif, a speaker of the upcoming Biohacker Summit UK and founder of HRV Fit (ithlete).
Contrary to what you might expect, the human heart does not beat with a metronome-like regularity at rest, but in fact continually varies to optimize the functioning of your body. These small beat to beat variations are known as heart rate variability (or HRV for short), and can tell a lot about how stressed or relaxed you are. In particular, HRV can tell us about the activity in the vagus nerve, which is the autonomic nerve associated with rest, digestion, recovery, inflammation and immune system regulation.
Although HRV has been known about for centuries, and employed in critical medical monitoring, space exploration and elite athletics systems for many years, it was only with easy-to-use mobile apps and devices became practical for athletes, sportspeople and biohackers to gain easy access to this revealing biomarker.
Prof Stephen Porges description of HRV as an ‘index of stress, and vulnerability to stress’ (1) has at least two important implications:
- HRV decreases with the total stress load placed on your body. This includes:
- Physical stress e.g. from workouts and manual labour
- Chemical stress from poor nutrition or toxins
- Mental / emotional stress from work deadlines, relationships, etc.
- The higher a person’s average (or baseline) HRV, the less vulnerable they are likely to be to stress from these sources.
I recently summarised a research paper by Chicago College of Medicine who led a study into this area. They recruited nearly 350 healthy subjects ranging in age from 10 to 99 years, and tracked their HRV over a 24-hour period. They were interested in the relationships between higher HRV and a longer lifespan, and in particular suspected that preservation of good autonomic nervous system function might be important to preserve life in old age.
What they discovered was that HRV exhibited a rapid decline between the ages of 20 and 50. The rate of decrease then slowed, reaching a minimum in the 70s. After this, they found an increase in HRV for the very oldest subjects.
The published paper shows a scatter plot of the results, which although clearly showing a decline with age is not very easy to apply, so what we did is to re-digitise each individual data point and plot this on the chart below as mean and ± 2 Standard Deviations, (i.e. approx. 95% of the population at a given age will be between these limits).
The fact that HRV declines throughout life for the population as a whole suggests that preservation of autonomic function could be important to healthy survival into old age. It is especially interesting to see the higher values of parasympathetic HRV in the very oldest members of society. The authors offer a couple of different explanations as to why this might be:
- That only the people with high levels of HRV in their younger years survive longer than average or
- That lifestyle modifications (i.e. healthy living) help preserve autonomic functions into later life.
It’s hard to reproduce this study on a personal level as there are few devices available to consumers that can record and calculate HRV for an entire 24 hr period. The closest may be sleep monitors such as Emfit QS, which record heart rate and HRV data during sleep hours and Firstbeat, which does continuous monitoring throughout the day. Both are Finnish companies.
Alternatively, ithlete users can look at their blue baseline for guidance, since this is an average of multiple readings. Considering my own personal data as an example there are a few interesting points.
When I started using the first version of ithlete in 2009, my baseline was at around 62. Having recently left a stressful executive job, and doing measurements on athletic beta testers who had scores in the 80s, I knew there was plenty of scope for improvement. One of the first major changes was to spend more of my time training at MAF intensity (below first threshold), and within a few weeks, my baseline had risen to around 69. It stuck there for a while, until I was persuaded to try Yoga breathing relaxation exercises. This produced the biggest jump I have witnessed, boosting my score to around 77. Since then, I’ve had ups and downs but have managed to keep the baseline level and recently have seen it start to rise again in spite of advancing age that would be expected to see a fall of 2-3 points over this 5-year period. I have attributed the most recent rise to a big reduction in sugar and refined carbs in my diet.
Maybe presenting at the Biohacker Summit in London will alert me to the next potential improvement!
Simon Wegerif is a biomedical engineer and inventor who lives with his family in the New Forest in Hampshire, UK. His professional background is in signal processing, having been a pioneer of digital broadcasting at the BBC in London and Philips Electronics in the UK and Silicon Valley, where he managed a number of technology start up activities. Simon founded HRV Fit Ltd., the company behind leading heart rate variability smartphone app ithlete, in 2009 and has since been totally dedicated to the company. As the team has grown Simon has been able to focus his time of product development and programming. Recreationally, Simon has been a keen endurance athlete most of his adult life, firstly in rowing, then running, triathlon and nowadays a competitive cyclist.
- Pediatrics. 1992 Sep;90(3 Pt 2):498-504. Vagal tone: a physiologic marker of stress vulnerability. Porges SW1
- Usman Zulfiqar, MD, Donald A. Jurivich, DO, Weihua Gao, PhD, and Donald H. Singer, MD., 2010. Relation of High Heart Rate Variability to Healthy Longevity. American Journal of Cardiology 2010; 105:1181–1185