Our guest for episode 10 is Marco Altini, a scientist, app developer and expert in using data from wearable devices to optimize health and performance. Many will recognize his name from the app HRV4Training, which integrates with TrainingPeaks. Marco’s background spans computer science, human movement and high-performance coaching. He’s also an avid runner, having qualified for the Boston Marathon and competed in European ultramarathons.
Our discussion digs into the details of HRV, an increasingly popular metric for endurance athletes. Marco breaks down what HRV actually measures, its history of use in scientific research, and how it serves as a marker of the body’s response to various stressors — from training to travel to simple daily life.
He also clears up some of the biggest misconceptions about HRV, like the idea that you can directly compare your HRV to someone else’s or that a single HRV reading can predict if you’re about to get sick or injured. Marco emphasizes the importance of context and tracking your individual trends over time to have a valid baseline to analyze your stress response.
Perhaps most importantly, we cover how HRV data is best used as one piece of the puzzle in understanding your body so that you can have productive training sessions.
Standout Quotes
Too Much Focus on the Score: “There is a bit of this idea that, you know, you have to increase it, and you have to do this and that, and you’ll get higher. And I think that can quickly get counterproductive because maybe you do something that is good and healthy for you, and it doesn’t change your HRV. I mean, it doesn’t mean anything. It doesn’t mean that it’s not good, what you’re doing. It doesn’t mean that it’s not good what you’re doing. So I think we should maybe think about it a bit differently.”
Understanding What HRV is Measuring: “When we look at HRV, it’s not stress that we are measuring, but if we measure it at the right time, after a few hours, we look at your response to stress. And that is key to understand, because sometimes people do maybe a hard session, and they look at the data the day after and they expect a suppression. Or they think they should see a suppression signaling more stress. But actually, if you responded well to that stimulus, then your HRV should be perfectly normal.
And indeed, in professional athletes that have, you know, a good training plan, know what they’re doing, applying the right stimulus at the right time, typically, the data should always be within their normal. It should not be suppressed. And it does not mean that they don’t train hard. Right? If you have a suppression, typically it’s just because something went wrong because your response was not good. Not that you haven’t experienced, you know, a more important or meaningful stressor.”
“If you don’t collect the data, then there’s no point doing this, right, with one data point per month.”
The importance of consistent health data collection
Awareness of the Health Data Lifespan: “If your normal [range] is just one month of data, then the system will start to think that being that [being] suppressed is normal for you. So you need to keep it a bit longer so that you’re anchored to some older data, but you don’t wanna take it too long. Like, three or six months would be way too long because then you’re basically attached to data that is meaningless today and is also linked to things that change and that are a bit outside of your control, for example, seasons.”
Sometimes Changes in the Data Are Meaningless: “We don’t only tend to compare between people, but we also look at our data, of course. And then if there is a change, we will always overinterpret that change. What I mean is that if today it’s a bit lower than yesterday, we will immediately think it’s lower, that it’s not good, and if it is a bit higher then we think I’d say it’s better. But the reality of things is that there is always variability in the data, and a lot of these changes are completely meaningless. So once you are within what we call the normal range, then there is always variability also there. But the only thing you can derive is that everything is normal.”
“So I think we should maybe think about [HRV] a bit differently. There’s huge differences between individuals. It does not determine in absolute terms your potential as not leader your performance. It is mostly useful, in my opinion, as a marker of your individual response to look at over time, to the days, weeks, months in relation only to your own frame of reference.”
Marco Altini on Athletes Comparing HRV Scores
The Individuality of HRV for Athletes: “So it’s important to understand that there are huge differences between individuals. It does not determine in absolute terms your potential as an athlete or your performance. It is mostly useful, in my opinion, as a marker of your individual stress response to look at over time of days, weeks, months, you know relation only to your own frame of reference, not to, you know, population level values. Even though there are some of these population-level differences like the data slightly decreasing with age and things like that.”
The Need to Admit There Are No Absolutes in the Data: “Sometimes, maybe you have a poor physiological response sometimes. [You might] find other times you have the opposite type. Maybe you feel a bit down, and the data shows that you’re fine. So those things do not necessarily align. Sometimes, there is something to learn there; sometimes, we just don’t have an explanation. I think it’s time that we say these things more clearly because people always expect that there is a reason for things [which] is not so simple. Physiology is complex, there are a million different reasons why things might change in a way that we don’t expect it.”
Marco Altini Online
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Marco holds a PhD cum laude in applied machine learning, a M.Sc. cum laude in computer science engineering, and a M.Sc. cum laude in human movement sciences and high-performance coaching. He has published more than 50 papers and patents at the intersection between physiology, health, technology and human performance. He is the co-founder of HRV4Training, advisor at Oura, guest lecturer at VU Amsterdam, and editor of the Wearables department of IEEE Pervasive Computing. He loves running.
