Recent articles and updates [May 2025]
Heart rate variability (HRV), endurance coaching, training talk, wearables, entrepreneurship, and some ramblings.
Hi there 👋
I hope all is well.
Here’s a new recap of articles, research, and updates from the past month. I hope you’ll find the articles useful and I would like to take the opportunity to thank you for your support.
Please feel free to comment below or in the articles should you have any questions, and I will follow up soon.
Take care!
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Endurance Coaching for Runners
If you are interested in working with me, please learn more here, and join the waiting list by filling in the athlete intake form, here.
Heart rate variability (HRV) 🫀
Normalized HRV
In the past few months, I’ve talked a few times about Normalized HRV, which you can now find in HRV4Training Pro (login here). A recent paper by Bulte et al., looked at this parameter in relation to training load in state and international-level swimmers, concluding that it “may provide a more comprehensive evaluation of an athlete’s physiological status compared with a sole parasympathetic modulation or tone marker“ - given their results in which Normalized HRV was the only parameter that correlated with training overload (while heart rate or HRV didn’t).
Learn more about Normalized HRV, here.
CoachCorner ⏱️
Should We Test?
I received this question from one of the athletes I coach. They were wondering whether we’d be including any specific tests, like a lactate threshold test, VO₂max assessment, or a critical power test, in the current training block, as we recently started working together. It's a great question, and it taps into something many athletes wonder about: do we need lab tests or structured assessments to identify limiters and guide training? Or can we get the insights we need simply by training and analyzing workouts? In this blog, I answer these questions and provide an overview of what I consider useful and not-so-useful physiological tests for endurance athletes.
Nutrition 🥑
Nutrition, Endurance Performance, and Cardiovascular Health
Over the past few months, I’ve made significant dietary changes and periodized my nutrition to improve (ultra)running performance. When I went into this experiment, I also had a goal of lowering my (LDL) cholesterol level, as my family has a history of high cholesterol (and associated issues), and mine was elevated. However, in March, my lab data came back with a large increase in both LDL and HDL, which I have to say, was a surprise to me. With a few changes, eventually, I could reduce dramatically both LDL and ApoB (which are considered key markers for atherosclerosis risk), which are now lower than before, when I was on a high-carb diet.
I wanted to report this because despite the confounding effect of losing weight, and some uncertainties about my tests in March, I think it is rather easy to eat lots of saturated fat or maybe inadvertently reduce fiber intake when on a low-carb diet (or a periodized diet with many low-carb days in a week), and that can have an impact on cardiovascular health. On the other hand, it is also clear that we can eat a healthy, periodized diet, and reach an optimal in terms of blood biomarkers (and performance!).
I’ve added a section in my Periodized Nutrition Blog to discuss these aspects and the dietary changes I have made. Please find it there if interested.
Podcasts and Interviews🎙️
Beyond Race Day: Marco Altini on Smarter Fueling
A few weeks ago, I had the pleasure of chatting with Mikki about my recent periodized nutrition experiment. From the show notes:
“Mikki speaks to Marco Altini—data scientist, athlete, and founder of HRV4Training—about his personal and professional exploration into periodised nutrition. Known for his evidence-based insights into heart rate variability and training readiness, Marco has recently turned the lens inward, experimenting with how varying his fuelling strategies around training intensity and adaptation goals can impact performance and recovery.
In this conversation, we dive into what led Marco to shift from a rigid, data-driven approach to one that embraces flexibility, intuition, and physiological feedback. We talk about the science behind carb periodisation, the mindset shifts required to break free from ‘high carb by default,’ and how this approach might offer not just better results—but a more sustainable relationship with training. Whether you’re a high-performing athlete or a time-poor weekend warrior, Marco shares insights that might just change the way you think about fuelling.”
The Hidden Flaws of HRV Tracking
I had a chat with Jonne Tiili about HRV, when it’s best to measure it, and what are some of the most important aspects when it comes to interpreting the data. Jonne put together a nice video interviewing other experts as well, which you can find below. I hope you’ll find some useful pointers in there.
Training Talk 🏃🏻♂️
100 km del Passatore, DNF (2025)
If you’ve been here for a while, you know I’m all about the process: training, testing, learning, adapting, and trying to get better at the sport I love. This means sharing the journey when things don’t go well, too. It’s part of the process after all. Here are a few thoughts about these past weeks before the 100 km del Passatore - where I had to DNF. You’ll find my training, racing, and learnings. I hope there is something useful for you in there as well.
That’s a wrap for this month. Thank you for reading!
Recent Updates:
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 is a certified ultrarunning coach.
Marco has published more than 50 papers and patents at the intersection between physiology, health, technology, and human performance.
He is co-founder of HRV4Training, Endurance Coach at Destination Unknown Endurance Coaching, advisor at Oura, guest lecturer at VU Amsterdam, and editor for IEEE Pervasive Computing Magazine. He loves running.
Social:
Ciao Marco, I have the same concerns with my cholesterol, I am really super impressed with the changes you get with more attention and fibers. I really like the attention to detail when you write that on low carb days getting the fibers is really difficult.
I am in no way a lipidologist but showing such a trend with a change in diet might be a clue that you are on the high absorbing side of people. I know that testing some sterols might help understanding this but again I have no expertise. (Also ezetimibe might be a strong tool if you are on the high absorbing side).
I am disappointed for you for the 100k after such progress...
Also I am back from a trail in the Dolomites and I had a lot of time to think about nutrition during the "race" since I was very slow, I have to shoot you a DM for something personal...
Very interesting use of normalized HRV in the case of an energy deficit 👌🏻