Recent articles and updates [October 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!
Heart rate variability (HRV) 🫀
The Heart–Brain Connection and What It Means for Heart Rate Variability (HRV)
We often say that HRV reflects vagal tone, but that is not entirely correct. HRV arises from the interaction of several systems: baroreflex function, parasympathetic modulation, hormonal and neurochemical regulation, and mechanical influences on the heart and blood vessels. HRV cannot be equated directly with vagal tone and can easily decouple from it, for example when measured continuously.
In my latest, The Heart–Brain Connection and What It Means for Heart Rate Variability (HRV), I look at a few recent scientific articles exploring heart rate modulation via brain stimulation and oxytocin, and how this plays a role in our understanding of HRV. Learn more, here.
The Latest on HRV-Guided Training
Last week, I was reading Carla Alfonso’s study, “Individual training prescribed by heart rate variability, heart rate and well-being scores in experienced cyclists“ (which you can find here). I met Carla a few years ago, and some of you might have even participated in her remote study, as we advertised in a past HRV4Training newsletter.
The study is an important milestone because it experimentally tested the kind of HRV-guided decision framework that I’ve been writing about for years, combining deviations from your normal range and daily subjective assessments for additional context to adjust training intensity dynamically (which is exactly what the app HRV4Training does).
On top of that, Carla also looked at adding resting heart rate to the picture, something I covered more this year when discussing normalized HRV - with promising results. Learn more, here.
TrainingTalk 🏃🏻♂️
I was sent this article the other day, showing how even at race intensity, and fueling with plenty of carbohydrates (and while being on a high-carb diet), prolonged exercise (> 6 hours) eventually leads the body to shift towards using fats as the main fuel source.
So interesting that I decided to do a little science experiment and replicate it. See how it went, here.
Here are some more training-related thoughts and experiments from the past month:
Packing more intensity in a short timeframe, here.
Maximal lactate steady state, here.
Testing running economy, here.
CoachCorner ⏱️
Was It the Type of Training, or Was It the Circumstances?
We often fixate on the workout. Was it 4x4 at VO2max pace, or a double threshold session, or another magic workout that led to progress? “We” love to dive into sessions as if their exact configuration is the key to performance.
But what if the real difference lies not in what the session was, but in when it was executed? Learn more, here.
Metabolic Testing: VO2max, Running Economy, Substrate Utilization, and Ventilatory Thresholds
As part of the work I do with the athletes I coach, I’ve started putting together a few protocols to look at aspects of our physiology that can be indicative of progress (or lack thereof) in our journey to become better long-distance endurance athletes.
In this blog, I look at VO2max, Running Economy, Substrate Utilization, and Ventilatory Thresholds.
Building 🛠️
Ambassador Program 2026
Our ambassador program for HRV4Training is open again.
Please see how to apply here, and thank you for your support!
Interviews and Podcasts 🎙️
La scorsa settimana ho avuto il piacere di fare una chiacchierata sulla frequenza della variabilità cardiaca con Nicolas Cicognani e Simone Cellini, la trovate qui.
Grazie mille a Nicolas e Simone per l’invito, e spero che la conversazione vi sarà utile.
Recent Updates:
Personal Coaching for Runners
If you are interested in working with me, please learn more here, and fill in the athlete intake form, here.
How to Show Your Support
No paywalls here. All my content is and will remain free.
As a HRV4Training user, the best way to help is to sign up for HRV4Training Pro.
Thank you for supporting my work.
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, advisor at Oura, guest lecturer at VU Amsterdam, and editor for IEEE Pervasive Computing Magazine. He loves running.
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