Recent articles and updates [July 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) 🫀
A Brief History of Heart Rate Variability-Guided Training
I’ve recently shown a simple case study for HRV-guided training, which you can see here.
In this blog, I cover the origins, research, and what would be my recommendations for people interested in using this approach to better balance training and other stressors.
HRV-Guided Training: When To Hold Back and When To PUSH
While discussing HRV-guided training with Dan Plews, he brought up some interesting papers showing a strong link between baseline HRV and training adaptations, highlighting how individuals approaching a period of training overload with a higher baseline HRV, would show larger improvements with respect to individuals approaching an overload period with a lower HRV.
This is a bit different from the HRV-guided training studies I discussed above, where data is normally used to decide when to hold back more than to push harder. Check out this blog to learn more.
More Evidence in Support of Morning Protocols
I recently came across a new paper by Thibaud Pirlot, Gregoire Millet, and colleagues, a team with a long track record of excellent research on autonomic nervous system responses to physiological stressors. While most HRV studies today rely on wearable data (despite known limitations), this group continues to use controlled morning orthostatic protocols, which remain much more informative.
Their latest work focuses on altitude acclimatization. Once again, they show that HRV at rest while lying down fails to detect meaningful changes, but after a simple orthostatic challenge, clear autonomic suppression is observed, highlighting the value of proper protocols over passive data collection. Learn more, here.
Another study was just published by Koulla Parpa and co-authors (full text here), looking at morning HRV measurements taken with the HRV4Training app in relation to COVID-19 positive tests in a cohort of elite female soccer players. The data shows large suppressions in HRV already 2 days before a positive test, as well as a re-normalization within a few days.
No wearables, no continuous monitoring, no distractions. Just a simple and effective protocol, 1 minute each morning.
Publications 📝
In the past few years, there has been a strong tendency and shift towards relying on (unreliable) estimates - often provided by apps or wearable sensors - as opposed to actually measuring the parameters of interest (something I’ve discussed in depth here).
As more apps and wearable devices are out there, researchers themselves often fall into the trap of believing that the estimates can replace measurements, for the sake of convenient data collection. This frequently happens when using apps or wearables that estimate menstrual cycle phases. Learn more in our latest paper, here.
CoachCorner ⏱️
In a previous blog (here), I covered a few ways in which we can use workout data to track progress and estimate performance (e.g., critical speed or race times).
Recently, I’ve been looking at the low-intensity side of things, putting together a script to track how internal and external load evolve over time during easy training sessions, for the athletes I personally coach. This is what we could call aerobic efficiency, or the ability to run quicker at a lower heart rate.
Below is the data for a runner I’ve been working with since March, showing great progress in the past few months. A simple but effective tool (which you can also find in HRV4Training Pro, as covered here)
When putting together these aspects, i.e. how an athlete is doing in terms of their ability to sustain different intensities, we can start looking at individual limiters, and then think about how to address them in the future.
More on this in future blogs. Love coaching!
That’s a wrap for this month. Thank you for reading and see you next month.
Recent Updates:
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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 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.
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