[CoachCorner] Bruna’s Trail Marathon Debut at Istria by UTMB
A tale of common sense, communication, trust in the process (also called patience), and, of course, a bit of luck.
About a year ago, I started working with Bruna Maia. She had been coming from two stress fractures in the past three years, and had run about 20 km for her longest run in the previous year and a half.
Here is where we were in June 2025, alternating a few minutes of running and walking, with cross-training:
while here is Bruna a few weeks ago, finishing 6th at her first trail marathon at Istria by UTMB (42 km +1000 m):
This post is about how we went from A to B, which was mostly about common sense, communication, trust in the process (also called patience), and, of course, a bit of luck.
But let’s start from the beginning.
I met Bruna when I was a guest on the Human Endurance podcast that she is hosting, and while the conversation was mostly on HRV and somewhat data driven, I think we clicked because of the nuance around it, and how eventually we think very similarly about training and how to develop as athletes, getting in tune with perceived effort, building gradually, thinking long term, and sometimes using data to aid the process (Bruna is a running coach as well).
As mentioned above, we started working together after her second stress fracture, rebuilding with a few walks in May 2025, and eventually doing our first continuous run on July 14th, 2025, which was our first 30 minutes of uninterrupted running in over 2 months. By August, we had added a few strides. The number one goal was always not to get injured, hence there was great focus on fueling (something Bruna has talked about in her blog) and on watching any niggles, but also in terms of training prescription, we never tried to push much running frequency or volume, given the past history of stress fractures.
In situations like these, it is key to have a plan, but it is even more important to be willing to adjust that plan should anything prompt more caution or simply should the circumstances around us change (because life happens, which could mean more work stress, travel, etc.). Bruna is also the founder of augo, (where I’m an advisor), a tool we’ve been using for feedback, communication, and that helped greatly in staying aligned and making all the necessary adjustments while working together remotely. Thanks to Augo, it was easier to stay on top of our nutrition and of any running-related niggles or difficulties that prompted adjustments to make sure we could get to race day as healthy as possible.
In the next section, we’ll look at how we planned the comeback.
High-Level Planning
Building from zero to Bruna’s first trail marathon, I mainly had two phases in mind, broken down as follows:
Generic Fitness:
Cross-training: we used cycling a lot as a low-risk tool to develop aerobic capacity. We also used strength training to put some more mechanical load, possibly impacting positively both injury risk and durability (for trails).
Develop running frequency: coming from an injury, we wanted to be able to run 3-4 times per week for a while, before adding more stress on the body. This was our first running goal.
Add running intensity: once we had developed frequency, we could start layering on top various intensities, to further develop our physiology (aerobic capacity, fatigue resistance) as well as our structural capacity.
Consolidate running frequency and intensity: we were going through big changes, and we could not simply keep adding without risking too much. At a certain point, we needed to decide we had reached a level we were happy with and consolidate it so that the body could make this new level its normal. This will be our base in the future, when we’ll get even better.
(Trail Marathon) Support + Specificity:
Develop durability: in the Generic Fitness phase, we kept long runs relatively short (~20km). Then, given our goal (trail marathon), we needed to work on our ability to sustain efforts twice as long, at least.
Develop trail skills: Bruna had mostly raced roads in the past, hence we needed to work on specific trail skills (climbing, hiking/running, descending quickly, etc.).
Nutrition: another key aspect for any long race or ultramarathon, as we are staying out for many hours and need to fuel the effort properly, while also making sure our gastrointestinal system can handle the type and amount of nutrition we are consuming.
Consolidate all of the above: as in the Generic Fitness phase, Specificity also adds many new stressors, especially on the mechanical side of things (longer runs, vertical gain, etc.) - hence, we cannot keep adding until race day, but need to develop our skills up to a point, and then consolidate.
Training prescription was always done using perceived effort, which I have discussed in more detail here and here. Obviously, we use all data available, pay attention to how our body responds in terms of internal load (e.g., our physiology), keep track of progress in key sessions in terms of external load (e.g., pace for track workouts), and can use both internal and external load as cues, caps or targets for specific sessions, but overall, we mainly aim at mastering our perception of effort at different intensities and for different durations, as we develop at athletes.
Generic Fitness: details
Quite importantly, there was no timeline attached to building Generic Fitness. We went on for as long as it was needed to reach a capacity that we thought would allow us to move forward without risking breaking down.
This is not an easy task, as we always have some event coming up, and at times, we need to simply recognize that we need a little more time, and patiently keep doing the work, consistently, until we have built that basic, generic fitness capacity required to race successfully. For example, Bruna was initially supposed to run the Chicago marathon in October, but having just done only a few strides and 20-30 km / week of running up to August, we talked it through and decided it was too risky to push a marathon block in September. This seems an obvious choice after the fact, but it’s not an easy one to make.
Looking in a bit more detail at the various aspects discussed above, we can first see that cross-training was a key aspect that allowed us to build and maintain fitness when running was either not possible or simply limited:
From the graph above, we can also see that the volume of cycling reduces over time, as we are able to run more. Below is our running volume, which we kept increasing, but only up to a point, as we noticed we could not go beyond 4 runs / week without setbacks, for now. There’s no golden rule for this; sometimes we had to try things (e.g., a slightly denser block), and see what would happen:
When looking at all workouts, we can see how weekly load was rather even across the year, even if we gradually reduced cycling and increased running as our capacity improved.
We found our sweetspot at 4 runs + 2 rides per week, 1 day off, 1 strength session, typically with one hard workout and one longer run, as part of our 4 weekly sessions:
In terms of intensity, we were in a phase (rebuilding fitness) where I think variability in the stimulus was more important than the specifics of any single session. The priority was not optimization, as it might be when preparing for a road marathon, but rather reintroducing and developing capacities that had not been stressed for a long time. This ranged from aerobic power to fatigue resistance, and eventually durability at race pace.
As a result, we touched on multiple systems and intensities, alternating different types of workouts across weeks and months, without dedicating extended blocks to a single stimulus. The goal was broad development rather than maximizing any one aspect of our physiology.
We ran short intervals, longer intervals, tempo blocks, strides, all with a specific purpose and logical progression of course, but without stressing any single aspect in particular.
By the end of the year, training was rather stable in terms of frequency and intensity, and we found a good balance and consistency, as well as improved performance, and as such, it was time to move to the next phase, picking a race and getting specific for trail running.
(Trail Marathon) Support + Specificity: details
I typically split more specific work into a Support block where we start e.g. doing trail runs, getting used to different terrain, vertical gain, and so on, but maintain ‘standard’ hard workouts, and an actual Specific block where workouts are also moved to race-terrain, and often get combined with long runs, so that we really stress durability and assess race capacity (e.g. long runs with tempo blocks or hard climbs/quick descents, etc.).
Depending on the athlete, this block might be very long or very short. For example, I discussed in the past how durability is a big limiter for me, and as such, how I’ve dedicated half a year recently to getting better at the longer distance from a muscular point of view (it worked). For Bruna, durability is a strength, and as such, we could limit our specific work to 2 blocks (4+4 weeks):
In terms of vertical gain, living in Zurich, we had some exposure throughout the year, even in less specific blocks, but eventually pushed it quite a bit in the past 2 blocks (again 4+4 weeks):
During these last 2 specific blocks, we kept running 4 times per week but often added a second long run on trails mid-week(about 90 minutes). Here are some of our key specific sessions:
Long runs on trails: 3h, 3h 30’, 4h, over three weeks (as intensity, RPE 2-3, or 10-15 bpm below the first threshold, hence quite a bit easier than race pace).
Hard workouts on trails or Long runs with race intensity (or slightly harder) blocks, e.g., 3 x 10’ @ threshold uphill, or 2 x 45’ moderate on trails. Once we had developed the capacity to run long and to run hard, we combined them.
To limit risks when adding very long runs or long runs with intensity, we often dropped intensity from the rest of the week, and typically added an indoor bike workout as the only high-intensity stimulus. In this final phase, we weren’t chasing fitness as much as we were trying to get ready for the specific demands of the event, learning to feel comfortable at race intensity, sorting out nutrition, shoes, and so on.
It’s always a balancing act.
Finally, it wasn’t all smooth sailing of course: we had a few more niggles than we’d liked (e.g. had to switch back to flat running during the specific block as we were having some issues when running downhill), and we had a few trips in which there was nothing but a treadmill to use for training, but we stayed focused on the long term goal, which was really not about doing ‘the perfect week’ or ‘the perfect workout’, but mostly about keeping doing the work consistently, day after day, maintaining good frequency, and adding layers of specificity as we got closer to the race.
The Race
For the race itself, we discussed strategy in terms of pacing/managing intensity using perceived effort as well as a heart rate cap for the first climbs (see also here), which was executed perfectly:
and which led to a fun race, overtaking the ones that probably weren’t as wise at the start, so to speak:
There is, of course, more to it, but I will leave you to Bruna’s blog for all the details about her race, which she’s covered brilliantly here.
Wrap up
It’s been a good year, one made of small steps toward a bigger goal, where common sense, patience, and close communication played the biggest role, overshadowing the things I often talk about here (a lot of talking, not much data!).
Of course, it’s easy to praise ourselves when things go well. We shouldn’t forget that, despite common sense (building gradually, keeping running frequency low, using cross-training a lot, etc.), patience (canceling races and taking more time to rebuild), and well-thought-out nutrition (pre, during, and post-workout) and training (from long-term periodization to weekly details), randomness always plays a role. We were certainly lucky that everything came together and that no small issue turned into something more serious over the past year.
We’ll see what the future holds, but for now, congratulations Bruna, and thank you for your trust.
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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, advisor at Oura, guest lecturer at VU Amsterdam, and editor for IEEE Pervasive Computing Magazine. He loves running.
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Thanks for the tip about augo. I’ve started testing it a few days ago and so far it’s brilliant from a coaching perspective
I’m so grateful to have you as my coach! Best decision 1,5 years ago. It’s just the beginning ❤️🔥