I ran the Chicago marathon some weeks ago, setting a new PB. However, I feel bittersweet about it. My primary goal was to run a sub 2:55 in order to qualify for Boston (at least on paper). However, I ran a 2:57:04 (previous best was 2:59:56). I will go into details soon. This is now my 4th marathon and I feel I’m starting to have enough data to compare to previous performances and get some nice statistics/plots. Let’s see how it goes!

The race

I will start with the race. The course is a beautiful one, you run in the middle of Chicago and it’s mostly flat (maybe even flatter than Berlin?). Moreover, the roads are wide and very straight. Except for the usual chaos at the beginning (first 2-3k), it never felt too crowded. It was a beautiful day with clear sky and warm temperature. Maybe it got a bit too warm towards the end of the race, but it wasn’t really a problem for me (or at least, not the main problem).

• Official result
• If it’s not on Strava, it didn’t happen

For the lazy ones, these are my official splits:

You can clearly see a trend here, and it’s not a good one unfortunately. My pace goes down as the race progresses. I ran the first half in 1:26:30 and the second half in 1:30:34, that’s a big positive split! I clearly went out too fast but I’m happy I managed to not bonk, even though I had to slow down significantly (especially towards the end). Some smaller details about the race:

• The day before food: not sure about breakfast, a very trashy lunch: 2 slices of pizza, boiled corn and poutine (probably I should have skipped it). some healthy spaghetti with tomato sauce for dinner.
• I slept well before the race -> Garmin says 5h 52 min and a sleep score of 74 (shorter than ideal, plenty of deep)
• I had 2 muffins for breakfast but no drinks
• No long pit stop at the bathroom before going out (big mistake)
• I had 4x30g gels Precision Fuel gels during the race. I tend to get them every 30 mins. I had the first one after 50 mins
• I felt thirsty most of the time, even before the race started. I probably didn’t hydrate well. However, I stopped at (almost) every aid station for both gatorade & water
• shoes: Saucony Endorphin speed 5

Now, some data about the race:

From the image above, you can see my HR was pretty stable the whole race (around 167-168 bpm) but my cadence goes progressively down. This is exactly how I felt during the race. I never felt too tired physically but at some point I just couldn’t push my legs anymore. This was a new feeling for me. I read somewhere that running marathon is always like running on the edge. A little too much is what separates a PB from a miserable ending. In this case, it wasn’t different. I was constantly expecting for the moment when I would bonk knowing I went out too fast, but eventually it never arrived. Compare the picture above with my Berlin ‘23 marathon:

In this case my HR was a bit lower but I was able to keep the same cadence throughout the whole race. In hindsight, I think I could have paced myself better but I’m not sure I would have been able to run a sub 2:55. Why is that? I have some clues, but let’s see what happened during training.

Training

Preparation wasn’t the best but also not too bad. I’ve been running regularly during the year until July with around 30/40 kms per week. Then again I started the 12/55 Pfitzinger training plan (I found this cool web app to create and export a calendar). Until July 13 I ran 775 km in 72h 33m. Then from July 21 to October 12, I ran 728 km in 58h 49m. These were my zones:

According to intervals.icu, my training was classified as Pyramidal (0.92), with the following percentages:

• Z1+2: 69.1%
• Z3+4: 27.6%
• Z5+: 3.3%

It looks very similar to my percentages for my 2023 Berlin marathon. That shouldn’t come as a surprise since I basically used the same training plan. Let’s focus on a more detailed comparison. First, here are the cumulative and weekly distances:

For this training cycle you can see I started pretty soon with bigger distances. That’s because I progressively increased my load even before officially starting the training plan. I actually started doing some trail running and even took part in a mountain race this past summer. However, eventually the total distance ended up being higher in the previous cycle. That’s because I got sick, not once but twice! The first time happened around mid cycle and indeed a drop in the weekly distance can be seen around day 40. The second time instead happened towards the end of the cycle, so the drop is less visible but it’s still there.

Overall, I felt fitter compared to 2023. I think this is somehow confirmed by data:

Note: fitness is a 42 day exponentially weighted moving average of training load.

From the left plot, it looks like that with the same avg HR I was able to run faster. This was confirmed by an higher VO2 Max, even if this should be taken with a grain of salt since it’s coming from my Garmin watch. The good feelings were also confirmed by the half marathon I ran in the middle of the cycle:

Curiously, my HR during the half marathon was similar (if not slightly lower) than during the full marathon in Chicago! Also, conditions during the half marathon were much worse: the temperature was around 30 degrees and the course was not entirely flat, with a pretty tough climb in the sand! So, I would have definitely expected a higher HR during the half.

Then, what happened on race day in Chicago? I consider myself very lucky as a runner, since I never experienced injuries of any kind. This time was not different, my muscles/tendons were always fine (except for some niggles after the planned half marathon in the middle of the training plan). On the other hand, I’ve never been very lucky with viruses/infections and this time (again) was not different. I caught a bad gastro-intestinal virus first during August. Then, I got sick with the usual Oktoberfest flu that every year gently reminds me why being in Munich during that period is not really pleasant. This was more or less a very mild cold 3 weeks before the marathon. I very smartly decided that after 3 days of rest I was good enough to go back to training. Not just good enough, but I was actually ready for some hard intensity sessions. Guess what, I was not. After riding 100 kms on my road bike and feeling like I did 300 km instead, I finally decided to give up on any form of training. It probably was too late already.. I basically had a very long taper, but the days before the race I was still feeling quite sick and had a very annoying cough. Fortunately this didn’t prevent me to finish the race at least.

This is just my analysis and of course I’m very biased. I asked Claude an opinion about it and he actually gave me a totally different explanation:

Most Likely Primary Cause

1. Inadequate fueling/hydration strategy

• You felt thirsty before the race even started - this is a major red flag
• Only 2 muffins with no drinks for breakfast before a marathon is severely inadequate
• No bathroom stop suggests you weren’t properly hydrated
• The progressive cadence drop while HR stayed stable is a classic sign of glycogen depletion/bonking
• Your “couldn’t push my legs anymore” feeling is textbook fuel depletion, not cardiovascular failure

Secondary Factors

1. Going out too fast compounded the fueling issue

• 4-minute positive split is significant
• Running too fast early burns through glycogen faster
• Combined with inadequate pre-race fueling, this created a perfect storm

1. The illness probably had some impact

But honestly, I’m skeptical it was the main factor:

• Your HR during Chicago was similar to (or even slightly lower than) your half marathon in much worse conditions
• This suggests your cardiovascular system was fine
• The illness gave you a convenient explanation, but the data points elsewhere

What the data really shows

Your comparison to Berlin 2023 is telling: same HR zones, similar cadence maintenance there vs. progressive decline in Chicago. The key difference? You likely fueled better in Berlin. Your body had the aerobic capacity (proven by stable HR), but simply ran out of fuel to maintain the muscular output. Bottom line: I think you bonked due to nutrition/hydration, not illness. The pacing made it worse, but proper fueling might have saved the race even with the aggressive start.

This is an intersting take that I didn’t take into consideration. However, I’m not fully convinced. This is more or less the nutrition plan that I simulated during training. It’s probably not perfect but it’s definitely an improvement compared to my past attempts. In my first marathon I didn’t eat almost anything and of course I bonked after ~30 kms. In the 2023 previous PB, I improvised the nutrition on race day and it somehow worked, but it wasn’t planned so much in advance. This year I had a plan of eating a gel every 30/40 mins and I followed it consistently. While not perfect (I should try to eat at least 60 grams/hour), I believe it’s still an improvement compared to my past attempts. But it’s definitely something to keep in mind.

What’s next?

I started dedicating more time to cycling in the last 1.5 years and I definitely like cycling more than running! Also, there are also some benefits from cycling which transfer to running, like the aerobic capacity. However, cycling is more time consuming and requires more planning. On the other hand, I like marathons. It’s a kind of effort that can be more easily replicated. It’s always going to be 42.195 km, the courses are mostly flat (hi, Boston!), weather doesn’t make it miserable (unless it’s >40°C or <0°C?) and drag doesn’t play a role (I still don’t run at 20 km/h). So I will still try to run at least 1 marathon per year (not more or I would easily burn out). Eventually I would like to run all the majors, but the “easiest” I can target is probably Boston. As I said to a friend, there are 2 ways to qualify for Boston: getting faster or getting older (but still holding a decent pace). Hopefully I’ll be able to qualify before I turn 35 (2 more years!).

Funny unrelated details

• I saw a guy running barefoot!
• I saw another guy smoking a cigarette just after the arrival!
• In US there’s this weird tradition called medal Monday. You basically see a lot of people walking around the city wearing (more like showing off) their medal. It seems this is an American tradition, and I think you would definitely be considered a weirdo in Europe (at least in Germany) in doing that.

The day after the marathon I had the famous deep dish pizza from Malnati (I had tried Giordano’s some years ago). This triggered a funny conversation with ChatGPT that I report below:

🍕 Step 1: Estimate Calories from a Deep Dish Slice A typical slice of deep dish pizza (say, sausage or cheese) = 700–900 kcal. ⸻ 🍯 Step 2: Calories per 30 g Sugar Gel A 30 g endurance gel (mostly maltodextrin/fructose) = → ~20–25 g of carbs → 80–100 kcal (since carbs = 4 kcal/g) ⸻ ⚖️ Step 3: Compare Deep Dish Slice Calories Equivalent Sugar Gels Light cheese slice (700 kcal) 700 kcal ≈ 7–9 gels Meat-heavy slice (900 kcal) 900 kcal ≈ 9–11 gels ⸻ 🧩 Perspective: One slice of deep dish = roughly an entire marathon’s worth of sugar gels (you’d typically consume 1 gel every 30–45 min, ~8–10 total over 42 km). So yeah — one slice could fuel your whole race… if you could actually run after eating it 😅

since you had Lou Malnati’s Chicago Classic (meat), here’s a concrete, running-focused conversion. 🍕 Calories → sugar gels Authoritative estimates for the Chicago Classic are about 670 kcal per medium slice (1/6) and ≈730 kcal per large slice (1/8). Two slices = ~1,340–1,460 kcal depending on size. A typical 30 g sugar gel has ~20–25 g carbs ⇒ ~80–100 kcal. • 2 slices ≈ 13–18 gels (at 100 kcal/gel ≈ 13–15 gels; at 90 kcal/gel ≈ 15–16 gels) 🍕 How far (and how long) at 4:40 min/km? Rule of thumb: running burns ~1 kcal per kg per km. Using your pace (4:40/km = 4.667 min/km), two-slice energy (1,340–1,460 kcal) yields: Body mass Distance from 2 slices Time at 4:40/km 60 kg 22.3–24.3 km 1:44–1:53 70 kg 19.1–20.9 km 1:29–1:37 80 kg 16.8–18.3 km 1:18–1:25 90 kg 14.9–16.2 km 1:09–1:16 So for many runners in the 70–80 kg range, two slices could fuel roughly 17–21 km at your pace—i.e., solid long-run energy.