What Effect Did Running A Marathon Have On My Body?

I knew I was in trouble when I found myself crying around mile 10. 

I was about 90 minutes into my first marathon and I honestly had no idea how, or more realistically, if I was going to finish. 

“This,” I thought, “sucks.”

What’s this all about?

A few days ago my brother Jonathan and I ran the Yorkshire Marathon. 

I wanted to use this week’s email to dig into the data that I found interesting about how the training and build-up affected my body, and also share my memory of the run alongside the insights.

Mile 1: 8:50 at 165 bpm (5:29/km)

Mile 1 was a blur. I remember running through York City centre and weaving in and out of the crowd of runners around me, trying to keep my brother in my sights. It was too early and the nerves were still too high to gauge how my body was feeling. But honestly, I was still recovering from the stress of the minutes leading up to the run…

The race was set to start at 9:30 am, and I was standing in line for the portaloo until 9:25. But as soon as I used it, I noticed there was no toilet paper and the flush on the portaloo was pretty weak and didn’t exactly clean things up. I couldn’t decide whether it would be worse to delay the other runners waiting outside or leave the portaloo a mess for them.

In the end, I landed somewhere in between and after a minute of disgustingly desperate attempts to get things clean, I got out and tried to put as much distance between me and the portaloo as possible. 

Most of this data is taken from Apple Health, so it might not be super accurate. My main hope is that it’s at least consistently inaccurate so any improvements should be more or less true. 

Year to date, I’ve run 442 miles (711 km), at an average pace of 8:54/mile (5:32/km) and an average heart rate of 156 bpm. 

Mile 2: 8:45 at 171bpm (5:26/km)

Mile 2 was still early enough that I hadn’t settled into the run, but I was starting to get signs that things weren’t quite right. My heart rate had already shot up into the 170s, which usually only happens when I’m running at my fastest, and my legs were feeling heavy. 

After I got out of the portaloo disaster, my brother and I joined the crowd in the queue for the start line. But as I remember it, within a few seconds of standing there, we noticed we were in the group of people trying to finish it in 6/7 hours. If we started here, we’d have to overtake and weave our way through a bunch of people during the first few miles.

Jonathan, who’s a pretty tall guy, simply stepped over the fence boxing in the queue so we could find the right group. I tried to step over, got caught straddling it, and somehow fell over the fence, scraping my knee on the way down and taking a nasty blow to the nether regions. Not the start I imagined. 

From January to March, my average resting heart rate was 61 bpm. 

Mile 3: 8:49 at 172bpm (5:29/km)

Around mile 3 I could tell Jonathan was ready to speed up, so I dropped back and let him loose. We’d just spent the first half hour trying to work our way out of the group we started with. Despite moving up, we still started somewhere around the 5-hour pacers and were trying to make up ground. My friend Jacob was running around the four-hour pacers and I wanted to catch him but knew that probably wouldn’t happen unless I ran at a faster pace than would be wise.

Still, starting in a slower group than your estimated finish is a pretty fun way to make yourself feel like a boss as you overtake everyone in front of you. (But don’t worry, plenty of people probably passed me back by the end so they had the last laugh…)

In September, my average resting heart rate was 52, about a 15% reduction. (A lower resting heart rate typically indicates better heart health and cardiovascular fitness.)

Mile 4: 8:57 at 170bpm (5:34/km)

Mile 4 is when I remember the first real doubts. For the last couple months, I’d been getting knee pain if I ran too far, and I was paranoid that it would get too painful to run on, which had happened before.

I wasn’t feeling intense pain yet but my legs felt off and I was worried it was going to get worse. It was really just a waiting game to see what would happen. But every mile I passed from this point felt like a big victory. 

My walking heart rate hasn’t really changed—87 to 88. 

Mile 5: 8:57 at 170bpm (5:34/km)

By mile 5 we were well out of the city and into the quiet of the countryside. All anyone watching would hear was the steady shuffle of feet on a wet country road. 

My Apple Health HRV (a measure of the variation between heartbeats, higher is better) has improved by about 10% from January to September but nothing too crazy. 

Mile 6: 8:59 at 173bpm (5:35/km)

I don’t recall exactly when, but it might have been somewhere around this point that I looked down at my watch and saw that my heart rate was 183bpm. As we learned earlier my average run is 8:54 at 156bpm. So I was a bit alarmed by this…

My Vo2 max (a measure of how much oxygen my body can utilise during exercise) started at 45.8, peaked at 55.4 in June and is sitting around 53.1 now. 

Mile 7: 9:11 at 172bpm (5:42/km)

At mile 7 I slowed down a little. Before the run, I’d made a playlist with chill songs for the first 2 hours and my ‘hard running’ songs for the second 2 hours. On mile 7 I was probably listening to ‘If I Had A Heart’ by Fever Ray, the opening song for the Vikings TV show. Felt pretty fitting as we were running through a former Viking city.

My ‘cardio recovery’ (a measure of how quickly your heart rate could drop after you reach your peak heart rate during exercise) was 46 when first recorded and is now 52. 

Mile 8: 8:58 at 175bpm (5:34/km)

I guess my previous split scared me a little so I sped back up here. This marked about a third of the way through the run.

Oh, and between January and now I’ve gained around 14 pounds of weight (intentionally.) Probably would have gained more if it weren’t for all the running. 

Mile 9: 8:58 at 176bpm (5:34/km)

Miles 8-18 are honestly a bit of a blur. Just one foot after another for hours. 

Yesterday I went back and in a spreadsheet scored every one of my training runs based on how strong I felt during that run. If I couldn't remember I just looked at what heart rate I was posting for the pace I was running. (i.e. running 8:40/mile at 149bpm would be strong, running 9:30/mile at 170 would be weak, and running 9:10/mile at 152 would be ok).

I gave each run a score—1 to indicate I felt weak that day, 3 if I was ok that day, and 5 if I was strong that day. 

I then took that set of data and calculated the correlation between those scores and a few other factors I’ve been tracking all year—like my sleep schedule, energy level, and recovery scores. 

Obviously, all these insights are unique to me and might not apply to anyone else. 

Mile 10: 8:47 at 177bpm (5:28/km)

As mentioned during the intro, around here is when I remember getting emotional. The run was getting so painful and I was less than halfway around. I saw someone holding a sign that said ‘you can do hard things’ and I won’t lie, it got to me. It was amazing to have so many people out and supporting us on the course. Definitely makes me want to pay it forward and do the same for other runners!

A quick explanation so we’re on the same page when I share these numbers:

When it comes to correlation, you can get values between -1 and 1. Numbers around 0 indicate no correlation, between 0 and -1 negative correlation, and 0 - 1 positive correlation. The bigger the number the stronger the correlation. 

Mile 11: 8:56 at 174bpm (5:33/km)

At mile 11 I was still running slightly faster than my target pace, but I was absolutely feeling it by this point. 

The time that I fall asleep apparently has a -0.26 correlation with the strength of my run the next day. There’s a slight trend suggesting that later bedtimes might be linked to feeling less strong during runs. 

Mile 12: 9:11 at 172bpm (5:42/km)

Almost halfway. Up to this point, I’d avoided taking water as I was terrified of needing to stop and pee. Historically my knees have often flared up when I stop running and start again, so I really wanted to avoid anything that might make me stop. But I figured that at around the 2-hour mark, I could take some water and hopefully not need to pee for a while. 

The time I wake up has a -0.21 correlation, which could suggest that getting up earlier leads to stronger runs and getting up later leads to weaker runs. 

Mile 13: 9:07 at 175bpm (5:40/km)

Mile 13 was nice to hit. Halfway. 

The one piece of data that surprised me was that the amount of sleep I got has a -0.13 correlation with my running strength, and the amount of restorative (REM and deep) sleep I get also has a -0.14 relationship with my runs.

This seems backward but also exposes the issues with correlation and why it’s important to remember that correlation is not causation. It could be that on days my body is more fatigued I tend to sleep more, which leads to a correlation between higher sleep duration and then feeling weak during the next day’s run.

Mile 14: 9:04 at 176bpm (5:38/km)

Little slower but still moving. 

My self-reported energy level has a 0.28 correlation with the strength of my runs—this is fairly obvious but there’s a positive relationship between how energised I report feeling during the day and how well my body performs while running. 

Mile 15: 9:05 at 177bpm (5:39/km)

Not much to say about this one. Just holding on. 

I also rate how clean my eating was each day, and when I measure the correlation between that and how strong I ran the next day, there’s a correlation of 0.11. I’d like to think this suggests how well I eat one day has at least a bit of an impact on the next day’s performance. 

Mile 16: 9:14 at 174bpm (5:44/km)

Mile 16 had some warning signs. Was the wall coming…?

Finally, what about the impact on my mental wellbeing?

Mile 17: 9:25 at 174bpm (5:51/km)

Everything felt so sluggish at this point. Running 9:00/mile pace felt like 8:00/mile. Weirdly I didn’t feel like I was slowing down too much but the time was going up so I definitely was. I guess my perceived effort was the same which is why I didn’t feel like I was slowing. 

So far, whether I run on any given day has a 0.06 correlation with my mental well-being, and how strong I feel during the run 0.07, so pretty much no relationship. But the distance I run has a 0.15 correlation, suggesting that my well-being is more affected by how far I run than whether I run at all or how good I feel during that run. 

Longer runs have a greater impact on my wellbeing. 

Mile 18 - 26: ? 

Ok. This is where things got interesting. At 17.25 miles my music suddenly stopped and I knew without looking down that my watch had run out of battery. 

I know plenty of people run without watches, but as someone who has got pretty reliant on it for pacing, this was a massive L to take midrace. It also meant my ‘hard running’ tunes never got their time in the sun. 

At this point, all I could do was keep watching for the mile markers and try not to fall apart too much. Sadly, falling apart is about the only thing I did at this point…

Somewhere around mile 20, I hit the wall, and my body slowed down so much I was basically walking. I took a second to walk and recover, but when I started again my knees flared up pretty bad.

I was so mad because I knew the whole time that stopping would mess with my ability to get going again, but all I could do was walk a little more and try again later. Luckily, when I tried again I found that if I ignored the initial pain I could settle back into a slow jog without the pain getting worse. This pattern continued for miles 20 - 24, at a pace of probably 12-13 minutes a mile (7-8/km).

At mile 24 I started to actually realise the race was going to end. I picked up the pace slightly, finding a little bit of juice I didn’t know I still had. 

At mile 25 I decided that the only way to redeem myself would be to absolutely send the last mile like a madman. This is the hilliest part of the run but somehow I don’t even remember this part hurting. I was just so ready to finish that I found myself passing everyone up this hill and down the other side. I felt like I was all out sprinting, but I’m pretty sure it was somewhere between 8 and 9 minutes so not as crazy as I felt. 

The finish line was tucked away and came into view just moments before I crossed the line in 4h:19m.

As soon as I did, all the emotion I’d been holding back just hit me like a ton of bricks—plenty of exhaustion and pain, but so much satisfaction and relief too. Happiness isn’t quite the right word for it, but maybe eudaimonia is. I put my hand over my face and started shaking. I heard my brother call my name and I met him at the fence, tears streaking my face like the relentless Yorkshire rain.

Benji and Jacob 

What Counts

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