Sub-3 on 3 Runs: Week 3 Durability Is Earned, Not Assumed

This week was a sharp reminder of how demanding running actually is — and why so many standard 16-week marathon plans, particularly those aimed at beginners, quietly unravel long before race day.

Not because people aren’t motivated.
Not because they don’t want it enough.
But because durability and fatigue resistance are massively underestimated.

These plans are rarely designed to help someone race a marathon. At best, they’re designed to get someone around one. They assume durability will appear simply by following a schedule, when in reality durability is something that has to be earned over months and years, not squeezed into a short block of increasing long runs.

Aerobic fitness can improve relatively quickly, which is why people often feel “fit enough” going into a marathon. Structural resilience and fatigue resistance don’t work on the same timeline. When runners struggle between 18 and 22 miles, it’s usually a combination of factors — pacing, fueling, and durability — but a lack of long-term structural preparation is often the quiet limiter that shows up first.

Today’s long run (For me) really drove that home.

On paper, nothing about it looked dramatic. Around 12 miles at a relatively easy pace. Nothing forced, nothing aggressive. And yet, over the final two or three miles, the familiar warning signs started to creep in, knees, hips, adductors, hamstrings, all tightening and stiffening as fatigue set in. It wasn’t pain, but it was a very clear message from the body: you haven’t earned this yet.

What struck me most is that I’m not unfit. I’m not starting from zero. I’d describe myself as being in “okay” shape — nothing special, but not a mess either. And still, the lack of fatigue resistance was obvious. That’s what happens when running consistency drops away over a period of months. The aerobic system might come back relatively quickly, but the structural resilience doesn’t. That takes time, repetition, and patience.

This is exactly where a lot of marathon plans fail people. They assume durability will magically appear as long as you follow the schedule. But durability isn’t something you switch on in Week 10 of a plan, it’s the result of years of steady, boring, consistent work. I’ve never been a high-mileage runner, but historically I’ve been very durable. Not through volume alone, but through long-term consistency. A deep back catalogue of decent weeks stacked on top of each other.

Right now, that catalogue is thinner than it used to be. And Week 3 made that very clear.

That’s also why this project places such a heavy emphasis on making sure i incorporate strength training and intent. When you’re only running three times a week, every run has to count. There’s no room for filler, and there’s no margin for sloppy execution. Strength work isn’t an accessory here, it’s a prerequisite. If I want to rebuild durability and fatigue resistance on reduced run frequency, the supporting work has to be nailed.

The reality is that, at the moment, the body still feels a long way off. Even running easy, there’s a sense that the system isn’t fully robust yet. And if easy running exposes that, then marathon pace — let alone holding it for close to three hours — is obviously some distance away. That’s not a concern. It’s information. We’re only in Week 3, and this phase is about collecting honest feedback rather than chasing reassurance.

There were positives this week too. Week 3 included my first proper interval session since September, five sets of three minutes with a minute recovery. It was genuinely nice to run a bit quicker again, but it also felt hard in a way that reminded me how unfamiliar sustained faster running has become. That’s not a bad thing. It’s simply part of reintroducing stress and teaching the body how to tolerate it again.

Friday’s run included a couple of 10-minute marathon-pace efforts. Once settled in, it was one of those sessions that messes with your head a bit. You remember a time when that pace felt automatic, almost casual. Now it requires focus, concentration, and intent. Again, not frustrating — just honest feedback on where things currently sit.

The rest of the week did its job quietly. All aerobic cycling, building capacity without impact. A couple of solid strength sessions, reinforcing the foundations that will make future running possible. No drama, no panic, no attempts to rush the process.

Overall, Week 3 was a good week — not because it felt easy, but because it was informative. It reinforced why consistency matters, why durability can’t be skipped, and why this project needs patience.

We build again next week.

Not by doing more.
Not by forcing progress.
But by continuing to stack sensible work on top of sensible work.

That’s how fatigue resistance is earned.

Until next week…

Si