The durability layer.

The missing layer.

Everything we've covered so far, power, your curve, your zones, all of that is measured when you're fresh. And I kept flagging that, because it matters. The numbers you see on test day, the profile you build from your best efforts, the zones you set from your CP, all of it describes what you're capable of at your best.

But you are almost never at your best when it counts.

You're four hours into a gran fondo. You're at the end of a hard training week. You're ninety kilometres into a race and the attacks are starting. And in those moments, the question isn't "what's your FTP?" The question is "what have you got left?"

This is durability. And I believe it's the single most important concept in cycling that almost nobody is teaching properly.

What durability actually is.

Let me give you the formal definition first, and then I'll explain what it actually means in practice.

Maunder and colleagues in 2021 defined durability as the time of onset and magnitude of deterioration in physiological-profiling characteristics during prolonged exercise. Hunter and colleagues in 2025 refined that to the resilience to deterioration of physiological variables and performance during or following prolonged exercise.

In English: how quickly your body starts to fall apart when you're tired, and how much it falls apart.

Every rider deteriorates under fatigue. Every single one. The question is how much and how fast. A durable rider might lose 5% of their threshold power after four hours. A non-durable rider might lose 20%. Same FTP on paper. Completely different riders at hour four.

And this is where I want to introduce a distinction that I think is the most useful idea in this entire course.

Capacity versus access.

Your capacity is what your body can produce when it's fresh. Your FTP, your CP, your sprint power, that's all capacity. And capacity matters. You need a big engine.

But access is how much of that capacity you can still reach when you're fatigued. And access, that's durability. That's the bit that decides whether you're still in the group at hour four, whether you can respond to the attack on the last climb, whether your gran fondo falls apart in the last thirty kilometres or holds together.

I chose to build my entire coaching system around this distinction because it explains the thing that frustrated me most as a coach. Riders who were fit. Genuinely fit, good numbers, ticking every box. But who kept cracking when it mattered. And the answer wasn't that they needed more fitness. They needed more access to the fitness they already had.

The four components.

So durability isn't one thing. It's at least four things happening at once, and understanding which one is failing is the whole game as a coach.

I've built this into a four-component model. And I should say, I didn't invent the research behind this. The researchers did. What I've done is take the evidence and organise it into something a coach can actually use on a Wednesday afternoon when they're looking at a rider's data and trying to figure out what went wrong.

Component 1: Physiological durability. This is the one most people think of. Your heart rate drifts up at the same power. Your lactate clearance slows down. The metabolic cost of the same effort keeps rising. Stevenson and colleagues in 2022 showed this. The thresholds themselves shift under prolonged exercise. Your CP at hour one is not your CP at hour four. Gallo and colleagues in 2024 showed that the magnitude of this deterioration differs enormously between riders of similar fresh-state fitness. Your fresh FTP alone isn't a good predictor of how durable you actually are, though aerobic markers like VO2max, gross efficiency, and fat oxidation capacity do carry real predictive weight. Practically, this is what you see when a rider's power holds but their heart rate climbs steadily. The body is paying more for the same output. Eventually it can't afford it.

Component 2: Neuromuscular durability. This is about the muscles themselves. Force production drops. Recruitment patterns change. Lepers and colleagues in 2002 showed an 18% decline in maximum voluntary contraction after five hours of cycling. Your muscles literally can't fire the same way. Practically, this is what you see when a rider's cadence starts drifting down late in a ride, or when they lose their ability to respond to surges. The pedal stroke changes. The snap goes out of their legs.

Component 3: Biomechanical durability. Movement patterns degrade under fatigue. Sanderson and Black in 2003 showed changes in pedalling mechanics. Hopker and colleagues in 2017 showed efficiency losses. Passfield and Doust in 2000 documented how the biomechanics of sustained effort change over time. Practically, this is the thing you can sometimes see. The rider who starts rocking, whose pedal stroke gets choppy, who looks different on the bike at hour five than they did at hour one. That's not just tiredness. That's biomechanical durability failing.

Component 4: Perceptual-cognitive durability. This is the one nobody talks about. Van Cutsem and colleagues in 2017 showed that mental fatigue reduces time to exhaustion, not through any physical mechanism, but through perception. The effort feels harder. Decision quality drops. Salam and colleagues in 2018 showed that cognitive load actually reduces W prime. Your anaerobic battery gets smaller when your brain is tired. Practically, this is the rider who makes bad tactical decisions late in a race. Who stops eating because they forget. Who doesn't respond to an attack they could physically handle because their brain says "I can't."

This is also where life load comes in. The stress from your job, your sleep quality, your family situation. Your body doesn't distinguish between the stress of a deadline and the stress of a threshold effort. It all lands in the same system.

The durability curve.

Here's how I think about it visually. Imagine a graph. Accumulated load on the bottom, that's everything you've done so far in the ride, measured in kilojoules or time or whatever metric you want. Available performance on the left side, what you can actually produce right now.

Every rider starts in the same place: the top left. Fresh. Full capacity available. And as load accumulates, that line drops. For everyone. The question is: what shape does it drop in?

A durable rider's line drops slowly and gradually. At four hours, at 3000 kilojoules, they've still got 85 to 90% of their fresh capacity available. A non-durable rider's line drops fast and steep, maybe by hour three they're already at 70%.

And here's the key thing. Two riders can have identical fresh numbers, same CP, same W prime, same FTP, but completely different durability curves. The traditional metrics don't tell you which one you're looking at. That's the gap. That's why I keep saying fresh metrics stop explaining.

When I'm coaching someone, I'm not just trying to raise the starting point of that curve. I'm trying to flatten it. I want the line to drop slower. That's the whole game.

Body, brain, life.

One more piece before we move on. Because durability doesn't just happen on the bike.

I use a model I call body, brain, life. Three channels of load that all converge on the same system.

Body load is the obvious one, the physical training stress. Hours, kilojoules, intensity.

Brain load is the cognitive and emotional cost. Concentration, decision-making, the attentional demands of your job, your commute, your family obligations. Your brain is not separate from your body. When it's taxed, everything else gets harder.

Life load is the rest. Sleep quality. Relationship stress. Work deadlines. Travel. The background hum of everything that isn't cycling but still drains the same battery.

And the reason this matters for durability is that your body doesn't separate these. It doesn't go "oh, that stress is from work, I'll put that in a different bucket." It all lands in the same system. A rider who's sleeping badly and stressed at work will show reduced durability on the bike even if their training hasn't changed. The freshness isn't there. The access narrows.

This is why I say coaching isn't just about writing a training plan. It's about understanding the whole picture and making decisions based on what's actually happening, not what the calendar says should be happening.

Why I built everything around this.

I want to be upfront about something. Durability is not a new idea. The research has been building for years. What I've done is take that research and build a coaching system around it, one that puts durability at the centre rather than treating it as an afterthought.

I chose to do that because it solved the problem I kept running into. Fit riders who cracked. Good numbers that didn't translate. Training plans that looked perfect on paper but fell apart in practice. And every time, the answer came back to the same thing: we were measuring capacity and ignoring access.

Once I started coaching through that lens, asking not just "how fit is this rider" but "how durable is this rider", everything changed. The training decisions got clearer. The results got better. And the riders started performing when it mattered, not just on test day.

So everything that follows in this playbook, how I think about periodisation, which workouts I choose, how I teach execution, the case studies at the end, all of it runs through this framework. Durability is the lens. If you understand it, everything else makes more sense. If you don't, you'll keep building a bigger engine that you can't access when you need it.

Now I want to take you inside the ride itself. What's actually happening to your body, system by system, hour by hour, when you're on a long ride. Because if you understand the mechanisms behind what I've just described, everything that comes after this will make more sense.