Durability in Cycling: The Hidden Metric That Separates Good Riders from Great Ones

Why two cyclists with identical FTPs can have completely different race results — and how to train the fourth dimension of endurance performance.

You've done the training. Your FTP is solid. Your VO2 max tests came back strong. On paper, you're as fit as you've ever been.

So why did you get dropped on the final climb of last weekend's sportive by someone you'd been riding away from all day?

The answer lies in a concept that's revolutionising how coaches and sports scientists think about endurance performance: durability.

What Is Durability in Cycling?

Durability refers to your ability to resist physiological deterioration during prolonged exercise. It's not about how strong you are when you're fresh — it's about how much of that strength you can retain after hours of accumulated fatigue.

The term was formally defined in a landmark 2021 paper by researchers Ed Maunder and Stephen Seiler as "the time of onset and magnitude of deterioration in physiological-profiling characteristics over time during prolonged exercise."

In simpler terms: how long until you start fading, and how badly do you fade?

Here's why this matters. A study comparing professional cyclists found that athletes with nearly identical lab-tested fitness markers showed wildly different power declines after prolonged efforts — ranging from less than 1% to over 30%. Same FTP. Same VO2 max. Completely different outcomes when the race got hard.

The Fourth Dimension of Endurance Performance

Traditional cycling fitness has been understood through three key metrics: VO2 max (your aerobic ceiling), lactate threshold (your sustainable intensity), and efficiency (how economically you convert oxygen into power). These form the basis of the Joyner model of endurance performance that's guided training for decades.

The problem? All three are measured when you're fresh and rested.

Professor Andrew M. Jones of the University of Exeter proposed in a 2024 paper in the Journal of Physiology that durability represents an independent fourth dimension of endurance performance. His research demonstrated that durability doesn't significantly correlate with VO2 max, threshold power, training volume, or years of experience.

Two riders can test identically in the lab and perform completely differently in a five-hour race. The fourth dimension explains why.

The Physiology: Why Some Riders Fade and Others Don't

Understanding why durability varies so much between athletes requires looking at four interacting physiological mechanisms.

Glycogen Depletion

Your muscles store carbohydrate as glycogen — the premium fuel that powers high-intensity efforts. During a long ride, muscle glycogen can decrease by approximately 77%. When stores drop below critical thresholds, your ability to produce power becomes directly impaired, regardless of how much fat you have available to burn.

Athletes with superior durability appear to spare glycogen more effectively, relying more heavily on fat oxidation at equivalent intensities and keeping those carbohydrate reserves available for when they're truly needed.

Neuromuscular Fatigue

After two hours of hard cycling, research shows an 11-15% reduction in muscular force production capacity. The signals travelling from your brain to your muscles become less effective — like a phone call breaking up in a tunnel. This peripheral fatigue accumulates progressively and affects your ability to respond to attacks or push over climbs.

Efficiency Decline

The longer you ride, the more oxygen you need to produce the same power output. Your body becomes less economical, requiring more energy for identical work. This efficiency drift compounds over hours, meaning the same 250 watts that felt comfortable at hour one feels significantly harder at hour five.

Muscle Fibre Recruitment Shifts

Your slow-twitch muscle fibres are efficient and fatigue-resistant. Your fast-twitch fibres are powerful but burn through fuel rapidly. As slow-twitch fibres fatigue during prolonged exercise, your body recruits more fast-twitch fibres to maintain power output.

The problem: fast-twitch fibres are less efficient and deplete glycogen faster, creating a cascade effect. You burn more fuel, fatigue faster, and recruit even more fast-twitch fibres. It's a vicious cycle that accelerates deterioration.

The Shifting Zones Problem

These mechanisms combine to create a crucial practical issue: your physiological training zones shift downward as fatigue accumulates. What started as a comfortable Zone 2 effort becomes physiologically harder. What felt like threshold pace at the start of the day might be well into VO2 max territory by the end.

This is precisely why decisive moments in Grand Tours happen on the final climb, not the first. By then, riders with poor durability are operating in a completely different physiological reality than those with good durability — even if they started the day as equals.

How to Measure Your Durability

The gold standard for assessing durability involves comparing performance in fresh versus fatigued states.

The Fresh-Fatigued Test

A practical protocol you can do yourself:

1. Perform a 5-minute maximal effort when fresh and note the average power

2. Complete 2-3 hours of moderate riding (approximately 1,000 kJ of work at 70-80% of your 20-minute power)

3. Perform another 5-minute maximal effort

4. Compare the two power figures

If you're within 5-8% decline, your durability is solid. At 10% or more, you've identified an area for improvement. Research from 2025 found that successful amateur racers showed only 6.5% power decline in these protocols, versus 12.5% for less successful competitors — despite equivalent fresh-state fitness.

Aerobic Decoupling

For ongoing monitoring, aerobic decoupling provides insight during any steady ride. Compare your efficiency factor (normalised power divided by average heart rate) between the first and second halves of a long effort. Decoupling exceeding 5% suggests durability limitations; values below 3-5% indicate strong aerobic fitness.

Tracking Durability Over Time

While formal testing provides valuable snapshots, the real insight comes from tracking durability trends across your training. This is exactly why we built the Durability Score into the Pedal Pulse app.

After every ride, Pedal Pulse calculates your Durability Score based on how your power output and efficiency held up over the course of the session. Rather than relying on occasional dedicated tests, you build a continuous picture of your fatigue resistance — and can see whether your training interventions are actually working.

Whether it's a structured training ride or a weekend group spin, you're gathering data on your fourth dimension.

How to Train Durability

The good news: durability is highly trainable. The key is incorporating fatigue-specific training that goes beyond traditional interval work.

Long Rides: The Foundation

Rides of 3-5 hours at controlled Zone 2 intensity form the foundation of durability development. The minimum effective duration appears to be 2.5-3 hours, with adaptations scaling to longer efforts.

The mechanism: prolonged riding at low intensity fatigues your slow-twitch fibres, forcing recruitment of fast-twitch fibres under aerobic conditions. Over time, these fast-twitch fibres develop enhanced aerobic capacity and fatigue resistance — essentially learning to behave more like slow-twitch fibres.

There's no shortcut here. Volume matters.

Late-Ride Intensity

Adding threshold or VO2 max efforts in the final hour of long rides builds race-specific durability by demanding power output when you're already fatigued.

A classic structure: 4-hour ride at Zone 2, then 2×10 minutes at threshold power in the final hour. It's demanding, but it teaches your body to produce power in exactly the state you'll need it during races.

Pre-Fatiguing Protocols

This approach places high-intensity work early in the session. Start with 6×3-minute intervals at VO2 max intensity, then continue with 2-3 hours of Zone 2 riding.

You get quality interval work done while fresh, but the subsequent endurance riding has a completely different training stimulus because you've already depleted glycogen reserves and fatigued key muscle fibres.

Progressive Consolidation

This clever method progressively increases time-in-zone under fatigue. If your goal is holding 280 watts for 6 minutes:

• Week 1: 15×45 seconds at 280W with short recoveries

• Week 2: 10×60 seconds

• Week 3: 6×90 seconds

• Week 4: 4×2 minutes

• Week 5: 2×4 minutes

• Week 6: 1×6 minutes

Each week, you spend more continuous time at target power while fatigued. By week six, you're executing the effort in a genuinely depleted state.

The Expert Approach

Dr Stephen Seiler's polarised training model — roughly 80% of training below the first ventilatory threshold, 20% above the second, with minimal time in between — develops both the aerobic base that underpins durability and the high-intensity capacity for race-winning efforts.

Dr Iñigo San Millán, coach to Tour de France winner Tadej Pogačar, emphasises Zone 2 training at precisely controlled intensities. His athletes perform 4-5 hour sessions targeting specific lactate concentrations, building the metabolic machinery that resists deterioration.

WorldTour teams now prescribe hard efforts based on accumulated work rather than time. Intervals aren't scheduled for "hour one" but for "after 3,000 kilojoules of work" — because that's when durability matters.

Nutrition Considerations

Carbohydrate availability directly affects durability. During races and hard training, aim for 80+ grams of carbohydrate per hour to offset glycogen depletion and maintain performance capacity.

For some training sessions — particularly easier Zone 2 rides — there's evidence that periodically training with lower carbohydrate availability can enhance durability adaptations by forcing greater reliance on fat oxidation. However, key high-intensity sessions should always be properly fuelled.

The principle: fuel for the work required.

Start Tracking Your Fourth Dimension

Durability represents a fundamental shift in how we understand endurance performance. It's independent of traditional fitness markers, highly trainable through specific protocols, and increasingly recognised as the factor that separates good riders from great ones at every level.

The first step is measurement. You can't improve what you're not tracking.

The Pedal Pulse app calculates your Durability Score after every ride, giving you continuous insight into your fatigue resistance and letting you see whether your training is building the fourth dimension. Download it and start building a picture of your durability today.

Because your FTP only tells half the story. What matters is how much of it you can access when you're five hours in and the road tilts upward.

Ready to track your durability? Download Pedal Pulse and get your Durability Score after every ride.