What FTP tells you

FTP is usually described as the highest power you can sustain in a quasi-steady state for about an hour. It gives you a useful reference point for structuring workouts and tracking changes in your threshold fitness. If your FTP increases, that is generally a positive sign. It may mean you can produce more power around threshold than before.

But that common definition hides two problems.

There is no real steady state

The idea of a “steady state” suggests that at threshold your body settles into a stable balance, where energy supply matches demand and nothing changes as long as you keep pedalling. In reality, that state never truly exists. Even when your power stays exactly the same, your body keeps shifting underneath it.

Your heart rate slowly drifts upwards as you lose fluid and your body works harder to cool itself. Oxygen uptake creeps up because muscle fibres fatigue and less efficient fibres are recruited to keep the same output. Glycogen stores gradually empty, and metabolic by-products accumulate. Your brain registers all of this, which is why the same wattage feels harder in minute 35 than in minute 5.

In other words, holding constant power is not the same as being in a constant state. The output is steady; the cost is not. Threshold is better understood as a boundary where fatigue develops slowly enough to hold an effort for a long time, not as a point where fatigue stops developing.

FTP is not an hour

The second problem is the hour itself. Although FTP is often defined as the power you can hold for 60 minutes, research shows that most cyclists cannot actually sustain their FTP for that long. When riders are tested to exhaustion at their FTP, they typically last around 40 to 50 minutes, with large differences between individuals. Some riders last well under that, a few go longer, but the full hour is the exception rather than the rule.

Consistency makes FTP valuable

None of this makes FTP useless. It makes it a metric that needs to be handled with care. FTP is most valuable when you measure it the same way every time: the same test protocol, the same warm-up, similar conditions, ideally the same power meter and a comparable level of freshness. Then changes in the number tell you something real about how your threshold fitness is developing.

Compare a ramp test in March with a 20-minute test in June, on different devices and in different states of fatigue, and the difference between the numbers may say more about the method than about you.

FTP also does not tell you everything that matters on the bike. It does not show how well you can repeat short efforts, sprint, climb after several hours or hold your power when fatigue builds. It also does not explain how much a particular effort costs you on a specific day. A higher FTP can make you faster, but it does not automatically make you a better cyclist in every situation.

Durability: the fitness FTP misses

One of the most important qualities FTP leaves out is durability, also called fatigue resistance. Durability describes how well you maintain your power as work accumulates over a ride.

FTP, and almost every other test, is measured when you are fresh. But races and long rides are rarely decided when you are fresh. They are decided on the final climb after four hours, or in the last hour of a gran fondo when the energy in your legs is running low. Two riders with identical FTPs can perform very differently at that point. One may still produce close to their best numbers, while the other has already lost a significant part of their power.

Research increasingly shows that this ability to resist fatigue separates riders at every level, from recreational cyclists to professionals. And it can be trained, through consistent endurance volume, long rides, good fueling and efforts completed on tired legs.

That is why JOIN now lets you see your durability directly. In the updated plan.join.cc, you can view your power curve after 1,000, 2,000 or more kilojoules of work. Instead of only seeing your best 5-minute or 20-minute power from fresh efforts, you can see what you can still produce once real fatigue has built up. If your 5-minute power after 2,000 kJ is close to your fresh 5-minute power, you are a durable rider. If it drops sharply, you know exactly where your next gains can come from.

Power measures the output

Power tells you how many watts you are producing. It is immediate, objective and extremely useful for pacing and controlling the intensity of a workout.

If your interval target is 250 watts, your power meter tells you whether you are hitting it. What it cannot tell you is what producing those 250 watts costs your body today. The same 250 watts can feel controlled after a good night’s sleep and much harder after a stressful week. Heat, fatigue, poor recovery, illness and low energy availability can all change your response, even when the number on your screen stays exactly the same.

Power measures the work coming out. It does not fully explain what is happening inside. Power measurement also has its own margin of error. Two power meters may not report exactly the same value, even when fitted to the same bike. Calibration, temperature, device location and normal measurement variation can all influence the number. Power is objective, but that does not make it perfect.

Heart rate measures the response

Heart rate gives you more information about how your body is responding to the work. If you normally ride at 200 watts with a heart rate of 140 beats per minute, but today the same power pushes your heart rate much higher, something may be different. It could be heat, dehydration, fatigue, stress or the beginning of an illness.

Heart rate also makes the missing steady state visible. During a long effort at constant power, a slowly rising heart rate is a sign that the internal cost is increasing, even while the output stays the same.

But heart rate also has limitations. It responds more slowly than power, especially during short intervals. It can also be influenced by temperature, caffeine, sleep, hydration, stress and many other factors.

That does not make heart rate unreliable. It means the number needs context. Learning how your heart rate normally behaves during different workouts takes time and experience. Power tells you what you are doing. Heart rate helps show how your body is responding.

RPE brings the signals together

RPE, rating of perceived exertion, describes how hard an effort feels.

Because it is based on feeling, cyclists sometimes dismiss it as less useful than power or heart rate. But your perception of effort is not random. Your brain is constantly processing information from across your body. Your breathing, leg fatigue, temperature, energy levels, motivation, sleep, stress, power and heart rate all contribute to how hard an effort feels. RPE turns those signals into one overall assessment.

That does not make RPE perfect. Experience matters, and it takes time to recognise the difference between discomfort, fatigue and simply not feeling motivated. But RPE can reveal something that power alone cannot: how much the effort is costing you today. If a familiar endurance pace suddenly feels like threshold, that matters, even if your power target says you are exactly where you should be.

When your numbers disagree

The most useful information often appears when power, heart rate and RPE do not match.

Imagine riding at your normal endurance power:

• Your power is normal, your heart rate is normal and the effort feels easy. Everything is aligned.

• Your power is normal, but your heart rate is unusually high and the effort feels hard. Heat, dehydration, stress or fatigue may be increasing the cost.

• Your power is normal and your heart rate looks ordinary, but your legs feel unusually heavy. You may be carrying muscular fatigue that heart rate does not fully reveal.

• Your power is lower than expected, but your heart rate and RPE are high. Forcing the original target may not be the best decision that day.

One number does not necessarily explain the whole situation. Together, the numbers give you a clearer picture.

Should you stop chasing FTP?

No. FTP remains a valuable training metric, especially when you measure it consistently. The problem begins when it becomes the only number that matters. A cyclist can improve without setting a new FTP record. You might become better at repeating hard efforts, holding power after three hours, recovering between intervals or completing training more consistently. You may also be able to produce the same power at a lower heart rate or with a lower RPE.

Those are meaningful improvements, even if your FTP has not changed.

Instead of asking only, “Did my FTP increase?“, ask:

• Can I hold my power for longer?

• Does the same power feel easier?

• Can I repeat hard efforts more consistently?

• Do I recover faster between intervals?

• How much of my power is left after 1,000 or 2,000 kJ?

• Am I training more consistently than before?

FTP is one part of performance, not the final definition of it.

Power to steer, heart rate to check, RPE to decide

Each metric has a different job.

Use power to steer. It helps you control the workout, pace your intervals and understand the external work you are producing.

Use heart rate to check. It shows how your body is responding and helps identify when the internal cost differs from what you normally expect.

Use RPE to decide. It adds the context that your devices cannot fully capture and helps you judge whether you should continue, adjust or back off.

None of these numbers should always override the others. Read them as a system rather than in isolation.

Train the cyclist who showed up today

Your FTP might be the same as it was yesterday, but you are not exactly the same rider. Your sleep, stress, recovery and accumulated fatigue change from one day to the next, and even from the first hour of a ride to the last.

That is why JOIN combines your training data with your feedback. Power helps measure the work, heart rate adds information about your response and RPE tells JOIN how the session actually felt. With the durability power curves in plan.join.cc, you can now also see how well your power holds up when the kilojoules start adding up. Together, they create a more complete picture of the cyclist who showed up today. Keep chasing progress. Just remember that progress is bigger than one number.