"How do I push harder?" is a question that assumes the answer lives in your legs. It usually does not. It lives about three feet higher up.
Here is the example I use, and my partner Emma will forgive me for it.
Emma would hate to be at the front of a festival crowd. Packed in, hot, sweaty, no room, no exit. I would love it. Jumping, dancing, singing, all day.
Now, we are both perfectly physically capable of standing in a crowd for a few hours. That is not the difference. The difference is that her mind is not willing to tolerate that particular discomfort, and mine is.
BLUF: your body is more capable than your mind gives it credit for. Every hard session you do is training two things, your fitness and your tolerance for discomfort. Most people only ever count the first one.
What actually stops you
For a long time the assumption was that endurance ends when the body physically cannot continue. Muscles out of fuel, lactate too high, engine done.
The evidence has moved on quite a bit. The leading explanation now, largely through the work of Samuele Marcora, is the psychobiological model: how hard something feels, combined with how much effort you are willing to give it, is what governs when you slow down.
Put plainly: you tend to slow because you feel unable to hold the pace, not because you have actually reached the physical limit.
And there is a study that demonstrates this rather neatly. Cyclists did a demanding 30 minute mental task before a time trial. Their performance dropped by around 15%. Their heart rate, their lactate, their muscle activation, all essentially unchanged. The only thing that shifted was how hard the effort felt to them.
Same body. Same physiology. Worse result. Purely because of the state of the mind that turned up to it.
Which means the discomfort is trainable
So, what that means is: if perception of effort is the thing regulating you, then getting better at handling that perception is a genuine training goal. Not a personality trait you either have or you do not.
And this is where hard sessions earn their place. When you do a set of intervals, you are getting two returns:
- The physiological one. The adaptations you would expect, aerobic and otherwise.
- The perceptual one. You spend time at an effort that feels awful, you learn that it is survivable, and next time it feels slightly less awful at the same output.
Repeat that in a structured, progressive way and your ceiling for discomfort rises alongside your fitness. That is a big part of why periodised training works better than doing the same comfortable thing forever, which we went through in the piece on giving every run a job.
The key message here is: you are not just building an engine. You are extending how much you can endure.
Discomfort is not damage
Now, this is the bit I want to be very clear about, because this idea gets twisted into something unhelpful.
This is not "push through at any cost". It is not about ignoring your body. It is about expanding the level of discomfort you can work through in order to make progress, and that is a different thing entirely.
So it helps to separate the two:
- Discomfort is heavy breathing, burning legs, a very loud voice suggesting you stop, a session that feels harder than you would like. That is the training stimulus. That is the bit worth getting better at.
- Damage is sharp or localised pain, something that changes how you move, pain that lingers after you stop, training while genuinely ill, or the creeping flatness of doing too much for too long. That is a signal to act on, not to override.
Getting that distinction wrong is how people end up injured, ill or burnt out, and none of those make you faster. Being able to sit in honest discomfort while still respecting real warning signs is the skill. Not toughing everything out.
How to train it deliberately
Here's what to do:
- Have genuinely hard sessions, and few of them. Two a week is plenty for most people. They should feel hard. That is the point of them.
- Keep the easy days properly easy. You cannot build tolerance to discomfort if you are mildly uncomfortable all the time. That is the grey zone problem covered in the Zone 2 piece, and it blunts both returns at once.
- Progress the exposure. Slightly longer at the effort, or slightly less recovery, over weeks. Small steps, same as you would with load in the gym.
- Rate the effort, not just the pace. Our RPE guide is built on exactly this idea, since perceived exertion is the thing you are learning to read and to stretch. Noting an honest 1 to 10 after each session tells you far more than the splits do.
- Notice what your head does when it gets hard. Most people have a predictable script. Knowing yours is the first step to changing it.
The bottom line
Emma is not less capable than me of standing in a crowd. She is just less willing to be uncomfortable in that particular way, and honestly, fair enough.
Running, riding and racing work the same. Most of us stop a long way short of what the body could physically do, because the mind called time first. Train that side deliberately, keep discomfort and damage clearly separated, and you get access to a version of yourself that was there the whole time.
To get something you have never had, you need to do something you have never done.
If you want to talk through where your ceiling actually sits, don't sit on it, let me know.