When the sun rose this morning, Shanti Pereira tried as usual to fly. Her legs were her wings. Her faith was her fuel. Her crowd was her coach. Her goal was unchanged.

"I want to be able to go as far as I can." Or as fast as she can.

Athletes after practice mostly look the same. Dishevelled. Glowing. Exhausted. Aching. Alone. Hungry. Pereira sits on a bench, her back turned to the track which she's just painted with sweat.

Is she faster today?

No.

Will she be faster tomorrow?

Maybe if she works like today.

Faster is an act of faith. There's no guarantee it will happen but the athlete has to believe it will happen. Has to believe that she, 18, will eventually finds bits of a second. Next week 0.1. Next season 0.3. She's like the shooter searching for an extra point and the gymnast looking for a cleaner dismount, a tribe whose hymn is distilled to a single word.

Improve.

You don't see these athletes at work because who watches training? It's dull but it's like laying the foundations of a building. All those laps, those sit-ups, those bench-presses, they're the steel and masonry of athletic beauty.

You don't hear athletes talk about pain as if it was just a minor irritation. Every day something hurts, Shanti?

"Ya, ya."

You don't see them fall, get up, train. Today, she laughs, "I died" in training. Fast striding - 120m, jog - 80m. Again, again, again, again. Till she feels "my legs are going to give way any moment". Till she says, "I can't breathe properly".

Feel like throwing up?

"Quite a few times."

Have you?

"Once or twice."

It's not fun?

"Err, no."

She grins.

Carli Lloyd, who scored a hat-trick in football's Women's World Cup final, works with her coach - as Sports Illustrated wrote - on Thanksgiving, Christmas, Easter. She won a Cup but most athletes won't win a major title, won't earn big money. Yet they give up eating ice cream for a year - as Paralympic swimmer Jessica Long did in 2012 - and go to work and want to throw up.

People sometimes can't comprehend this penance but maybe it's because athletes hear something no one else does.

Ray Charles, the late singer, once said: "I was born with music inside me. Music was one of my parts. Like my ribs, my kidneys, my liver, my heart."

Maybe running for Pereira, and football for Lloyd, is as visceral. The sport is who they are. As Pereira says, "the feeling I get (at the track) is something different from daily life". Elsewhere she is like everybody, here she is somebody. "It's the place," she says, "where I can truly show my full potential."

But potential doesn't always translate into progress. You need patience, trust, diligence. You experiment as Jasmine Ser has with a shooting position. Or as Tiger Woods does with his swing plane. But you can work, and work, and nothing may happen.

Consistency evades golfer Tseng Ya-ni, brilliance eludes footballer Jack Wilshere, confidence dodges tennis player Eugenie Bouchard. Sometimes it happens because you're older, injured, distracted. Sometimes for no apparent reason "better" just won't come.

For three months this year, Pereira can't get faster and it's deflating. But what is toughness? It is returning to the start line, clock at zero, and trying again and she does this and one day it happens.

She flies.

It happens at practice, no crowd there, no medal on offer, but it's something more profound. "Pure satisfaction," she smiles. She's like the swimmer who has mastered a turn finally. She has proof of labour.

Improvement is like a drip, it comes gradually but it replenishes you.

Pereira has gone faster this year, which makes her believe she can go even faster. She's beaten her time but of course no one ever beats the clock. It's there every day. Tick, tick, tick, it asks the same mocking question.

Can you fly again?

So Pereira - and the shooter, the gymnast, the diver - will train in anonymity. Then sit alone, aching, exhausted, hungry. Then train again. Over weeks, months, years. To find a quicker time takes time. Sometimes you just have to go fast slowly.