You should re-read the bit in the book, like I did after seeing this photo. It's unbelievable.
Hang on, I'll paste the excerpt here (this is on leg two, after Polly's):
The trig point stood among clumps of broom, with other paths leading off in every direction – it was impossible to see where to. Our home in Wales had been deep in mountainous countryside and whenever we had a moment spare, we walked in the hills. The children were pre-school when they climbed their first mountain, but as they grew older it often took some imagination to encourage them to be out in the cold on an arduous walk. Whenever we reached a trig point Moth would jump on and plank for a photo, lying on his stomach on the column and pretending to fly, anything to cheer up kids who were ready to give in. It became a family tradition, so the sight of the Golden Cap trig point was too appealing, CBD or not.
‘Do you think you can do it without hurting yourself?’
He dropped his pack down and putting his hands over the top of the column hoisted himself on. I waited for the cry of pain, the inevitable self-rebuke for having been so silly. It didn’t come. He spread his arms and flew into the clouds, free and floating, for all the world as if he would live forever. I ran around taking photos as if it was the first time he’d flown, or the last.
‘Maybe it’s the cabbage rub.’
His face was clear, he wasn’t even hiding pain, and he was laughing. In the fog-bound heather we hugged and jumped, laughing, kissing, shouting. Was this possible? From the point of not being able to get out of bed, back to strong and in control of his limbs in just under two weeks. This shouldn’t be possible. But it was. I should have noticed that I was no longer seeing the drag in his footprints, but it hadn’t registered.
‘Maybe it’s because we had a rest in Weymouth. Maybe my body’s adjusted quicker, like acclimatizing to altitude.’
‘But how? How can the stiffness have receded so quickly? On the north coast it took weeks.’
‘I’ve no idea; I knew it was feeling easier over the last couple of days, but I didn’t dare hope.’
‘Do you think it could be something to do with oxygen? I know we thought it before, because the path makes you breathe so deeply. That huge wash of oxygen – can it somehow affect the brain? It can’t be, though. If it was that simple, the hospital would just hand out oxygen tanks.’
‘I don’t know. It’s obviously got something to do with heavy endurance exercise. It must cause some sort of reaction that we don’t understand. I don’t know how it works, I just feel great.’ We jumped and danced in the fog of Golden Cap.
‘Be careful on the stairs.’
‘Don’t plan too far ahead.’
‘We don’t need to – we’ve got Paddy for that. Even if everything he says is backwards.’
[I wonder why we've never seen these photos?]