These are the hard yards, the lengths that nobody sees. Six blocks of 400 metres all-out max, No 1 stroke, see what time you can hold, and having been in the pool since 7am, Rebecca Adlington is hurting. But this is what she knows, and the familiarity is reassuring.
A few minutes after the session finishes, Britain's golden girl is still sitting pink-cheeked by the poolside, legs drawn up, arms protectively around her knees. But this is nothing, she smiles ruefully; the coming week will include nine such sessions, plus gym work, running... "You do get tired," she admits, a little unnecessarily. "But at least the weather's not too bad yet. I remember last winter, when it had really snowed, and Bill [coach Bill Furniss] still wanted to take us running."
Adlington begins to giggle. "It was about a foot deep, and we were, like, 'You can't be serious'. He was, and off he went. We just stood and watched. He'd gone quite a long way before he realised we weren't following."
She is laughing now, the natural, infectious laugh that became familiar in interviews and media appearances after she won gold in the 400m and 800m freestyle in last year's Olympics. After she reached such heights it was a shock when she finished third and fourth at the World Championships this summer, though, as she points out, it was hardly the disaster it was painted as.
"I was actually really pleased with my 400m, going two seconds quicker than I did at the Olympics. The 800 I obviously wasn't so pleased with, but looking at the time it was OK, it was an all-right swim, I just would have liked to have gone a little bit quicker.
"Coming fourth is the worst place, but I definitely learnt a lot from it. It did all go a bit crazy after the Olympics media-wise, and though we tried to ration it, I probably did a bit too much. But hey, I'm 20, still getting used to it all, so I'm going to make mistakes. It's just whether I learn from them, and hopefully I have."
A two-week holiday in Crete during which she insists she did nothing except sleep, eat, and lie by the pool left her refreshed and ready to apply herself to what she does best. "I'm actually very, very good at doing nothing, it's one of my best talents, but I did need that time away, and feel so much better for it. Switching off completely is important mentally as well as physically."
Adlington stands to shake hands with Arthur van Hoogstraten, the 44-year-old IT manager from London whose bid of £2,200 secured one of the most sought after lots in The Independent's annual Christmas charity auction.
Arthur, a brave man, is to race Adlington over 200m, and tells her he once swum competitively, as a child in the Netherlands, and that he has been training hard.
Adlington's eyes widen. "And I've just finished a heavy session. Ooh, you're going to be beat me!"
In truth, Arthur has about as much chance as, well, a haddock taking on a porpoise. Even when the porpoise is exhausted, cold and gives the keen as mustard haddock 40 minutes one-on-one training advice first, there's only ever going to be one result. Especially when the haddock hasn't mastered the art of the tumble turn.
For Van Hoogstraten, however, the hour spent is one he will not forget. Adlington's affability and generosity of spirit make her perhaps the most personable of our current sporting greats, and Van Hoogstraten, like most who have met her, is rather bowled over.
He is also a much better swimmer for it, after Adlington belies her insistence that she doesn't have the patience to be a coach by explaining and often demonstrating how Arthur can improve. Constantly reassuring, – "Don't worry, I'm always worse in the morning too", she tells him – when the session ends with a race over a distance at which Adlington has a short-course best time of 1min 54sec, she does her darndest to drag him to a personal best. Unfortunately our haddock – I'm sorry, reader – goes off too quickly and runs out of energy in the last 50m.
Happily signing photographs afterwards, Adlington acknowledges this has been a relatively rare extra-curricular commitment. The European Short Course Championships, and being part of the European team taking on the Americans in the made for TV Duel in the Pool in Manchester on 18 to 19 December, now have her full attention. But so for a while did Arthur, who through sponsorship has managed to raise a further £1,800 for the charity Voluntary Service Overseas.
"She's a brilliant swimmer, and a really nice down to earth person too," he panted, afterwards. "I've enjoyed every moment."