How many 50-metre lengths could you swim before mind-numbing boredom, never mind tiredness, set in? Twenty, perhaps 30 on a good day. Graeme Smith ploughed up and down Stockport Metro's pool 2,180 times a few weeks ago, 109,000 metres in the space of a week.
All world-class swimmers pound at the pool for hour after hour, but Smith has to endure this water torture for longer than most because he is in the hardest event of all, the sport's equivalent of the marathon. Throw in weightlifting sessions and you get an idea of the punishment he inflicts on himself.
Not without reward, though. Smith won a bronze medal in the 1,500 metres at the Atlanta Olympics and, at 21, is the right age to be among Britain's best hopes of turning the currency into gold in Sydney in two years' time. It is not beyond the realms of possibility, either, that he might arrive at the 2000 Games as the world champion courtesy of his work in Perth next week.
The World Championships began on Wednesday - though the swimming programme itself does not start until Monday - and Smith and Paul Palmer, the two medallists in Atlanta, remain the country's bright prospects. Ah, Palmer, I can hear you thinking, I remember him, but Smith? Wasn't she the Irishwoman who won all those golds at Atlanta?
Having the same surname as Michelle hardly helped the profile of Britain's Smith at the last Olympics, but although the record books do not show it, the Scottish swimmer was not far away from becoming a gold medallist. He thought he would be when he entered the pool for the final in Atlanta and he still believes he should be now.
"People ask me if I was happy with the bronze and looking back I suppose I am. I'm proud that I was among only 15 or 16 Britons who got a medal but at the time I was gutted. My friends told me I looked like I was going to hit Sharron Davies when she interviewed me for the BBC afterwards.
"It was only when I got back to Manchester Airport arrivals lounge and all my friends started cheering that it struck me that I'd done anything impressive. It's other people who make you realise what you've done."
The reason why Smith was furious with himself was Kieren Perkins. The Australian is the double Olympic champion at 1,500 metres and his world record is 20 seconds faster than anyone else has ever covered the distance, but at Atlanta he only just qualified for the final in last place.
He was hardly out of Smith's mind - "when he got through I thought `Oh, no, you can never count this guy out of it'" - but he was out of sight in lane eight and had established a race-winning lead before the supposedly faster swimmers in the centre were aware of him.
"It wasn't until the turn at 400 metres that I noticed, `Oh God he's so far ahead'. By 500 I knew the gold medal was his unless he blew up completely." That jolt, plus the effort of trying to chase Perkins, meant that Smith was pipped for silver by 500th of a second by another Australian, Dan Kowalski. The long chase, as the leader was slowly but not completely reeled in, and the race for silver, made it one of the best races in the Georgia Tech Aquatic Centre.
Time has brought a sense of proportion with it, and Smith concedes that if he had to be finger-tipped away from a place it was better to have not been so close to gold or to have been pipped for a medal at all. But knowing that gold could have been his is why he goes in the pool every morning. It is why he has continued with a sport that, despite lottery money, barely rewards its athletes.
"I'm probably worse off than I was before," he said. "I get one big grant now, whereas before I had three or four. People think that Olympic medallists are rolling in it but it just isn't the case. My fear is that we'll go to Sydney, not do as well as we are expected to do and everyone will wonder why the money's been spent. If it wasn't for the prospect of an Olympic gold I'd have probably given up the sport."
Another spur in Perth is that Perkins did not qualify, the frailty that was hidden so emphatically in the Olympic final having floated to the surface. "I've no idea how Kieren improved so much in Atlanta," Smith said. "I spoke to him after and he said he'd been practising a longer stroke in the heats and when we got to half-way he felt rubbish. He went back to his old style and suddenly it clicked again.
"He was my hero, no, he still is. You've got to admire what he's done. Double Olympic champion, world champion and world record holder, he's awesome really. It will make a difference that he's not going to be at the World Championships. You can be ranked No 1 in the world but you know he's swum 22 seconds faster than I've ever done. In the back of your mind you know that if he hits his best the gold medal is his. In Perth it's going to be wide open."
Smith has qualified to swim in the 400m freestyle, too - the event in which Palmer got his Olympic silver - but as many of his rivals for the 1,500m are racing in that event, he might rest for the longer race. "They could take something out of themselves," he said. "If I'm fresh it might make the difference."
As Smith flew out with the British squad for the World Championships on Boxing Day, rest is relative. Perhaps just 1,000 lengths this week.