I am asking for some professional judgement (randome thoughts are welcome too). The Chinese girl Liu Zige who beat Jessic Schipper to win the 200m butterfly improved her PB by 5 seconds to break the world record.

Is such dramatic improvement in results reasonable? If not, what drug can cause a swimmer is performance to improve so much?

Realistically that much improvement is not possible, without some chemical help.
Since she passed her tests you can not say she was using drugs.
Well, you can say it, but you can not prove it.
The biggest problem with drug cheats is that now anyone who improves is thought to be a cheat also.
There are lots of steroids that can assist performance along with HGH, and EPO.

That is an interesting question.

But, Zige was also coached by Schipper is coach, who is one of the best butterfly coaches in the world.
A hard training with a great coach in a home court, l think, can produce a world record even with a significant improvement.
The doping argument, without any evidence, is out of merit.

well now we may not be able to trace a certain drug in a test but in a few years it will probably be proven positive that they cheated.

She did have an Australian coach to help her technique.
Plus the swimsuit do help swimmer swim faster.

The truth is most athletes are taking some sort of drug and it is not illegal to take them till they find out about them. Athletes are one step ahead of science when it comes to performance enhancing drugs. This is not just the chinese but most olympic athletes take some kind of performance enhancing drug.it is just a matter of scientists discovering it and then having people banned from taking it.

Can the same be said about Michael Phelps?

That is a very interesting question. Finally someone asks a reasonable question about Chinese athletes, not one about their gymnasts.

Anyway, the pool in Beijing was very fast for multiple reasons. The biggest being it is a metre (3 feet) deeper than the average Olympic pool. Most Olympic pools r about 7 feet deep, it was 10. It was also faster because of the way the water flow in & out of the pool worked. It was at the bottom, instead of the sides. There was a few more which l can not remember.

Also with the new Speedo LZR Racer, everybody was lowering their personal bests, albeit not by 5 seconds. l know almost every Canadian record was broke at this event or the Trials, obviously American & Australian records were broken as well. It would make sense this would increase a swimmers chance of winning.

So while normally I'd say she would have to be using performance enhancing drugs to lower her time by 5 seconds, l think it may have just been it was a fast pool, with a fast suit, & the best swim of her life.

so if an Aussie or American did this would these questions be asked?.. l think not. it would be credited to a terrific performance. from what l saw in the pool there was nothing to suggest the Chinese were cheating.. just improving. considerably so.

talent and willpower are her drugs

Many swimming records were broken at these Games and be seconds too. l doubt she was on drugs. The swimsuit and the pool probably helped.

Just because this girl won the gold medal and you assume she is on drug? You are pathetic. What about Michael Phelps ?