Athletes who are in peak form recuperate quickly. If you yourself are an athlete or have compete, I'm sure it's happened that you've been surprised or realized at times how quickly you're able to start the next interval or how you after a competition how quickly you recovered.
Remember, these guys are professional athletes and train at least two times a day on the off season and are used to it.
They also have the possibility to rest all day and sleep between their workouts, not like the rest of us who have to work the entire day and then run home from the office.
It's athletes who aren't in form that lay on the track or puke in their shoes. This can also happen to professional athletes, but when they're not in shape.
Also referring to your comment about the agents. There are those who work with over 80 to 100 athletes. Do you think the agents know or are in charge of providing drugs for all these people? I am the first to admit that, of course, there are agents who help dope their athletes, but this is not mainstream and primarily doping is a problem with individual athletes and his/her choice to take drugs, or/and their coach (or some other closely related person) who may influence them.
As for those of you who think all the athletes at the top are drugged, if you spent time with them and watched how their careers go up and down (or steadily improve) you'd realize this is nowhere near being the case. Look at the 800m for example; most of the athletes who run this event at the highest level have been around for years or are constantly fighting to gain a tenth or so on their rival. There aren't many who improve by "leaps and bounds."
That is running 1'48" the first year on the circuit and then running 1'42" the next.
I know for certain that most of these guys take out-of-competition tests or voluntarily give there whereabouts to the anti-doping department of the IAAF, ona regular basis, so that the testers can drop by when they want to, to make a surprise test. This goes for during and after the summer season.
Seeing the amount cases that come up I understand that many of you lose faith in the sport at times or want to bag it, but knowing personally many of the top athletes and the fact that they are clean, I hate to see them be generically classified and accused as "doped"...for example, your comment of all finalists in the 1500m not being clean...Well, if your image of the sport has reached that low then you might as well follow curling.