PED's aside, there seems to be as much a mental barrier that's broken as there is a physical barrier when a record falls. Once it's been broken, people seem to feel they have a sort of permission to go beyond the limits of what was previously thought impossible.

I think about swimming and Caleb Dressel. 20 yrs ago, the 50 yd free in swimming stood firmly at 19.05 seconds. After that, you'd see the second fastest time at 19.06, 19.07, 08... It seemed like the limit to human potential was set. Then a French dude at Auburn swam 18.8 and shattered the previous record. His teammate then went 18.6 and then 18.4. everyone thought that record would be absolutely impossible to touch. Caleb Dressel swam it in 17.63. right now, nobody is even close to him, and yet, I think we'll see a ton of 17 second freestyle times in the next decade at championships.

Look at other types of sports where PED's may be less obvious. They may be using Adderall but i think it's a gray area. Remember when a backflip on a motorcycle was thought to be impossible? Now the announcers hardly raise their voice at double backflips or front flips.