Most non-elite 400m runners see a slowing of roughly 9% of their best 200m time. If you want to break 60 seconds, you must be able to run a 27.5 second 200m or faster, since (27.5 x 2) x 1.09 = 59.95 seconds. A few elite runners have been known to drop as much as 20% of their best 200m time, but this occurs only once every so many years. The most effective way to break 60 seconds is to find a way to cut 10 meters off your best 200m time. It may be possible with training and nutrition, but it's difficult. The next best option is to find a fast runner who has broken 60 before and copy his or her strategy. The third option is to recruit an elite runner who can help guide you through the process. There are very few cases where athletes have successfully defended their titles with a slower time than the previous year. In conclusion, breaking 60 seconds in the 400m is difficult but not impossible. The fastest man alive, Michael Johnson, was unable to defend his title at the 1988 Seoul Olympics after breaking 51 seconds in the preliminary round. The next year he broke one second in the world record trial, but did not improve upon this time when the event was added to the Olympic program. He was also never again able to defend his title.