How Impressive Is Usain Bolt? A Freakonomics Quiz

Last week, the sprinter Usain Bolt ran 100 meters in 9.58 seconds, shattering the existing world record. For his feat, Bolt may just be named athlete of the year.
In some ways, what is more remarkable than Bolt’s feat is how slow the improvement has been in the 100-meter dash.
Back in 1968, Jim Hines became the first person to break the 10-second barrier, finishing the race in 9.95 seconds. In 1991, Carl Lewis got the world record down to 9.86 seconds. In 1999, Maurice Green ran 9.79 seconds. Asafa Powell ran 9.72 in 2008.
Thus, between 1968 and today, the world record time had improved by 3.7 percent, or less than 0.1 percent per year.
This is in spite of the fact that there have surely been technological advances in tracks and shoes, as well as expanding knowledge of weight training and fitness. The world’s population has increased substantially, as have nutrition levels, especially in developing countries.
The biggest puzzle to me is not how remarkable Usain Bolt is, but rather why it’s been so hard to get people to sprint faster.
So here is the quiz: what human activity is the polar opposite of sprinting in the sense that the gains achieved over the last 40 years are most extraordinary?
Here are the ground rules.

1. It has to be something done by humans.
2. It has to be an activity in which achievements have been consistently tracked for at least 40 years.
3. It cannot be an activity in which the improvements have been driven primarily by changes in technology. (For instance, anything that has to do with the use of computers would be excluded from the contest because it is likely driven by the explosion in computing power.)

I have in mind one activity that has seen the most remarkable improvements I can think of. The first person to highlight that same activity wins a prize. In addition, if people can come up with even better examples than my own, another prize goes to the person whose activity has shown the greatest improvement.
Good luck to all. We’ll accept contest entries for 48 hours.
Addendum: The winner is announced here.