Why do we have limits?

Usain Bolt ran 100 meters in 9.58 seconds, Petra Felke threw the javelin 80 meters. These are absolute limits that no one has been able to "break" to this day. Or rather: no human being. Because in the animal kingdom, there are creatures like the flea or the cat that are far superior to us. Why is that – and couldn't we learn from these animal specialists?