5 of the most amazing human athletic performances of all time

Every so often an athlete does something that the rest of the world didn't yet know was possible. They take whatever we thought were the "limits" of human performance and show that we haven't yet found the point beyond which we can go no further.

Athletes now tend to approach sports with equipment and even techniques that their predecessors didn't use, which is largely responsible for the impression that humans are still getting "stronger" and "faster," according to Dr. Michael Joyner, a physician and Mayo Clinic researcher who is one of the world's top experts on fitness and human performance.

Because of that, these achievements or records almost never last forever. But there's something special about certain achievements that sets them apart, and so we asked Joyner to name a few of the most impressive achievements of all time. These aren't all in the past, either — at least one of these athletes will be competing in the Rio Olympics in August of 2016.

Roger Bannister: On May 6, 1954, Bannister became the first person ever clocked running a sub-four-minute mile.

Eddy Merckx: In 1972, the Belgian cyclist set the record for the furthest distance traveled in an hour, speeding 49.431 km around a high altitude track in Mexico City.

Tenzing Norgay and Edmund Hillary: Joyner says the first time mountaineers summited Mount Everest, which Norgay and Hillary did in 1953, certainly deserves a spot on the list.

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Jim Ryun: "For pure dominance, Jim Ryun's world record in the mile in 1967 is at some level the performance all other endurance performances should be measured against," says Joyner. Ryun's time of 3 minutes and 51.1 seconds would be beat in 1975, but Joyner says that if you calculate the difference that track improvements have made over the years, Ryun would be competitive with the fastest ever.

Katie Ledecky: "She's among the greatest endurance athletes ever, full stop," says Joyner. Ledecky dominates the freestyle discipline and currently holds the world records for the 400, 800, and 1,500 meter distances. She'll be competing in four freestyle races in Rio.

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