Charles Eugster may be 93, but he has no less spring in his step than he did as a young man. In this talk from TEDxZurich, he brings us a powerful statistic: 92% of Americans over the age of 65 have one or more chronic diseases. While many clearly cannot be avoided, Eugster points out that inactivity is to blame for many of the diseases those who have lived long lives endure.

During the golden years, people retire and tend to slow down  – and yet there is a connection between work and one’s physical and mental health. But life doesn’t need to finish after retirement, which Eugster calls “voluntary or involuntary unemployment for up to 30 years.” That’s why Eugster has taken up rowing. And weightlifting. Watch this TEDxTalk about the factors for successful aging from a formidable speaker, who urges us to “break off the shackles of convention!”

This past Monday, swimmer Diana Nyad made her fourth attempt to swim from Cuba to Florida. Though this attempt ended when weather and jellyfish conditions took a turn for the worse, we can look back at her talk from TEDMED 2011 to understand how she — and all of us — found “grace in the face of defeat.” From her experience and that of other TEDsters who tell inspiring stories of pushing their body to its limits, we can better understand humanity and society from its extremes.

Diana Nyad: Extreme swimming with the world’s most dangerous jellyfish
In this talk, Diana Nyad shares her dream to swim from Havana to Key West — a multi-day, open-ocean route whose challenge is as much mental and environmental as physical. (Environmental? Yes. When Nyad spoke to reporters this afternoon, she told CBS News: “I’m not a quitter, but the sport and this particular ocean are different than they used to be. These jellyfish are prolific. And, you know what? To me, there’s no joy in that.” The backstory here: As the world’s oceans become depleted of large fish, jellyfish are moving in to take their place. Watch Jeremy Jackson’s powerful TEDTalk, “How we wrecked the ocean,” for more on the jellyfish population explosion.)

Lewis Pugh’s mind-shifting Everest swim
Lewis Pugh goes for “symbolic swims” in extreme locations to draw attention to global climate change. These athletic feats are physically grueling — imagine swimming 5,000 feet up in the freezing water of a lake on Mount Everest, in just a Speedo — but that’s nothing compared to the mental challenge. In this inspiring talk from TEDGlobal, Pugh shares what he learned, and how we can apply these ideas to climate change, the “Mount Everest of all problems.”

Ben Saunders skis to the North Pole
Pushing human capacity to its limit at the end of the world is what Ben Saunders does best. His record-breaking Arctic adventures explore the limits of physiology, psychology and of technology, testing how far humans can push themselves, while raising awareness of the rapidly changing situation at the North and South Poles. In October 2012 he plans to complete the South Pole route last traveled by Captain R.F. Scott.