Staying healthy is part of the presidential job description. A few weeks after Bill Clinton's 1992 victory, Ronald Reagan advised his successor to go to Camp David whenever he could; Reagan said the air, the rest and the space would do him good. And while in office, George W. Bush jogged regularly and, after a knee injury, went mountain biking with Lance Armstrong, who called him "one competitive dude."

Staying healthy, however, is no less important for nonpresidents — or ex-presidents. After the nonstop pressures of the country's highest office, former White House occupants seem to gravitate toward exercise that provides an adrenaline rush. Carter climbed Mount Kilimanjaro and, at 62, took up skiing. George H.W. Bush famously jumped out of an airplane when he was 85. Clinton would visit the Bush clan in Kennebunkport and was barely able to hold on to his lunch as Bush the elder bounced him over the Maine waves in his speedboat. "He drove like a bat out of hell," Clinton recalls. "He's got these three giant engines that were so quiet … until he revs 'em up right, and then we were practically levitating across the water at the speed of sound. I thought the g-forces were gonna kill me."

Joking aside, Clinton did face a life-threatening health crisis after he left office: He underwent quadruple bypass surgery in 2004. Since then, he has given up meat, eggs and dairy and lost more than 20 pounds.

Among those who monitored Clinton's health most closely during the crisis was George H.W. Bush, who by then had become "the father he never had," as Barbara Bush put it. After the senior Bush heard that Clinton had had follow-up surgery in 2005 to remove some fluid and scar tissue from his left lung, he called Clinton within hours, probing his friend about his condition, asking him what his doctors were thinking, pinning him down about whether he was strong enough to exercise. The bond between the two men grew so strong that the younger Bush made it a punch line, telling one dinner gathering that Clinton had emerged from surgery "surrounded by his loved ones: Hillary, Chelsea, my dad." In fact, the extended Bush clan has bestowed on Clinton a nickname: They call him their "Brother From Another Mother."

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