When presidential candidates choose a running mate, voters can't help but think about the circumstances that could lead to the No. 2 moving into the Oval Office.

No vice president has been called on to take on the duties of the preisdency full time since Gerald Ford, but it has become relatively routine for the vice president to be prepared when the president is expected to be unfit for office for a time, such as during surgery.

If Barack Obama, 47, and Joe Biden, 65, take November's election, however, there's not much in Obama's medical reports that indicate he is likely to have to sit out for a while.

A letter covering Barack Obama's medical history was released on May 29 showing that he is "in excellent health."

Dr. David L. Scheiner, a board-certified general internist, reported that the only concern was Obama's smoking habit, which he is trying to overcome by avidly chewing Nicorette.

Although cancer is seen in his family history, Obama's medical examinations have returned normal, including average blood pressure, cholesterol, triglycerides, and pulse. All of his systems appear to be fine, and the 46-year-old continues to have regular examinations where issues including upper respiratory infections, skin rashes and minor injuries have been addressed.

According to the New York Times, Obama's lean and muscular frame is maintained by both a daily basketball game in the hotel gym with his right hand man, Reggie Love, or jogging three miles.

Obama's diet is balanced with "good intake of roughage and fluids," said Scheiner. This is maintained by his foods of choice: roasted almonds, protein bars and vegetables, especially broccoli and spinach, said Love.

What About Biden

Biden is said to be in good health, though he has had a major scare.

In 1988, the year after her first ran for president before pulling out of the Democratic primaries, Biden had an aneurysm in his brain that nearly killed him, according to his campaign biography.

He needed two surgeries to recover, but Time magazine said that by late September of that year, despite a small scar from his surgeries, he looked like the fittest person at a campaign picnic.

He has been in good health since, reports say.