In this telegenic, mass-media age, the health and fitness of presidential candidates often is equated with their fitness to lead.

But should someone’s health, vigor and resting pulse rate make a whit of difference as a barometer of performance as president? And is it fair to compare the health and wellness of candidates who have a 25-year age gap, as is the case with Barack Obama and John McCain?

Yes, says presidential historian Allan Lichtman, author of “The Keys to the White House” and other political books.

“Sure, it reflects the superficiality of politics, but it also reflects a reality a modern president has to go through,” says Lichtman, a professor at American University in Washington, D.C. “Health and fitness of a candidate is a legitimate issue. The president is under enormous pressures and tensions.

“And when you look at the two candidates, the electorate is bound to make (physical) comparisons. Robust health has been a positive image for a president for over a century.”

Recent media coverage provides a glimpse into how the Democratic and Republican candidates are perceived as physical specimens during this election season.

There was Obama, on his overseas trip, stalked by a German tabloid reporter documenting his every bead of sweat during what had been a private workout at a Berlin health club. And there was McCain, campaigning in Bakersfield, Calif., around the same time and recovering from the removal of another skin lesion from his face.

So at the same time Obama was being peppered with questions about the number of biceps curls he does, McCain was assuring reporters that the bandage on his cheek did not mean his melanoma had returned.

McCain, who will turn 72 later this month, has a history of skin cancer and other ailments, and the injuries he sustained as a prisoner of war in Vietnam have limited his ability to exercise.

Obama, 47, has been depicted as a jock — shooting hoops, doing squats, riding a bike — though his bowling score, 37, was mocked by red and blue bloggers alike.

Projecting an aura of vigor, even if it has to be manufactured, is essential, according to Robert Gilbert, a historian at Northeastern University in Boston and author of a book on Calvin Coolidge’s depression.

“Look at (Ronald) Reagan,” Gilbert says. “When he had his first debate with (Walter) Mondale (in 1984), he stumbled badly. The Wall Street Journal even ran an editorial questioning senility. But Reagan came back strong in the second debate. But I think everyone knows that during his second term he was not operating at peak capacity.”

It’s doubtful, presidential scholars opine, that the rotund William Howard Taft (well over 300 pounds) could be elected today. Late-night comedians would have a field day with the fact that he got stuck in the White House bathtub.

By the same token, it would be more difficult for a wheelchair-using Franklin D. Roosevelt or a multiply afflicted John F. Kennedy to get elected. In their epochs, the media conspired to withhold the extent of their infirmaries.

Throughout the years, presidents such as Grover Cleveland (jaw cancer), Woodrow Wilson (paralyzed from a stroke) and Coolidge (clinical depression) concealed their conditions. It was only recently, too, that details of Reagan’s limitations from Alzheimer’s disease during his second term have come to light.

While Gilbert says it’s more difficult today to keep health issues a secret, it still can be done.

“I don’t think everything should be publicized,” he says. “Candidates and presidents have privacy rights like the rest of us.”

Yet since the early 1970s, candidates routinely have released their medical records to the press.

McCain, in May, released 1,173 pages of medical documents, his doctor concluding that he is physically fit for the job. He was said to have a strong heart, but he takes medications for high cholesterol, degenerative arthritis and occasional dizzy spells.

Obama’s campaign, a week later, released a one-page letter in which the candidate’s personal physicians deemed him in “excellent health” with no conditions. The only blemish: Obama was a regular smoker until he quit in 2007. (For the record: McCain smoked for 25 years, stopping in 1980.)

The number of documents reflects the scrutiny being felt by the respective candidates.

Neither Obama nor the media have made an issue of McCain’s age or health, and Obama recently told the Chicago Tribune, “I don’t think that’s going to be an issue people vote on.”

Maybe not, but appearance often is reality in the political arena. Which is why it’s smart for McCain’s campaign staff to stress the Arizona senator’s energy level, says University of California, Davis, history professor Robert Huckfeldt.

“McCain’s people are always talking about how they can’t keep up with him on the campaign trail,” Huckfeldt says. “I don’t think it’s an issue for most voters. Voters think, as long as you can get out on the stump, you’re fine.”

Even when candidates are not. In the 1992 campaign, when former Sen. Paul Tsongas’ bouts with cancer were revealed, the candidate donned a Speedo suit and swam laps for reporters. Tsongas died in 1997 and would have been battling cancer had he been elected.

“That’s why health is an issue,” Lichtman says. “In 1944, the rumor was FDR was gravely ill and would not survive another term. … Roosevelt countered that by doing a late vigorous campaign tour and going abroad to visit leaders. Of course, he really was gravely ill.

“And Kennedy kept his health problems as quiet as possible in 1960. (Republican candidate Richard) Nixon asked President Eisenhower to make an issue of Kennedy’s health problems. Eisenhower wouldn’t do it — probably because Eisenhower himself had health issues in office.”

If McCain wins in November, he will be the oldest president elected to a first term. Reagan was 69 in 1980 and, at that time, had no health concerns such as McCain’s cancer history.

“Certainly, there are serious questions about McCain’s health, and he’s got to counter them,” Lichtman says. “He’s not as robust as Reagan was back then.”

Because of McCain’s injuries after being shot down over Hanoi in 1967 — both arms fractured, a broken right leg, no cartilage in his knees and a smashed shoulder — he is not able to pose for photo ops at health clubs. But McCain says he does engage in “light exercise.” His aides say he walks and once hiked the Grand Canyon from rim to rim.

Of course, that pales before Obama’s fitness regimen. He’s said to run three miles daily, work out on light weights at the gym and play pickup basketball, often against players half his age.

Obama’s athleticism, however, might just backfire. Some have speculated that he might be too fit, too thin, too healthy to relate to an increasingly obese U.S. populace.