President Biden underwent the third physical exam of his presidency on Wednesday amid concerns over his age as he campaigns for a second term.

Mr. Biden, 81, traveled to Walter Reed National Military Medical Center for his annual physical, according to the White House. The visit was not announced ahead of time but was on his schedule, according to two people familiar with the plans but who were not advised to speak about them publicly.

Mr. Biden spent about two and a half hours inside Walter Reed. The White House is expected to release a summary of Mr. Biden’s physical later on Wednesday.

Events over the past few weeks have cast a spotlight on Mr. Biden’s age. He was described in a special counsel report over his handling of classified documents as a “well-meaning elderly man with a poor memory.” Polling shows that a majority of Americans have concerns about his age and ability to run for a second term. And Mr. Biden has made unforced errors at events, including recalling interactions with foreign leaders who would have been dead at the time those interactions took place.

As the presidential election heats up, the president has tried in recent days to assuage concerns over his age by reframing the focus on his likely Republican challenger, former President Donald J. Trump, who is four years younger and who makes a number of untrue, exaggerated or outright false claims at each of his public appearances.

“You got to take a look at the other guy,” Mr. Biden said during an appearance this week on “Late Night With Seth Meyers.” “He’s about as old as I am, but he can’t remember his wife’s name,” he added, referring to a video in which Mr. Trump, 77, appeared to forget the name of his wife, Melania.

White House officials have been asked for weeks about whether and when Mr. Biden would make the trip to Walter Reed. Last February, Kevin C. O’Connor, the president’s longtime physician, gave Mr. Biden a clean bill of health, calling him a “healthy, vigorous 80-year-old.”

But Mr. Biden’s advisers have declined to say definitively whether the president — the oldest in the nation’s history — will take any tests to assess his memory and cognitive abilities. (In recent weeks, Mr. Trump has bragged about taking the Montreal Cognitive Assessment, a test that can help detect dementia and cognitive decline, but he has distorted the facts about the contents of the test. And the Montreal test, experts say, is neither definitive nor diagnostic.)

Mr. Biden has also become noticeably slower in his movements in recent months, walking stiffly as he makes his way to the podium at appearances and taking the short stairs directly into the belly of Air Force One, rather than the taller stairs to the plane’s upper door.

Last year, Dr. O’Connor said the stiffness in Mr. Biden’s gait was the result of “significant spinal arthritis, mild post-fracture foot arthritis and a mild sensory peripheral neuropathy of the feet,” for which the president undergoes physical therapy to maintain flexibility.

His gait is somewhat halting, a characteristic that multiple people close to the White House say is partly because of his refusal to wear an orthopedic boot after suffering a hairline fracture in his foot before taking office.