US president Joe Biden is visiting Walter Reed National Military Medical Centre in Maryland for his annual physical examination – with the results sure to be closely watched as the 81-year-old seeks re-election.

Mr Biden is already the oldest president in American history and would be 86 by the end of a second term, should he win one.

After his last physical check-up, performed in February 2023, doctors declared Mr Biden “healthy, vigorous” and “fit” to handle his White House duties.

But voters are approaching this year’s election with misgivings about Mr Biden’s age, having scrutinised his gaffes, his coughing, his slow walk and even a tumble off his bicycle.

The White House said it will release a written summary of the “routine” check-up later in the day.

Former president Donald Trump, 77, is the favourite to lock up the Republican nomination later this month, which would bring him closer to a November rematch against Mr Biden. Mr Trump was 70 when he took office in 2017, which made him the oldest American president to be inaugurated, until Mr Biden broke his record by being inaugurated at 78 in 2021.

A recent special counsel’s report investigating Mr Biden’s possession of classified documents repeatedly derided the president’s memory, calling it “hazy,” “fuzzy,” “faulty,” “poor”, and having “significant limitations”.

It also noted that Mr Biden could not recall defining milestones in his own life such as when his son Beau died or when he served as vice president.

But addressing reporters on the evening of the report’s release, Mr Biden said “my memory is fine” and grew visibly angry as he denied forgetting when his son died of brain cancer in 2015 at the age of 46.

Mr Biden’s last physical showed that the president had a lesion removed from his chest over the previous year, but the results then otherwise largely matched the findings after Mr Biden’s previous examination in November 2021.

That report said his occasional coughing was due to acid reflux, while his stiffened gait was the result of spinal arthritis, a previously broken foot and neuropathy in his feet.

The White House also announced last summer that Mr Biden had begun using a continuous positive airway pressure, or CPAP, machine at night to help with sleep apnea.

Mr Biden had a colonoscopy in 2021, in which a 3mm “benign-appearing polyp” was identified and removed.

In 1988, Mr Biden had surgery to repair two brain aneurysms, which are weak bulges in arteries, one of which was leaking. Mr Biden has never had a recurrence, his doctor said, citing a test in 2014 that examined his arteries.

Many Americans, including Democrats, have expressed reservations about Mr Biden seeking a second term during this autumn’s election.

Only 37 per cent of Democrats say Mr Biden should pursue re-election, down from 52 per cent before the 2022 midterm elections, according to a poll from The Associated Press-NORC Centre for Public Affairs Research.

Polls have shown similar reluctance about Mr Trump too, however, and that has not stopped either from closing in on their party’s nominations.

While he was president, Mr Trump’s annual physical in 2019 showed he had gained weight and was up to 243lbs or 17.4 stone.

With his 6ft 3in frame, that meant his body mass index was 30.4. An index rating of 30 is the level at which doctors consider someone obese under this commonly used formula.

Mr Biden won Michigan’s Democratic primary handily on Tuesday, but an “uncommitted” campaign organised by activists disillusioned with the president’s handling of the war in Gaza far surpassed the 10,000-vote margin by which Mr Trump won Michigan in 2016.

That was a goal set by organisers and it was seen as a potential source of embarrassment for Mr Biden’s re-election campaign.