How long is too long for a handshake?
Donald Trump's bone-crushing, toe-curlingly long handshakes may be an attempt to assert power, but they could be causing more harm than good.
Scientists have suggested that a handshake lasting more than three seconds could spell doom for a working relationship.
Researchers in Dundee found extended power-grabs could even trigger anxiety.
They could also negatively impact business meetings and affect relationships.
Although a small study, the results highlight the importance of introducing ourselves appropriately.
And it's bad news for the world's most prolific hand shakers - the politicians.
'Power and domination'
US President Donald Trump is renowned for his push-and-pull, steel-gripped, lengthy handshakes.
His extended greetings with other world leaders can last almost 20 seconds and body language experts have described them as a display of "power and domination".
Mr Trump and Japan's Prime Minister Shinzo Abe's awkward handshake at the White House in February 2017 lasted for 19 seconds.
Donald Trump and Emmanuel Macron have a well-documented history of aggressive hand-shaking.
At their first meeting, the US and French leaders shook each other's hands so tightly their knuckles went white.
The two presidents took their handshake to the next level at the Bastille Day parade in Paris in July 2017. The never-ending handshake seemed at times like a tussle, with the French premier stumbling while still in the grip of his contemporary and at one point it involved the first ladies. The bizarre display lasted 29 seconds.
The historic first meeting between Mr Trump and Kim Jong Un in Singapore in June 2018 was the end of a well-choreographed build-up and lasted for a total of 13 seconds.
In February 2019, Canadian Prime Minister Justin Trudeau decided to take the initiative on his first meeting with the US President to avoid any doubt and go straight in with an accompanying shoulder grip.
But Donald Trump is not the only one who strikes fear in a new acquaintance.
When Kim Jong Un met the South Korean president Moon Jae-in at the demilitarised zone, the greeting was 12 seconds long.
And no one can leave out the master of the long handshake, Banzai's Mr Shake Hands Man.
He managed to catch a grip with actress Angelina Jolie for a very uncomfortable 67 seconds.
The University of Dundee masters students concluded that participants showed less "interactional" enjoyment after a longer handshake, laughing less and showing increased anxiety.
Study leader Dr Emese Nagy said: "Handshakes are a particularly important greeting and can have long-lasting consequences for the relationships that we form.
"There has been evidence to suggest that many behaviours, such as hugs, fall within a window of approximately three seconds and this study has confirmed that handshakes that occur in this time frame feel more natural to those who participate in the greeting.
"While shaking hands for longer may appear to be a warm gesture on the surface, we found that they negatively affected the behaviour of the recipient, even after the handshake was finished."
So what does this mean for the world's most powerful hand-shakers?
Dr Nagy said: "Our findings suggest that while doing so might look impressive for the cameras, this behaviour could potentially jeopardise the quality of their working and personal relationships from the beginning, which could have repercussions for millions of people."