Golfers' yips are down to cramp similar to those experienced by writers and musicians, US experts say.
Anxiety can make for jerky putts
The yips is a term for jerky movements that get worse when the player is anxious and can cripple their putting and chipping skills.
Some say the root of the problem is psychological, while others say it is a form of movement disorder, or dystonia.
The Mayo Clinic team told a neurology conference in Miami, Florida, how their lab tests showed it was down to spasms.
For the study, they asked 20 male golfers, 10 with yips and 10 without, to hit a total of 75 putts, varying from three, six and eight feet.
The golfers were rigged up to a machine that tested arm muscle activity and were asked to rate the quality of their strokes.
None of the golfers had any abnormal arm muscle movements at rest, when they held their arms outstretched, or while standing still holding the putter.
However, under all putting conditions, half of the golfers with a history of yips had detectable spasms or co-contractions of their forearm muscles just prior to striking the balls.
Yet only two of these golfers were aware that they had experienced yips.
None of the golfers with no history of yips had abnormal muscle contractions during the putting.
When the researchers looked only at the golfers with a history of yips, they found the five who had shown abnormal muscle contractions in the experiment were older, had higher current and best previous handicaps and had yips for fewer years than the other five.
The same golfers also missed more putts and by a greater degree.
Investigator Dr Charles Adler told the American Academy of Neurology meeting: "The co-contractions were similar to those of task-specific dystonias, or movement disorders, such as writer's cramp and musician's cramp."
Mike Rotheram, of Sheffield Hallam University's Centre for Sport and Exercise Science, said: "There are two opinions about yips.
"Some believe they are task-specific cramps and that the more times you do the same movement, you get disruption in the movement programme that carries out that task.
"Others say it is severe anxiety, or choking. Every time they come under pressure, that causes them to reinvest in, or revert back to, an earlier stage of learning.
"But because that skill is automatic, like riding a bike, there is no information or knowledge base for them to draw on.
"The trouble is, we don't know what's at the root of the problem at the moment."
He said the research still did not prove what was causing the muscle spasms.
"I firmly believe there is an emotional element to it. You also see it in other sports, such as darts and cricket."
Mr Rotheram is currently doing research, surveying different sportsmen about yips and in what situations they occur, to find out more.
He said there was no known treatment that worked to cure the yips.
Some have tried relaxation techniques and others have tried changing the way they carry out the motor activity, such as holding the grip of their club differently, he said.