"Being weak with laughter is no joke," reports
Reuters Health news service. Laughing causes our muscles to
go limp, according to a study published in the journal The
Lancet. Researchers at Leiden University used a neurological
reflex to study the effect of laughter on muscular activity.
Tapping the shinbone causes the calf muscle to reflexively
contract. When volunteer subjects were laughing, the reflex
disappeared. When they were merely smiling, there was no
One of the researchers, Dr. G.J. Lammers, noted that the
phrase, "weak with laughter" exists in several
languages. "Up to 15.5% of individuals reported muscle
weakness during various emotions," he said. The
researchers speculated that their study might shed new light
on a condition known as cataplexy, where strong emotion
causes muscle weakness so severe that the person collapses.