Why belly laughs make us weak at the knees
Friday 03 September 1999
Researchers at Leiden University, in the Netherlands, decided to investigate why some people become "weak with laughter", a phrase that is used in many languages. They recruited volunteers who were shown, or told, jokes, and while they laughed their physical responses were monitored.
The team measured a reflex in the subjects' legs by stimulating a nerve behind the knee and measuring the contraction of the calf muscle. This is known as the H-reflex and provides a measure of how ready people's muscles are to move.
The researchers found that when people were told jokes that made them laugh out loud, the reflex almost disappeared, but it was unaffected by jokes that only brought a smile. Gert van Dijk, a member of the research team, said: "When the reflex is strong, you can say the muscles are ready to fire. When it is low, you know the spinal cord has said to the muscles they had better shut up for a while and not move."
The aim of the study, published in The Lancet medical journal, was to look at a phenomenon called cataplexy, a rare side-effect of the sleep disorder narcolepsy. When sufferers from the condition laugh, they drop to the floor and are unable to move for several minutes while remaining fully conscious. Scientists believe there is a switch in the brain, which normally operates only during sleep to prevent people acting out their dreams, but which may also be triggered by laughter in susceptible individuals. While this is extreme in narcoleptics, one ordinary person in six has laughter-induced weakness.
"We hoped we would see people with narcolepsy have a bigger drop in the reflex," Dr van Dijk said. "But that is not what we found. They did have a drop, but normal people had exactly the same reaction. You do get weak at the knees if you laugh out loud."
But he was unable to spread the jokes that made the study's subjects fall about. "They were told by students," he said. "I don't know what jokes they told and I don't think I want to know. From outside the room it was clear that the volunteers certainly found them funny and that was the point."
Malaysia Airlines plane crash exposes alarming flaw in airline security: over one billion flights made last year without stolen-passport check
Kim Jong-un wins 100% of the vote in North Korean elections
Teacher shows sex tape featuring herself to pupils during class by mistake
Malaysia Airlines Flight MH370: Oil slicks in South China Sea ‘not from missing jet’, officials say
Swarm of killer bees sting woman 1,000 times
Britain's top vet sparks controversy with call for ban on slashing animals' throats in 'ritual' slaughters for halal and kosher meat products
If you're horrified by a flame-roasted dog, you should be shocked at a hog roast
Poor 'live like animals' says Boris's privately educated sister after going on 'poverty safari'
Exclusive: Impact of immigrants on British workers ‘negligible’
Vince Cable: Teachers 'know absolutely nothing' about the world of work
Ukraine crisis: Russia pledges to 'retaliate against sanctions' as Ukrainian president says Crimea vote will not be recognised
- 1 International Women's Day 2014: The shocking statistics that show why it is still so important
- 2 Australian man Rod Sommerville reacts to bite from deadly snake by reaching for cold beer
- 3 Teacher shows sex tape featuring herself to pupils during class by mistake
- 4 David Cameron resorts to paying for Facebook fans because not enough people like him
- 5 Steve Irwin’s final words: Cameraman present at death opens up about deadly stingray attack for the first time
£3360 - £16800 per annum: Randstad Education Nottingham: Cover Supervisor requ...
£6720 - £33600 per annum: Randstad Education Nottingham: Male and Female PE te...
£130 - £161 per day: Randstad Education Nottingham: Do you have a qualificatio...
£6720 - £33600 per annum: Randstad Education Nottingham: The school is much la...