Muscles under unusual control, muscles that twitch, and muscles some people do not have.
Showing 29 oddities.
Skeletal muscle usually works as a team, several muscles moving one joint together. This region collects the cases where a single muscle, or a missing one, stands out on its own.
Palmaris longus and plantaris muscle are both muscles a large share of people simply do not have, with no loss of strength either way. Platysma display and raising one eyebrow are about isolating a muscle that normally moves alongside its neighbours. Flaring nostrils is a muscle almost everyone uses without thinking, that only some can move on command.
What separates these entries from a reflex or a trick elsewhere in the catalogue is the focus on the muscle itself. The question is not what triggers it, but whether you have it, and whether you can control it apart from the muscles around it.
Results narrow the list below as you type.
Small visible twitches in the eyelid, calf, thumb, or arm that come and go with no weakness. One survey found them in about 70% of healthy clinicians. They are very rarely a sign of nerve disease.
A widening of the gap between the two halves of the six-pack muscle, seen in nearly every first pregnancy and in some men. A bulge down the midline when you sit up is the usual sign.
Widening the nostrils on purpose. No study has counted how many people can do it on command. It also happens on its own during hard breathing and in strong emotion such as anger.
An extra tendon link in the forearm that ties the thumb to the index finger. When the thumb bends into the palm, the index fingertip bends with it. Roughly 1 in 5 people have it, but counts vary widely.
A thin tendon that stands out in the wrist when you press your thumb and little finger together. About 1 in 7 people do not have it at all, and they lose nothing.
A small calf muscle with a very long, thin tendon that medical students mistake for a nerve. Between 7% and 20% of people do not have it.
Tensing the thin sheet of muscle under the skin of the neck so that cords stand out from jaw to collarbone. Everyone has the muscle. Nobody has counted how many can flex it on its own.
A sudden, cramping pain deep in the rectum that lasts seconds to minutes and then goes away completely. It has no known cause, and it is harmless.
Lifting a single eyebrow while the other stays down. Informal estimates say 30% to 35% of people can do it without training. No study has measured how many of the rest can learn it.
These entries belong to another region first, and touch this one too.
Using both hands equally well for every task. About 1% of people are truly ambidextrous. Many people who say they are ambidextrous are mixed-handed: right hand for some jobs, left for others.
Folding the tongue into three lobes, like a clover leaf. In one Dutch study, about 15% of adults could do it. It is usually called the hardest tongue shape.
Turning both eyes inward toward the nose on purpose. Most people with normal two-eyed vision can do it. Your eyes will not get stuck that way.
Swallowing opens a small tube between your throat and your middle ear for a fraction of a second. The faint click you can hear is that tube letting air through to balance the pressure.
Up to about half of all people can make a low roar inside their own head by tensing a tiny muscle in the middle ear.
Moving the outer ears using three small muscles that most mammals use to point their ears at sounds. About 1 in 5 people can wiggle their ears. Some people can learn.
Tiny muscles at the base of most hairs pull the hair upright when you are cold, scared, or moved. In a furry animal this traps warm air or makes it look bigger. In a human the raised hair does almost nothing.
A sudden jolt of the arms, legs, or whole body just as you fall asleep, sometimes with a feeling of falling. Most people get them, and they are harmless.
A tap on the tendon below the kneecap makes the lower leg kick. The signal goes to the spinal cord and straight back through one connection. It is a classic example of a one-synapse reflex.
Put a finger in a newborn's palm and the fingers close around it, hard. The grip is strong enough to hold the baby's weight for a moment. It fades by about six months and is replaced by grasping on purpose.
Making the tip of the tongue narrow and sharp, like a pencil point. About 55% of people in one Chinese survey can do it. It and tongue rolling are the two most common tongue tricks.
A single brief shudder that runs down the spine or through the whole body when you are not cold. Many people report them. Nobody has counted them.
You wake up, or start to fall asleep, and cannot move or speak for a few seconds to minutes. Sometimes a threatening presence seems to be in the room. It is the normal paralysis of dreaming sleep running a little late.
The low thump or rumble in your ears when you yawn or shout is a tiny middle ear muscle tensing to protect your hearing from your own noise.
Folding the tip of the tongue backward over itself inside the mouth. Studies find that between 1.5% and 27.5% of people can do it.
Between 65% and 84% of people can curl the sides of the tongue up into a tube. For decades it was taught as a simple one-gene trait. It is not.
Turning the tongue on its side so the edges face up and down, or all the way over. Between 12% and 36% of people can twist it at least halfway.
Opening the tubes that link the middle ear to the throat on command, without swallowing or pinching your nose. You hear a click, and your own voice gets loud. Some divers and freedivers learn it, but most never do.
About 8% of people can make both eyes shake rapidly from side to side on command. It looks alarming and is harmless. It is tiring and lasts only seconds.
Turning both eyes outward, away from the nose, on purpose. Nobody has counted how many people can do it. Most people can learn the mild version, parallel viewing, from Magic Eye pictures.