Why Your Legs Jiggle Without You Noticing - The Mechanism and What It Does for the Body

You Notice Your Leg Is Moving

In the middle of a meeting, the person beside you lightly presses your knee. Only then do you notice your own leg had been bouncing up and down in small movements. You decide to stop and you stop, but a few minutes later it has resumed.

In some cultures this movement is treated as bad manners and even carries a dismissive name. But the property of resuming after you try to stop it shows that the movement is occurring at a layer below the will.

Movements that occur below the will usually have a function. Here we look at two of them.

Raising Your Own Level of Alertness

The first function is regulating alertness.

The human brain tries to hold alertness within a range suited to activity. Too low and you get drowsy and your attention scatters; too high and you tense up and your thinking will not come together. The adjustment that keeps you inside this range is carried out without being noticed.

In monotonous situations, alertness tilts downward. A long meeting, a task with little variation, a stretch of waiting. To hold alertness up in this state, one means employed is moving the body to manufacture sensory input. Moving a leg, spinning a pen, touching your hair, shifting posture. Every one of these is a movement that manufactures input.

Conversely, the same movement appears when tension is too high. In that case it works in the direction of discharging elevated alertness. Just before an exam, in a waiting room before an interview, waiting your turn in a nerve-racking setting. Moving consumes a state of bodily readiness that has nowhere to go.

So this movement comes out both when alertness has dropped too far and when it has climbed too high. The directions are opposite, but as an adjustment aimed at returning to the range, the work is the same.

A Body That Keeps Sitting, and Blood Flow

The second function concerns circulation.

Returning blood from the legs to the heart takes more than the force of the heart alone. When the calf muscles contract they compress the vessels, and combined with the valves in the veins a mechanism operates that pushes blood upward. Walking keeps this mechanism running continuously.

Keep sitting and the mechanism stops. Blood pools in the legs and registers as swelling or heaviness. This is one of the reasons long periods of sitting are treated as a health risk.

Moving a leg in small movements keeps those muscles contracting on a small scale. The effect does not match walking, but circulation is maintained better than in complete stillness. The picture is one of an unconscious movement partly compensating for the disadvantage of continuous sitting.

Indeed, that so many people move a leg in situations of long sitting is explained naturally if the body detects the pooling and prompts the movement.

Why It Increases During Concentration

One situation in which this movement increases is when you are concentrating. Reading, calculating, thinking something through.

Here the maintenance of alertness is what operates. Taking on a difficult task creates a need to gather attention onto that task. Meanwhile, a still body lets alertness fall. To resolve this contradiction, one solution employed is to run an automatic movement unrelated to the thinking in parallel.

The same thing happens with sound. Some people find it easier to concentrate with a steady background sound than in complete silence, because external input is being used to maintain alertness. The mechanism by which noise helps concentration and the movement of a leg satisfy the same function through different routes.

Forcibly stopping the movement during concentration can therefore lower the concentration itself. Stopping it on grounds of manners and the efficiency of the work do not necessarily point the same way.

How It Differs From Restless Legs

Some states involving leg movement do require medical attention. Here are the markers for telling them apart.

Unconscious repetitive movement occurs during the day, the person is barely aware of it, and it carries no pain or discomfort. You notice only when it is pointed out, and it stops temporarily if you decide to stop it.

A state in which there is an unpleasant sensation in the legs and you cannot keep from moving them in order to relieve it is a different thing. This state intensifies from evening into the night, worsens when you stay still, and eases temporarily when you move. It often comes on strongly at bedtime and prevents sleep, which affects quality of life directly.

If your case fits this description, iron deficiency or another condition may be involved, and it becomes a matter for consulting a medical professional. Check the causes and responses when leg discomfort keeps you awake, and if it applies, consider getting seen.

Similarly, if the movement is confined to one side, if it moves involuntarily on a large scale, or if there are involuntary movements in other parts of the body, evaluation on the neurological side becomes necessary.

Substituting to Fit the Setting

Function or not, in settings where those around you are a concern, substituting a different form is the practical route.

The conditions for a substitute are that it satisfy the two purposes, maintaining alertness and circulation, while being hard to see. Raising and lowering your toes inside your shoes, pressing the floor with the soles of your feet, tensing and releasing your thighs lightly. All are hard to read from outside, and muscle contraction still occurs.

The other route is to break up the sitting time in the first place. Standing and walking once an hour satisfies both the need for circulation and the need for alertness. Creating occasions to change posture is more fundamental than enduring the urge.

And if you are the one bothered by someone else's movement, knowing that it may be coming out in service of that person's concentration or physical upkeep changes how you raise it. Before correcting it as a matter of manners, looking at the fact that this person is enduring a long stretch of sitting helps more in practice.