The Child Who Says Their Legs Hurt at Night

"Every evening they cry that their legs hurt, but in the morning they are running about perfectly fine."

This is something mothers say often. For a long time I wondered why it is the evening, of all times, that these children have trouble. And usually this follows: "People call it growing pains — is it really because they are growing?"

A Name and a Cause Are Not Always the Same Thing

Let me start with the name. The term growing pains has been used for a long time, but the evidence that growing taller is itself what makes the pain is weaker than you might think.

There are findings that the period when height grows fastest and the period when this pain is frequent do not line up with each other. And the places where bone grows are near the knee or the ankle, while the places children say hurt are usually the muscles — the calf, the front of the thigh, behind the knee.

So I do not explain this pain to parents as "hurting because they are growing." I look at something else instead.

How Much Pain a Person Feels Differs from Person to Person

Given the same stimulus, one child says it hurts and another just passes over it. The body has a line at which it decides to call something painful, and that line sits in a different place in each person. This is called the pain threshold.

When children who say their legs hurt every evening are measured, this line has been reported to come out lower than in their peers. And not only at the legs — at several places on the body. It is closer to say that there is no problem in the legs; the whole body is hearing signals a little louder.

If this picture is right, a few things follow. Why both legs hurt together, why there is no swelling or heat, why tests turn up nothing, and why it is gone after a night's sleep.

That Line Also Moves Within a Single Day

One more thing lies on top of this. That line is not a fixed value.

On a day of a lot of running about, the evening hurts more. Once muscle has done a day's work the conditions in that place change, and while it is recovering the same stimulus is heard louder. It is the same place as an adult's calves being unusually heavy on the evening of a long walk.

This is also why this pain gathers between late afternoon and night. Around that time the other signals that came in during the day fall away. When there is nothing left to play with and nothing left to watch, a signal that was buried during the day comes forward. The child is not putting it on. It really is heard louder then.

There Is a Reason Rubbing Helps, Too

Mothers tell me the child likes it when they rub the legs. This too is not merely comfort.

The sensation of touch and pressure travels up nerves that are thicker and faster than the ones pain uses. When that signal arrives first, the pain signal following behind passes on less at the spinal cord. And warming the place increases circulation there, so recovery comes faster.

So rubbing the legs at night is a good thing to be doing.

What I Look At in My Clinic

I do not look at the legs alone.

I ask together about how the child sleeps, how much they run about during the day, how they eat, and whether they often say other places hurt as well. In a child whose pain threshold has come down, it is rare for the legs alone to be like this. Often they say their stomach hurts frequently, their sleep is light, and they are sensitive to sounds and smells too.

I think this is the same place from which this medicine has long looked at children apart from adults. Rather than holding on to one spot, it looks at the whole set of conditions the child is placed in. Tending to those conditions together does more than holding on to the legs alone. A child's body is not a scaled-down adult's, so when one thing wavers, several places waver with it. (A Child's Body Is Not a Scaled-Down Adult's)

When Testing Comes First

That said, there are pictures that must not be passed over as growing pains.

If only one leg hurts, if the child points exactly at one particular spot, if that spot is swollen or red or hot, if it is stiffer in the morning instead, if fever or weight loss comes with it, or if the child limps or does not want to walk — then testing comes first. These are not the picture of growing pains.

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We began with the question of whether it hurts because they are growing.

My answer is this. It is closer to say that growing taller is not what makes it hurt; the line at which pain is felt has come down. And that line differs from evening to evening according to how much the child moved during the day and how well they slept.

So I do not leave this pain as merely something to wait out. I think looking at why that line has come down leaves the child, and the mother, with something.

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References

• The clinical picture of growing pains and when to be concerned — Sports Health, 2017
• Children with growing pains came out with a lower pain threshold than their peers — Pediatric Rheumatology Online Journal, 2007
• On days of more activity than usual, pain is more frequent and stronger — a survey of 863 children — PAIN Reports, 2024

Written by Dr. Heo Ji-young (PhD in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)