The perception that children seem to grow taller overnight is likely true, researchers said on Thursday.

Scientists at the University of Wisconsin’s School of Veterinary Medicine in Madison placed sensors on the leg bones of lambs to monitor bone growth in the animals. Ninety percent of bone growth occurred when the animals were sleeping or otherwise at rest, according to the study published in the Journal of Pediatric Orthopedics.

“We observed this noncontinuous pattern of growth, but what was really interesting was that the bones were growing only when the animals were lying down, and almost no growth occurs when the lambs are standing or moving around,” study author Norman Wilsman said.

He reasoned that growth plates consisting of soft cartilage at the ends of bones become compressed when walking or standing, preventing growth. When lying down, the pressure on the growth plates is off and the bones elongate.

Co-author Kenneth Noonan said: “This is a study that points out that growth is not a continuum. There are growth spurts, which may occur within the daily life of lambs and possibly humans too.”

Previous research has shown children grow in spurts that may last just a few days. Children sometimes complain of intense growing pains at night that emanate from the ends of their lower extremities where the growth plates are, Wilsman said. There is no treatment for growing pains.

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