In overweight children, exercise can put pressure on their developing feet, say Australian researchers.
They point out that overweight children are at risk for foot pain and discomfort because they tend to have fatter and flatter feet, which can lead to increased pressure on the arched portion of the sole.
That, in turn, could stop kids from participating in physical activity, they warn in a recent paper.
"Physical activity is certainly crucial to health and well-being, and halting weight gain is important," said Diane L Riddiford-Harland of the University of Wollongong, who led a study of the effect of exercise on overweight kids' feet.
Since these children might be uncomfortable while exercising, alternate forms of activity are probably necessary, she explained.
"Non-weight bearing physical activity such as swimming or cycling may be a good option," Riddiford-Harland told Reuters Health in an email. "There are all types of aquatic movement activities and cycling-type activities children can participate in, but going to the pool/beach or on a bike ride with an adult can be enjoyable and are usually quite affordable."
She and her coauthors had found in a previous study that overweight kids had higher "plantar pressures" on the middle and fore-foot areas of the sole while walking than normal-weight kids.
They also linked the higher pressures and a flattening of the arches to a likelihood the kids would be less physically active.
In the new study, they divided a group of children who were already participating in a obesity treatment trial into three groups. One group focused on getting the children to be more physically active. A second group emphasised activity plus a parent-centred diet-modification programme. The third group did not involve physical activity, only the dietary modification.
Thirty-four kids participated. They were five to nine years old and generally healthy, except for being their obesity.
After six months, all the children had grown in height and lost some weight.
All the children's feet also grew in length and arch height, representing normal growth, but none of the other proportions of their feet had changed.
The lack of structural differences between the kids who exercised and those who didn't was surprising to the researchers. But, they say, the measurement at six months may have taken place too long after the 10-week weight-loss trial ended to detect changes caused by exercise.
"As the musculoskeletal system is still developing in young children, carrying excessive body mass will likely lead to long term health complications as they continue to age," Riddiford-Harland said.
"We still need to systematically determine just what causes the pain or discomfort that has been reported by these children, how prevalent it is, what makes it worse and does anything make it better, because being physically active and remaining physically active throughout life is imperative for good health," she added.
Podiatrist Alan MacGill, a fellow of the American College of Foot and Ankle Surgeons who wasn't involved in the study, pointed out that supportive shoes and orthotics would help children with flat feet.
"The devices can help control excessive motion in the foot," he said. "The shoe should be the correct size for the child and not too flimsy from toe to heel."