Strict rest may not be the best medicine for kids with concussions, a Canadian study found, challenging the idea that physical activity should be avoided until symptoms disappear.

A month after their concussions, ongoing or worse symptoms were more common in children and teens who were inactive during the week following injury, compared with those who engaged in physical activity during that first week. Activity was mostly light exercise including walking and swimming.

The results were similar even among those who early on had three or more concussion symptoms, which can include nausea, headaches and confusion. Physical activity still seemed to reduce chances for lingering symptoms a month after the concussion.

"It's still important to have caution in the immediate post-injury period," said lead author Dr. Roger Zemek, an emergency medicine specialist at Children's Hospital of Eastern Ontario. After a sports-related concussion, kids "should always be removed from play and not return that day."

To avoid re-injury, kids should generally be sidelined from the sport or activity that led to the concussion until a doctor clears them to return, he said. But the study results suggest they can resume sports or other physical activities sooner than previously thought, he said.

The researchers surveyed about 2,400 kids aged 5 to 18 treated for concussions in nine emergency departments in Canada. Most were sports-related injuries and most kids had at least one concussion symptom in the first week.

Results from the 2013-2015 study were published Tuesday in the Journal of the American Medical Association .

Current guidelines recommend rest until symptoms disappear to avoid additional concussions, which can increase chances for permanent brain damage. But an editorial published with the study says that advice "''has resulted in some athletes resting for weeks or months, at which point rest may be less helpful and perhaps even harmful."

The study authors say resuming physical activity may increase blood flow to the brain, while inactivity may deprive patients of not only that benefit but also the psychological benefits of activities they enjoy.

Patients in the study and their parents were asked about symptoms and physical activity at seven and 28 days after the concussion

In the early-activity group, 29 percent reported ongoing or worsening symptoms 28 days after concussions versus 40 percent of the group reporting no extra physical activity beyond daily living activities.

Among kids who reported having three or more symptoms in that first week, those who engaged in early physical activity regardless of intensity were 25 percent less likely to have ongoing or worse symptoms at 28 days than the no-activity group.

Zemek said more research is needed to determine the ideal timing and intensity of physical activity to recommend after a concussion "to provide the best balance between symptom resolution and safety."

Until there are clear answers, the editorial says doctors and parents "should use common sense about allowing limited physical activity as tolerated and be cautious about resting a previously active athlete for prolonged periods."