People who downloaded and played the mobile game Pokemon GO ended up walking more, a study found. But the increased activity didn't last long.

A man uses a mobile phone in front of an advertisement board bearing the image of Pokemon Go at an electronic shop in Tokyo, Japan, July 27, 2016.

The augmented reality game, which launched in July, requires people to use mobile devices like smart phones to locate and capture cartoon characters that pop up on their screens at real-world locations. They can then battle other players at specific locations known as gyms.

Christian Suharlim, one of the study's lead authors from the Harvard T.H. Chan School of Public Health in Boston, said it had been suggested that players may get health benefits from walking around looking for the fictitious creatures.

"We wanted to investigate the impact of Pokemon GO on physical activity," Suharlim told Reuters Health.

Suharlim and colleagues recruited 1,182 young adults in the U.S. to take part in an online survey. Nearly half had reached at least level five in Pokemon GO, which means they had played for at least around two hours and unlocked some of the game's key features. The other participants didn't play the game; including them allowed the researchers to account for factors, such as weather, that may affect people's activity levels.

All participants had iPhone 6 mobile devices, which automatically tracked their steps.

"We basically asked them to upload their steps from before and after (they had installed) the game and we were able to get a snapshot of how their walking patterns changed," said Katherine Howe, who is also one of the study's lead authors.

Overall, they found Pokemon GO players walked an average of 4,256 steps per day during the month before installing the game. The average increased by 955 steps per day in the first week after they installed it. That translates into about 11 extra minutes of walking each day, the researchers write in The BMJ.

The added steps would account for about half of the World Health Organization's recommended 150 or more minutes of walking each week.

Unfortunately, however, the amount of walking decreased each week. After six weeks, the players' step counts returned to pre-game levels.

"There is a big improvement in the first week and then it slowly goes away," said Suharlim.

The study can't explain why the increase in walking disappeared over time, but Suharlim said it could be that people lost interest, or complications - such as the game's servers crashing - caused people to stop playing.

"There is potential for augmented reality gaming to improve physical activity and mental wellbeing," said Howe, pointing to the large increase at the beginning of play. The trick is to find out how to keep people engaged in the game.

Suharlim said it would be interesting to study the differences between people who continued playing Pokemon GO and people who lost interest or stopped playing.

Also, he said, it's important to examine other potential benefits and harms of the game. For example, benefits may include more time spent outdoors, and harms may include an increased risk for accidents.

"In public health, we kind of see any type of public health intervention as having benefit and risk," said Suharlim. "We only quantified the benefit of physical activity."

Reuters