NEW YORK (Reuters) – American children aren't the only couch potatoes with nearly one third of children globally spending three hours a day or more watching TV or on computers, according to study of over 70,000 teens in 34 nations.

From Argentina to Zambia, Regina Guthold of the World Health Organisation in Geneva and her colleagues found most children aren't getting enough exercise and it made no difference if they lived in a rich or a poor country.

"With regards to physical activity levels, we did not find much of a difference between poor and rich countries," Guthold said. "Growing up in a poor country does not necessarily mean that kids get more physical activity."

The study, published in The Journal of Paediatrics, looked at 72,845 schoolchildren aged 13 to 15 from around the world.

The researchers defined adequate physical activity as at least an hour of exercise outside of gym class at least five days a week.

Children who spent three or more hours a day watching TV, playing computer games, or chatting with friends — aside from time in school or time spent doing homework — were classified as sedentary.

The researchers found only one quarter of the boys and 15 percent of the girls were getting enough exercise by these definitions. A quarter of boys and nearly 30 percent of girls were sedentary and didn't get enough exercise.

Uruguay had the highest percentage of active boys, at 42 percent, while Zambia had the lowest, at eight percent. Girls from India were the most active, with 37 percent meeting exercise recommendations, while girls from Egypt were the least active, with just four percent getting adequate exercise.

The most sedentary nations were St. Lucia and the Casyman Islands, with 58 percent of boys and 64 percent of girls spending at least three hours a day in sedentary activities.