This is the VOA Special English Education Report.

Too much eating. Too many unhealthy foods. Too many advertisements for food. Too little activity.

Different explanations are offered for America's weight problem -- a problem increasingly shared by other countries. Almost one-fifth of American children and teenagers are overweight.

Dana Cooper hangs upside down on a climbing wall in her P.E. class at Northport High School in New York State

Schools have been urged to increase physical education, an important tool for public health. And many have. Yet now comes a study showing an increase in the number of injuries in "phys ed" class. Injuries increased one hundred fifty percent between nineteen ninety-seven and two thousand seven.

The study involved injuries treated in hospital emergency departments. Only two percent were serious. 

The researchers did not try to identify the causes of the increase, but they have some theories.

Lara McKenzie from Ohio State University was the lead researcher. She says one possibility is a decrease in the number of school nurses during the period they studied. For example, a two thousand four study showed that the number of school nurses nationally failed to meet federal guidelines.

Schools without a nurse on duty may be more likely to send an injured child to a hospital.

Another possible reason for more injuries is a change in the traditional idea of physical education. This "New P.E." expands the kinds of sports that are taught. But activities that some schools offer now, like rock climbing walls and skateboarding, can also expand the risks, says Cheryl Richardson. She is with the National Association for Sport and Physical Education.

Also, she says not all states require P.E. teachers to be specially trained. Untrained teachers could be less likely to recognize unsafe conditions.

Cheryl Richardson also points to one of the study's findings -- that injuries are often the result of contact with a person or a structure. This tells her that the teachers were not giving each student enough space to move around safely.

Six activities produced seventy percent of all injuries: running, basketball, football, volleyball, soccer and gymnastics.

The study appeared online this week in Pediatrics, the journal of the American Academy of Pediatrics.

The researchers say larger class sizes are another possible reason for the increase in injuries. Larger classes can mean less supervision. The National Association for Sport and Physical Education says twenty to thirty students in a P.E. class should be the limit.

And that's the VOA Special English Education Report, written by Nancy Steinbach. I'm Steve Ember.