Cheerleading remains one of the safest sports high school students can participate in, but the comparatively few injuries that do occur can be serious, a study indicates.

Concussions are the most serious injuries sustained, especially as cheerleading becomes increasing competitive and athletic, the researchers say.

Still, in terms of overall injury rate it ranks near the bottom of high school sports, the study appearing in the journal Pediatrics says.

"We found that cheerleading is actually relatively safe compared to the other high school sports we studied, ranking 18th out of the 22 sports we looked at in terms of overall injury rate," says lead study author and doctoral student Dustin Currie at the School of Public Health at the University of Colorado.

However, when cheerleading injuries did occur they tended to be serious, resulting in the second highest proportion of injuries resulting in time loss of at least 3 weeks of all the sports studied, he said.

"Anecdotally, it's pretty clear to most people over the past few decades that cheerleading has shifted from a sideline activity to a competitive sport itself," Currie says. "This may have resulted in an increase in injury."

Concussion, at 31.1 percent, led the cheerleading injury list, followed by ligament sprains (20.2 percent,) strained muscles  (14.2 percent,) and finally fractures (10.3 percent.)

Four percent of injuries—mainly sprains and fractures—required surgery, the researchers found.

Most cheerleading injuries happen during increasingly complex stunts, often occurring during dismounts, they say.

Cheerleading routines have evolved to be increasingly complex as the activity's popularity grows; it is estimated around 400,000 students participate in the U.S.

One way cheerleading can be made safer, researchers suggest, is for states to classify the activity as a true sport rather than a club activity.

Currently, the high school association in each state is charged with making that determination. California recently passed laws designating cheerleading as a sport; Colorado also considers it as such.

"It is time that every state high school athletic association recognizes the vast majority of today's high school cheerleaders are athletes," says study senior author Dawn Comstock at the School of Public Health's Program for Injury Prevention, Education and Research.

 "So even if the state does not recognize cheerleading as a sport, at a minimum, they should ensure cheerleaders benefit from the same safety measures and risk minimization efforts afforded to all other high school athletes," says Comstock, a recognized expert on athletic injuries.