Broad Run's Emma Kerns, left heads the ball away from Godwin's Morgan Hall during Broad Run's defeat of Mills Godwin 2 - 1 in overtime in the Virginia 5A girls' soccer state semifinal at Lake Braddock High School Burke Va., June 12, 2015 (Photo by John McDonnell/The Washington Post)

From pee wee groups to elite high school travel teams, soccer has become one of the fastest growing youth sports in America over the past three decades with injuries to match. Of special concern to doctors are concussions and other knocks to the brain which have become a subject of enormous public concern after reports surfaced that athletes suffering such injuries in a different sport -- football -- experienced memory loss, depression and other issues long after they stop playing.

With concussion rates rising among children playing soccer -- Brandi Chastain called attention to the issue during the Women's World Cup last year -- researchers from the University of Colorado set out to find out what's causing the injuries.

Researchers have known that soccer players brains look very different from those of other athletes like swimmers and have theorized that it may be due to their brains being shaken during play.

Many have assumed that the bulk of the injuries are due to heading, hitting the ball with one's head to make it go where you want it to go. The practice, allowed under most youth league rules, has come under fire in some parts of the country with calls by some sports doctors, professional players, parents and educators to ban heading for those under 14.

In a study published in JAMA Pediatrics on Monday, R. Dawn Comstock, an epidemiologist who focuses on sports and recreational injuries, and her co-authors, found that while heading does appear to lead to the bulk of concussions that wasn't the end of the story. In the vast majority of cases, the athlete's head was running in to something other than the ball.  In fact, an analysis of data from the National High School Sports-Related Injury Surveillance Study collected from 2005-2006 through 2013-2014, shows that 68.8 percent of concussions in boys and 51.3 percent of concussions in girls resulted from hitting of the head on another player rather than the ball, the field or other surface.

"Previous researchers discussing the safety and risk of soccer heading may have been asking the wrong question," they wrote. In fact, they argued, the "ball striking the head during heading has less of a role in soccer concussions than the athlete-athlete contact that occurs during contested or challenged heading opportunities."

Comstock and her fellow researchers noted that soccer has been allowed to become a much more physical sport over time and said that they feel bans on heading will only be effective at reducing concussions if there is also an effort to reduce contact between athletes during games.

In reviewing footage of FIFA tournaments and professional soccer matches other researchers have also noted that the most common cause of head injury was athlete-athlete contact during heading.

Robert Cantu, a co-founder of the Sports Legacy Institute in Boston which has been advocating for the ban on heading in youth soccer for players under the age of 14, explained in an interview with Scientific American last year that children's brains are more vulnerable than adult's due to a number of structural and metabolic reasons:

The brains of youngsters are not as myelinated as adult brains. Myelin is the coating of the neuron fibers — kind of like coating on a telephone wire. It helps transmission of signals and it also gives neurons much greater strength, so young brains are more vulnerable.

Youngsters also have disproportionately big heads. By the age of five, their heads are about 90 percent of their adult circumference, but the neck has not nearly developed to that point. They have big heads on very weak necks and that bobblehead-doll effect means you don’t have to impact the head as hard to cause damage.

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