A small study out May 1 from Loyola University Health System bolsters evidence that young athletes who play one sport year-round are more likely to be injured than those who mix it up a bit.

Researchers looked at 154 athletes, all around 13 years old, visiting Loyola for sports physicals, or to have sports injuries treated. Among athletes being treated for injuries, more than 60% specialized in a single sport, while just over 31% of the uninjured athletes specialized.

Signs researchers used to determine whether athletes specialized:

• Training more than 75% of the time in one sport

• Training to improve skill, or missing time with friends to train

• Quitting other sports to focus on one sport

• Considering one sport more important than others

• Regular out-of-state travel for sports

• Training more than eight months per year, or competing more than six months per year

This study is a follow-up to an earlier Loyola study that found junior tennis players who specialized in tennis were more likely to be injured during tournaments than were players participating in multiple sports. Both the study’s authors and the American Academy of Pediatrics say young athletes should be discouraged from specializing in a single sport before adolescence, and should instead participate in a variety of different sports activities.

The current study was presented at a meeting of the American Medical Society for Sports Medicine in Salt Lake City.