Those hits to the head can add up, new research suggests. Jocks in contact sports really do perform worse on tests than their non-sporting peers.

Tested at the beginning and end of one season, 22 percent of those students who participated in contact sports scored significantly lower in memory and learning skills than expected, as opposed to only 4 percent of non-contact sport athletes.

"These results were found shortly after the season and we do not know how long the effect [of the head impacts] lasts," study researcher Thomas McAllister, of Dartmouth College, said in a statement. "While it may be bad for the 22 percent, the good news is that overall there were few differences in the test results between the athletes in contact sports and the athletes in non-contact sports," he added.

The study subjects were drawn from Dartmouth College and other Division I schools. The groups, numbering more than 250 in total, included football and hockey players, who were compared to participants in track, crew, and Nordic skiing — the contact vs. non-contact sports athletes.

The study was published May 16 in the journal Neurology.