A study into traumatic brain injuries has found a fifth are caused during sport, and the number of cases is on the rise.
Researchers at the Auckland University of Technology and Waikato and Otago universities studied 1369 cases of brain injury and found 21 percent happened during sport.
The research, published in the Journal of Science and Medicine in Sport, showed adults were most likely to suffer a brain injury playing rugby, horse-riding or trail-riding.
Children were most likely to hurt their head while cycling, playing rugby or football, or swimming.
It said 46 percent of the injuries recorded were identified as having a high risk of further complications.
The research said previous studies had shown up to 15 percent of traumatic brain injuries were caused during sport.