A systematic review of the association between body checking and injury in youth ice hockey.

OBJECTIVE: The objective of this study is to systematically examine the risk of injury associated with body checking in youth ice hockey. DATA SOURCES: A systematic review of the relevant electronic databases was conducted including PubMed and Web of Science. The main search terms included "hockey, ice hockey, injury, body checking, child, adolescent, and pediatric." STUDY SELECTION: The initial search identified 898 potential articles, and, after verifying inclusion criteria, 260 articles were selected for further assessment. The Downs and Black instrument for nonrandomized studies (Downs 1998) was used to assess the quality of the articles. DATA EXTRACTION: Studies included reported on body checking as a mechanism of injury and compared injury rates in checking to non-checking leagues in children 20 years or younger. DATA SYNTHESIS: Twenty studies met the inclusion criteria and they predominantly found increased injuries associated with body checking. The relative risk of injury associated with body checking in comparative studies ranged from 0.6 to 39.8. Checking was the reported mechanism of injury between 2.9% and 91% of injuries. All but 1 study that met our inclusion criteria found an increased risk of injuries when body checking was permitted. CONCLUSIONS: Increased injuries attributable to checking were found where checking was allowed. This study supports policies that disallow body checking to reduce injuries in young children.

Successful biological invasion despite a severe genetic load.

Understanding the factors that influence the success of ecologically and economically damaging biological invasions is of prime importance. Recent studies have shown that invasive populations typically exhibit minimal, if any, reductions in genetic diversity, suggesting that large founding populations and/or multiple introductions are required for the success of biological invasions, consistent with predictions of the propagule pressure hypothesis. Through population genetic analysis of neutral microsatellite markers and a gene experiencing balancing selection, we demonstrate that the solitary bee Lasioglossum leucozonium experienced a single and severe bottleneck during its introduction from Europe. Paradoxically, the success of L. leucozonium in its introduced range occurred despite the severe genetic load caused by single-locus complementary sex-determination that still turns 30% of female-destined eggs into sterile diploid males, thereby substantially limiting the growth potential of the introduced population. Using stochastic modeling, we show that L. leucozonium invaded North America through the introduction of a very small number of propagules, most likely a singly-mated female. Our results suggest that chance events and ecological traits of invaders are more important than propagule pressure in determining invasion success, and that the vigilance required to prevent invasions may be considerably greater than has been previously considered.