INTRODUCTION Track and field is one of the most popular sports in the world. Despite the popularity of the sport, injuries are still a common occurrence. Hamstring strain injuries (HSIs) are reported to be highly prevalent in track and field, particularly during events involving high speed running. The Penn Relays Carnival, held annually by the University of Pennsylvania, is the oldest and largest track and field competition in the United States. Between 2002 to 2004, on average 16,158 athletes participated, making the Penn Relays Carnival an ideal event to observe the rates of HSIs in track and field. Therefore the purpose of this study was to determine the relative rates of HSIs across a wide number of events, age groups and genders in the Penn Relays Carnival between the years of 2002 and METHODS Over a 5-year period between 2002 to 2006 all injuries treated by the medical staff at the Penn Relays Carnival were recorded. This included injury type anatomical location, event in which the injury occurred, level of competition as well as demographic data of the injured athlete. For the years 2002 to 2004 detailed participation data were recorded to enable relative injury rates of HSIs to be calculated, expressed as the number of HSIs per 1000 participants. For years 2005 and 2006 detailed participant data were not collected and as such data for the entire 5- year observational period is expressed as a percentage of total injuries attributed to HSIs. RESULTS The number, gender and competition level of participants from can be found in Table 1. Relative incidence of HSIs across different genders and competition levels between 2002 to 2004 can be found in Figure 1, 2 & 3. The relative incidence of HSI, quadriceps strains and calf strains in the three most heavily participated events (4 x 100m, 4 x 200m & 4 x 400m) between 2002 to 2004 can be found in Figure 4. The ten most prevalent injuries between 2002 to 2006, expressed as the percentage of total injuries can be found in Figure 5. CONCLUSION HSIs were the most prevalent injury across 5 years of observation at the Penn Relays Carnival. Masters level athletes appeared to be most prone to this injury type and events that require high speed running combined with fatigue (4 x 400m) were most injurious. HSIs are problematic in track and field and a greater focus on prevention of this injury is warranted. A 5-year study into hamstring strain injuries at the Penn Relays Carnival. David Opar 1, Jonathan Drezner 2, Anthony Shield 1, David Webner 3, Brian Sennett 4, Rahul Kapur 4, Marc Cohen 4, James Ulager 4, Anna Cafengiu 4, Peter Cronholm + 1 School of Exercise and Nutrition Sciences & Institute of Health and Biomedical Innovation, Queensland University of Technology, Australia 2 Department of Family Medicine, University of Washington, USA 3 Crozer-Keystone Health System, Pennsylvania, USA 4 University of Pennsylvania, USA Table 1. Participation data of athletes who competed in the Penn Relays Carnival between 2002 to Figure 1. Relative injury rates of HSIs in male and female athletes from Junior Boy HS Boy College Men Masters Men Total Male Junior Girl HS Girl College Women Masters Women Total Female Total Athletes ,4733, , ,7582,697257,79215, ,5603, , ,5632,636177,52415, ,4812, , ,0512,58207,92516,756 Total91214,5149, , ,3727, ,24148,473 Figure 2. Relative injury rates of HSIs separated by competition level from No ‘Junior’ athletes reported HSIs. Figure 3. Relative injury rates of HSIs separated by competition level and gender from No ‘Junior’ or ‘Masters Women’ reported HSIs. Figure 4. Relative injury rates of lower body strains during relay events from Figure 5. Top ten injuries, expressed as a percentage of total injuries, from HS, high school.