Association of Hamstring Strain Injuries with Season and Temperature in Track and Field Collegiate Athletes in Japan: A Descriptive Epidemiological Study

Background: Few descriptive epidemiological studies have investigated the prevalence and risk factors of hamstring strain injury in athletics. Objectives: To investigate the variations in the incidence of hamstring strain injury between seasons in track and field athletes, and further to investigate the relationship between environmental temperature and occurrence of hamstring strain injury. Methods: We recruited track and field athletes and recorded information about hamstring strain injuries between January 2013 and December 2016. Each year was divided into four seasons (March - May: early-season; June - August: mid-season; September - November: late-season, and December - February: off-season), and the incidence of hamstring strain injury in each season was calculated. The incidence rate ratio for each season was calculated according to the temperature of the day when an injury was recorded. Results: In total, 183 hamstring strain injuries were recorded (16.98/100 person-years). The incidence was significantly higher in early-season (IRR = 2.23) than in other seasons. The incidences in mid- and late-seasons (IRR = 0.64, and 0.57, respectively) were significantly lower than those in other seasons. The very-high-temperature zone showed a significantly lower incidence of hamstring strain injuries (IRR = 0.53) than did other temperature zones. The lower-middle-temperature zone showed a significantly higher incidence of hamstring strain injury (IRR = 1.46) than the other temperature zones. Conclusions: This study results suggest that hamstring strain injury is most likely to occur in early-season, possibly due to the low temperatures that characterize this season and the rapid increase of running speed required for subsequent competitions.