Objective-To prospectively establish risk factors for hamstring muscle strain injury using magnetic resonance imaging (MRI) to define the diagnosis of posterior thigh injury. Method-In a prospective cohort study using two elite Australian Rules football clubs, the anthropometric characteristics and past clinical history of 114 athletes were recorded. Players were followed throughout the subsequent season, with posterior thigh injuries being documented. Hamstring intramuscular hyperintensity on T2 weighted MRI was required to meet our criteria for a definite hamstring injury. Statistical associations were sought between anthropometric and previous clinical characteristics and hamstring muscle injury. Results-MRI in 32 players showed either hamstring injury (n = 26) or normal scans (n = 6). An association existed between a hamstring injury and each of the following: increasing age, being aboriginal, past history of an injury to the posterior thigh or knee or osteitis pubis (all p<0.05). These factors were still significant when players with a past history of posterior thigh injury (n = 26) were excluded. Previous back injury was associated with a posterior thigh injury that looked normal on MRI scan, but not with an MRI detected hamstring injury. Conclusions-Hamstring injuries are common in Australian football, and previous posterior thigh injury is a significant risk factor. Other factors, such as increasing age, being of aboriginal descent, or having a past history of knee injury or osteitis pubis, increase the risk of hamstring strain independently of previous posterior thigh injury. However, as the numbers in this study are small, further research is needed before definitive statements can be made. (Br J Sports Med 2001;35:435-440)

Objectives: To assess in a single team of Australian Rules football players the effect of a specific intervention program on the incidence and consequence of hamstring muscle strain injuries. Method: A prospective study was performed with a single team being followed for four playing seasons for hamstring injury. Magnetic resonance imaging was used to confirm the diagnosis of hamstring muscle injury. After two playing seasons an intervention program was implemented with the number of athletes with hamstring injury, competition days missed, and incidence of hamstring match injuries per 1000 h of playing time being compared pre-and post-intervention. The intervention program involved stretching whilst fatigued, sport specific training drills, and an emphasis on increasing the amount of high intensity anaerobic interval training. Results: In the seasons prior to the intervention, nine and 11 athletes sustained hamstring injury compared to two and four following intervention. Competition days missed reduced from 31 and 38 to 5 and 16 following intervention and match incidence decreased from 4.7 to 1.3 per 1000 h of playing time. A beneficial effect was demonstrated with a smaller number of players having hamstring injuries (p = 0.05), a lower number of competition games missed being recorded (p,0.001), and a decrease in hamstring strain incidence per 1000 h of playing time (p = 0.01) following the intervention program. Conclusions: Increasing the amount of anaerobic interval training, stretching whilst the muscle is fatigued, and implementing sport specific training drills resulted in a significant reduction in the number and consequences of hamstring muscle strain injuries.

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Study Design: Prospective cohort study. Objective: To examine clinical and magnetic resonance imaging (MRI) features of hamstring muscle injury to determine if any are predictive for recurrent injury. Background: Hamstring muscle strain injury and subsequent recurrent injury are common. Little information exists on factors that may increase the risk for recurrent injury. Methods and Measures:The subjects were athletes from 3 professional Australian Rules football teams (n = 162). Anthropometric measurements, clinical signs, convalescent interval, and MRI assessment and measurement were undertaken and recorded in athletes with hamstring muscle strain injury. Athletes were followed for the presence, or absence, of recurrent injury to the same-side posterior thigh over the same and subsequent playing seasons. Results: Thirty athletes met criteria for hamstring injury. Twelve (40%) of 30 athletes had recurrent injury within the same season, with an additional 7 athletes having recurrent injury in the subsequent season. None of the features examined were associated with increased recurrent injury risk within the same playing season. Statistical analysis demonstrated that when combining the same with the subsequent playing season a larger size of initial hamstring injury, as measured by MRI, was associated with an increased risk for recurrent injury (P Ͻ .01). A measured transverse size of injury greater than 55% of the muscle, or calculated volume of injury greater than 21.8 cm 3 , resulted in an increased risk for hamstring recurrence of 2.2 (95% CI, 0.88-5.32) and 2.3 (95% CI, 0.94-5.81) times, respectively, when compared to athletes with hamstring injuries below these measurements. Conclusions: A larger size of hamstring injury was indicative of higher risk for recurrent injury but only after the subsequent playing season was considered along with the same playing season.None of the other parameters tested, including a shorter convalescent interval and clinical features, were associated with an increased risk for recurrent injury. However, due to low sample size the certainty of these conclusions may be limited. J Orthop Sports Phys Ther 2006;36(4):215-224.

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