Hamstring injuries carry a high injury burden and are more prevalent in males than females. This study is designed as a cross-sectional study with two groups. Forty elite rugby union players (20 males; 20 females) will have their hamstring muscle architecture (fascicle length, pennation angle and muscle thickness) measured using B-mode ultrasound. Muscle architecture is a modifiable risk factor associated with hamstring injuries. The aim of this study will be to determine whether differences exist in the hamstring muscles (Bicep Femoris long head, Bicep Femoris short head, Semitendinosus and Semimembranosus) architectural characteristics of elite- level male and female rugby union players.