Different areas of the leg flexors can be specifically trained via the exercise selection

The hamstrings are multi-joint muscles that flex the knee and extend the hip. Injuries to the leg flexors typically occur during hip extension in activities such as sprinting, jumping and cutting (a discipline in western riding). Many people perform leg curls instead of hip extension exercises to rebuild the leg flexors after an injury.

An interesting study led by Brad Schoenfeld of CUNY Lehman College in New York found - using eletromyography measurements - differences in regional activation of the leg flexors during leg curls and straight-leg deadlifts. Straight leg deadlifts showed greater activation of the upper portion of the muscles, while leg curls showed greater activation of the lower portion.

This study has important implications for the development of leg curls in bodybuilders and for rehabilitation training after leg curl injuries.

(Journal Strength Conditioning Research, 29: 159 - 164, 2015)