Leg curls are an isolation exercise to strengthen the muscles at the back of the thigh. To perform a leg curl, flex your lower leg toward your buttocks against resistance. The move may be done in a standing, lying, or sitting position on selectorized lever machines, plate-loaded lever machines or cable machines. Leg curls target the hamstrings but also require synergist muscles and antagonist stabilizers.
Gastrocnemius
The gastrocnemius forms the upper part of the calf muscle. It runs from two heads just above the knee down to the heel. The gastrocnemius functions to flex the knee and the ankle, and is essential for walking, running, jumping, and standing. This muscle is used as a synergist muscle during leg curls -- it assists the hamstrings throughout the movement. Calf raises specifically target the gastrocnemius muscle.
Sartorius
The sartorius muscle is in the back of the thigh. A long, thin muscle, it runs obliquely from just under the buttocks to the inner leg beside the knee. This muscle assists in the flexion, lateral rotation, and abduction of the hip, and flexion of the knee. The sartorius is used as a synergist during leg curls. Hip abduction exercises specifically target the sartorius muscle.
Gracilis
The gracilis muscle is at the inner thigh and is also called the adductor muscle. It is responsible for adduction of the hip and flexion of the knee. The gracilis also is a synergist during leg curls. Hip adduction exercises such as the side lying leg lift and side lunges directly target the gracilis.
Tibialis Anterior
The tibialis anterior muscle is in the front of the lower leg near the shin. It is responsible for inverting and dorsiflexing the foot and assists with walking, running, kicking a ball, and keeping the leg vertical. The tibialis anterior is used as an antagonist stabilizer during leg curls -- it contracts to maintain tension in the calf.
Rectus Femoris
The rectus femoris muscle is one of the heads of the quadriceps muscle. It is responsible for extending the knee and flexing the hip. The rectus femoris is a direct antagonist to the hamstring and is used as an antagonist stabilizer during leg curls. Most quadriceps exercises directly target the rectus femoris muscle.
References
- "American College of Sports Medicine Resources for the Personal Trainer"; American College of Sports Medicine; 2007
- "Bodybuilding Anatomy"; Nick Evans; 2007
- "Strength Training Anatomy"; Frederic Delavier; 2006
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