Agonistic Muscles for Left Leg Extensions

The left leg extension targets the muscles on your upper thigh. The leg extension is typically performed in a weight-training machine with weight plates used as resistance. Other options for the leg extension include using only the weight of your leg for resistance, or performing the exercise standing with an exercise band secured to your ankle. Regardless of the way you choose to extend your leg, one muscle group is the agonist.

  1. Left Leg Extension

    • The leg extension machine is used by one or both legs at a time. The single-leg extension focuses all of the resistance on one leg, and when you train this way, it results in an equal amount of training for both legs. Sit in the leg extension machine with your back supported against the back rest. Adjust the position of the back rest until the backs of your knees are touching the seat pad. Adjust the height of the rollers until they are just above your left ankle. Slide your left leg behind the roller and flex your left foot by pulling your toes toward your shin. Exhale, straighten your left leg and push up against the roller. Inhale and slowly return to the starting position.

    Agonist

    • An agonist muscle is the muscle that is responsible for the motion. The agonist contracts to flex or extend a joint and create movement. An agonist muscle has an opposing muscle known as the antagonist, which performs the opposite action. For example, during the left leg extension, your leg moves from a flexed to an extended position. The agonist performs that motion. When you release the extension and return to a flexed-knee position, the antagonist controls the movement.

    Quadriceps

    • Your quadriceps are the agonist during the left leg extension. The quadriceps are located on the front of your upper thigh. The muscle group begins on the hip bones and inserts below your knee. When the quadriceps shorten, your knee extends. The quadriceps are a four-muscle group that includes the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius muscles.

    Training Guidelines

    • Warm up your legs for five to 10 minutes before you perform strength training. Do this with full-body exercises such as walking, swimming, cycling or skating. Complete one to three sets of eight to 12 left leg extensions. Always perform an equal number on your right leg. Finish with a quadriceps stretch. For example, stand on your right foot, bend your left knee to raise your left foot behind you and hold onto your left ankle with your left hand.