Your muscles work together to help you walk, run or jump. Most muscles of the arms and legs come in pairs. An example is your biceps muscles on the front of your arm and the triceps muscles on the back of the arm. Your thighs also have a dual set of opposing muscles that work together to perform extension movements that enable you to extend your legs away from the center plane of your body.
Function
Muscles work together in shortening and lengthening movements synchronized for specific function. To extend your leg at the hip or the knee, one set of muscles lengthens and an opposing set shortens, allowing movement of muscles between joints. This shortening and lengthening action enables you to bend your arm, sit down, step over something or kick a football. Multiple actions are at work for extension of your leg muscles.
Muscles
Major muscles of the upper legs include the quadriceps muscles on the front of the thigh and the group of three hamstring muscles on the back of the thigh. Major muscles serving as leg extensors include the gluteus maximus muscle of the buttocks, and the biceps femoris, semimembranosus and semitendinosus muscle on the back of your thigh, known as your hamstrings.
Extension
During a leg extension, you increase the angle of a joint. Sit in a chair, lift your foot off the floor and extend your leg upward to the level of your chair. That's an extension because you have created an 180 degree angle from the hip joint rather than a 90 degree angle. After your brain sends nerve signals for your leg to extend, several things happen to initiate this muscle extension movement. In the thigh, your quadriceps muscles shorten while the hamstring muscles lengthen. This action starts in the hip or knee joint when the angle and movement of muscles between the hip and the foot increases.
Exercises
A lever leg extension machine at your gym is effective in toning the thighs and hamstrings and allows you to extend your legs at the knees to hip level. Weight or tension is added to the padded bar in front of your ankles. You may also perform seated leg extensions at home with or without ankle weights. Do standing leg extensions by standing with your side facing a chair, counter or other solid surface, holding onto that surface for stability. Lift your leg straight outward from your hip, or bend your knee, lift your thigh to hip level and then extend your foot away from your body to create a straight line.
