A trainer can send you to a leg curl or leg brace machine to work your leg. Both of these machines work on the opposite side of your thigh. Use a leg curl machine to load the muscles behind or at the back of the leg, especially the hamstrings. The leg extension machine has straightened your leg against resistance and thus works the muscles in the front or anterior part of the leg – your quadriceps.
When using a sitting or lying curl machine, the muscles at the back of your thigh contract to bend your knees. The hamstrings are made up of three muscles: the biceps femoris, semimembranosus, and semitendinosus muscles. The largest of the three is the biceps femoris.
The quadriceps are flexed when you use the leg extension machine. This muscle consists of the rectus femoris, broadus lateralis, medialis vastus, and broadus intermedius. During this exercise, the rectus femoris is the muscle that works the most. At the end of the motion, when your knee is nearly straight, the medialis vastus then contracts.
Your calves help with leg extension. The calf muscle is made up of two muscles, namely the gastrocnemius and soleus. But the most often used when rolling the legs is the gastrocnemius, which is the most superficial. This crosses the back of the knee and helps the hamstrings to bend the knee when using one of the leg curl machines.
When using any machine, it is important to keep the correct shape. Avoid extending the knee completely when using the leg spray machine as this can create a shear force in the knee. This can damage the tissue around the knee.
Use challenging weights, but don’t be so challenging that your shape falls apart. The weight that is too heavy on leg curls or leg extensions can cause you to become blocked through your pelvis and back. This puts you at risk of injury and reduces the effectiveness of the machine to target your feet.