The calf muscle is divided into two general parts. One main part is the gastrocnemius, which is U-shaped. The function of this part is to raise your body in an upright position up by the toes. The other part is the soleus, which is below the gastrocnemius. It is used as well to raise your body, but in a position when your knees are bent.
The calves are a very stubborn muscle to train. It is a fast twitch muscle which means that you have to train it with more intensity. You must fully stretch the calves at the bottom portion of the repetition and contract them in the full range of motion. It is recommended that you hold the contraction for a few seconds to really stimulate all of the calf muscle tissues. There will be a build up of lactic acid as you perform the repetition, however this is the point where you must do a few more reps to get results. Remember, train your calves like they are any other body part, do not put them aside.