The calf muscle is medically known at the gastrocnemius muscle. The calf muscle is a very powerful large muscle mass located on the posterior aspect of the leg below the thigh. The calf muscle functions to plantar flex, or point the toes. The tendon that connects the calf muscle to the heel bone is commonly referred to as the Achillies tendon.
The calf muscle is involved in standing, walking, running, and jumping. It allows us to maintain our balance in stance as well as push ourselves off the ground. It works in conjunction with the soleus muscle, a muscle deep to the gastocnemius that also acts to plantar flex the foot.
The calf muscle often becomes shortened due to a variety of reasons. The position we sleep in, the high heeled shoes we wear, and our choice of exercise activities and sports all lead to a tightening of this muscle.
To prevent injuries, it is important to stretch the calf muscles. I am often asked to review a few easy calf stretching exercises. So, let’s review:
Calf Stretching Made EasyPhoto courtisey of posetech.com

what can I do if my ackilles tendon and the lateral calf hurt alot?
In what position should I sleep in so they get stronger and bigger?
What a great, constructive conversation this is
In answer to the sleep question, I just saw an ankle specialist yesterday and he prescribed a sleep splint, which keeps your foot at 90 degrees during sleep to prevent the achilles from shrinking back which it normally does.