How does the structure of the skeletal muscle it perform its function

The structure of the skeletal muscle helps it perform its function because its striations allow for big movements. 
Unlike smooth muscles which don't have much to do with movement and keeping your body together, skeletal muscles are made up of sarcomeres, which are a type of striations, which enable the skeletal muscle to move and keep your body in one place.

Spherical shaped cell might increase the surface area and decrease the volume.