Muscle fiber sizes vary

When you look at the muscle groups, you will find that the muscles are tied up with a series of steel fiber-like muscle fibers. These steel cables are combined into thicker and longer cable groups, and when the muscles are stressed, they shrink like a spring. Within those thickest cables are muscle fibers, nerves, blood vessels, and connective tissue. Each muscle fiber is made up of smaller myofibrils. Each myofibril is composed of two filamentous proteins (myosin and actin) entangled together. This is the most basic unit of muscle.