The primary muscle involved in this exercise is the rectus abdominis.

The primary muscle is the biceps femoris.

The primary muscle of respiration is the diaphragm, a dome-shaped sheet that sits below the lungs.

This is because those small accessory muscles are being used as if they were the much bigger and more powerful primary muscle of respiration.

This is the primary muscle for maintenance of continence of urine.

An injury can result if, in a particular exercise, the primary muscle is stronger than its stabilising muscles.

The primary muscle of respiration, the "diaphragm", is the large dome-shaped muscle that dissects the body.

They interconnect ribs, and are therefore the primary respiratory skeletal muscles.

This is the primary muscle for prohibiting the release of urine.

Each of these primary muscles of mastication is paired, with each side of the mandible possessing one of the four.