The flex
The homophone for a part of the body and a deed of strength or skill is "muscle" and "muscle."
The sartorius muscle is found in the thigh. It is the longest muscle in the human body and runs from the hip to the knee.
the muscle
Of course, if it's part of your body, it's a body part.
The diaphragm is the main breathing muscle in your body. It is a dome-shaped muscle located at the base of the lungs that contracts and expands to help with the inhalation and exhalation of air.
A flexor muscle.
Flexor
The flexor is a muscle that bends part of your body.
Spine. Bone, not muscle.
knee
An extensor straightens part of your body.
A muscle which bends or flexes any part; as, the flexors of the arm or the hand; -- opposed to extensor.
the ciliary muscle is the smooth muscle of the ciliary body
A flexor muscle is a muscle which bends or flexes a limb. Most flexor muscles are located on the anterior aspect of the body.
bends leg
Quadriceps femoris
Flexor