The external and internal oblique muscles rotate and side bend the trunk. These muscles also stabilize the spine.
internal and external obliques
erector spinii
core muscles
The Penis
Your abdomen muscles are included in the lower torso as well as your obliques.
There is not a single muscle that rotates the upper arm. The name of the muscle that contributes in rotation of the upper arm is deltoid muscle.
The "Subscapularis" This muscle rotates the arm medially (sub = below, scapulo = shoulderblade)
Trunk isnt a muscle. It refers to the torso or upper part of the body.
Levator scapulae
Gingerceps
it flexes and rotates the head
Name of the muscle is trapezious. It has an extensive origin from spines of verebral column.
The inferior oblique muscle of the eye, abducts, elevates and laterally rotates the eye
Upper and lower legs and torso are good groups to work.
Chin-ups, just as most exercises use a primary & secondary muscle group. The primary muscle group would be the back (or latissimus dorsi). This is what helps to give that "V" - shape in the torso area. (along with slimming down the torso area, of course) The secondary muscle group would be the biceps. Depending on your grip position, you can focus either more on your "lats", or arms.
Chin-ups, just as most exercises use a primary & secondary muscle group. The primary muscle group would be the back (or latissimus dorsi). This is what helps to give that "V" - shape in the torso area. (along with slimming down the torso area, of course) The secondary muscle group would be the biceps. Depending on your grip position, you can focus either more on your "lats", or arms.