It exercises your upper abdominal, and lower too, depending on the exercise, - The plank: targets arms legs and back and tummy.- sit ups: They merely tone the abdominals.- Running: Really helps lose...
Voluntary muscles are skeletal muscles (under somatic control) and involuntary muscles involve the heart, smooth muscles and anything under autonomic control.
Primarily quadratus lumborum, unilateral contraction of spinalis muscles (you can feel these contract in your lower-mid back on the side to which you're bending against resistance) and, to a lesser...