Because the latissimus dorsi origin is from the back and it inserts on the humerus. It doesn't cover the abdomen at all.
The erector spinae is the muscle you are looking for, however is should be noted that technically this is a large group of muscles.
Pull-ups primarily target the latissimus dorsi muscle group in the back, though many other muscles are involved in the movement. These assisting muscles include the brachialis, brachioradialis, biceps brachii, teres major, deltoid muscle, infraspinatus, teres minor, rhomboids, levator scapulae, trapezius lower, trapezius middle, and pectoralis minor.
They are rhomboid major and rhomboid minor. You have trapezius muscle. The latissimus dorsi gives or takes the support is not clear.
The latissimus dorsi muscle group may make it difficult to palpate the twelfth rib near the spine. This large muscle group overlies the lower ribs dorsally.
The upper-body muscle groups are worked when one does lat pull downs. The muscle groups mainly worked are the ones in your back called latissimus dorsi. They also work other muscle groups like traps.
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.
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.
The two major muscles of the upper arm are the biceps on the front and the triceps on the back.
the abdominal muscles
Mainly back and bicep. Or specifically the sternal portion of the pectoralis major, latissimus dorsi, teres major, posterior deltoid, the rhomboids, the middle and lower portions of the trapezius, and the elbow flexors. It also depends on if you're doing chin ups, pull ups or lat pull ups.