The differences between the pull up and chin up are very subtle.
The body and head are more vertical on the pull up. The back is arched slightly further back on the chin up so the head can clear the bar.
Both the chin up and pull up involve shoulder adduction and scapula downward rotation. Due to the small difference of the angle of the torso, the chin up also includes a small degree of of shoulder transverse extension and scapula adduction (retraction); hence the additional muscles involved.
On the pull up the clavicular head of the Pectoralis major is involved in shoulder adduction since the body is more vertical. This vertical posture is even more pronounced on the rear pull up.
The body and head are more vertical on the pull up. The back is arched slightly further back on the chin up so the head can clear the bar.
Both the chin up and pull up involve shoulder adduction and scapula downward rotation. Due to the small difference of the angle of the torso, the chin up also includes a small degree of of shoulder transverse extension and scapula adduction (retraction); hence the additional muscles involved.
On the pull up the clavicular head of the Pectoralis major is involved in shoulder adduction since the body is more vertical. This vertical posture is even more pronounced on the rear pull up.
