This is a transition posture and you will do it again 13 more times before the end of the series. Each time you do the sit-up there is a sharp double exhale, through the mouth, at the very end of the posture when you to touch your forehead to your knees.
The exhale at the end of the sit-up, when you are folded in half, has the benefit of sucking your abdomen in further to massage your internal organs. Be sure to pay special attention to the use of your legs in the sit-up; they must always be straight, from contracting muscles (locking the knees) and squeezing together to use the inner thighs to help support the lower back in this movement.
