Settle into a decline bench as you would for a normal sit-up with your legs secured and arms in front of your chest. Recline until your back is parallel to the ground. When you reach this position, freeze and hold the contraction for 10 seconds before returning back to the starting position. Then drop back and hold the contraction at the parallel position for nine seconds before returning back to the starting position, then eight seconds, then seven, and so on down to one second. During each round, maintain proper back posture and focus on contracting the abs rather than the legs to hold the sit-up plank.