Day 14 is four exercises and a new one in the middle: 6 sit-ups, 6 hundreds, 12 high crunches and 6 heel taps, run back to back before you rest. The hundred is done face up with the shoulders curled off the floor, the legs raised and the arms held straight and low beside the body, pumping up and down - each pump counts as one rep.
What makes the hundred work is not the arms, it is the position they are pumping from. Holding the shoulders up and the legs raised is an isometric ab hold, and the pumping arms simply refuse to let you settle into it; six reps is a short exercise on paper but every second of it is spent under continuous tension. That is the theme of the whole session. Sit-ups move a long way, high crunches move a short way with the legs already in the air, heel taps barely move at all - and the hundred sits in the middle holding a position while something else keeps moving. Range shrinks across the day while the demand goes up.
In the hundred, keep the arms straight and the pumps small and firm, breathe in a steady rhythm rather than holding your breath, and press the lower back into the floor for the whole set. Sit-ups stay controlled in both directions. In high crunches, keep the legs pointing up and lift the shoulders toward them without swinging. On heel taps, curl up first and stay curled - reaching from a flat back turns the exercise into a shoulder stretch.
Four exercises, almost no room to swing, and every rep paid for in tension.
Make it Harder: Straighten your legs out to a low hover during the hundreds instead of keeping the knees bent.
Make it Easier: Bring the knees directly over the hips for the hundreds and keep the shoulders low to the floor.
