Day 4 opens the second kind of training day. Abs & core days run on the same circuit rule as Day 2 - all six exercises in order is one set, 2 minutes rest between sets - but with their own level ladder: Level I is 3 sets, Level II is 4, Level III is 5. Everything on this card happens lying down: 10 crunches, 20 heel taps, 10 crunches, 20 side leg raises, 10 crunches and 20 side leg raises again. Crunches turn up three times, so each set carries 30 of them.
The card alternates between the front of the trunk and its sides. Crunches curl the shoulders off the floor with the knees bent and feet flat, working the abs directly. Heel taps keep the shoulders lifted and reach one hand toward the same-side heel, then the other, 20 touches in all, which pulls the obliques into the job. The side leg raises are the lying version: on your side, propped on your forearm, lifting the top leg straight up and lowering it with control. The two side leg raise pictures are mirrored for a reason - do the first 20 on one side and the last 20 on the other, so both hips get the full count. These are the muscles that keep your pelvis level with every stride, which is why they get equal billing with the abs on a runner's program.
On crunches, lift with the abs rather than pulling on your neck; the movement is small and the top of it should feel like a squeeze. Keep your lower back on the floor through the heel taps and let the reach come from the side of your waist. For the side leg raises, stack your hips, keep the toes pointing forward rather than up, and lift the leg from the hip without letting your torso tip backward.
Runners are built from the middle out, and this is where the middle starts.
Make it Harder: Lift your feet off the floor for the crunches so your knees stay bent above your hips for the whole set.
Make it Easier: Cut the heel taps and side leg raises to 10 each and keep the crunches as written.
