Day 12 is an abs & core circuit, 3, 4 or 5 sets by level, 2 minutes rest, and it brings in the hips. The top row is 10 side bridges on the right, 5 bridges, 10 side bridges on the left. The bottom row is 10 crunches, 5 bridges, 10 crunches. Bridges appear twice, so each set carries 10 of them, and the side bridges are stated per side on the card.
A side bridge is a moving side plank: lying on your side propped on your forearm, knees straight and feet stacked, you lift your hips off the floor until your body is a straight line, then lower them under control and lift again. It works the obliques and the outer hip together, the muscles that stop your pelvis dropping every time you land on one foot. Bridges are the glute exercise between them: on your back, knees bent, feet flat, driving the hips up until your body is straight from knees to shoulders, squeezing at the top and lowering. Crunches finish the card with the front of the abs, the same movement you learned on Day 4.
In side bridges, keep your elbow directly under your shoulder and push the floor away with your forearm so the shoulder does not collapse; the hips travel up and down, the rest of you stays in line. In bridges, drive through your heels and finish with your glutes rather than arching your lower back. Crunches stay small and controlled, chin off your chest, elbows wide.
Hips that lift from the side and from the back - the two directions a runner's pelvis has to be able to resist.
Make it Harder: Do the bridges on one leg, switching the working leg with every set.
Make it Easier: Bend your knees for the side bridges so the pivot point moves from your feet to your knees.
