Plank Jack Targets shoulders, abs, butt, hamstrings, and calves Start on floor in full plank position with feet hip-width apart, palms directly under shoulders. Hold plank for 30 seconds, then hop feet out wider than shoulder-width (as if doing a jumping jack) and back in again. Do 10 reps. Do 3 sets, lowering knees to floor to rest for 15 seconds in between.
Backside Boost: Works: Butt, Lower Back, Abs, Hips Start in push-up position with shins on top of ball. Lift left leg (as shown), hold for 1 count, then return to plank. Repeat on opposite side for 1 rep. Do 12 reps. Source: Larsen & Talbert