Army crawl leg extension Targets shoulders, back, chest, abs, glutes and inner thighs Lie facedown with hands under shoulders, elbows bent, right leg at 90 degrees with inner thigh on the floor and left leg extended straight back on the floor (A). Push up until arms are straight, bend left leg until kneeling (keep foot off the floor) and extend right leg straight back (B). Lower down, pulling right knee back into a 90-degree angle. Return to start. Repeat 30 to 40 times.