Core-Strengthening Exercise: V-Up "This exercise is simple to do for those looking to strengthen their core" without putting a strain on your back, said Villarson. "Toe touches work your entire rectus abdominis, core muscles from your pubic bone and ending at the sternum." Lie face up with arms and legs extended and resting on the floor. Keep abs tight and lift hands and feet to meet over torso. Lower your arms and legs toward the floor. This counts as one rep. To modify this move, bend your knees. Image Source: POPSUGAR Photography