Kneel next to your office chair so your left side is against the chair. Lean to your left, planting your left forearm in the center of the chair's seat, your forearm placed perpendicularly to your body. Press straight down through your elbow as you lift your right hip, carefully extending your legs, stacking them one on top of the other. It's important to center your shoulder directly over your elbow to keep the chair from rolling. Hold this position, your body forming a straight line from heels to head, for the duration of the exercise.
Chair side plank, right side
Repeat the same side-plank exercise to the opposite side.
Perch on your tailbone toward the front of your chair's seat. Lean back, your torso straight, and grasp your chair's arm rests or the edges of your chair, just behind your hips. Lift your knees up so your thighs and torso form a "V." From this position engage your abs and extend your legs as a single unit, controlling them so your feet don't drop to the floor. After extending your legs fully, draw them back toward your body to return to the "V" position.