Side Plank On Knees
Lie on your left side with your left forearm and elbow on the floor. Your elbow should be in line with your shoulder, and your torso sagging toward the floor. Lean into your forearm, lifting your hips in the air to form a straight, rigid line while supporting your weight on your forearms and knees. Hold for 20 seconds. Repeat twice and then perform again lying on your right side.
Advanced Side Plank: Try to increase your hold time to 1 to 2 minutes. If this gets too easy, hold a light weight against the hip that's on top.