Lie on your back with your knees bent and feet flat on the floor.
Rest your arms on the floor by your sides.
Keeping your knee bent, lift one foot off the floor.
Press your other foot against the floor and lift your hips up.
Try to straighten your hips so that you have a straight line from your shoulders to your knee.
In a controlled manner lower your hips back down, and repeat.
Keep your pelvis level throughout this exercise.