At home Everyone
MediumAbout 4 minOn your own
A plank with the forearms on a Swiss ball, making small circles. Tough work for the trunk.
Video: Muscle & Strength
Forearms on a Swiss ball, legs straight behind you, feet about shoulder-width apart, body in a plank.
You need: A Swiss ball
Hold the plank on the ball without circles, or knees down.
Bigger circles, or feet closer together.