Also known as a moving side plank, this exercise really works the oblique muscles and also improves shoulder stability. (ab-core-and-stomach-exercises.com)
According to Ho, all it takes is one set of the Windmill to really work your obliques. (health.com)
A great way of working the obliques using the same piece of equipment can be achieved by raising your knees / straight legs to the side. (fitbodyhq.com)