Seated trunk rotation against resistance band
Muscles used in this exercise
Both the core and the pelvic floor muscles are involved to try and balance you on the ball. Your trunk and spinal rotator muscles are activated during the twist.
Purpose
The aim is to improve your ability to stabilise the lower trunk whilst you twist via the upper trunk. Many sports will require this component of movement (golf, basketball, soccer, footie, pole dancing, ballet, etc.) and therefore it makes sense to work on them.
To do this exercise
Attach a theraband to something stable like a door handle.
Sit on a ball with good posture and rotate away from the theraband using your upper back while keeping your lower back stable.
Extend through your upper back without moving your lower back.
Return to the starting position.
Repeat in the other direction.