Lying Side bends
This is a suitable exercise for all levels. Lie with one side on a Bosu, supporting the weight of your head with your hands.
You may wish to bend your lower leg and even have your top foot resting against a wall, to help fix your position. If your working on a wooden floor, use an exercise mat under the Bosu to prevent it from sliding during the movement.
Exhale and raise up, aiming to take your upper elbow towards your hip, whilst keeping your chest and shoulders facing forward throughout the movement.
Inhale as your lower back down under control, repeating the movement, for desired number of repetitions.
Focus on using your side oblique muscles to perform the movement in a smooth controlled manner, avoiding any bouncing off the Bosu, to assist with the lifting phase.