Knee Ups
Sit slightly forward of the central part of the Bosu, leaning back to about 75 degrees, with both hands behind you, securing your upper-body position with your arms.
Bend your legs to 90 degrees, keeping your heels off the floor throughout the exercise; however aim to also keep them off the Bosu in order to keep the abdominal muscles contracted.
Keeping your upper-body fixed in position with your arms, exhale and contract your lower abs in order to bring your knees up towards your chest in a slow smooth motion.
Inhale and extend your feet directly out, aiming for a smooth controlled motion, keeping your feet pointing away from you.
Beginners should aim for 6 - 10 reps, for 2 sets, keeping their legs slightly bent to reduce both the resistance and stress on the lower back.
Intermediates aim to work for 10 - 15 reps in full action, for 2 sets.
Advanced aim to work as above, however hold in both the upper and lower phase for 1 - 2 seconds.
This exercise can be made harder by taking your hands away from the Bosu, and having them either out to the side to aid balance, or across your chest to increase difficulty.