Difficulty: Medium to advanced

Doing any exercise that you can do standing can usually be made more challenging by doing the same exercise while sitting on a balance ball.  In this video a simple bicep curl which tones and tightens your arms is done on a balance ball.  This requires you to activate your abdominal muscles, buns, thighs and calves to maintain balance.  Try alternating left and right arms for an even more challenging work out.