Incorporating a Bosu Ball into your weight routine in the gym is a great way to strengthen your overall stability and core. But if you integrate too much Bosu use into your workout plan, you could be unintentionsally neglecting other important areas of your training. Its no secret that one thing most people want to achieve from their time invested in the gym is a nicer stomach, but is that the only thing?
Think of it this way, say for your arm workout, you're doing bicep curls or tricep extensions standing on a Bosu. How much of your focus and energy is directed at the exercise itself and how much of your focus and energy is direct at staying on the Bosu? Naturally your arm workout is going to take a backseat. If you're focus is on the Bosu, not only will you not be able to lift an appropriate ammount of weight to reach the full benefits of the exercise, but your technique will likely suffer.
This isn't to say a Bosu Ball is detrimental or a bad training device, in fact for functional or athletic training it can be the perfect multi-use training tool. But for the average gym-goer, you will have much more success in the gym and find your "six pack" abs with proper technique and a well balanced routine.