Training on an unstable surface, such as an exercise ball or wobbling board, can improve your balance and stability in a workout program.

However, a new study found in the Journal of Strength and Conditioning Research suggests that training on unstable surfaces may actually hinder your workout progress. The study used a group of Division II soccer players making them perform half of their exercises on a BOSU ball. A BOSU ball is that “blue half-ball” you see in the gym; it looks like a stability ball cut in half. The study found that it didn’t offer these athletes any progress in speed or agility and actually decreased their jumping ability. The issue with this is that such unstable devices trains your body to compensate in undesirable ways. Training on an unstable service tends to recruit the wrong muscles. The muscles you’re trying to train (the agonists) end up firing less. The muscles found on the opposite side of the joint (the antagonists) fire more in an effort to stabilize the joint in an unstable position. Your body tries to achieve balance, which can get in the way of strength improvements.

For instance, if you try to do front shoulder raises on the stability ball, it will work your front delts less than intended. Your rear delts and back are going to be much more involved to stabilize the joint and prevent injury. When standing on a flat surface to perform front delts, you will focus on the front delts and hit them with much more intensity. Building muscle is about relaxing the antagonistic muscles in order to more fully engage the muscle you are intending on working. So, when we are hitting the front delts, we want to use as much weight. With the stability ball, first we have to use less weight because of the balance added.

Second, we are more concentrated with balancing the weight and “getting it up” than we are with working the muscle. That is the biggest no-no when it comes to working out. You need to stimulate the muscle and maximally contract 100% of the muscle fibers in the muscle in order for it to grow by using maximal loads that stress the muscle based on the concept of progressive overload and by focusing on the muscle by using a mind muscle connection, making sure you relax the muscles that are not supposed to be worked. However, such unstable devices can be effective at training joint stability such as rehabbing ankle sprains and also to increase coordination, balance, and engage your core a little more.

Source

http://news.menshealth.com/stability-training-myths/2012/02/14/