Exercising on unstable surfaces, such as BOSU balls, Swiss balls, and wobble boards is a central component of many core-strengthening programs. A study form California State University, Northridge, led by James Kohler, showed that training on stable surfaces overloaded and recruited the core muscles best. Reseachers measured core muscles activation during the shoulder press performed on stable and unstable surfaces, using electromyography, which measures the electrical activity of muscles.
Core muscle load decreased with the instability of the surface. Exercising on firm ground is best overloading core muscle groups. (Journal Strength Conditioning Research, 24:313-321, 2010)
