Over the past several years performing exercises on unstable surfaces has grown increasingly popular among physical therapists, strength coaches, personal trainers, sports teams and health clubs. This type of training engages and increases the activation of the core muscles consisting of pelvic floor muscles, transversus abdominis, multifidus, internal and external obliques, rectus abdominis, erector spinae (sacrospinalis) especially the longissimus thoracis, and the diaphragm.
Though training on unstable surfaces like stability balls, balance boards or even a bosu balls increases activation of core stabalizer muscles, it is not a complete or ideal form of training for enhancing potential for increased athletic performance. When it comes to developing acceleration, speed and jumping ability the most important factor is an athlete's ability to absorb and generate force as quickly as possible which is effectively developed by strength and power training utilizing heavy loads dynamically on a stable surface. A recent study supporting this theory was conducted by University of Connecticut scientists who found that lower body strength training on stable surfaces produced better improvements in athletic performance than unstable training in elite college soccer players over a 10-week period. Unstable training caused few changes in measures of power important in sports such as softball, tennis, golf or volleyball.
Researchers concluded that unstable training does not overload the muscles enough to produce meaningful improvements in strength, power and Athletic Performance. While unstable training may promote recovery from injuries, it is not an effective way to increase strength and power for sports. (Journal Strength Conditioning Research, 21: 561-567, 2007)