Unstable surface training UST is used to improve trunk muscle strength and core activation. But, there is enough research and an excellent article at Science of Running that debunks this idea, here is a summary.
When working with stability exercises on devices such as the swiss ball, bosu balls, wobble boards etc. we will have agonist and antagonist muscles involved. For a positive improvement the agonist muscle needs to be engaged and the antagonist involvement decreased. What research is showing is that UST is doing the opposite. Most of the research has been done by Behm (2002) and the research has shown significant activation in antagonistic muscle when performing exercises with UST which has led to greater reduction in peak power output and a reduction in agonist muscle activation. Thus a negative adaptation.
One of the biggest 'side effects' of UST training seems to be a reduction in force which eliminates the effect of adaptation, as much as 59.6% force reduction. Willardson, 2004, showed that UST will lead to improper muscle recruitment patterns, so UST has no place in sport specific skills. Stanton et al. (2004) found that runners were unable to improve running performance or posture using UST devices compared to non UST runners.
NCAA Division I soccer players performed their normal strength and conditioning programs, except that one group performed the final exercise of each training session on an unstable surface (Cressey et al., 2007). After ten weeks of training, the UST group saw performance decrements in bounce drop jump, countermovement jump, 10- and 40-yard sprint times compared to the group which did the same exact workout except for the last exercise (Cressey et al., 2007).
The core is activated more during a stable floor exercise such as a squat or any other stable floor exercise than druring the same exercise performed on a UST device (Drake et al., 2006). A study done by Kavcic, found that of 8 exercises that focus on the muscles that stabilize the spine. The least effective exercise done was also the only exercise using UST.
The idea that replacing a chair with a swiss ball and that it will improve posture has been proved wrong.
Other research has been conducted by researchers (Anderson & Behm, 2004; Cressey et al., 2007; Drake et al., 2006; Hamlyn et al., 2007; Kavcic et al 2004; McBride, 2006; McBride et al., 2006; McBride et al., 2009; Nuzzo et al., 2008) have found similar results from the combination of UST and traditional resistance training exercise.
The one thing that stability training seems to do positively is that using UST is the only thing that we will become good at using! We may improve our balance but from the research done, core activation and force output is found to be negatively influenced using stabilization devices. If you want to effectively improve the core it seems a squat is still the best option, you may not get a six pack from squatting, but then do you really need a six pack for performance? If you want stability and balance, sport specific is still the best sensible option. Often overlooked is the diaphragm which is a major core stabilization muscle which if weak will lead to quickly 'falling' apart when fatigued. Specifically strengthening the diaphragm with breathing work focused on strength, will do more core activation and core stabilization than traditional core stability exercises performed on UST and dare I say even traditional core exercises.
We are so focused on finding the magic session that will improve us that we so often forget to do our own research into why and how a new activity, training session or device will influence or outcome on performance and that we seem to be happy just to follow the crowd, just because we accept that it is the right thing to do.
