Catching up on research here while I have a few minutes to dig into the latest Journal of Strength and Conditioning. Among those that caught my eye was a piece of research out of the Univeristy of Valencia, Spain.
The purpose of the study was to see if "core" muscles were better stimulated by placing someone on an unstable surface, or on the ground.
Before getting into this the disclaimers are that there are studies showing unstable training does show positive results, and studies showing it does not. Surprise.
Obviously there is a time and place for every tool, and the bosu etc... are good tools for the appropriate goal, but if we are talking increased activation of the core musculature then this study says sorry, standing on a bosu or T-Bow (sort of wobble board) while deadlifting will not.
A previous study by McBride (22) showed a 45% reduction in force when squatting on unstable surfaces compared to flat ground, so how about deadlifting.
The researchers attached electromyography electrodes to 31 subjects and had them perform a barbell deadlift on flat ground, on a T-Bow, and on a bosu.
The data shows a 8.8% decrease when standing on a T-Bow, and a whopping 34% decrease when standing on a bosu. Seeing as the bosu is more unstable than a T-Bow the lesson we can draw here is that the more unstable a surface the less force muscles will be able to produce.
Referencing work by Gray Cook, Dr. McGill, Eric Cressey, and others the reason is that when on an unstable surfaces the body's top priority is to remain upright. In order to do that muscles that might normally act as prime movers may be called upon to function as stabilizers.
Therefore those muscles will not be able to produce as much force - in other words if the goal is to get stronger and improve force production in core muscles, then unstable surface training may not be ideal.
So while a person may find it more "challenging" to perform an exercise on unstable surfaces the reason may not be because of weak stabilizers, but due to the joints and associated muscles having to prevent the person from losing balance.
To put another nail in the coffin Dr. Stuart McGill has noted that sitting on a swiss ball increases compression on the spine - not what the majority of people need that typically sit in a chair for many hours a day.