Whether the goal is rehabilitation from injury, improved performance, or injury prevention, training regimens should include a component of exercise on unstable surfaces.  The interface between the foot (in most cases) and the ground (in most situations) can vary not only in the firmness of the surface, but also the material, texture, and pitch.  The challenge for the movement specialist when considering how to train on unstable surfaces is to decide:

  • For what purpose is the altered surface being used
  • When during the training chronology should it be introduced
  • What type of surface / alteration is to be utilized
  • How much emphasis should be placed on this training component

What is the Purpose?

Many sports activities are conducted in environments where there is some level of unpredictability regarding how forces applied by the feet can be used by the body to execute the desired movements.  If the activity / sport is analyzed, then an “authenticity spectrum” is created that runs from very stable to very unstable.  If a sport has a very unstable environment (surfing, beach volleyball) the purpose would be to reproduce actual situations that will be encountered.  If a sport is performed on a very stable surface (basketball, volleyball, hard court tennis), then unstable surface training would not be authentic, but would be used to create challenges to the neuro-musculo-skeletal system that create a “buffer of success”.  This “buffer of success”, if created logically, can improve performance and reduce the chance of injury.  Many sports occur in environments that fall at different points on the spectrum (skiing, baseball, football, soccer).

When Should Unstable Surfaces Be Introduced?

As a general rule, unstable surfaces should not be introduced until the movements can be executed on a stable surface.  The movement specialist must decide if the movement / exercise demonstrates the:

  • Logical degree of motion from all the joints contributing to the movement
  • Proper sequence of contribution of these joint going into and returning from the movement
  • Quality of control that demonstrates both mobility and stability

When the unstable surface is introduced, some degradation in the execution of the movement (usually in the quality of control) is to be expected in response to the increased challenge.  However, if the contribution from certain joints is completely lost, or the sequence of the movement changes substantially, then the degree of instability is too great.  The altered movement may be so different from the original that it ceases to be effective.

What Type of Surface?

The movement specialist must consider the flatness, firmness, and the movement of the surface (friction and pitch can also come into play).  If the degree of firmness and the potential movement of the surface can be altered in increments, it is easier to progress clients through the training program successfully.  Here, the nature of the sport / activity will influence choices.

Some examples are:

  • Foam pads that can have a different thickness and compliance
  • Items that are filled with air to create different levels of instability
  • Equipment that tilts, rocks, or rotates under the feet

One example is the Air Baps (trademark) that provides instability from the bottom in all three planes, but also has a flat top surface filled with air that can be changed to alter the firmness.

How Much Instability is Too Much

If a little instability is good, then is more instability better?  If more instability is not better, then how much is too much?  If the there is authentic instability of the surface (e.g surf board), then a large component of unstable surface training is warranted.  However, if the surface is flat, firm, and stable (e.g basketball), then the purpose is to create the “buffer of success” and unstable surface training would likely be a much smaller component of the overall program.

Not only can the instability component of the training program be too large, the actual degree of instability used can be too much as well.  At the Gray Institute, this is called training BEYOND the “threshold of success”.   If the environment or tool creates too much instability, the movement may become very stiff and limited (unlike the desired movement).  Hitting golf balls while standing on two air filled bladders is a perfect example of this.  The instability created by the tool is so great that the legs need to choose stability over movement resulting in a swing that is arm and trunk dominant.  This will degrade performance, not improve it.

Clearly, there are many factors to be considered when utilizing unstable surfaces to optimize programs in order to reach the desired training goals quickly and safely.