Lets take a quick look at how using unstable surfaces in training evolved from my personal perspective. About 25 years ago I began to experiment using unstable surfaces with healthy athletes after observing that athletes coming back for ankle sprains and even ACL tears seemed to have better functional balance and control of their bodies. I felt that if we could incorporate what they had done in rehab with healthy athlete’s training that we should be able to see similar gains. Initially this certainly was the case. I did not devote much time to this, perhaps five minutes and occasionally ten minutes a day, we seemed to get good returns. Typically as often happens in coaching I decided that more had to be better, so instead of using a simple K Board or a foam pad I began to seek out even more exotic unstable surfaces. I even did several talks were I stated that when you used unstable surfaces, the more unstable the better, the point being that it was another way to achieve overload. It was not long before I began to get very uncomfortable with this approach. What I saw that instead of making the athletes better I was taking the athletes farther and farther away from the performance arena. They were learning circus tricks; the exercises became an end to themselves. But by that time, the late nineties, this whole thing had taken on a life of its own. What I want to do with this post is bring a degree of sanity and most importantly logic to this the use of unstable surfaces.
Most of the science regarding the use of unstable surfaces comes from the rehabilitation arena. There is a very good article on ACL prevention using a balance routine to prevent knee injuries in high level soccer player, Cerulli, G. Benoit, D.L. Caraffa, A. Ponteggia, F. “Proprioceptive Training and Prevention of Anterior Cruciate Ligament Injuries in Soccer” Journal of Orthopaedic & Sports Physical Therapy. Volume 31 #11 November 2001 pp. 655-660.
The best place to start is with is the surface that you must perform on. Ask yourself why you have to deviate from that surface in your training. What is your goal(s) on using an unstable surface? How are you going to use it? These are very important questions to objectively answer before you even consider using unstable surfaces in training. My fundamental observation is that the majority of people in many sports can make very good use of normal surfaces, just by increasing the amplitude and speed of movement.
Certainly unstable surfaces are not inherently bad. The key is the application. It is legitimate to ask if the movement will transfer. Is the movement sport appropriate? If it is sport appropriate it will have some carryover to the sport. It is not sport appropriate if the athlete has to spend undue amount of time learning a new skill set in order to train with unstable surfaces. What do I mean by a new skill set? I mean skills and movements that exaggerate movement through significantly larger amplitudes and speeds of movement that are not similar to the sport movements. The key is significantly changes, it may look similar, but that is where the similarity ends. By the same token this criterion applies to heavy sled pulls or even to some over speed training. They may look similar, but they either extremely slow the movement down or make it too fast to apply.
What are unstable surfaces? An unstable surface is anything that the body perceives as inherently unstable, to the eye it may not appear unstable but proprioceptively the body perceives it as unstable. It can run the spectrum from a lumpy grass field or a sandpit to a foam pad, or apparatus like a wobble board, k board or a balance beam. It does not take very much for the body to perceive the surface as unstable. The body is sensitive to small changes in surface and usually can quickly self-correct to allow the body to achieve appropriate positions for the movement. These rapid adjustments are based on the proprioceptive input in the body that detects speed and stretch. The body’s proprioceptors act as very sophisticated motion sensors. It is this motion detector function that we are attempting to train by using uneven surfaces. What then are advantages of using unstable surfaces? It certainly will challenge the proprioceptive system; it will improve body awareness and can improve spatial awareness. These improvements are not always very measurable because they can be quite subtle and in many respects they should be quite subtle, because in most movements the body only has to adjust to subtle changes.