Unstable surface training became popular in the 1990’s with the widespread use of exercise and BOSU balls, wobble boards and small inflated discs, among therapists and trainers. It is rare to find a gym these days that doesn’t have these items as standard equipment.
However, they are widely misused by both those in the industry and in gym goers alike. Their use can be beneficial, but we have to look at the available research to understand when and why.
Historically, the use of unstable training and equipment were used in a clinical rehabilitation setting primarily to address unstable ankles following serious sprains. A serious sprain can cause ankle instability due to the peroneals (muscles on the outside of the lower leg) firing slower.
If this is not addressed during healing then you are more prone to spraining your ankle again. Using balance work can help improve your proprioception, essentially your body’s ability to control movement, and aid recovery from injury.
Successful treatment of these injuries led to physical therapists applying this to other patient populations , some with no history of previous injury. These type of treatments were studied in athletes too.
One 2004 study found that unstable training was effective in treating those with a history of previous sprains, but didn’t provide a preventative effect for athletes who had no history of sprains. Conversely, what this study did show was an increase in knee injuries following unstable training.
This latter finding was also reinforced in a 2000 study, which found that elite female soccer players appeared not to have a decrease in injury rates to their lower limbs using unstable training. What they actually reported was an increase in these types of injuries, especially knee injuries.
A key study in 2007 studied two groups of athletes. One group incorporated unstable training into their programme, the other did not. Unstable training produced poorer jump test results and sprint times when compared to the group only performing stable training.
This is thought to be largely due to a reduction in the force you can produce on an unstable surface, thus reducing the speed of your movement. This in turn reduces your overall speed and power. If you train slow, you become slow.
The more stability you have during an exercise the more you will work the big prime mover muscles, with less activation required in the smaller stabiliser muscles. When you train on an unstable surface the opposite is true.

Another Wumin on a Baw
A common argument of proponents of unstable training is that they are training balance. Unstable training can indeed help train balance, but balance can also be trained on stable surfaces without any of the issues associated with unstable training. Training should always be specific to the individual and their requirements.
Unless you are rehabilitating an ankle injury, unstable training offers little benefit for lower body exercises or reduced injury rates. However, the evidence for its use in upper body exercises is much more solid.
Unstable loads used in upper body exercises can maintain muscle activation, but reduce the stress on the shoulder and elbow joints. This muscle activation is especially important in the stabiliser muscles around the shoulder, as this promotes stability in what is the body’s most mobile joint.
Therefore, unstable training is suitable for the upper body, especially for the core and exercises involving the shoulder joint. While these can be done using equipment like exercise or BOSU balls, or TRX type straps, unless you rehabilitating an injury, you will get on just as well using single leg exercises for the lower body and dumbbell exercises for the upper body, with some other type of core training.
While the story with unstable training is mixed, one thing that is important to remember is that if you struggle to perform an exercise on solid ground then, then you need to master that first. Training should always progress from the simple to the complex, not the other way around.

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