Bosu balls, inflatable discs for under your feet, and other stability trainers have been marketed as tools for building balance, core strength, and thus increasing overall power and athletic performance. These claims are based upon several theories; each of which is bunk. If you’re an athlete looking to improve core strength and power, you should stick with free weights on a stable surface. Keep reading to find out why…
Claim #1- Proprioception:
The creators of these instability products claim that by enhancing proprioception, or your body awareness in relationship to the ground or space, you can train balance. While it’s true that training on an unstable surface activates proprioceptors in the body, you likely won’t make any significant gains in body control this way. Proprioception is developed in childhood, and very few, if any gains can be made in this arena beyond about age 12. That’s especially true for athletes, though it is worth noting that the extremely detrained and sedentary, or the elderly may be able to REGAIN proprioceptive ability that they had in the past but have lost over time.
Olympic weightlifting has been shown to be a better option for the experienced lifter. The advanced motor learning and extreme body control necessary to master these lifts has been shown to carry over even for the most advanced athletes.
Claim #2- Core Activation:
Bosu Ball gurus will tell you that training on an unstable surface will increase your core muscle activation when performing traditional exercises. This is based on several flawed studies. Scientists measured core activation in squats with 50% of 1RM on a Bosu Ball and 50% of 1RM on a stable surface. The results did show greater core activation, in this case, when squatting on the Bosu Ball. However, studies like this fail to consider that without the limiting factor of an unstable surface, the trainee on a stable surface can increase his load MUCH more. When training with loads upwards of 75% of a 1RM, core activation on a stable surface catches and surpasses that which is achieved on a Bosu Ball. Plus, the lifter on the solid floor can keep increasing that load. He can continually increase his core activation as load increases while simultaneously building significant strength and power in the primary movers (in this case the legs and glutes). It is impossible to produce this kind of force production with the submaximal loads you’re forced to train with on an unstable surface. In scientific studies, squats performed on an unstable surface have shown reductions in peak force, rate of force production, and agonist muscle activity.
There are still other options for increasing core activation. As I mentioned, the first way is to increase load. The second way is to train unilaterally (one arm or one leg at a time). Unilateral exercises can provide additional challenges to the core muscles while maintaining high levels of resistance. A third option to increase core activation is ballistic training. Ballistic or explosive movements as in Olympic weightlifting or plyometric drills also create a spike in core muscle activity.
#3- Greater overall muscle activation and RPE:
Certain studies claim that exercisers performing tasks on unstable surfaces reported a higher Rate of Perceived Exertion, citing an overall feeling of working “harder” than when on a stable floor. These same studies also claim to record greater overall muscle activation when performing these unstable exercises.
It might be true that the participants in these studies are working harder, and firing more muscles on an unstable surface. However, that’s not always a good thing! In fact, in this case, it might be a very bad thing. You see, a certain “stiffening” effect takes place in our body in response to an unstable surface. Our body does fire additional muscle. It fires the ANTAGONIST to the primary mover you’re trying to work; or the muscle that works in opposition to the muscle you’re trying to train. This natural body reaction protects the connective tissue around your joints and prevents hyperextension in the case of a slip or fall on that unstable surface. It also LIMITS your body’s ability to fully fire the agonist, or primary mover simultaneously. So, again, you won’t be able to create the same peak power as you would on a stable surface. If you’re looking to become a better athlete, you’re spinning your wheels here (though this type of training has some merit during the early stages of rehab after injury).
So, to sum that all up…
Instability training might work for you if you’re extremely de-conditioned, a senior citizen, or rehabbing from an injury; but if you’re healthy and athletic you’re wasting your time! Get your butt on a stable surface, pick up from free weights (which provide a sufficient amount of instability in their own right), and lift heavy loads. Train for core strength and body awareness with Olympic weightlifting, isolated core work, and sport specific practices instead.
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Wahl, M.J. and Behm D.G. 2008. Not all instability training devices enhance muscle activation in highly resistance-trained individuals. Journal of Strength and Conditioning Research 22 (4): 1360-1370
Behm, D.G., Leonard, et al 2005. Trunk muscle EMG activity with unstable and unilateral exercises. Journal of Strength and Conditioning Research 19 (1): 193-201
Nuzzo et al 2008. Trunk muscle activity during stability ball and free weight exercises. Journal of Strength and Conditioning Research 22 (1): 95-102