This is not medical advice.
This can be a big debate in strength and conditioning coach circles. I will try to present both sides of the argument. Largely this depends on context. What are your goals? Is this for sports or rehab/balance?
The legit argument
The positive that I like the most, is that an uneven surface is going to recruit more muscle fibers. My theory is that we are hard wired for survival, and will naturally fire as few fibers as possible to get the job done, mostly to conserve energy.
The body will automatically fire more muscle fibers to help balance. The strength coaches against this argument will say that a heavier resistance or weight will recruit more fibers (true), and that you can’t get as strong if you are trying to balance.
I agree with this line of thinking. If you want to be stronger, you need to be on a solid foundation, and increase the amount of weight lifted.
Difference between agility and strength
One strong argument for these surfaces is Mikaela Shiffrin. She is now the all time leader for most World Cup downhill skiing wins.
I recently saw one of her training videos, and it is truly impressive. She does a mix of pure traditional weight lifting for strengthening, and some agility and balance drills.
I would argue that her record is some good anecdotal evidence that both venues are legitimate. Her life depends on her ability to balance and adjust to changing surface conditions, in a fraction of a second, travelling at 60-80mph.
In this first video she is using an unstable surface. In the video below she is using mostly flat or stable surfaces.
Courts and fields
One argument against uneven surfaces is that most athletes are competing on a stable surface. So they want to push as much weight as possible in the gym with a stable surface.
There are some balance and agility strengthening drills with flat surfaces also, pictured below. Athletes are going to have to deal with outside forces pushing them off balance.
Are top weightlifters agile?
One argument against just strengthening, is that the strongest weightlifters are not the most agile. They are very large. Most are also incredible athetes with speed and power, but they do not have the speed and agility to beat world class soccer players or downhill skiers, etc. Different skill sets.
So which one is best?
I’m usually going to lean more towards strengthening on a flat surface, yet every case is different. Some people might get burned out doing the same exercises all the time, or reach a plateau.
Hard strengthening on flat surfaces might be more appropriate for off season conditioning. Balancing on uneven surfaces can improve some balance and agility as you get closer to a season. Will it help prevent injuries? That may not be definitively proven in studies, but I am willing to bet it wouldn’t hurt. I tend not to doubt Mikaela’s Olympic coaches.
It's like anything it will be context dependent. There may be a sports specific case with something like the woman in the video.
Agree with Jason, there can be good carry over with older clients with just using the ball for balance, I wouldn't normally get people trying to squat on it.
For average younger gym rats, it tends to be used as a novelty. Something they've picked up from Instagram or YouTube or reddit but it's unclear it's really doing anything for them.
I think there is a place for this type of training. As you mentioned, it really comes down to where the client is and what their immediate goals are. Ultimately, getting stronger checks a lot of boxes and flat, sturdy surfaces do better with that.
In my experience, the older population is the most receptive to the unstable surface training. Especially if balance and fall risk reduction is an area of concern. I have seen some make great progress with it as well!
Great article.
Cheers,
Jason