Bosu balls are a popular implement for people looking to perform “functional” training. For some reason, training on an unstable surface is commonly considered more “functional” than training on normal ground.
Functional training is a term that has been bastardized over the years. I view functional training as training that helps prepare you for real life activities. These can include picking something up off the ground, carrying a suitcase, and movements that occur in sports. You’re most likely never going to do anything of these things while trying to balance on a ball, so why train that way?
Here are a few reasons why bosu balls are (mostly) worthless.
1). You’ll get weaker. Strength is a product of force production. Standing on an uneven surface naturally limits force production. Don’t believe me? Stand on normal ground and jump as high as you can. Then stand on a bosu ball and jump as high as you can. Did you jump higher the first or second time? (Side note: please don’t actually do this unless you’re purposely trying to injure yourself. I think you can probably guess which time you’ll jump higher.) This applies especially to athletes.
2). You’ll burn fewer calories. To burn more calories, you’ll need to use more weight (stress the body). On an unstable surface, you’ll naturally have to use less weight. Therefore, you’ll burn fewer calories.
3). You actually have a greater chance of getting injured on the bosu ball. Ok, this point is a little “clickbaity” but it’s not hard to find videos of people performing back squats or other similar exercises on a bosu ball/unstable surface. Most people struggle to perform these types of movements correctly on flat ground. You’re just asking for trouble if you try to do this on an unstable surface because you saw it on Instagram.
4). You’re not getting special core work by standing on the ball. This is the point that bugs me the most, and it’s probably the most common reason people use the ball. You can get just as much core work doing other exercises that will have much more carryover (ex 1 arm farmers walks, 1 dumbbell step ups, etc) The ball does not have special powers.
Now, there can be times where the bosu ball is a good implement to use. Most notably, it can and in many cases should be used during the rehab of an ankle/lower extremity injury. The demands for balance can help improve proprioceptive feedback from the injured location. It can also be a useful tool for performing pushups (flip it over so that the flat side is facing up) and increasing the demands for shoulder stability. Again, it’s more useful for an injured population.
If you’re healthy, you’re best bet is to focus your training on solid ground and forget the gimmicky unstable surface training.