Actually, it's worse than stupid, it's really stupid.
Here's why.
But before I explain, let me say that I didn't say that trainers who teach functional training are stupid. I also didn't say that people who engage in functional training are stupid.
I said, functional training is stupid. And it's dangerous. And needless, worthless, etc.
According to Richard Schmidt, Ph.D, motor learning principles clearly dictates that skill improvement at a task is best achieved by perfect practice of that skill or task. In other words, if you want to excel at your golf drive, don't hit golf balls standing on a wobble board.
That makes sense, right?
Says Dr. Schmidt:
A common misconception is that fundamental abilities can be trained through various drills or other activities. The thinking is that, with some stronger ability, the athlete will see gains in performance for tasks with this underlying ability.
For example, athletes are often given various "quickening" exercises, with the hope that these exercises would train some fundamental ability to be quick, allowing quicker response in their particular sports.
Coaches often use various balancing drills to increase general balancing ability, eye movement exercises to improve vision, and many others. Such attempts to train fundamental abilities may sound fine, but usually they simply do not work. Time, and often money, would be better spent practicing the eventual goal skills.
There are two correct ways to think of these principles. First, there is no general ability to be quick, to balance, or to use vision. Rather, quickness, balance, and vision are each based on many diverse abilities, so there is no single quickness or balance ability, for example, that can be trained.
Second, even if there were such general abilities, these are, by definition, genetic and not subject to modification through practice. Therefore, attempts to modify an ability with a nonspecific drill are ineffective. A learner may acquire additional skill at the drill which is, after all, a skill itself, but this learning does not transfer to the main skill of interest.
Our muscles allow us to function. The stronger we make our muscles, the better they will function. If we want to be good at a function, like golf, tennis, arm wrestling, etc., we must practice that function as perfectly as possible. It is not a smart idea, nor will it work in your favor to do things like this:
Resistance training is designed for one thing and one thing only - getting stronger. Of course, there are a million and one ways to perform resistance training. My suggestion, no matter what your preferred flavor is, do it safely. If you hurt yourself in the weight room, your pet skill or sport will suffer. That said, don't do it in a manner that simulates a sport or skill.
Keep resistance training and skill practice separate and distinct.
I hope I have saved many of you from hours of wasted effort engaging in these nonsensical practices.
Remember:
Muscles function. The stronger they are, they better they will function.
Practice makes perfect but only if the practice is perfect to begin with.