In my words, functional training is exercise that is specifically tailored towards replicating and optimising movement patterns. These movement patterns should be those that an individual uses on a daily basis or must use in the foreseeable future.
We typically think of two ends of the spectrum when it comes to training. The traditional and isolated end and the functional end.
The isolated training end is what most people picture when thinking about working out at the gym. Bicep curls and knee extensions, as well as the more compound movements such as squats and deadlifts. Whether you're training for size, performance, or rehabilitation, these types of exercises are vital to the process. Without targeting and isolating a single muscle or select group at a time, an individual's strength and progress will eventually plateau. However, the usefulness of isolated training will eventually run out as a person graduates towards needing a program that's more tailored for their specific performance goals. If we use the example of a baseball player who needs to be able to generate high-power for pitching, bicep curls and tricep dips will cease being useful after a certain point. Sure, the bodybuilder workout will help an athlete or a tradesman to gain size, but when it comes to needing to coordinate those strength benefits into specific, useful tasks, the transfer has its limits.
In contrast, we have the functional training end of that spectrum. This is when the exercises we do become more specific to the activities required of us at optimal capacity once we leave the gym. Athletes will need to eventually move to this side of things in their later off-season and rehab will consist of a lot of this in order to regain daily function. Even the average gym-goer should be working this type of training in to maintain their daily ability as they become stronger. If we speak in black-and-white terms, this type of training may consists of overhead pressing or carrying a load to simulate work, box jumps to train our muscular systems for sprinting, or rotational movements to teach core stability while swinging a baseball bat.
And that's where the thought process tends to stop. However, we often see an additional far-end of the spectrum when we're at the gym. For the purposes of this post, let's call it "complex movement"; although some of the more opinionated professionals may have less-polite names for it.
When we see people moving into this category, they'll almost always continue to call it "functional training". They're using a high number of multiple muscle groups to target balance and power in multiple planes of motion. The problem here is that, often, these people have now surpassed the realms of functional. That is, unless the individual is a Cirque de Soleil performer.
Gym-goers very often get carried away and assume that the more complicated an exercise is, the more functional it is for our daily ability. It's harder, so by default it must be better. There's a certain capacity in which that logic holds true, but it breaks down quite quickly once we add more and more complexity to the movements.
I once saw Stuart McGill, one of (if not the) world's leading experts on spinal health and rehabilitation put on a seminar. I had the eye-popping experience watching him, with his booming voice and towering demeanour, border on becoming angry at a physiotherapist in his audience; she had argued for the usefulness of standing clients on top of BOSU Balls.
"Tell me," he said, "how having a client balance on a BOSU would be productive to their recovery." No one could come up with a scientific answer. In his opinion, when we're trying to train a person's core to support the spine, removing their base of support beneath their feet is counterproductive.
To make the point more clear, when we talk about "daily function", are we normally required to balance on top of rounded surfaces while pressing weights? Do we usually need to stand ourselves on our hands? Should I hold a static pistol squat while passing a medicine ball back and forth with a partner? If you checked no to all of the above, then proceed with the essay question of: Then why are we training ourselves to do those things?
Inherently, these complex exercises are not damaging to an individual so long as they have been conditioned enough to do them safely. However, when we're selling people on the "functionality" of these exercises, whether it's being sold by a trainer, an athletic therapist, or a physio, we need to be careful of trading productivity for glamour. If there's a specific goal of exercise, then overdoing it with complex movements becomes more of a waste of time that simply looks cooler to do than is useful. If you need to train your balance, then external perturbations rather than unstable surfaces are what will more accurately simulate their needs. And if the shoulders need to be exceptionally stable, it's more likely for the purposes of open-chain movements such as throwing and climbing, rather than weight-bearing.
To sum up, more does not mean better. Isolation has it's necessary purpose, functionality has defined borders, and over-complicating movement does not equal health. As one of my brilliant college professors once stated, follow the KISS Principle.