Functional Training and Corrective Exercise
In his T-Nation article, trainer Mike Robertson addresses the concept of functional training in terms of the popular trend toward using devices like BOSU balls, wobble boards, etc., that are said to help develop better stability and prevent injuries. Mike discusses why the current trend to using instability devices isn't always productive and how it actually gets away from the concept of functional training. I highly recommend Mike's article, and I want to give some additional context for it here.
The idea of "functional training" was originally to move away from isolation exercises like leg extensions and curls and instead have people do things that were more like the specific challenges they expect to face, forcing them to support, move, and stabilize themselves in controlled ways to prepare to handle real physical challenges better without injury, and in the process, correct more basic weaknesses.
Trainers began to notice that people don't use their bodies in the way that an isolation mentality would predict; the parts are interdependent in important ways when we move. Various neural and connective tissue mechanisms linkn our body parts together to stabilize them as they move through space and exert force against resistance. This led to increasing use of exercises emphasizing multi-joint movements that more closely mimicked real sports movements and real life movements, and led to a growing distinction between training specifically to lift heavy weights in particular ways, training to build big muscles, and training to perform better and avoid injury in other activities. "Corrective" and "functional" training came to increasingly mean doing exercises on unstable surfaces or training the abs, and this starts to drift away from the original concept.
Why is this a drift away from true functional training? ...
Two very important concepts underlie this trend: the "core" and the "kinetic chain."
When someone gets hurt, especially repeated patterns of injury that don't have another obvious cause, it is currently "best practice" to try to track this down to a problem somewhere stabilizing the body properly during movement. Particularly when someone experiences a range of different injuries on the same side of the body, trainers will tend to suspect a problem with the "core." This refers to the central trunk stabilizing muscles and structures.
The "core" obviously doesn't do all of the work of movement. You can think of it as like a platform that we push off in order to move. Actual movement occurs when muscles contract in a precisely timed sequences, where movement at one joint decelerates followed by acceleration at the next joint in the sequence. Thus a "kinetic chain" or simply chain of movements.
The motor cortex in the brain appears to be organized to coordinate muscles in terms of these sequences rather than to fire individual muscles, so this is considered a very fundamental idea. The constant alternation and interplay between producing force at one joint and reducing force at another is coordinated by complex neural mechanisms that are considered an important aspect of proprioception, a general term for our inner body sense.
A synopsis of this topic would be remiss if I didn't mention the first widely read book on the topic, and the one that first fascinated me with it: Total Body Training by Richard Dominguez and Bob Gajda. Many of the concepts that are now widely taken for granted in functional training originated in that very book which is now somewhat hard to find. In fact, this book appears to be the first place where the now ubiquitous late-night infomercial term "core" was used seriously to mean the stabilizing platform for movement. Dominguez is a sports medicine orthopedist and Gajda did his Ph.D thesis in biomechanics. Total Body Training was the result of that work. It is also worth noting that Gajda was a very successful bodybuilder before his work in functional training, having once beaten Arnold for the Mr. Universe title.
The trend toward using wobble boards and such to improve performance and prevent injury begins with Gajda and Dominguez's ideas and is based on improving proprioception skills. The idea is that weaknesses in "core" strength are transmitted by means of the "kinetic chain" to become problems that don't bear any obvious relationship back to the "core."
It's a little like the medical notion of referred pain. Problems in stabilizing the trunk get "referred" to injuries in more remote places in the body. When people try to correct for problems with their gait, their posture, and their basic movements, they compensate by using other muscles and end up with patterns that induce strain and eventually injury.
So one of the ideas is to improve proprioception by exercising on unstable surfaces, forcing us to develop better stabilization skills rather than overcompensating with the wrong muscles. Especially if we lack adequate balance, which isn't uncommon.
The problem is that while stabilization by learning balance skills is important, it is only part of the problem and not neccessarily the best focus for remediation. One of the most common "core" problems appears to be when certain tight core muscles inhibit other muscles through a neural mechanism called reciprocal inhibition. This causes a deep inefficiency that is transmitted to other areas of the body. One common example is when a tight muscle on the front of the hip diminishes hip extension and inhibits the use of the glutes. This imbalance is transmitted through the movement chain to cause problems with other parts of the leg during activity.
The point is that you won't neccessarily best fix this kind of problem by wobbling on a board or a ball. You have to assess the problem and come up with movements that help address the imbalance. Assessment isn't black magic, there are some basic tests that are widely used by therapists and trainers. It does take a little experience to watch a movement and recognize problems with it, but the assessment tests are designed to amplify the basic problems so you can see them better. If you don't have a trainer handy and want to know more about assessment, Gray Cook's book The Athletic Body in Balance is a good start. His "functional movement screen" is a good example of a simple assessment tool.
There's nothing wrong with doing work for proprioception skills and limb stabilizing strength, but it shouldn't be your primary focus since injuries are more likely to be the result of underlying deeper stabilizing muscle imbalances, somewhat obscured by the actions of the kinetic chain.
If you remember that movement starts from a platform, and operates through a chain, it makes sense to assess the integrity of the platform first rather than trying to adjust the wobbling at the end of the chain.
That's why I think Mike's approach to training with functional corrective exercise is so helpful.