Panjabi divided the motor control system for the spine into three distinct subsystems - passive, active and neural. I like applying this idea to the whole body, partly because I find it an interesting way to distinguish different strategies for movement and posture, based on preferential use of one subsystem over the others.
The passive subsystem
The passive musculoskeletal subsystem includes bones, ligaments, joint capsules, connective tissue, discs, and the passive mechanical properties of the muscles and fascia. This subsystem creates tension and stability through passive restraints to movement. The stretchy elements (muscle, fascia and tendons) can store and then return elastic energy, and the bones can act as levers and transfer force from place to place. So all of the work done by this system is “for free” because it does not require any expenditure of metabolic energy.
The active subsystem
The active musculoskeletal subsystem consists of muscles. The work of this subsystem is energetically expensive - muscles require energy to contract.
The neural subsystem
The neural subsystem consists of the various motion sensors located throughout the body, and the nervous system, which reads signals from the body and the sends signals to fire motor units. Nervous system activity requires energy. Although the brain accounts for only 2% of the bodies’ weight, it consumes up to 20% of the body’s energy.
You can think of someone's movement style as being preferentially oriented toward the passive or active system. (Everyone uses the neural system, just more or less intelligently.)
The passive strategy
If someone has long, skinny, flexible limbs, and elastic muscles and tendons, they will probably learn to rely to a large extent on their passive system. They don't have much muscle to generate power, but their structure is well suited to do lots of work. Flexibility allows them to easily reach end ranges of motion that store elastic energy and provide free stability. The long levers generate power after summating motion at many joints. These body types start moving slowly through lazy graceful arcs, but finish movements at great speed like the cracking of a whip. Think of the long, flowing whip like movements of a lanky tennis player like Gael Monfis, a golfer like Phil Mickelson, a fighter like Jon Jones, or quarterback like Tom Brady. The impression is effortless lazy power.
This style of movement can be pathological when it gets too lazy or sloppy, and places excess stress on the ligaments and other connective tissues that make up the passive system. Imagine the posture of a slouching bored teenager - one hip kicked out to the side, hyperextended knees, collapsed chest and forward head position. In this position they are basically hanging off their ligaments. This is energetically efficient because it requires less muscular work, but it places excess stress on the physical health of the passive subsystem.
A great deal of “poor form” that we see in the gym or in sports is a result of excessive use of the passive system, possibly due to deconditioning and reluctance to use the active system. This makes movement look sloppy, floppy, or poorly aligned. Movements are controlled too much by passive restraints created by an end range of motion, as opposed to active muscular restraints which keeps the joints better centrated. Some classic examples would be valgus knees in a squat position, or a rounded lower back in a dead lift. In each case, the passive elements are doing too much stability work as the muscular system relaxes. This strategy is energetically efficient in the short term, but creates excess stress on the passive structures, and fails to create the joint centration and alignment that is required for optimum coordination, balance and power.
The active strategy
Now let's look at the movement style of someone with a stockier, stiffer, more muscular build. They will probably learn to preferentially rely on the active system. They have plenty of muscle for generating power, but they lack the range of motion and long levers that create large, flowing whip like motions. Instead, their movements look short, compact, controlled, punchy, and piston-like. The movements start fast and end fast, unlike the slow build up of the passive athlete. Balance and change of direction is easier because their joints spend more time near a neutral position. Think of the punching of Mike Tyson, the pitching of Roger Clemens, the racquet work of Andre Agassi, or the water bug changes of direction by Lionel Messi. These athletes don't look lazy and effortless, they look like frighteningly dynamic.
The active strategy can be pathological if taken to extremes. This might happen if the athlete fails to relax antagonists, or to pause long enough to elastically load the joints before firing them. Movements will then appear stiff, musclebound and awkward, like they are fighting against themselves or driving with the parking brake on. This style is very metabolically expensive and energetically inefficient.
I usually end a blog post by asking what practical takeaways we can derive from whatever analysis I just performed. In this case, I'm not sure there are any! I just think this is an interesting topic.
Actually, here's a few possible ideas. Different bodies will gravitate towards different styles of movement, which have their relative strengths and weaknesses. If you're going to imitate another athlete's style at something - say their golf swing or tennis stroke or throwing style - make sure they have a similar body type to yours.
Further, these concepts might help you to find a weak link in your movement strategy. Personally, I am a classic "passive" type - long skinny limbs that tend toward floppiness. So it is not surprising that I really benefit from strength training. Others with a more "active" style might need an opposite strategy - more focus on mobility and relaxation. And of course, everyone can learn to use their neural system more intelligently. There's always room for improvement there.
Any thoughts? Share in the comments.
UPDATE: I just came across this article by Sam Sturgis at Mike Reinold's site about the effects of rhythmic stabilization on ROM and throwing velocity in college pitchers. It seems the effects of the intervention depended on the "style" of the pitcher. Very on point!