The Crossroads of the body - The trunk in function
Now we know how important yet complex the core and trunk is, in all functional movements the abdominal muscles have to stabilize the spine and joints, all forces have to be transferred from the legs through the core (the back in particular) to the arms or vice versa.
The big muscles of the abdomen, back and hips are most important to producing force, decelerating, exploding, inhibiting unnecessary movement and stabilizing. In real life the trunk has to deal with ground reactions, gravity, momentum and mass.
In traditional conditioning, people tried to create artificial stability (such as being on the floor) to get the muscles to contract isometrically, to limit motion instead of facilitate it, to train the muscles too much in sagittal (forward and back) plane while ignoring transverse (rotational plane).
Research by Hodges and Richardson from Australia sheds light on how the core and trunk work. They not only looked at motions of the trunk, but they made a point of looking at motions with the arms and legs. They showed that when you initiate arm motion in any plane you get motion and muscle activity in the spine prior to the arm moving.
This research is important because one of the reasons that core conditioning - in the past - failed is that people tried to restore function in the spine and core without recognizing forces that came from the arms down into the trunk from the top, and from the ground through the legs into the trunk and spine.
In this research, people were standing. They were upright relative to gravity, and they were able to experience forces from above and below. It was functional.
This research demonstrates that the trunk really is the crossroads of the body, with the movement of the arms and legs the muscles of the abdominals were turned on.
To get appropriate action and reaction of the muscular skeletal system, the proprioceptors (proprioception – one’s own perception, there are receptors in the muscles and joints and along the spine which provide feedback about relative location of different parts of the body, whether the body moves with the required effort, and monitor stresses and forces at the tendons and joints) have to be turned on, the way they are in function. This cannot happen if we try to make it simple and isolate.
We can isolate the transverse abdominus (deep abdominal wall, which together with the pelvic floor, multifidus and diaphragm is firing before extremity movement to stabilize the spine according to the research) muscle by itself, in a position where the body is horizontal to gravity. This can be done if the muscle is dormant, or weak relatively to it antagonists and synergist muscles (such as with an inactive person, or after injury).
Isolating the transverse abdominus is done to restore the communication between the nervous system and the muscle and to restore base strength, but only as a means to later integrate with the rest of the body in functional movements. If the muscle is strong in isolation it does not at all mean that it will be functional in whole body movement.
We need to train the muscle to work in integration with the rest of the body.
It would seem in the research that the arms and legs are what turned on the abdominals relative to momentum, gravity and body weight.
If the trunk on the other hand is being stabilized artificially by the ground with forces below or above the trunk being absent, the proprioceptors that turn on the abdominal muscles would be confused.
The core muscles turn on, in reality, before you move your arm because you need that stability first. Stability and mobility are linked with functional proprioception. The muscles will turn on but not because someone is consciously trying to contract them in isolation.
The goal is to place the athlete in the most functional positions and let them go through the most functional motions in all three planes and make them succeed, meaning being able to turn on the abdominal and back muscles both to stabilize the spine while produce the movement and interact with the extremities, while reacting to ground reactions, momentum and external loads.
In order to do this we need to turn on the proprioceptors that help to make precise coordination within the kinetic chain. We also need to choose the proper movement patterns, ranges and loads to allow each person to succeed and from there challenge his/her limitations.
In the conditioning or karate classes we use mainly functional movements such as lunges, squats and rotations to turn on the proprioceptors, and the abdominal and back muscles as they should interact with the extremities.