Submitted by: Jeremy Nelson MPT
I was reading a book on engineering and design of bicycles not too long ago. Cycling had been a very big part of my life and I was interested in what gave a bike a certain “feel”. Another way to say was how the bicycle behaved over different circumstances, cornering, climbing, descending, sprinting. In other words why it functioned as it did. The more I read about the design process and the goal of changing the COG over the BOS of the bicycle with the addition of a rider, I recognized many of the same considerations in the practice of PT.
It’s as if the therapist is playing the role of the engineer, working on behalf of the brain, which is seeking to balance the forces created by the COG BOS relationship. The cerebral captain of the corporeal ship is always changing course, ordering the crew with an ongoing changes in the position of sails and rudder to stay the course, or react to changes in the environment. In a presentation, Robert Fritz describes the thoughts of Peter Senge who writes about the interaction of design and performance. Mr Fritz and Mr. Senge ask “Who has more influence on the ship, the captain or the ships designer?” After consideration of the role of cause and effect in how something behaves, they provide the answer: “It’s the ships designer as the design of the ship will determine how the ship moves through the water. ”
The role of the designer is to organize the ships form to create a distinct COM/COG and a BOS relationship that takes advantage of the natural forces of buoyancy. This is not a trivial task. Have you ever seen or been on a aircraft carrier? Every time I am looking over San Diego bay I see the aircraft carriers based in Coronado and wonder, how it is that these huge masses of metal float like corks in the water. And as a result provides a distinct functional capability that the captain organizes his decisions around.
As clinicians we have a role as a designer, an architect and engineer of a plan and actions to produce new relationships for the brain to utilitze. Each body, whose structural proportions are fixed, have interrelated components that move in relationship to each other to provide function. Change the relationships of COG and BOS relationships and new levels of performance are made available.
Likewise the re-structuring of the segments of the human form such that there is greater efficiencies in controlling the COG over a wider variety of BOS configurations. Each different organization of the COG and BOS imposes new demands on the brain to position the extremities and core in ways that maximize there capacities. If one area is inadequate to task, others are called upon to take more of the strain. This lack of component capacity limits the effectiveness of all the other parts of the neuromuscular structure.
Our body has proportions that also work to guide and direct forces, like the ship or the plane. Our body creates a tension, as does the planes structure. Based on the form of a ship or plane there is a zone of most efficiency when piloting these crafts, a path of least resistance for the operation of the ship. The structure of the vehicle creates a 3D zone of most available motions that are most efficient, that due to the structure of the vehicle can attenuate forces the best. Pilot these vehicles out of the zone and the structure are tested as shearing forces are created that can damage the structure and lead to failure.
Our human form has a path of least resistance that is seen in beauty of the spiral form, curves of motions, and ballet type moves of gracefulness. We are not linear in nature, robotic, prone to 2 degrees of freedom. Robots move with extremities acting in support themselves, while the human body is a continuous form, with all motion emanating from the core. When the brain is trying to shift the COG anteriorly over the BOS from an upright seated position in the sitting pattern what is going on under the hood is a changing of force. to maximize the kinetic energy such that the muscles can work efficiently to change the position of COG relative to the BOS.
When seen in this way, therapeutic exercise is no longer a focus on just correcting malposition’s, but become intensifications of the functional movements that are required to perform the functional task. In order to sit and stand, the hip hinge is used to translate the COG over the BOS to the position of most efficiency before standing up. The approach that thinks of the body as a summation of the strength and flexibility could conclude that the problem is inadequate LE strength and begin the process of LE ther ex to improve sit to stand ability. Returning to our ship analogy, if the COG is to high and the BOS is to narrow, the ship will be unsteady, and likely capsize because of the force of buoyancy. Planes need to have their wings positioned in relation to their COG to produce adequate lift to fly. If we though that the lack of flying was a strength issue, we would add a bigger engine creating greater forces on the frame of the plane and stressing the wings even more, possible to the point of failure. See, it’s not a strength issue, but an issue of COG and BOS.
One more, returning to the bike example we started with. By placing the COG of the bicycle and rider towards the rear of the bike, stability is increased and the bike has a smoother more relaxing ride. This is the type of bike that even a novice could ride with their hands off of the handle bars and safely cruise around. A rider participating in a race with many turns and need for fast acceleration would find this type of bike working against her. It would be difficult to make the turns and the rider would have to work extra to accelerate.
Now take the same rider, and put them on a bicycle which has a COG towards the front of the bike in relation and the rider will find themselves quickly cornering and accelerating out of each corner with ease. Now keep in mind, same rider, same strengths, and different bikes with all things equal other than the COG BOS relationship different. The point is that the COG BOS relationship is imposing different demands, and as a result the brain will have to reorganize its coordinated efforts to complete the tasks at hand.
As rehabilitation and performance professionals we often see our clients and patients performing awkward patterns of movement when trying to complete a task. As professionals we can misinterpret these compensations as areas of weakness, thinking it is the compensatory part that is to blame. We then go to work to correct the compensating area. However, if we ask what is happening at the COG BOS level to impose the demand on the body, we may then see that the area is attempting to make the COGBOS relationship work. Other areas are resulting in the inadequacies. Start with the COG and BOS relationship as dominant data points when organizing your change effort and you will find it is easier to understand what is causing the patients difficulty in being involved in their life as they desire.