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John Scherger
05-29-2003, 10:04 AM
Rethinking lever systems



In physics and especially relative to biomechanical or kinesiological study of human movement we are suggesting elimination of the classic structural 3 classes of lever system identification in favor of a true functional identification system.



On our website spinalfitness.com we have posted a hyperlink on the main page under a unified functional definition of lever systems where we demonstrate the functional nature of the structurally defined 2nd and 3rd class levers. Within this demonstration, we show simply due to effective effort arm and effective resistance arm length changes, that a 3rd class lever system can produce a lever with better mechanical advantage (a lever that takes less force of effort than force of resistance). This is where we feel the structural definitions of lever systems fall apart when trying to apply structural applications to a mechanically functioning system.



The true functional identification system would use either 1st or 3rd class lever systems.



Within a functional identification of a lever system, a 1st class lever system is characterized functionally by the ability to develop 180 alignment of the true resistance arm (resultant force) and the true effort arm. This functionally creates a lever system with complete compression being created between the two arms at the fulcrum. A 3rd class lever system is characterized functionally by the ability to develop a 90 alignment between the true resistance arm (resultant force) and the true effort arm. This functionally creates a lever system with complete shearing being created between the two arms at the fulcrum.



Within a lever system there is the functional ability to create both shear and compression.

When compression and shear exist, and the shear force vector direction is towards line of pull, or into the force of effort vector, this is functionally identified as a 1st class lever system. Conversely, when compression and shear exist and the shear force vector direction is away from the line of pull, or away from the force of effort vector, this is functionally identified as a 3rd class lever system.



In order for us to effectively communicate lever systems relative to function in the human spine it was necessary to develop and use this true functional identification process. Peer reviewers within the field, and accustomed to identifying and applying lever system analysis by structural identification, had difficulties with our concepts because our functional concepts didn't conform to what they had always been taught. After numerous demonstrations, and examination of our functional identifications by engineers, physics professors and strength and conditioning experts, the peer reviewers could not find fault with our concepts.



It is our perception if our functional lever identification system was accepted for use, it would improve the functional understanding and clarify communication in biomechanical study.

John Scherger D.C. Ridgefield WA

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