Biomechanical Cutting [Mechanical engineering]

# Biomechanical Cutting

To improve movement, each coach and/or athlete must have a firm understanding of the function of the kinetic chain and its relationship and interaction with ground reaction forces and momentum. Once this understanding is developed a logical progression can be implemented to correct and enhance movement skills.

Ground Reaction Forces

The foundation for all movement resides in the knowledge that movement is completely dependent on the ability of the athlete to utilize and manipulate forces, most importantly the forces that interact with the ground (ground reaction forces GRF).

The ability to powerfully apply force to the ground is crucial to movement, but is only part of the equation. We must also efficiently deal with the force the ground supplies back into the body. These are the primary forces that propel and stop the body.

Thanks to Isaac Newton's Third Law of Motion (1687), we know that for every action there is an equal and opposite reaction. With respect to movement, this means that when we push against the ground with X pounds of force, the ground is going to push back with that same (X) amount of force (dependent upon the surface).

I call this the FIFO (force in = force out) response. When you further examine the FIFO response you will see that the harder you push into the ground, the harder the ground pushes back. This concept will become increasingly important later when we start to discuss acceleration and deceleration.

During movement we must not only be concerned with the magnitude or amount of force we produce, but also with the direction of application of the force vector. For the purposes of this article, a force vector will be defined as an imaginary line that defines the direction of application of a force. Understanding force vectors allows us to visualize the forces we apply and receive.

Note: When you push against the ground with your foot, you create a force vector dependent on the direction of push. In response, the ground is going to directly oppose that force vector with its own. It is important to visualize both vectors when we start to analyze the movement.

We must know how to appropriately direct forces to create clean movement. If we misdirect the force we apply to the ground, the resultant reaction will not efficiently help us create or deviate movement.

Although the foot is the point of contact with the ground, it does not determine the force vector created by the push. Rather, one must consider the segment of the leg from the knee down to the foot. It is this segment that determines the direction of that vector.

One must also consider the center of gravity (COG). The relationship between the location of the COG and the angle of the GRF becomes very important during movement.

### FAQ

##### The 7 biomechanical principles of human movement? | Yahoo Answers

All seem fine but you seem a bit unsure about levers.
The first link will give you lots of useful info.
Basically a lever requires a rigid beam (eg humerus) and a moving joint (eg shoulder) and uses this to multiply the force available - or - the distance moved.
For a given input the output force * distance is a constant -
so more movement = weaker movement.
Hope this helps.

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