Personal Trainer Course - Canadian Fitness Education Services

Chapter 5 Biomechanics and Applied Kinesiology

In Summary:

Lever = Bones

Fulcrum = Axis of Rotation = Joint

FM = Muscular Force = the muscle contraction

FR = Resistive Force = body weight, load

MM = Moment Arm of the Muscular Force

MR = Moment Arm of the Resistive Force

In general, if a force acting on the lever is great enough

to offset the weight (or resistance), then the lever will move.

In a lever system there is a balance. To move this lever there

must be enough force at one end to offset the resistance of the

weight at the other end. If the moment arm of the resistance is

longer than the moment arm of the applied force or muscular ef-

fort, then more force will be required to move the lever. In other

words, the further away the resistance is from the fulcrum, the

more force required to move the lever.

Mechanical advantage refers to the ratio of the output force

to the applied force or the ratio of the length of the moment arm

of the resistive force or load (MR) to the length of the moment arm

of the applied force or muscular effort (MM). A mechanical advan-

tage of greater than 1.0 means that the force exerted on the load

by the lever is greater than the applied force. A mechanical ad-

vantage of less than 1.0 means that the force exerted on the load

by the lever is smaller than the force applied to the lever.

First Class Levers

In  a   first   class   lever   the joint   (fulcrum)   

lies between the muscle (the applied or

muscle force) and the load (the resistive

force).     The body    has few first   class   levers.     

An example of a First Class Lever in

the human body involves extension of the

neck:

The fulcrum — top of the cervical ver-

tebrae

The resistance — the weight of the

skull

The muscle force — the cervical exten-

sors

With prolonged reading of a book, the

chin pokes forward and drops toward the

chest.      The load    or  the weight  of  the skull   increases   significantly   

and the muscular force or effort to hold that posture increases

substantially. Usually the muscle is not able to counteract the

load; therefore may people experience discomfort and tightness in

p

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Sample Pages PDF Extract

This is not the

complete chapter

Sample Pages PDF ExtractThis is not the complete chapter