Mechanics in Exercise

Part I | Part II


Movement in the body is produced by a system of levers. These series of levers work together to produce coordinated action, some by actual movement (dynamic) and others by stabilization (static).

First Class Lever

Second Class Lever

Third Class Lever

Lever Arm Length

F x FA = R x RA
Force x Force Arm = Resistance x Resistance Arm

Initial Example   Change insertion 1 cm   Change point of resistance 1 cm 
F x 2 cm = 10 kg x 9 cm
2 F = 90 kg
F = 45 kg
F x 3 cm = 10 kg x 9 cm
3 F = 90 kg
F = 30 kg
F x 2 cm = 10 kg x 8 cm
2 F = 80 kg
F = 40 kg

Variable Resistance Levers

Resistive force (R) is initially relatively short [close to fulcrum (A)]. As motive force (F) acts on lever, resistive arm becomes longer requiring progressively greater motive forces throughout movement.

Angle of Pull

Components of force due to angle of pull
>90 degrees
includes stabilizing component
=90 degrees
100% rotary force
<90 degrees
includes dislocating component

Gravity Vectors

Also see Tension Potential and its impact on force production.

Part I | Part II

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