Spinal Biomechanics Lecture 3 Forces And Lever Systems

Front 1

Shear Forces

Back 1

any forces that are parallel to contacting surfaces, attempting to move one object on another.

Front 2

Friction Forces

Back 2

potentially exist whenever there is contact force & is opposite the direction of shear forces. Must have a shear force to produce a friction force.

Front 3

Torque/Moment Force

Back 3

the strength of rotation produced in an object when an isolated force does not pass through the Center of Mass. A combination of rotatory & translatory motion.

Front 4

Parallel Force Systems

Back 4

two or more forces applied to the same object that are parallel to each other.

Front 5

Torsional movement

Back 5

– occurs when torque forces produce a rotation of a segment around its long axis

Front 6

Torsional forces

Back 6

create a “twisting” motion between two objects, i.e. joints.

Front 7

Anatomic pulleys

Back 7

bones or bony prominences that alter the direction of pull of a muscle. They deflect the action line of a muscle away from the joint axis, thus increasing the Moment Arm (MA) and torque produced by a muscle force.
MA of a force & torque are greatest when at 90 degrees to the segment, and minimal at 0 degrees.

Front 8

First class lever

Back 8

the axis lies between the effort force and the resistance force

Front 9

First Class lever system example

Back 9

rare in the human body; the supraspinatus muscle acts on the humerus proximal to the axis of rotation and the Center of Mass is just above the elbow. This is a 1st class system whether the supraspinatus is the EF or RF.

Front 10

Second class lever

Back 10

the resistance force lies between the axis and the effort force

Front 11

Second class lever system example

Back 11

– occurs when gravity is the EF and the muscle is the RF, producing active lengthening of the muscle (eccentric contraction), i.e., lowering the leg slowly against gravity (deceleration).

Front 12

third calss lever

Back 12

the effort force lies between the axis and the resistance force

Front 13

third class lever system example

Back 13

a muscle creating joint rotation in its direction of pull, i.e., the quadraceps muscle (EF) extending the knee against gravity (RF).
An active shortening of the muscle (concentric contraction)

Front 14

When muscle is EF, it is what type of contraction?

Back 14

concentric contraction

Front 15

When muscle is RF, it is what type of contraction?

Back 15

eccentric contraction