Biomechanics Final Exam Review: Levers

What is a lever?

-A rigid bar that rotates about an axis, or fulcrum.

-A force applied to a lever, motive force, moves a resistance, or resistive force.

-Locations of the applied motive force, the resistance, and the fulcrum, determine the lever's classification.

A Lever is a rigid bar that ___ about an ___.

Rotates about an axis, or fulcrum

Axis, aka

Fulcrum

Force applied to a lever, aka

Motive Force

In the body, what is the lever, or rigid bar?

The bones.

In the body, what is the motive force, or applied force?

The muscles

In the body, what is the resistive force?

Distal body part's weight, dumbbell, or external weight.

In the body, what is the fulcrum or axis?

Joints

4 Components to a Lever

1. Motive Force: Agonist. Prime mover. Force that is applied and produces an action.

2. Resistive Force: Antagonist. Opposite action as the motive force.

3. Lever, Body, Bone: rigid bar which rotates about axis.

4. Fulcrum: axis of rotation.

Motive Force

-Applied force.

-Agonist. Prime mover.

-Force that is applied and produces an action.

-In the body, muscles.

Resistive Force

-Antagonist.

-Opposite action as the motive force.

-In the body, body weight, external weight.

The biomechanics of human movement is based on the _____.

Lever System

Force should be exerted ___ to the levers

Perpendicular.

First-Class Levers

-The axis, [fulcrum], is found between the Motive force and the Resistive force.

--Depending on the moment arm, can be both Mechanically DIS-advantaged, or advantaged.

--In the body, simultaneous action of the agonist, [applied motive force], and antagonist, [resistive], muscle groups on opposite sides of a joint axis is the same as a first class lever.

[Seesaw, scissors, pliers, crowbar.]

[Knee extension using quads. Stepping on brakes.]

Depending on the moment arm, can be both Mechanically DIS-advantaged, or mechanically advantaged.

First-Class Lever's mechanical advantage

In the body, simultaneous action of the agonist, [___], and antagonist, [___], muscle groups on opposite sides of a joint axis is the same as a ___ lever.

Applied motive force.

Resistive force.

First-Class.

Second-Class Lever

-Both Motive Force and Resistive Force are on the same side of the axis, but the Resistive force is closer to the Axis, [fulcrum], than the motive.

-Only Mechanical Advantage.

-Eccentric Muscle Contractions.

[Wheel Barrow, Lug Nut Wrench, Nut cracker.]

[Jaw movement, calf raise.]

[Eccentric Elbow flexion, down phase of a curl. Create muscle-bone 2nd class lever]

Agonist Muscles are the ___ force

Applied, or Motive force.

[Muscles.]

Antagonist Muscles are the ___ force

Resistance. Resistive force that works opposite of the agonist.

Eccentric Elbow flexion during the down phase of a curl. This resistance exercise creates a muscle-bone ___ class lever.

Second-Class

Examples of First-Class Levers

[Axis between M and R.]

[Mechanical advantage depends on moment arm]

-Seesaw.

-Scissors.

-Pliers.

-Crowbar.

-Knee extension using quads.

-Stepping on brakes.

Examples of Second-Class levers

[R is closer to axis than M.]

[Mechanical ADvantage.]

-Eccentric Elbow flexion during the down phase of a curl.

-Jaw movement.

-Calf raise.

-Wheel Barrow.

-Lug Nut Wrench.

-Nut cracker

Examples of Third-Class levers

[M is closer to axis than R.]

[Mechanical DIS-advantage.]

-Biceps at the elbow.

-Patellar tendon at the knee.

-The medial deltoid at the shoulder.

-Hip Extension.

-Dorsiflexion.

-Curls.

-Elbow flexion.

--Canoe Paddling, and Shoveling:

--Only if the top hand acts as the axis, applying no force.

Third-Class Levers

-Both Motive Force and Resistive Force are on the same side of the axis, but the Motive force is closer to the Axis, [fulcrum], than the Resistive.

-Only Mechanical DIS-advantage.

-Concentric Muscle Contractions.

-Most movements in the human body.

[Hip extension, Dorsiflexion. Curls. Elbow flexion. Biceps at the elbow. Patellar tendon at the knee. The medial deltoid at the shoulder.]

[Canoe Paddle, Shoveling. Only if the top hand acts as the axis, applying no force.]

Mechanical DIS-advantage, and Concentric Muscle Contractions are characteristics of which type of lever?

Third-Class

Mechanical ADvantage, and Eccentric Muscle Contractions are characteristics of which type of lever?

Second-Class

If the motive force is closer to the axis than the resistive, then its a ___ class lever

third

If the resistive force is closer to the axis than the motive, then its a ___ class lever

second

Hip extension, Dorsiflexion. Curls. Elbow flexion. Biceps at the elbow. Patellar tendon at the knee.

All which type of lever system, and what type of muscle contractions?

Third-Class, Concentric.

The Mechanical effectiveness of a lever for moving a resistance, found by using the ratio of the Motive Force's moment arm to the Resistive Force's moment arm, is known as what?

Motive Arm ÷ Resistive Arm = ___

Mechanical Advantage

A Lever's Mechanical Advantage

-The Mechanical effectiveness of a lever for moving a resistance, expressed qualitatively.

-The ratio of the Motive Force's moment arm to the Resistive Force's moment arm.

[MA = Motive arm / Resistance arm]

Advantage:

-When the Motive arm is greater than the Resistive Arm, the magnitude needed by M to move R is less than the total magnitude of R.

MA= Greater than 1.

Disadvantage:

When the Resistive arm is longer than the Motive arm, the resistance can be moved a larger distance around the axis.

MA= Less than 1

-A force that is larger than the resistance must be applied to cause motion of the lever.

A lever is mechanically dis-advantaged. Why? What type of lever? And what number value is it given?

When the Resistive arm is longer than the Motive arm, the resistance can be moved a larger distance around the axis.

MA= Less than 1

-A force that is larger than the resistance must be applied to cause motion of the lever.

-Third Class Levers. [Some first.]

A lever is mechanically advantaged. Why? What type of lever? And what number value is it given?

When the Motive arm is greater than the Resistive Arm, the magnitude needed by M to move R is less than the total magnitude of R.

MA= greater than 1

-Second Class Levers. [Some first.]

When the Motive arm is longer than the Resistive Arm, the magnitude needed by M to move R is ___ than the total magnitude of R.

M needs Less magnitude to move R.

Mechanical Advantage.

MA= greater than 1.

When the Resistive arm is longer than the Motive arm, the resistance can be moved a larger distance around the axis.

Mechanical Dis-Advantage.

MA= Less than 1.

-A force that is larger than the resistance must be applied to cause motion of the lever.

Maximizing effective Moment Arm length generates more ___

Torque.

[Technique pitchers, and tennis players often use]

Technique pitchers, and tennis players often use to maximize torque

Maximizing the length of the effective moment arm for force application

In the human body, most muscle-bone lever systems are of the third class, therefore they have a Mechanical advantage of ___ [#]

Less than 1.

The force of muscular tension is resolved into two force components:

*One perpendicular to attached bone.

One parallel to the bone.*

The Perpendicular Component of muscle force, aka [the rotary component], is what causes the bone to rotate about the joint center/axis.

The Parallel Component of muscle force pulls the bone either away from the joint center, [dislocating component], or towards the joint center, [stabilizing component].

The Perpendicular Component of muscle force

aka [the rotary component], is what causes the bone to rotate about the joint center/axis.

The Perpendicular Component of muscle force aka

the rotary component.

What Component of muscle force causes the bone to rotate about the joint center/axis?

The Perpendicular Component, aka rotary component

The Parallel Component of muscle force

pulls the bone either away from the joint center, [dislocating component], or towards the joint center, [stabilizing component].

The Parallel Component of muscle force pulls the bone away from the joint center, known as ____

the dislocating component

The dislocating component

Part of the Parallel Component of muscle force pulls the bone away from the joint center

The Parallel Component of muscle force that pulls the bone toward the joint center, known as ____

The stabilizing Component

The Stabilizing Component

The Parallel Component of muscle force that pulls the bone toward the joint center