9/5d Biomechanics Part III

Question 1

Static Rotary Equilibrium

Answer 1

Internal Moment/Torque = External Moment/Torque

Question 2

First Class Lever in Static Rotary Equilibrium

Answer 2

Axis of rotation is in the center of the two forces.
the muscle effort/force is on the opposite end of the joint as the external force/weight of the head acting ont the center of mass

Question 3

Second Class Lever in Static Rotary Equilibrium

Answer 3

The axis of rotation lies closer to the external force than to the muscle/internal force. AKA the external force moment arm is smaller than the internal force moment arm
Ex: joint in the foot proximal to the head of the big toe is the axis of rotation, the calf muscle lifts up (internal force) and acts farther away than the total body weight acting on the center of mass of the foot (closer to the joint)

Question 4

Third Class Lever in Static Rotary Equilibrium

Answer 4

the axis of rotation (joint) is closer to the internal/muscle force and the external force/gravity and body mass acting on the center of mass of a segment is farther away from the axis of rotation
Ex: Bicep at 90 degrees

Question 5

Mass Moment of Inertia

Answer 5

the body's inherent resistance to a change in angular velocity (I)
Dependent on: 
-the amount of mass of a body
-the distribution of mass of a body
Changes with the position of the body

Question 6

Newton’s laws

Answer 6

1. Law of Inertia - mass moment of inertia, the way your body’s mass is distributed changes the amount of resistance needed to be generated by the body
2. Law of Acceleration - F=ma (linear), T=I*alpha(rotational), alpha changes depending on the rotary angle
3. Law of Reaction - anytime a force is exerted on an object, the object exerts an equal and opposite force

Question 7

when do joint reaction forces arise?

Answer 7

Joint reaction forces are created in response to a muscle pulling one bone against the other during activation

Question 8

does changing a joint angle affect the torque?

Answer 8

when you change a joint angle, the torque also changes.

At 90degrees the torque exerted by the muscle is at it’s highest

Question 9

Are all joint reaction forces compressive?

Answer 9

NO - in certain positions, joint reaction forces can be the opposite of compressive and they distract