Introduction to biomechanics (lecture 4)

Question 1

MUSCULOSKELETAL (MSK) SYSTEMS

Answer 1

systems capable of resisting or generating motion at joints

Question 2

skeleton (passive)

Answer 2

• bones
• cartilage
• joints
• ligaments

Question 3

active part of the MSK

Answer 3

muscles (tendons)

Question 4

What is biomechanics?

Answer 4

The study of the structure and function of living systems through principles of mechanics

Question 5

What is biomechanics in MSK

Answer 5

largely the study of movement (e.g., locomotion)
• Forces (kinetics)
• Movement (kinematics)

Question 6

Function of biomechanics

Answer 6

Treating muscles-bone- joints as lever systems helps to understand their function, even if you can’t remember it

Question 7

the dysfunction of biomechanics

Answer 7

Many patients will have symptoms that reflect inability
and/or weakness in performing certain movements

Question 8

Lever

Answer 8

A simple machine consisting of a rigid body that can rotate at a fixed point, or fulcrum, in response to forces applied somewhere along its length

Question 9

Torque (def)

Answer 9

the tendency of a force to cause an object to rotate around a certain point

Question 10

equation of the torque

Answer 10

FORCE x PERPENDICULAR DISTANCE TO FULCRUM, aka LEVER

Question 11

what is the levers, the fulcrum and the forces applied in a MSK

Answer 11

Levers = bones
• Fulcrums = joints
• Forces applied: external
(e.g., gravity), or muscular
• Create torques at the joints

Question 12

the composition of MSK lever systems

Answer 12

> 2
muscles generate opposite torques on
opposite sides of a joint.

Question 13

how muscles work?

Answer 13

Muscles work through tension: they can’t push to produce force, they can only pull, through contraction, to generate force

Question 14

Agonists

Answer 14

perform the action
• E.g., biceps flexes elbow.

Question 15

Antagonists

Answer 15

performs opposite
action
• E.g., triceps extends elbow
• Note: it’s all relative!

Question 16

Synergists

Answer 16

assist agonists
• E.g., brachialis assists biceps in elbow
flexion

Question 17

Stabilizers

Answer 17

stabilize joints, fine- tune movement
• Anconeus stabilizes elbow joint in
extension

Question 18

Most common external forces:

Answer 18

• GRAVITY
- Of an object
- Of a body part
• GROUND REACTION FORCES
- Newton’s 3rd law: Action = reaction!
• FRICTION

Question 19

external force (torque)

Answer 19

load

Question 20

distance to load (Torque)

Answer 20

load arm

Question 21

internal (muscle) force (torque)

Answer 21

effort

Question 22

distance to effort (torque)

Answer 22

lever arm

Question 23

Equilibrium

Answer 23

torques are equal, cancel out

Question 24

Angular motion

Answer 24

torques not equal, angular motion
(i.e., rotation) direction and speed depends on which torque is greatest

Question 25

Need more torque (T)? T = F x d┴

Answer 25

-increase F (~larger muscle) or
increase d┴
• Longer lever arm

• Some muscle lever systems are
‘boosted’ by bony protrusions
that lengthen the lever arm
• Processes, tubercles, sesamoids,
etc.

Question 26

Angular motion

Answer 26

rotation

Question 27

fulcrum

Answer 27

center of rotation = axis

Question 28

forces

Answer 28

• External force = load = out-force = resistance
  • Internal force = muscle force = effort

Question 29

Levers:

Answer 29

• Load arm = out-lever
  • Lever arm = in-lever

Question 30

Torque

Answer 30

moment of force