Lecture 4

Question 1

What happens from around 30 years old?

Answer 1

• A gradual increase in the loss of muscle fibres
• These fibres are replaced with intramuscular fat, and visible reduction in muscle mass may not be apparent until advanced years

Question 2

What can the reduction of elasticity of muscle and bone lead to?

Answer 2

The reduction in the quality of joint movement in the elderly

Question 3

What are muscles composed?

Answer 3

They’re composed of long thin fibres

Question 4

What happens when muscles are stimulated?

Answer 4

When they’re stimulated by electrical impulses from the central nervous system, the muscle contracts briefly, therefore exerting a force

Question 5

What is a force?

Answer 5

A push or a pull

Question 6

What does rate of force development determine?

Answer 6

• It determines the force that can be generated in the early phase of muscle contraction (0–200 ms)
• Can train muscles to be able to generate more force quicker (sprinters) or to generate force over a longer period of time (long distance)

Question 7

What can determine the size of the force (tension) generated?

Answer 7

The cross sectional area:
- The bigger the muscle, the bigger the force it can produce

The length of the muscle:

• Max tension is achieved when the muscle is stimulated when its in its relaxed state (free length)
• The reason why athletes shake out their muscles before competing. They’re trying to get their muscles in a relaxed state, bc that gives them more force

How the muscle fibres are laid down:
- If the muscles fibres run along the same direction as the muscle length (fusiform)
_ If the muscle fibres run on an angle to the muscle length (pennate)

Question 8

What does ML=FL mean?

Answer 8

When muscle length=fibre length, the muscle fibres run along the same direction as the muscle length

Question 9

Fusiform (parallel) muscles?

Answer 9

• Long fibres run parallel and along the length of the muscle
• Wider and cylindrically shaped in the centre and taper off at the ends
• The line of action in this muscle type runs in a straight line between the attachment points which are often tendons
• Have a large range of motion, but can’t generate as much force as pennate muscles
• Most skeletal muscles are parallel muscles
  e. g. Biceps

Question 10

Pennate (penniform) muscles?

Answer 10

• Fibres are at an angle to the force-generating axis (pennation angle) and usually insert into a central tendon
• Pennate muscles contain more fibres per unit of muscle volume and the fibres are shorter
• They can generate more force than parallel fibered muscles of the same size, however, they have a smaller range of motion

e.g. Glutes

Question 11

Different categories of pennate muscles?

Answer 11

• Unipennate
• Dipennate
• Multipennate

Question 12

Line of action?

Answer 12

• Along the fibre direction

- Direction that the muscle shortens or lengthens

Question 13

Normal and Antagonists?

Answer 13

• Muscle movement typically involves the use of multiple groups of muscle (agonist/normal/prime movers and antagonist)

Normal:
- Bring the desired movement

Antagonists:
- Help the normal’s by active controlled relaxation, so that the desired movement is smooth and precise. They cooperate with the prime movers rather than oppose them

Question 14

Levers?

Answer 14

• A lever consists of a beam or rigid rod (e.g. a bone) pivoted at a fixed hinge or fulcrum (e.g. the elbow) that is capable of rotating
• They bring about simple movements and motion for joints using muscles and tendons
• Can be used to magnify the size of a force or change its direction

Question 15

The load (resistance)?

Answer 15

The object you are trying to move

Question 16

The effort (applied force)?

Answer 16

The force applied to move the load

Question 17

The fulcrum (pivot)?

Answer 17

The point where the load is pivoted

Question 18

Mechanical advantage (MA)?

Answer 18

The ratio of the load force to the applied force

MA = Fl/Fa

Fl = Resistance load (weight)
Fa = Force applied by muscles

MA > 1 = efficient
MA < 1 = inefficient

Question 19

Class I Lever?

Answer 19

• Load Force (Fl) and Applied Force (Fa) are on either side of the fulcrum
• Can be either efficient or inefficient

Designed for:

• Strength when fulcrum is near load force
• Speed and range of motion when fulcrum is near applied force

Question 20

Class II Lever?

Answer 20

• Fl is between the fulcrum and Fa
• Always efficient
• Designed for strength

Question 21

Class III Lever?

Answer 21

• Fa is between the fulcrum and Fl
• Always inefficient
• Designed for speed
  and range of motion

Question 22

How do levers operate?

Answer 22

Through the applications of moments and torques

Question 23

Moment or torque?

Answer 23

• A force which causes some rotational motion about a fixed point
• The torque is the quantity that indicates the ability of a force to cause rotation

Question 24

The magnitude of the torque equation?

Answer 24

T = F x D

• The magnitude of the torque generated is the product of the force (F) and the perpendicular distance to the pivot (D)

Question 25

What if the force is applied at an angle which is not 90°?

Answer 25

Torque about P:

T = DFsinθ

Question 26

When is the torque maximum?

Answer 26

When the force F is applied perpendicular (at 90°) to the direction of D as sinθ = 1

Question 27

What two conditions have to be met for a body to be in equilibrium?

Answer 27

1. Net Force = Zero.

2. Net Torque = Zero.

Question 28

Torque equation (clockwise vs. anti-clockwise)?

Answer 28

Sum of Clockwise = Sum of Torques Anti-Clockwise
Torques

F1X1 = F2X2