Lecture 4 Flashcards
What happens from around 30 years old?
- 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
What can the reduction of elasticity of muscle and bone lead to?
The reduction in the quality of joint movement in the elderly
What are muscles composed?
They’re composed of long thin fibres
What happens when muscles are stimulated?
When they’re stimulated by electrical impulses from the central nervous system, the muscle contracts briefly, therefore exerting a force
What is a force?
A push or a pull
What does rate of force development determine?
- 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)
What can determine the size of the force (tension) generated?
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)
What does ML=FL mean?
When muscle length=fibre length, the muscle fibres run along the same direction as the muscle length
Fusiform (parallel) muscles?
- 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
Pennate (penniform) muscles?
- 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
Different categories of pennate muscles?
- Unipennate
- Dipennate
- Multipennate
Line of action?
- Along the fibre direction
- Direction that the muscle shortens or lengthens
Normal and Antagonists?
- 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
Levers?
- 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
The load (resistance)?
The object you are trying to move
The effort (applied force)?
The force applied to move the load
The fulcrum (pivot)?
The point where the load is pivoted
Mechanical advantage (MA)?
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
Class I Lever?
- 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
Class II Lever?
- Fl is between the fulcrum and Fa
- Always efficient
- Designed for strength
Class III Lever?
- Fa is between the fulcrum and Fl
- Always inefficient
- Designed for speed
and range of motion
How do levers operate?
Through the applications of moments and torques
Moment or torque?
- 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
The magnitude of the torque equation?
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)
What if the force is applied at an angle which is not 90°?
Torque about P:
T = DFsinθ
When is the torque maximum?
When the force F is applied perpendicular (at 90°) to the direction of D as sinθ = 1
What two conditions have to be met for a body to be in equilibrium?
- Net Force = Zero.
2. Net Torque = Zero.
Torque equation (clockwise vs. anti-clockwise)?
Sum of Clockwise = Sum of Torques Anti-Clockwise
Torques
F1X1 = F2X2
