Lesson 9 - Resistance Training I Flashcards
Why is skeletal muscle important?
Functions of muscle skeletal
- Producing movement
- Maintaining posture
-Stabilising joints
- Generating heat
- Organ protection
Athletic performance considerations
- we lose muscle mass with aging (sarcopenia) which leads to frailty, morbidity and morality
Structure of muscle
For movement, muscle must produce force
Force is transmitted from muscle to bone via tendons
To produce movement at a joint, a muscle must cross that joint
Muscles create torque
Can only produce pulling force
- As muscles act across joints, the linear forces they produce creates rotational forces on the bones = Torque
Torque = force x distance
Depends on magnitude of force produced by muscle and then perpendicular distance from the muscles line of action to the joint centre
Muscle movement arms vary with joint angle
Joint torque equal to muscle force times perpendicular distance
This distance may change through arms range off motion
This is a force length relationship where 90 degrees is strongest
Line and angle of pull
Line of pull: along axis of the muscle
- direction that muscle will pull its two attachments together
Angle of pull: angle between long axis of bone and muscle line of pull
Muscle architecture
Muscle fibres can be arranged in
a variety of orientations relative
to its longitudinal axis
Parallel fibred muscles have
fibres orientated along the long
axis
Pennate muscles have fibres that
run oblique to the long axis of
the muscle
The angle of pennation is equal
to the angle between the
orientation of the muscle fibres
and the long axis of the muscle
- 0 degrees corresponds to no
pennation
Consequences of fibre pennation
More force with more fibres parallel, proportional (cross sectional area)
Pennangle = being able to stuff more fibers at certain angles
By inserting obliquely, pennation allows for a greater number of parallel fibers to be arranged (functional significance)
- Will be proportional to the cosine of the pennation
angle - Anatomical CSA: perpendicular to muscle line of
pull - Physiological CSA: perpendicular to fibre line of pull
Hierarchy of muscle structure
Whole muscle
-Surrounded by epimysium (connective tissue)
Muscle fascicles
- Bundles of muscle fiber
-surrounded by perimysium
Muscle fibers (cells)
- Surrounded by sarcolemma (cell membrane) and endomysuim
Myofibrils
-units of muscle for contraction
Myofilaments
-protiens that make up myofibrils
Sarco = muscle related
Z line, I line and A band
A band = thick filament, centered in between z line
Z line: defines the boundary of the sarcomere, on both ends
I band: thin filament
Neural muscle of control
Motor cortex upper motor neurons
to
Down CNS (spinal)
to
Alpha motor neuron, lower motor neuron
to
muscle fibre for contraction
Cross bridge cycling
Know that binding of ATP is used for muscle attachment of muscle relaxation
Power stroke causing cross bridges to attach
Force-calcuim and force frequency relationship
Muscle recruitment and calcium releases is 1:1 relationship
Higher firing frequency leads to more calcium, more attached cross bridges and more force
What is activation
Typically (broadly) refers to the amount of Ca2+ released within a muscle
fibre
* Therefore, activation corresponds to the amount of force produced
- Higher frequency of stimulation = higher level of activation
- At whole muscle level, we control force by increasing firing frequency
and/or increasing the number of active motor units (MU recruitment)
Red and white muscle
due to pigment in the muscles themselves
-found in myoglobin
-binds to O2
Red=slow twitch
White = fast twitch
Twitch=repsonse time to electrical impulse
Fast-twitch fibres exhibit higher maximal shortening
velocity and power output
- Fast-twitch fibres have a much
higher maximal shortening
velocity than do slow-twitch
fibres
-The higher shortening velocity
at any force output equates to
a much higher power output
for fast-twitch fibres
