Factors Affecting Strength & Power: Mechanical Factors Flashcards
What is Strength?
The maximum force that a muscle can generate at a specified velocity
Five MECHANICAL factors of strength?
- Types of muscular actions
- Length & velocity of isolated muscle
- Moment arm
- Joint velocity (muscle groups)
- Joint position (muscle groups)
Six STRUCTURAL factors of strength?
- Cross sectional area
- Pennation angle
- Fibre length
- Fibre distribution
- Type of fibre types stimulated
- Innervation ratio
Two neural factors of strength?
- Number of motor units activated
2. Frequency of stimulation
Single Muscle Fibre force is greatest at intermediate lengths and decreases at shorter and longer lengths, why?
More binding sites available and greater number of cross-bride attachments at intermediate lengths
Why are African distance runners so dominant?
Longer Achilles tendons
Shorter contact times during hopping
Greater jumping power
Four mechanisms that have been proposed for dominant distance runners?
- Increased time available for force generation
- The storage and subsequent use of elastic energy
- The force of cross-bridges is enhanced as a result of the pre-ceding stretch
- Additional sensory feedback
Provide examples of when the length-tension relationship is relevant to applied practice?
Range of motion testing
Cycling
In what type of muscle action is force production greatest?
A greater force is generated during lengthening contractions (eccentric phase) possibly due to
The stretching of incompletely activated sarcomeres
An increase in the mean force during cross-bride cycles and
A faster reattachment phase
Eccentric and concentric facts
- Eccentric contractions can produce greater force than concentric contractions through different
- Eccentric contractions are more efficient
- Eccentric contractions present different neural control strategies - EMG amplitude greater during concentric than eccentric actions
- The contribution of ECC and CON actions to
hypertrophy is unclear
Force-velocity relationship in a single muscle fibre
The force that the fibre exerts decreases as the speed of shortening increases due to limited availability of binding sites.
Maximal shortening velocity of a single
fibre depends primarily on fibre-type maximum when a muscle shortens at about details
Force-velocity relationship in a whole muscle
Maximal shortening velocity of a whole muscle depends on its fibre-type composition, fibre length, pennation angle and the rate of change in pennation angle.
According to Hill (1938) power production is maximum when a muscle shortens at about one-third of its maximal shortening velocity
The peak torque exerted during concentric
actions decreases as the angular velocity increases
- knee extensor peak torque at 240 o/s smaller by approx 40% than peak torque at 60o/s
- knee flexor peak torque at 240 o/s smaller by 20-50% than peak torque at 60o/s
What are differences in Pmax between men and women were mainly explained by?
Differences in velocity capabilities
Power =
Force x Velocity
Mechanical action of muscle at this level is not the force it exerts but what?
The torque produced around the joint
Variation in net muscle torque depends on?
The location of the attachments to the skeleton
The attachment location influences what?
The number of joints spanned by a muscle
What is moment arm?
Shortest distance from > Joint centre > Line of action of the force (tendon)
T =
F x D
What is effort arm?
What is resistance Arm
Distance from > Axis > Point of force application
Distance from > Axis > Point of force resistance
What are the advantages and disadvantages when the tendon inserts further from the joint?
Advantages -
The muscular moment arm will be longer, and the mechanical advantage increased
Disadvantages -
The muscle has to contract more to make the joint move through a given ROM – translates to less speed
Effort Arm vs Resistance Arm
Effort and resistance arms can be equal or unequal in length
- Lever arrangement can amplify force
- Lever arrangement can reduce force
- Effected by the ratio of the force moment arm to the resistance moment arm
How does moment arm explain hamstring injuries?
Inter-muscle differences in hamstring moment arms about the hip and knee may be a factor contributing to the greater propensity for hamstring strain injuries to occur in the BF muscle.
Watch lecture slides
3: 39 - 20:03
26: 47 - 37:39
https: //replay.leedsbeckett.ac.uk/Panopto/Pages/Viewer.aspx?id=8f94bc3f-0fa2-4d37-a4ae-a95f00e43917
