Factors Affecting Strength and Power: Mechanical Factors Flashcards
Define Strength
The maximum force that a muscle can generate at a specified velocity
How crucial is strength? What increases with strength.
As strength increases so does... -RFD -Power -Jump Height -Sprint performance -COD performance -Potentiation BUT Injury occurrence reduces
What are the mechanical factors of Strength & Power?
- Types of muscular actions
- Length & velocity of isolated muscle
- Moment arm
- Joint velocity
- Joint position
What are the architectural/structural factors?
- Cross sectional area
- Pennation angle
- Fibre length
- Fibre distribution
- Type of fibre types stimulated
- Innervation ratio
What are the neural factors of Strength & power?
- Number of motor units activated
- Frequency of stimulation
In terms of linking factors together, what is RFD related to?
RFD is related to muscle structure and architecture as well as neural factors.
In terms of linking factors together, what is Peak force related to?
Peak Force is related to muscle architecture, the angle of Pennation will affect PF. Innervation ratio, muscle fibre types.
How does the force-length relationship differ between single-fibres and muscle-tendon units?
The single-fibre force-length relationship dictates that fibres are stronger at intermediate lengths because there are more binding sites available = greater number of cross-bridge attachments. When the connective tissue is added, the muscle-tendon unit is stronger at longer lengths.
Which changes occur during an isometric muscle action?
Muscle fibres shorten by up to 30% but there is no change on the muscle-tendon length.
Explain the force-velocity relationship.
The force-velocity relationship dictates that the force a fibre exerts decreases as the speed of shortening increases with peak power occurring ~30% of maximal shortening velocity
What is muscle stiffness?
Muscle stiffness is the force produced relative to the amount of displacement occurring
What is torque at a joint influenced by?
The moment arm of muscle effort and the moment arm of resistance
When can the length-tension relationship be applied to relevant applied practice?
- Cycling position/Saddle height - higher seat more effective as muscle-tendon unit stronger at longer lengths
- Prescription/manipulation of gym exercises
- The sticking region during certain lifts
What were the findings of “joint-angle specific strength adaptations influence improvements in power in highly trained athletes”?
-Shorter ROM had better transfer to improvements during jumping + sprinting
-The more trained the athlete = more pronounced changes become
WHY
Neural control
Similar hip + knee angles
What are the mechanical adaptations of length-tension relationship?
Length-tension changes with training. IN CYCLING RF properties adapt to cope with demands - cyclists are stronger at short RF lengths
Force-length properties of RF for cyclists = negative
for runners = positive
How does the force-velocity relationship differ at Whole muscle level?
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.
Hill 1938 = power production is max when muscle shortens @ 1/3 of its max shortening velocity.
How does the force-velocity relationship differ at Joint Level?
Peak torque exerted during concentric actions decreases as the angular velocity increases.
- knee extensor PT @ 240 o/s smaller by 40% than PT @ 60 o/s
- knee flexor PT @240 o/s smaller by 20-50% than PT @ 60o/s
Which four mechanisms have been proposed towards the SSC?
- 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
Why are african runners so dominant?
- Longer Achilles tendons
- Shorter contact time during hopping
- Greater jumping power
What does variation in net muscke torque depend on?
- The location of the attachments to the skeleton
- The contribution of multiple muscles to the net effect about a joint (1 vs 2 - joint muscles)
What is a moment arm?
Perpendicular (shortest) distance from the joint centre to the line of action of the force (tendon)
What are the advantages/disadvantages when tendon inserts further from the joint?
Advantage - muscular moment arm will be longer, the mechanical advantage increased.
Disadvantage - Muscle has to contract more to move joint through the ROM = less speed.
How oes 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 @ Biceps Femoris muscle.
How does moment arm explain the effect of stature?
Tall athletes are immediately at a disadvantage because levers are long and form huge resistance arms.
