Factors affecting strength and power Flashcards
What is strength?
The maximum force that a muscle can generate at a specified velocity
The importance of strength (Study) findings?
Strength increased Rate of force development Power Jump height sprint performance COD performance potentiation decreased injury occurrence
Mechanical factors affecting strength
Types of muscular actions Length and velocity of isolated muscle moment arm joint velocity joint position
Force-length relationship
The curve of the length-tension relationship is a combination of two components: the contractile (sarcomere) and the elastic component
When is force greatest?
At intermediate lengths
How does the stretch shorten cycle help perfromance
Improves the economy (reduced metabolic cost)
Why are African distance runners so dominant?
Longer Achilles tendons
Shorter contact times during hopping
Greater jumping power
Four mechanics propesed from 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
Testing stiffness
Hopping, running and jumping
Joint angle selection
Shorter ROM has better transfer to improvements in jump and sprint performance
has been linked to neural control
Length tension changes with training
Cyclists stronger at short RF lengths
RF adapt to cope with demands
Types of muscle action
Static - isometric
Dynamic - isotonic
What is isometric
No change in length
What is isotonic
Change in length
What is a concentric movement
Muscle shortens
What is a eccentric movement
muscle lengthens
In what type of muscle action is force production greatest?
A greater force is generated during lengthening contractions 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 contractions vs concentric contractions
Eccentric contractions can produce greater force than concentric contractions
Eccentric contractions are more efficient
Eccentric contractions present different neural
control strategies - EMG amplitude greater during concentric than eccentric actions
Single muscle fibre - force velocity relationship
The force that the
fibre exerts decreases as the speed of
shortening increases due to limited
availability of binding sites.
Whole muscle fibre - force velocity relationship
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.
Power
Force x velocity
Influence of moment arm
The joint position affects the magnitude of the torque produced by the muscles
What is a moment arm
perpendicular (shortest) distance from the joint centre to the line of
action of the force (tendon)
Resistance arm
The distance from the axis to the point
of resistance application
Effort arm
The distance from the axis to the point of force application is called the
What are the advantages when the tendon inserts further
from the joint?
The muscular moment arm will be longer, and the mechanical advantage increased
What are the disadvantages when the
tendon inserts further from the joint?
The muscle has to contract more to make the joint move through a given ROM – translates to less speed
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.
How does moment arm explain the effect of stature?
Tall athletes immediately at a disadvantage because levers are long
and form huge resistance arms
Shorter levers = better suited to strength
activities
